Study on the mechanism of laser-arc hybrid welding in improving the weld quality of 2507 super duplex stainless steel

Study on the mechanism of laser-arc hybrid welding in improving the weld quality of 2507 super duplex stainless steel | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Study on the mechanism of laser-arc hybrid welding in improving the weld quality of 2507 super duplex stainless steel Jianxin Wang, Zhaorong Sun, Chuantai Yu, Wang Zheng, Ran Zong This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8819933/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 3 You are reading this latest preprint version Abstract To address the challenge of uncontrollable welded joint quality in the application of 2507 Super Duplex Stainless Steel (2507 SDSS) in high-performance industrial fields, this study systematically compared the effects of four welding processes - Laser Beam Welding (LBW), Gas Metal Arc Welding (GMAW), Laser-Arc Hybrid Welding (LAHW), and Oscillating Laser-Arc Hybrid Welding (OLAHW) - on the weld formation, microstructure, mechanical properties, and corrosion resistance of 2507 SDSS. Special focus was placed on exploring the regulatory mechanisms of hybrid welding process parameters (laser power, welding current, welding speed, heat source spacing) and oscillation parameters (oscillation frequency, oscillation amplitude). The results indicated that, compared with single-heat-source LBW and GMAW, LAHW achieved optimized cooling rate (between LBW and GMAW) through the laser-arc synergistic effect, promoted the dispersed precipitation of austenite, and significantly improved mechanical properties and corrosion resistance. The further introduction of beam oscillation in OLAHW enhanced molten pool agitation and improved thermal distribution homogeneity. This not only resulted in the greatest penetration depth but also achieved grain refinement, significantly suppressed the formation of Widmanstätten austenite (WA), and increased the intragranular austenite content (IGA). The OLAHW welds exhibited properties equivalent to or even superior to the base metal in terms of microhardness, tensile strength, elongation, and corrosion resistance. This study revealed the regulatory mechanism of OLAHW on the weld quality of 2507 SDSS, providing key technical support for the selection of welding processes and parameters for this material in harsh environments such as marine and chemical industries. 2507 Super Duplex Stainless Steel Laser-Arc Hybrid Welding Microstructure Mechanical Properties Corrosion Resistance Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1 Introduction 2507 SDSS, a typical high-performance corrosion-resistant alloy, combines the high strength of ferritic stainless steels with the excellent toughness and corrosion resistance of austenitic stainless steels due to its unique duplex microstructure. It exhibits outstanding performance, particularly in resisting stress corrosion cracking and intergranular corrosion, and has thus become a core material in harsh service environments such as marine engineering, chemical equipment, and offshore oil and gas extraction [ 1 ]. In these fields, the quality of welded joints directly determines the structural integrity and service life of the entire equipment, yet the welding process of 2507 SDSS faces critical technical challenges: the welding thermal cycle tends to disrupt its inherent phase balance, leading to an abnormal increase in ferrite content in the weld zone (even exceeding 70%), while also potentially inducing the precipitation of detrimental phases such as σ phase, χ phase, and chromium carbides. These microstructural changes ultimately result in degraded joint toughness and impaired corrosion resistance [ 2 , 3 ]. Industrial standards explicitly require that the content of the minority phase (typically the austenite phase) in 2507 SDSS weld joints should not be less than 30%. Therefore, achieving the synergistic optimization of weld microstructure and properties through welding process control has become a central issue for the engineering application of this material [ 4 ]. Currently, welding processes applicable to 2507 SDSS mainly include GMAW, LBW, and LAHW, but each has certain limitations in performance control [ 5 ]. GMAW, with its high heat input and relatively slow cooling rate, provides sufficient time for austenite nucleation and growth, partially restoring the phase balance. However, it tends to cause coarsening of weld grains. Furthermore, the high heat input accelerates the diffusion and precipitation of Cr and Mo elements at grain boundaries, forming Cr-rich carbides (e.g., M 23 C 6 ) and creating Cr-depleted zones along the boundaries, which substantially reduces the corrosion resistance of the joint [ 6 ]. LBW, with its extremely high energy density, greatly increases the cooling rate. Although it suppresses the precipitation of harmful phases, it severely hinders the diffusive phase transition of austenite in the ferrite matrix, leading to a significantly high ferrite content in the weld (> 80%). This ultimately manifests as a sharp increase in joint hardness (> 340 HV 0.5 ) and a substantial decrease in plasticity (elongation < 15%), making it difficult to meet mechanical performance requirements under complex service conditions [ 4 ]. LAHW, as a hybrid heat source welding technology, integrates the respective advantages of laser and arc: the high energy density of the laser increases weld penetration and reduces the heat-affected zone (HAZ) width; the arc improves the wettability of the molten metal, suppressing defects like lack of fusion and porosity, while simultaneously creating a suitable temperature window for austenitic transformation by regulating the heat input [ 7 ]. In recent years, with the development of beam oscillation technology, OLAHW has further expanded the scope for performance control. By employing periodic oscillation of the laser beam (e.g., linear, circular oscillation patterns), it enhances the convection and heat transfer of the liquid metal, breaking the directional growth trend of columnar crystals and achieving grain refinement [ 8 ]. Simultaneously, the oscillating action homogenizes the chemical composition of the molten pool, reduces elemental micro-segregation, provides more nucleation sites for austenite, and thus optimizes the weld microstructure and properties [ 1 ]. Existing research has confirmed the significant advantages of LAHW in welding metallic materials. Qi et al. found that when the distance between the laser beam and the welding wire in LAHW was controlled at 2 mm, the coupling effect between the laser and arc was optimal, and the austenite content in 2507 SDSS welds increased linearly with heat input [ 9 ]. Chen et al. achieved an acceptable phase ratio (α:γ = 3:1) in 2507 SDSS joints using oscillating laser beam welding, with the joint tensile strength increasing by 10%-15% compared with conventional LBW [ 1 ]. Hao et al., in the study on Q235 steel, demonstrated that OLAHW could increase weld elongation by 8%-12% while reducing microhardness by 5%-8% [ 8 ]. Su et al., investigating the influence of laser oscillation frequency and amplitude on LAHW stability and porosity, found that oscillating laser improved the macro morphology of joints, significantly reduced porosity and impurity segregation, and increased elongation [ 10 ]. Ma et al. discovered that the addition of oscillating laser altered the energy distribution in the hybrid welding pool. The oscillating beam directly heated the sidewalls, improving the wetting ability between the molten pool and the sidewalls, which effectively suppressed the occurrence of lack of fusion defects [ 11 ]. Chen et al., studying the effects of four laser oscillation modes on weld joint morphology, microstructure, and mechanical properties, pointed out that the morphologies of welded joints differed significantly among the modes. Circular oscillation achieved the maximum weld penetration, the finest columnar grains, and the largest equiaxed grain area, resulting in significantly superior joint mechanical properties [ 12 ]. However, most existing research focuses on the influence of single process parameters or other metallic materials. Systematic studies on OLAHW for 2507 SDSS remain relatively scarce, particularly comparative studies on the effects of different welding processes (LBW, GMAW, LAHW, OLAHW) on the weld formation, microstructure, and properties. The regulatory mechanisms of oscillation parameters (frequency, amplitude) in OLAHW on the duplex phase balance and corrosion resistance of 2507 SDSS have not been clearly defined, and the optimization of relevant process parameters lacks theoretical support. Based on the aforementioned research status, this study used 2507 SDSS as the research object and systematically conducted welding experiments using four processes: LBW, GMAW, LAHW, and OLAHW. It focused on investigating the influence laws of key hybrid welding parameters (laser power, welding current, welding speed, heat source spacing) and oscillation parameters (frequency f , amplitude A ) on weld formation (penetration, width), microstructure (grain size, phase ratio, harmful phase content), mechanical properties (microhardness, tensile strength, elongation), and electrochemical corrosion performance (corrosion potential, corrosion current density, passivation range). By revealing the internal relationship of "beam oscillation - molten metal flow - microstructure evolution - performance response" in OLAHW, the optimal welding process scheme for 2507 SDSS was identified, providing a theoretical basis and technical reference for the welding engineering application of this material in harsh environments. 2 Materials and methods 2.1 Base material and filler wire Rolled 2507 SDSS plates with dimensions of 200 mm ×70 mm × 6 mm were used as the base metal. The welding wire was ER2594 with a diameter of 1.2 mm, which was specifically designed in composition to match the high chromium, molybdenum, and nitrogen content of 2507 SDSS, aiming to compensate for element burn-off during welding and promote austenite formation to maintain the required duplex phase balance and corrosion resistance of the weld metal. The specific chemical compositions were shown in Table 1 . Before welding, the plates were mechanically polished, followed by cleaning with anhydrous ethanol to remove surface oxides and oil stains, ensuring process stability and weld quality. Table 1 Chemical composition of 2507 SDSS and ER 2594 (wt.%) Material C Mn Si Cr Ni Mo P S Cu N 2507 0.018 0.91 0.55 25.43 7.11 3.60 0.02 0.001 0.05 0.26 ER2594 0.017 1.50 0.53 24.11 8.69 3.03 0.02 0.002 0.08 0.21 2.2 Welding system and evaluation modes The experiment adopted a laser-arc hybrid welding system as shown in Fig. 1 (a), primarily consisting of a 3 kW fiber laser (wavelength 1064 nm), a digital GMAW power source, and a beam oscillation module. The laser beam was transmitted via optical fiber, and then entered the beam oscillation system, where it was driven by oscillating motors to perform periodic oscillations along preset trajectories in the X-Y plane, finally focusing on the workpiece surface with a spot diameter of approximately 1 mm. During welding, a cooperative mode with the arc leading and the laser trailing was adopted. The GMAW torch was tilted backward, and the laser beam was tilted forward, maintaining angles of 70° and 80° with the workpiece surface, respectively. The distance between them varied according to the experimental design, as shown in Fig. 1 (b). High-purity argon was used as the shielding gas, with flow rates set at 20 L/min for both the arc and laser. Based on the principle of single-variable control, 18 groups of welding experiments were systematically designed on the basis of benchmark parameters (laser power 2.5 kW, current 250 A, welding speed 20 mm/s, heat source spacing 2 mm, oscillation off), covering four processes: LBW, GMAW, LAHW, and OLAHW. In the OLAHW experiments, the laser beam adopted a linear oscillation mode, as shown in Fig. 1 (c). The effects of oscillation frequency (100–500 Hz) and oscillation width (1–5 mm) on weld formation and organizational properties were specifically studied. Detailed welding parameters are listed in Table 2 . Table 2 Parameters of welding process No. Process Laser power (kW) Current (A) Voltage (V) Welding Speed (mm/s) Inter-beam Distance (mm) Oscillating Frequency (Hz) Oscillating width (mm) 1 LBW 2.5 - - 20 - - - 2 GMAW - 250 25.5 20 - - - 3 LAHW 2 250 25.5 20 2 - - 4 LAHW 2.5 250 25.5 20 2 - - 5 LAHW 3 250 25.5 20 2 - - 6 LAHW 2.5 200 20.0 20 2 - - 7 LAHW 2.5 300 30.0 20 2 - - 8 LAHW 2.5 250 25.5 15 2 - 9 LAHW 2.5 250 25.5 25 2 - - 10 LAHW 2.5 250 25.5 20 0 - - 11 LAHW 2.5 250 25.5 20 4 - - 12 LAHW 2.5 250 25.5 20 6 - - 13 OLAHW 2.5 250 25.5 20 2 100 3 14 OLAHW 2.5 250 25.5 20 2 200 3 15 OLAHW 2.5 250 25.5 20 2 300 3 16 OLAHW 2.5 250 25.5 20 2 500 3 17 OLAHW 2.5 250 25.5 20 2 300 1 18 OLAHW 2.5 250 25.5 20 2 300 5 After welding, X-ray non-destructive testing was used to analyze internal defects such as porosity. Sampling was performed according to the scheme shown in Fig. 2 . Metallographic specimens of the weld cross-section were obtained by wire electrical discharge machining. After etching with Beraha's reagent (20 ml HCl + 80 ml H₂O + 1 g K₂S₂O₅), a stereomicroscope and optical microscope (OM) were used to observe the macrostructure and microstructure. Electron backscatter diffraction (EBSD) was employed to analyze grain morphology and phase distribution, with an operating voltage of 20 kV and a step size of 0.5 µm. Mechanical property tests included: transverse and longitudinal microhardness mapping was performed using a Vickers hardness tester (load 500 gf, dwell time 15 s) along the paths shown in Fig. 2 (b). Tensile tests were conducted at room temperature at a rate of 1 mm/min, and the fracture morphology was observed using a scanning electron microscopy (SEM) to analyze the fracture mechanism. 3 Results and discussions 3.1. Weld bead formation Figures 3 and 4 present the weld surface morphology, cross-sectional macrostructure, X-ray non-destructive testing results, and weld formation for the four welding processes (LBW, GMAW, LAHW, OLAHW). Macrostructure analysis revealed significant differences in penetration depth, weld width, and formation quality among the different processes. 3.1.1 Comparison of weld formation In terms of weld surface morphology (Figs. 3 a-d), the LBW weld surface was the brightest and continuous, with a width of only 2.72 mm, exhibiting typical laser welding characteristics. The GMAW weld surface had slightly lower glossiness, with a width reaching 5.19 mm, showing the typical wide weld characteristic of arc welding. The LAHW weld surface appeared dark gray, with the width increasing to 6.05 mm; whereas the OLAHW weld surface was the darkest, with the maximum width of 7.02 mm, indicating that beam oscillation significantly altered molten pool flow and thermal distribution uniformity. Comparison of weld cross-sectional morphology found that the LBW weld was flat-shaped, characterized by a large weld width and a small penetration, and belonged to heat conduction welding. The GMAW weld was bowl-shaped, with the shallowest penetration (1.05 mm) but the widest HAZ, reflecting its high heat input characteristic. The LAHW weld achieved better coordination between penetration depth (1.72 mm) and weld width, demonstrating the synergistic enhancement effect of laser and arc. OLAHW, through the stirring action of beam oscillation, achieved the maximum penetration depth (1.81 mm), with the most ideal molten pool morphology. X-ray non-destructive testing results showed varying characteristics of porosity and undercut defect distributions for different processes. Welds from the LBW and GMAW showed no obvious defects. In LAHW, when laser power was too low (2.0 kW) or current was too small (200 A), the fluidity and existence time of the molten pool were insufficient, exacerbating the tendency for porosity and undercut formation. In OLAHW, when oscillation frequency was too low (100 Hz) or amplitude too small (1 mm), the stirring effect was weak, which was not conducive to gas escape and prone to porosity. By comparing welds under different parameters, it was found that minor changes in process parameters significantly affected formation quality. OLAHW under the optimal oscillation parameters ( f = 300 Hz, A = 3 mm) had the most ideal weld formation, featuring the best coordination between weld penetration and width, the fewest defects, and fully demonstrated the significant advantages of beam oscillation technology in improving weld formation. 3.1.2 Influence mechanism of process parameters on weld formation Figure 4 , by systematically comparing weld dimensions (penetration, width) under different process parameters, clearly reveals the influence of each parameter on weld formation. Within the laser power range of 2.0–3.0 kW, the penetration and width did not increase monotonically with power but instead showed a trend of first decreasing and then increasing (Fig. 4 a). The mechanism was as follows: increased power enhanced the laser-induced plasma, which guided and compressed the arc, but excessively strong plasma also shielded the incident laser energy [ 13 ]. Before reaching the critical power threshold, the shielding effect was dominant, resulting in insufficient laser energy effectively used for deep penetration; beyond the threshold, the laser energy density was sufficient to penetrate the plasma, the deep penetration effect was enhanced, and the synergistic effect reached the best. When the welding current was in the range of 200–300 A, the increase in current directly led to higher total heat input and a wider arc action range, thereby significantly increasing penetration and width (Fig. 4 b). More importantly, the increased arc plasma had a "dilution" effect on the laser-induced plasma, reducing its shielding effect on the laser, thereby improving the absorption efficiency of the base metal for laser energy and achieving a "1 + 1>2" synergistic enhancement effect [ 14 ]. When the welding speed increased from 15 mm/s to 25 mm/s, the linear energy density decreased, leading to a significant decrease in penetration and width (Fig. 4 c). In the high-speed range (20–25 mm/s), the penetration decrease rate slowed down, which proved a key advantage of the LAHW process: it could adopt a higher welding speed while maintaining the same penetration, thereby improving production efficiency and reducing total heat input. The inter-beam distance directly controls the strength of the synergistic interaction between the laser and arc. At a distance of 0 mm, the laser directly passed through the arc center, leading to arc instability and excessive expansion, forming a wide and shallow weld. At distances of 2–4 mm, the synergistic effect was strongest, with the laser's stabilizing and compressing effect on the arc being most significant, resulting in the most concentrated energy and thus a narrower weld width. When the distance increased to 6 mm, the two heat sources operated almost independently, the synergistic effect disappeared, and the weld morphology resembled that of single GMAW. 3.1.3 Effect of beam oscillation parameters on weld formation In OLAHW, at low oscillation frequencies (100–200 Hz), the oscillation period was long, equivalent to a slowly moving "linear heat source", leading to energy dispersion. The weld penetration and width were even smaller than those without oscillation (Fig. 4 e) [ 15 ]. At medium frequency (300 Hz), the oscillation produced the best regulatory effect. At this point, intense periodic stirring enhanced internal convection within the molten pool, efficiently transferring heat to the bottom of the pool, while avoiding excessive energy dispersion, thus achieving the maximum penetration (1.81 mm). At high frequency (500 Hz), the laser beam scanning speed was extremely fast, transforming its heat source character from a "point heat source" to a "surface heat source", preheating the workpiece over a large area, resulting in a significant decrease in energy density, so the penetration decreased. At the same time, the intense stirring effect violently pushed the liquid metal to the edge of the molten pool, causing a sharp increase in weld width (to 9.27 mm). When the oscillation amplitude increased (from 1 mm to 3 mm), the intensity and range of molten pool stirring were enhanced, which was more conducive to heat transfer to the depth direction, so the penetration and width increased synchronously (Fig. 4 f). However, when the amplitude was too large (5 mm), the laser beam scanning path was too long, and the energy density and residence time per unit area decreased again, leading to limited penetration growth and even a decrease in weld width. Comprehensive analysis indicated that process parameters macroscopically influence weld dimensions by controlling the total heat input and laser-arc synergistic effect, whereas beam oscillation parameters (frequency, amplitude) achieve micro-regulation of weld formation by altering the energy distribution state and molten pool fluid dynamics behavior. The optimal oscillation parameters (300 Hz, 3 mm in this study) achieved the best balance between energy concentration and molten pool stirring, resulting in a weld with deep penetration and favorable morphology. 3.2 Microstructure characterization of the weld Using OM, EBSD, and grain size statistical analysis (Figs. 5 – 7 ), the influence laws of different welding processes on the microstructural evolution of 2507 SDSS welds were systematically revealed, clarifying the differences in microstructure morphology, phase ratio, and grain size under various processes. 3.2.1 Microstructure of the base metal The 2507 SDSS base metal had a typical duplex microstructure, consisting of nearly equal proportions of ferrite (α phase, dark area in OM image) and austenite (γ phase, bright area in OM image), where the γ phase was uniformly distributed in the α phase matrix in island or strip form (Figs. 5 (a-c)). EBSD grain size statistics showed that the average grain size of the α phase was 8.6 µm, and the average grain size of the γ phase was 4.4 µm (Fig. 5 (d)). The microstructure was uniform and fine, providing a benchmark for subsequent comparison of weld microstructure and properties. 3.2.2 Weld microstructure morphology Figure 6 shows the microstructures of the 2507 SDSS weld fusion line and center under four welding processes (LBW, GMAW, LAHW, OLAHW). LBW, with its low heat input and extremely high cooling rate, resulted in the α phase growing directionally from the fusion line towards the weld center, forming coarse columnar grains (Fig. 6 (a1)). Its HAZ width was the narrowest, but slight grain coarsening of the α phase still occurred within the HAZ. The diffusion-based phase transformation of the γ phase in the weld was significantly inhibited, and only a small amount of discontinuous grain boundary austenite (GBA) was formed at the α phase grain boundaries, with the GBA morphology conforming to the contours of the α phase grains (Fig. 6 (a2)). This led to a significantly high α phase content (> 80%) in the weld zone, resulting in a severe imbalance in the duplex phase ratio. GMAW had high heat input and slow cooling rate, providing sufficient time for γ phase nucleation and growth. The weld contained numerous coarse GBA and feathery WA growing perpendicular to the fusion line. Its HAZ width was the widest, and grains were severely coarsened, becoming a weak performance area (Fig. 6 (b1)). There was a small amount of IGA in the weld, which contained less Cr, Mo, and N elements than GBA, leading to reduced material toughness, increased brittleness, and decreased fatigue strength and corrosion resistance [ 16 , 17 ]. In LAHW, the laser-arc synergistic effect resulted in a weld cooling rate intermediate between LBW and GMAW. Its HAZ width was also intermediate, and the degree of grain coarsening was weaker than in GMAW (Fig. 6 (c1)) [ 18 , 19 ]. The GBA in the weld was slenderer, the WA content was significantly reduced compared to GMAW, and the IGA content increased markedly, appearing as acicular/particulate dispersions within the α phase (Fig. 6 (c2)). The microstructure was significantly improved, and the degree of duplex phase ratio imbalance was alleviated compared with LBW. OLAHW introduced periodic beam oscillation, which enhanced the convection of liquid metal and made the temperature distribution more uniform in the molten pool. Its HAZ width was narrower than that of LAHW, and there was no obvious grain coarsening phenomenon (Fig. 6 (d1)). The α phase grains in the weld were finer, providing more nucleation sites for the γ phase, leading to the formation of numerous fine IGA particles, appearing as acicular/particulate dispersions within the α phase (Fig. 6 (d2)). The GBA became slenderer and more discontinuous, the proportion of WA further reduced, resulting in the optimal microstructure. 3.2.3 Quantitative analysis of grain and phase distribution Quantitative analysis of grain size and phase distribution in the welds of the four processes was performed using EBSD Inverse Pole Figure (IPF) maps and phase maps (Fig. 7 ), with results summarized in Table 3 . Due to the excessively fast cooling rate of LBW welds, the duplex phase ratio was seriously imbalanced, only a small amount of discontinuous GBA was distributed at the α grain boundaries. The α and γ grain sizes of GMAW welds were 18.4 µm and 6.7 µm respectively, the duplex phase ratio was the most balanced, but the microstructure was coarse, and there was more WA, affecting the microstructure uniformity. LAHW achieved grain refinement and phase ratio optimization through synergistic effect. The α and γ grain sizes in the weld were 16.2 µm and 5.3 µm respectively, the contents of GBA and WA decreased, and the IGA content increased significantly. By virtue of the molten pool stirring effect of beam oscillation, OLAHW obtained the most ideal microstructure: the finest α phase grains (14.6 µm), with the γ phase predominantly in the form of uniformly dispersed IGA, and a relatively balanced duplex phase ratio, laying a microstructural foundation for performance enhancement. Table 3 Average grain size phase ratio of the weld bead under different welding processes Process Size of α (µm) Size of γ (µm) Ratio of α (%) Ratio of γ (%) BM 8.6 4.4 51.8 48.2 LBW 36.1 2.7 94.0 6.0 GMAW 18.4 6.7 37.9 62.1 LAHW 16.2 5.3 60.1 39.9 OLAHW 14.6 5.0 62.1 37.9 3.2.4 Microstructure evolution mechanism Welding processes dominated the microstructure evolution path by regulating thermal cycles and molten pool fluid dynamics behavior, and the core mechanisms could be divided into two aspects: Cooling rate dominated phase transformation behavior: the LBW cooling rate far exceeded the critical value for the diffusion-based phase transformation of the γ phase, forming a high proportion of α phase structure, leading to duplex phase ratio imbalance [ 20 ]. GMAW, with high heat input and slow cooling, promoted γ phase nucleation and growth but easily caused grain coarsening and WA formation, and sufficient element diffusion led to grain boundary segregation [ 16 ]. LAHW and OLAHW had cooling rates intermediate between LBW and GMAW, providing sufficient time for γ phase precipitation while avoiding excessive grain coarsening. Molten pool flow regulated microstructure homogeneity: OLAHW, through periodic beam oscillation, enhanced molten pool convection, broke the directional growth trend of α phase columnar grains in traditional welding, increased nucleation sites, and promoted the formation of equiaxed grains and IGA [ 21 ]. Simultaneously, the oscillation action homogenized the chemical composition of the molten pool, reduced micro-segregation of elements like Cr, Mo, and N, avoided local phase transformation abnormalities due to compositional inhomogeneity, and achieved dual optimization of "grain refinement + compositional homogenization". In summary, OLAHW, leveraging the synergistic effect of "moderate cooling rate + forced molten pool convection", outperformed the other processes in terms of grain refinement, phase ratio control, and compositional homogeneity, providing an ideal microstructural foundation for the enhancement of mechanical properties and corrosion resistance of the weld. 3.3 Mechanical properties and corrosion resistance 3.3.1 Microhardness test Figure 8 shows the microhardness distribution of weld zones under four welding processes (LBW, GMAW, LAHW, OLAHW). In the transverse hardness distribution (Fig. 8 (a)), the LBW weld had the highest microhardness, reaching 342.3 HV 0.5 , which was higher than its HAZ hardness (325.3 HV 0.5 ). This was because the extremely fast cooling rate of LBW inhibited austenite precipitation, forming a high proportion of ferrite, leading to weld hardening. The GMAW weld hardness was 283.2 HV 0.5 , between LAHW and OLAHW, and lower than its HAZ hardness (296.0 HV 0.5 ). High heat input and slow cooling coarsened the weld microstructure, and generated a large amount of GBA and WA with low hardness, leading to weld softening. Its HAZ had a higher ferrite proportion and relatively higher hardness. The LAHW weld hardness was 297.6 HV 0.5 , higher than OLAHW. Its moderate cooling rate promoted finer GBA and more acicular IGA, balancing strength and toughness, and avoiding excessive hardening of LBW and excessive softening of GMAW. The OLAHW weld had the lowest hardness of 272.4 HV 0.5 , which was close to the HAZ hardness (279.8 HV 0.5 ) and the most matched with the base metal hardness (274.1 HV 0.5 ). Beam oscillation strengthened molten pool stirring, significantly promoted austenite transformation, especially increased IGA content, which mainly softened the weld and made the hardness closer to the base metal. In the longitudinal hardness distribution (Fig. 8 (b)), the central region of the LBW weld maintained a high average hardness (345.1 HV 0.5 ), reflecting the microstructure inhomogeneity caused by rapid cooling. The central hardness of the GMAW weld was generally low (average 279.1 HV 0.5 ) with large fluctuations, and the peak value (298.5 HV 0.5 ) appeared in the HAZ. This was consistent with the characteristics of HAZ grain coarsening and weld microstructure softening. The central hardness distribution of the LAHW weld was relatively uniform with a narrow fluctuation range (270–287 HV 0.5 ). The laser-arc synergistic effect created a balanced thermal process, refined the microstructure, and promoted uniform austenite precipitation, reducing hardness differences. The central hardness distribution of the OLAHW weld was the flattest, with the lowest overall hardness value (average 275.6 HV 0.5 ). Beam oscillation made the weld microstructure highly uniform, providing the weld with better plasticity and crack resistance. Combining transverse and longitudinal hardness data, the hardness differences among the four processes essentially represented the relationship of "thermal cycle - microstructure evolution - hardness response". The cooling rate dominated the hardness foundation: LBW rapid cooling → high ferrite → high hardness; GMAW slow cooling → coarsened structure + austenite → low hardness; LAHW and OLAHW intermediate cooling → balanced phase composition → medium hardness. Beam oscillation optimized hardness uniformity: OLAHW, through periodic beam oscillation, not only adjusted the phase composition but also eliminated microstructure segregation through molten pool stirring, making the weld and HAZ hardness tend to be consistent and approach the base metal hardness, laying the foundation for enhanced comprehensive mechanical properties. 3.3.2 Mechanical tensile test Room temperature tensile tests were conducted to test the properties of welded joints under four welding processes (LBW, GMAW, LAHW, OLAHW), with results shown in Fig. 9 and Table 4 . The tensile strength of all process joints was equivalent to or slightly higher than that of the base metal (823.7 ± 9 MPa), meeting the engineering strength requirements. However, each process showed significant differences in yield strength, elongation, and fracture location, reflecting the profound influence of different thermal processes on properties. Due to the extremely high cooling rate, the LBW weld had a ferrite content exceeding 80%. Although it exhibited the highest tensile strength (842.8 ± 13 MPa) and relatively high yield strength (693.3 ± 4 MPa), its plasticity was severely degraded, with an elongation of only 16.9 ± 1%. During tensile testing, plastic deformation concentrated in the relatively softer base metal region, leading to fracture located in the base metal (Fig. 9 (a)), exhibiting a characteristic of "weld hard and brittle - base metal weak" performance imbalance. GMAW, with high heat input and slow cooling, promoted austenite precipitation (relatively balanced duplex phase ratio), contributing to improved plasticity, with an elongation (23.3 ± 2%) second only to the base metal and OLAHW. However, severe grain coarsening in the HAZ made it a performance weak zone, initiating fracture, demonstrating a defect of "good weld plasticity - insufficient HAZ strength". The LAHW weld, influenced by the laser-arc synergistic effect, had a cooling rate intermediate between LBW and GMAW. The austenite content increased, but the distribution uniformity was general. The joint performance was intermediate: tensile strength 835.1 ± 10 MPa, yield strength 724.3 ± 4 MPa, elongation 19.6 ± 3%. The fracture location was in the weld zone, reflecting the constraint on plasticity due to insufficient microstructural homogeneity in the weld. OLAHW introduced beam oscillation, enhancing molten pool stirring, achieving grain refinement and dispersed austenite distribution (predominantly intragranular austenite). The joint plasticity significantly improved, with elongation reaching 24.8 ± 2% (second only to the base metal); tensile strength 815.8 ± 10 MPa, yield strength 688.2 ± 5 MPa, showing the highest match with base metal properties. The fracture location returned to the base metal, indicating that the weld and HAZ achieved a balanced performance with synergistic optimization of "strength-plasticity". Table 4 Detailed tensile test results Tensile specimen Tensile strength (MPa) Yield strength (MPa) Ductility (%) Fracture location Base metal 823.7 ± 9 677.2 ± 6 26.3 ± 2 - 1-LBW 842.8 ± 13 693.3 ± 4 16.9 ± 1 BM 2-GMAW 833.2 ± 11 741.8 ± 9 23.3 ± 2 HAZ 4-LAHW 835.1 ± 10 724.3 ± 4 19.6 ± 3 WB 15-OLAHW 815.8 ± 10 688.2 ± 5 24.8 ± 2 BM Observation of the tensile fracture surfaces via SEM (Fig. 10 ) revealed that all four processes exhibited ductile fracture characteristics (visible dimples), but there were significant differences in dimple morphology and associated features. The LBW fracture surface had uneven dimple sizes, with local cleavage planes visible, indicating limited plastic deformation capacity during fracture, consistent with the hard and brittle characteristics caused by the high ferrite proportion, and matching the lowest elongation test result. The GMAW fracture surface had a larger number of dimples, but some dimple bottoms contained second-phase particles (nitrides or carbides precipitated during welding). These particles became nucleation sites for microcavities during tensile deformation. Although the elongation was not significantly reduced, it reflected the micro segregation problem caused by slow cooling. The LAHW fracture surface showed cleavage steps and cleavage planes, with a lower dimple density than GMAW and OLAHW, indicating poorer plastic deformation capacity, consistent with the inhomogeneous austenite distribution and insufficient microstructural homogeneity in the weld. The OLAHW fracture surface was covered by a large number of uniformly deep, densely arranged equiaxed dimples, without obvious cleavage characteristics or second-phase particle aggregation, indicating that microcavities could fully grow and coalesce during tensile deformation, reflecting excellent plastic deformation capacity, directly corresponding to its refined and uniform microstructural characteristics. In summary, the correlation between tensile properties and fracture morphology indicated that the "strength-plasticity" balance of 2507 SDSS welded joints depended on the process's ability to regulate the microstructure. Specifically, through the dual effects of "grain refinement + austenite dispersion", OLAHW solved the problems of insufficient plasticity of LBW, weak HAZ of GMAW, and inhomogeneous microstructure of LAHW, achieving the optimal mechanical properties matching the base metal. 3.3.3 Corrosion resistance Potentiodynamic polarization tests were conducted to evaluate the electrochemical corrosion behavior of welds and base metal in a 3.5% NaCl solution at room temperature (simulating marine corrosion environment). The polarization curves were shown in Fig. 11 . The extracted results of key electrochemical parameters (self-corrosion potential E corr , breakdown potential E b , passivation interval ∆E p , self-corrosion current density I corr ) were shown in Table 5 . E corr reflected the thermodynamic stability of the material in the corrosion environment. The higher the value, the more difficult the material was to corrode. I corr was a direct indicator of the corrosion rate. The lower the value, the slower the corrosion rate [ 22 ]. The E corr of the LBW weld was higher than that of the base metal, but the I corr was about 1.8 times that of the base metal. Its higher E corr was due to the rapid cooling inhibiting the precipitation of harmful phases, but the high proportion of ferrite (> 80%) still led to a higher corrosion rate than the base metal. The E corr of the GMAW weld was lower than that of the base metal, and the I corr was about 4.5 times that of the base metal. High heat input and slow cooling promoted the precipitation of Cr and Mo elements at grain boundaries to form Cr-rich carbides, leading to Cr-depleted zones at grain boundaries, which became corrosion active sites and significantly accelerated the corrosion process. The E corr of the LAHW weld was lower than that of the base metal, and the I corr was about 2.0 times that of the base metal. Although the laser-arc synergistic effect optimized the cooling rate, the lack of molten pool stirring led to element segregation, and the corrosion rate was significantly higher than that of the base metal. The OLAHW weld had the highest E corr among all tested samples, and the I corr was only slightly lower than that of the base metal, indicating that the introduction of beam oscillation significantly improved the electrochemical stability of the weld and reduced the corrosion rate. ∆E p represented the ability of the material to resist pitting corrosion after forming a passive film. The wider the interval, the stronger the pitting corrosion resistance [ 23 , 24 ]. The base metal performed the best, reflecting the excellent pitting corrosion resistance of its original duplex structure. The LBW weld had the narrowest ∆E p . Although there was no obvious element segregation, the excessive ferrite led to inhomogeneous composition of the passive film, resulting in the weakest pitting corrosion resistance. The ∆E p of GMAW and LAHW welds were slightly narrowed, reflecting the damage to the integrity of the passive film caused by improper heat input control or inhomogeneous microstructure. The ∆E p of the OLAHW weld was only minimally smaller than that of the base metal, indicating that after grain refinement and uniform phase distribution by beam oscillation, the stability of the weld passive film was close to that of the base metal. Table 5 Extracted data from the polarization curves E corr (mV vs. SSE) E b (mV vs. SSE) ∆E p (mV vs. SSE) I corr (nA/cm 2 ) BM -415 1011.8 1426.8 153.2 LBW -398 896.2 1294.2 273.6 GMAW -478 875.3 1353.3 685.5 LAHW -458 925.2 1383.2 311.2 OLAHW -384 1016.1 1400.1 143.9 The differences in corrosion resistance among the four processes were essentially a chain effect of "welding thermal cycle - molten pool behavior - microstructure - corrosion response", and the core regulatory mechanisms could be summarized into two points: The first was the balance of phase ratio and suppression of harmful phase. The corrosion resistance of 2507 SDSS depended on a balanced α/γ ratio (industrial requirement γ ≥ 30%). LBW rapid cooling led to insufficient γ phase precipitation (< 20%), while GMAW slow cooling, although achieving balanced phase ratio, induced coarse WA, both of which damaged the microstructure stability. Through "moderate cooling rate + beam oscillation stirring", OLAHW promoted the dispersed precipitation of IGA while suppressing the formation of WA, forming an ideal balanced α/γ structure, laying the structural foundation for corrosion resistance [ 25 ]. The second was microstructure homogeneity and element segregation control. In OLAHW, beam oscillation strengthened molten pool convection, effectively breaking the directional growth of α phase columnar grains, achieving grain refinement (the average size of α phase was 14.6 µm, the finest among the four processes), and increasing the nucleation sites of the passive film [ 26 ]. It also significantly homogenized the molten pool composition, alleviating micro-segregation of key corrosion-resistant elements like Cr and Mo, avoiding the formation of local Cr-depleted zones, thereby ensuring a uniform and dense passive film. This was directly manifested as excellent electrochemical performance: "high E corr , low I corr , wide ∆E p ". In summary, OLAHW, through the synergistic regulation of molten pool behavior and microstructure evolution by beam oscillation, significantly improved the "phase imbalance" of LBW, the "element segregation" of GMAW, and the "microstructural inhomogeneity" of LAHW. This resulted in weld corrosion resistance not only superior to the other three processes but also matching that of the base metal, providing key technical support for the engineering application of 2507 SDSS in harsh corrosive environments. 4 Conclusions This study systematically compared the effects of four processes (LBW, GMAW, LAHW, and OLAHW) on the weld formation, microstructure evolution, mechanical properties, and corrosion resistance of 2507 SDSS, and the following conclusions were drawn: (1) The process synergistic effect determined the weld formation quality, and beam oscillation achieved formation optimization. LAHW combined the synergistic advantages of laser and arc, resulting in weld penetration depth and width superior to single heat source processes. After introducing beam oscillation (OLAHW), under suitable parameters (frequency 300 Hz, amplitude 3 mm), the molten pool flow and thermal distribution were further optimized, achieving relatively large penetration (1.81 mm), the best formation quality, and the lowest defect rate. (2) Cooling rate and molten pool flow synergistically regulate the microstructure, constructing the optimal morphological structure. LAHW, through the laser-arc synergistic effect, regulated the cooling rate, promoted IGA precipitation, and alleviated the duplex phase imbalance, but the lack of molten pool stirring led to insufficient microstructural homogeneity. OLAHW, through the dual action of "moderate cooling rate + forced molten pool convection," broke the directional growth of α phase columnar grains, promoted uniform dispersion of the γ phase, significantly suppressed WA formation, and constructed the optimal microstructure of "fine-grained α phase + dispersed IGA". (3) Mechanical properties matching the base metal were achieved, solving the "strength-plasticity" imbalance problem. The OLAHW weld had the lowest hardness and the most uniform distribution. Its tensile strength reached 815.8 MPa, and its elongation reached 24.8%, showing the closest match to the base metal properties. The tensile fracture surface was covered with dense and uniform equiaxed dimples, with no obvious cleavage planes or aggregation of second-phase particles, indicating excellent plasticity and crack propagation resistance. (4) Beam oscillation enhanced corrosion resistance, enabling applicability in harsh corrosive environments. OLAHW, through grain refinement, increased passive film nucleation sites, while homogenizing the distribution of corrosion-resistant elements like Cr and Mo, avoiding the formation of local Cr-depleted zones, and ensuring a dense passive film. This resulted in the weld exhibiting the highest corrosion potential, the lowest corrosion current density, and a passivation range close to that of the base metal, representing the optimal corrosion resistance. In summary, OLAHW, through the synergistic regulation of process parameters and oscillation parameters, outperformed the other processes in terms of grain refinement, phase ratio control, and compositional homogeneity. It achieved synergistic improvement in weld formation, mechanical properties, and corrosion resistance. The regulatory principle of "beam oscillation - molten pool flow - microstructure evolution - performance response" provided direct technical reference for the engineering welding of 2507 SDSS and theoretical guidance for the optimization of welding processes for other stainless steels. Declarations Competing Interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Funding This work was supported by the Shandong Provincial Natural Science Foundation [grant number ZR2023ME139], Central Guiding Local Technology Development Funding Projects [grant number YDZX2024113]. Author Contributions Jianxin Wang : Writing – original draft, Data curation. Zhaorong Sun : Formal analysis, Resources. Chuantai Yu : Investigation, Visualization. Wang Zheng : Methodology. Ran Zong : Writing – review & editing, Supervision. Acknowledgements This work was supported by the Shandong Provincial Natural Science Foundation [grant number ZR2023ME139], Central Guiding Local Technology Development Funding Projects [grant number YDZX2024113]. Data availability Data will be made available on request. References Chen H, Cui H, Ma G et al (2026) Mechanical and corrosion behavior of oscillating laser beam welded 2507 super duplex stainless steel: Synergistic effects of acidic seawater and strain states. J Mater Sci Technol 251:227–240. https://doi.org/10.1016/j.jmst.2025.07.010 Cui S, Shi Y, Cui Y, Zhu T (2019) The influence of microstructure and chromium nitride precipitations on the mechanical and intergranular corrosion properties of K-TIG weld metals. Constr Build Mater 210:71–77. https://doi.org/10.1016/j.conbuildmat.2019.03.212 Fellicia DM, Sutarsis, Kurniawan BA et al (2017) Study of sigma phase in duplex SAF 2507. Iop Conf Ser: Mater Sci Eng 202:012039. https://doi.org/10.1088/1757-899X/202/1/012039 Vinoth Jebaraj A, Ajaykumar L, Deepak CR, Aditya KVV (2017) Weldability, machinability and surfacing of commercial duplex stainless steel AISI2205 for marine applications – A recent review. J Adv Res 8:183–199. https://doi.org/10.1016/j.jare.2017.01.002 Verma J, Taiwade RV (2017) Effect of welding processes and conditions on the microstructure, mechanical properties and corrosion resistance of duplex stainless steel weldments—a review. J Manuf Processes 25:134–152. https://doi.org/10.1016/j.jmapro.2016.11.003 Chu Q, Yang D, Chang Z et al (2024) Investigation on microstructure evolution, mechanical properties and corrosion resistance of dual phase stainless steel joints welded by GTAW and SAW methods. Int J Press Vessels Pip 209:105183. https://doi.org/10.1016/j.ijpvp.2024.105183 Acherjee B (2018) Hybrid laser arc welding: State-of-art review. Opt Laser Technol 99:60–71. https://doi.org/10.1016/j.optlastec.2017.09.038 Hao K, Gao Z, Huang J et al (2023) Comparisons of laser and laser-arc hybrid welded carbon steel with beam oscillation. Opt Laser Technol 157:108787. https://doi.org/10.1016/j.optlastec.2022.108787 Qi K, Li R, Wang G, Sun Z (2019) Structure and mechanical properties of laser-MIG hybrid welded SAF 2507 super duplex stainless steel joints. Int J Mod Phys B 33:1940037. https://doi.org/10.1142/S021797921940037X Su R, Li H, Chen H et al (2024) Stability analysis and porosity inhibition mechanism of oscillating laser-arc hybrid welding process for medium-thick plate TC4 titanium alloy. Opt Laser Technol 174:110569. https://doi.org/10.1016/j.optlastec.2024.110569 Ma C, Chen B, Meng Z et al (2023) Characteristic of keyhole, molten pool and microstructure of oscillating laser TIG hybrid welding. Opt Laser Technol 161:109142. https://doi.org/10.1016/j.optlastec.2023.109142 Chen C, Zhou H, Wang C et al (2021) Laser welding of ultra-high strength steel with different oscillating modes. J Manuf Processes 68:761–769. https://doi.org/10.1016/j.jmapro.2021.06.004 Gao M, Zeng XY, Hu QW (2006) Effects of welding parameters on melting energy of CO2 laser–GMA hybrid welding. Sci Technol Weld Join 11:517–522. https://doi.org/10.1179/174329306X148138 Meng Y, Gao M, Zeng X (2018) Effects of arc types on the laser-arc synergic effects of hybrid welding. Opt Express 26:14775. https://doi.org/10.1364/OE.26.014775 Shi L, Jiang L, Gao M (2022) Numerical research on melt pool dynamics of oscillating laser-arc hybrid welding. Int J Heat Mass Transf 185:122421. https://doi.org/10.1016/j.ijheatmasstransfer.2021.122421 Geng S, Sun J, Guo L, Wang H (2015) Evolution of microstructure and corrosion behavior in 2205 duplex stainless steel GTA-welding joint. J Manuf Processes 19:32–37. https://doi.org/10.1016/j.jmapro.2015.03.009 Wang S-H, Chiu P-K, Yang J-R, Fang J (2006) Gamma (γ) phase transformation in pulsed GTAW weld metal of duplex stainless steel. Mater Sci Engineering: A 420:26–33. https://doi.org/10.1016/j.msea.2006.01.028 Mohammed G, Ishak M, Aqida S, Abdulhadi H (2017) Effects of heat input on microstructure, corrosion and mechanical characteristics of welded austenitic and duplex stainless steels: A review. Metals 7:39. https://doi.org/10.3390/met7020039 Wang H-S (2005) Effect of welding variables on cooling rate and pitting corrosion resistance in super duplex stainless weldments. Mater Trans 46:593–601. https://doi.org/10.2320/matertrans.46.593 Köse C, Topal C (2022) Texture, microstructure and mechanical properties of laser beam welded AISI 2507 super duplex stainless steel. Mater Chem Phys 289:126490. https://doi.org/10.1016/j.matchemphys.2022.126490 Ge C, Meng Y, Xie Y et al (2024) Microstructures and mechanical properties of laser-arc hybrid welded high-strength aluminum alloy through beam oscillation. J Mater Res Technol 32:3015–3024. https://doi.org/10.1016/j.jmrt.2024.08.144 Zhang Y, Yang C, Zhao L, Zhang J (2021) Study on the electrochemical corrosion behavior of 304 stainless steel in chloride ion solutions. Int J Electrochem Sci 16:210251. https://doi.org/10.20964/2021.02.01 Zhao Y, Wang Y, Tang S et al (2019) Edge cracking prevention in 2507 super duplex stainless steel by twin-roll strip casting and its microstructure and properties. J Mater Process Technol 266:246–254. https://doi.org/10.1016/j.jmatprotec.2018.11.010 Zheng J, Hu X, Pan C et al (2018) Effects of inclusions on the resistance to pitting corrosion of S32205 duplex stainless steel. Mater Corros 69:572–579. https://doi.org/10.1002/maco.201709723 Moura VS, Lima LD, Pardal JM et al (2008) Influence of microstructure on the corrosion resistance of the duplex stainless steel UNS S31803. Mater Charact 59:1127–1132. https://doi.org/10.1016/j.matchar.2007.09.002 Ralston KD, Birbilis N (2010) Effect of grain size on corrosion: A review. Corrosion 66. https://doi.org/10.5006/1.3462912 . 075005-1-075005–13 Supplementary Files Graphicalabstract.tif Highlight.docx Cite Share Download PDF Status: Under Review Version 1 posted Reviewers invited by journal 01 May, 2026 Editor assigned by journal 10 Feb, 2026 First submitted to journal 07 Feb, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8819933","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":632864479,"identity":"6952ca06-e729-4d69-9e79-b9243535577b","order_by":0,"name":"Jianxin Wang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Jianxin","middleName":"","lastName":"Wang","suffix":""},{"id":632864480,"identity":"23bdb109-d950-45c8-87ef-da486c7a1b5f","order_by":1,"name":"Zhaorong Sun","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Zhaorong","middleName":"","lastName":"Sun","suffix":""},{"id":632864481,"identity":"b3c3d09b-c9c0-4617-bcca-5bdd48cc6c2a","order_by":2,"name":"Chuantai Yu","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Chuantai","middleName":"","lastName":"Yu","suffix":""},{"id":632864482,"identity":"031620cf-991b-412e-93c0-a935fac185d5","order_by":3,"name":"Wang Zheng","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Wang","middleName":"","lastName":"Zheng","suffix":""},{"id":632864483,"identity":"842dee4d-749d-44ad-b909-bbe2a014fb6a","order_by":4,"name":"Ran Zong","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1klEQVRIiWNgGAWjYBADOQaGBBDNTLwWY6AWxgaStCQ2EK1Fvr338OuKmjvp89tzzB8wVFgnNrCfPYBXC2PPuTTLM8ee5W4488awgeFMemIDT14CXi3MEjlmhg1sh3M3SOQYNjC2HU5skOAxwKuFDazl3+F0+RkgLf+I0MIjkWP8sLHtcALDDZCWBiK0SPCcMWNs7DtsuOHMs8IZCcfSjdt4cvBrkW/vMf7Y8O2wvHx78oYPH2qsZfvZz+DXAvYOnJkA4hJSDwTMH4hQNApGwSgYBSMZAAA9TUZ8niHMtgAAAABJRU5ErkJggg==","orcid":"","institution":"Shandong University of Technology","correspondingAuthor":true,"prefix":"","firstName":"Ran","middleName":"","lastName":"Zong","suffix":""}],"badges":[],"createdAt":"2026-02-08 07:58:24","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8819933/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8819933/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108954871,"identity":"8b074709-58e2-413a-a37a-995ada1dfac4","added_by":"auto","created_at":"2026-05-11 08:00:06","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":367912,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of welding system: (a) Welding platform, (b) Welding torch position, (c) Laser beam oscillation mode\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8819933/v1/e99ecb2cab58269a3d6e7805.png"},{"id":108954886,"identity":"891aedda-1a9f-40d4-b346-13649304612c","added_by":"auto","created_at":"2026-05-11 08:00:11","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":92698,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of experimental samples: (a) Sampling location, (b) Positions of microstructure observation specimen, microhardness test and dimensions of tensile test specimen\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8819933/v1/9159969b963420088d50394a.png"},{"id":108954880,"identity":"214ee029-0ded-4dd2-8d6e-c78577d54dfd","added_by":"auto","created_at":"2026-05-11 08:00:10","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1225035,"visible":true,"origin":"","legend":"\u003cp\u003eWeld surfaces, cross sections, and X-ray NDT results of different welding processes and parameters. (a) LBW, (b) GMAW, (c) LAHW, (d) OLAHW\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8819933/v1/fd14dedf2c8130195b110fbc.png"},{"id":108954870,"identity":"7bfabe6d-3630-4460-b8d2-07af72b244c4","added_by":"auto","created_at":"2026-05-11 08:00:06","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":344443,"visible":true,"origin":"","legend":"\u003cp\u003eThe influence of process parameters on weld formation\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8819933/v1/c42079488f60d1fe9ba768e4.png"},{"id":108978091,"identity":"ac59eda8-d147-4ed9-9647-5dbc863292a1","added_by":"auto","created_at":"2026-05-11 11:34:01","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":653451,"visible":true,"origin":"","legend":"\u003cp\u003eMicrostructural characteristics of base metal: (a) OM image, (b) EBSD IPF map, (c) Phase map and (d) Average grain size\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8819933/v1/2b6527be25b50d9c9dd4efee.png"},{"id":108954898,"identity":"3cac67fe-44a7-4394-9c87-766a680e64b7","added_by":"auto","created_at":"2026-05-11 08:00:18","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1758184,"visible":true,"origin":"","legend":"\u003cp\u003eOM images of fusion line and weld zone under different processes: (a1-a2) LBW, (b1-b2) GMAW, (c1-c2) LAHW, (d1-d2) OLAHW\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8819933/v1/9b200120c451a700b6b2a08b.png"},{"id":108954885,"identity":"702acd61-407b-422c-9f87-5858eece1c72","added_by":"auto","created_at":"2026-05-11 08:00:11","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":1563571,"visible":true,"origin":"","legend":"\u003cp\u003eEBSD IPF maps and phase maps of interface and WB: (a1-a4) LBW, (b1-b4) GMAW, (c1-c4) LAHW, (d1-d4) OLAHW\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-8819933/v1/f78ac9cc2ed18d8f7745e51c.png"},{"id":108977595,"identity":"4e9c4848-d9fd-4d58-b910-3fa5863e4213","added_by":"auto","created_at":"2026-05-11 11:32:15","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":148350,"visible":true,"origin":"","legend":"\u003cp\u003eMicrohardness distribution of the welds with different welding processes: (a) Horizontal microhardness distribution, (b) Longitudinal microhardness distribution, (c) Average 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10","display":"","copyAsset":false,"role":"figure","size":1171855,"visible":true,"origin":"","legend":"\u003cp\u003eFractured surface morphologies with different welding processes: (a1-a2) LBW, (b1-b2) GMAW, (c1-c2) LAHW, (d1-d2) OLAHW\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-8819933/v1/22b1057964be94b03162fcdc.png"},{"id":108954840,"identity":"24834925-b1a1-4d2d-8bb1-ddb193d857ca","added_by":"auto","created_at":"2026-05-11 07:59:47","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":16595,"visible":true,"origin":"","legend":"\u003cp\u003ePotentiodynamic polarization curves for WB and BM with different welding processes (3.5%NaCl, room temperature)\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-8819933/v1/ad06f517b047d20fc02cd6f2.png"},{"id":109067542,"identity":"dc08e457-924a-46d9-a380-b26e3dd8bb52","added_by":"auto","created_at":"2026-05-12 09:55:39","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":9997560,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8819933/v1/a1cdf16e-ec6b-4b0c-99ac-e2741ba907fa.pdf"},{"id":108954897,"identity":"de15d5f3-6889-4cdc-be26-49fa443fca83","added_by":"auto","created_at":"2026-05-11 08:00:17","extension":"tif","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":3682412,"visible":true,"origin":"","legend":"","description":"","filename":"Graphicalabstract.tif","url":"https://assets-eu.researchsquare.com/files/rs-8819933/v1/09b9928f68a234b3f52bcd37.tif"},{"id":108954887,"identity":"98d5a7b4-0adc-489a-9a94-13bc6b6d2faf","added_by":"auto","created_at":"2026-05-11 08:00:11","extension":"docx","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":16179,"visible":true,"origin":"","legend":"","description":"","filename":"Highlight.docx","url":"https://assets-eu.researchsquare.com/files/rs-8819933/v1/36e6f939533c8e2154778370.docx"}],"financialInterests":"","formattedTitle":"Study on the mechanism of laser-arc hybrid welding in improving the weld quality of 2507 super duplex stainless steel","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003e2507 SDSS, a typical high-performance corrosion-resistant alloy, combines the high strength of ferritic stainless steels with the excellent toughness and corrosion resistance of austenitic stainless steels due to its unique duplex microstructure. It exhibits outstanding performance, particularly in resisting stress corrosion cracking and intergranular corrosion, and has thus become a core material in harsh service environments such as marine engineering, chemical equipment, and offshore oil and gas extraction [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. In these fields, the quality of welded joints directly determines the structural integrity and service life of the entire equipment, yet the welding process of 2507 SDSS faces critical technical challenges: the welding thermal cycle tends to disrupt its inherent phase balance, leading to an abnormal increase in ferrite content in the weld zone (even exceeding 70%), while also potentially inducing the precipitation of detrimental phases such as σ phase, χ phase, and chromium carbides. These microstructural changes ultimately result in degraded joint toughness and impaired corrosion resistance [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Industrial standards explicitly require that the content of the minority phase (typically the austenite phase) in 2507 SDSS weld joints should not be less than 30%. Therefore, achieving the synergistic optimization of weld microstructure and properties through welding process control has become a central issue for the engineering application of this material [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eCurrently, welding processes applicable to 2507 SDSS mainly include GMAW, LBW, and LAHW, but each has certain limitations in performance control [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. GMAW, with its high heat input and relatively slow cooling rate, provides sufficient time for austenite nucleation and growth, partially restoring the phase balance. However, it tends to cause coarsening of weld grains. Furthermore, the high heat input accelerates the diffusion and precipitation of Cr and Mo elements at grain boundaries, forming Cr-rich carbides (e.g., M\u003csub\u003e23\u003c/sub\u003eC\u003csub\u003e6\u003c/sub\u003e) and creating Cr-depleted zones along the boundaries, which substantially reduces the corrosion resistance of the joint [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. LBW, with its extremely high energy density, greatly increases the cooling rate. Although it suppresses the precipitation of harmful phases, it severely hinders the diffusive phase transition of austenite in the ferrite matrix, leading to a significantly high ferrite content in the weld (\u0026gt;\u0026thinsp;80%). This ultimately manifests as a sharp increase in joint hardness (\u0026gt;\u0026thinsp;340 HV\u003csub\u003e0.5\u003c/sub\u003e) and a substantial decrease in plasticity (elongation\u0026thinsp;\u0026lt;\u0026thinsp;15%), making it difficult to meet mechanical performance requirements under complex service conditions [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eLAHW, as a hybrid heat source welding technology, integrates the respective advantages of laser and arc: the high energy density of the laser increases weld penetration and reduces the heat-affected zone (HAZ) width; the arc improves the wettability of the molten metal, suppressing defects like lack of fusion and porosity, while simultaneously creating a suitable temperature window for austenitic transformation by regulating the heat input [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. In recent years, with the development of beam oscillation technology, OLAHW has further expanded the scope for performance control. By employing periodic oscillation of the laser beam (e.g., linear, circular oscillation patterns), it enhances the convection and heat transfer of the liquid metal, breaking the directional growth trend of columnar crystals and achieving grain refinement [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Simultaneously, the oscillating action homogenizes the chemical composition of the molten pool, reduces elemental micro-segregation, provides more nucleation sites for austenite, and thus optimizes the weld microstructure and properties [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eExisting research has confirmed the significant advantages of LAHW in welding metallic materials. Qi et al. found that when the distance between the laser beam and the welding wire in LAHW was controlled at 2 mm, the coupling effect between the laser and arc was optimal, and the austenite content in 2507 SDSS welds increased linearly with heat input [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Chen et al. achieved an acceptable phase ratio (α:γ\u0026thinsp;=\u0026thinsp;3:1) in 2507 SDSS joints using oscillating laser beam welding, with the joint tensile strength increasing by 10%-15% compared with conventional LBW [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Hao et al., in the study on Q235 steel, demonstrated that OLAHW could increase weld elongation by 8%-12% while reducing microhardness by 5%-8% [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Su et al., investigating the influence of laser oscillation frequency and amplitude on LAHW stability and porosity, found that oscillating laser improved the macro morphology of joints, significantly reduced porosity and impurity segregation, and increased elongation [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Ma et al. discovered that the addition of oscillating laser altered the energy distribution in the hybrid welding pool. The oscillating beam directly heated the sidewalls, improving the wetting ability between the molten pool and the sidewalls, which effectively suppressed the occurrence of lack of fusion defects [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Chen et al., studying the effects of four laser oscillation modes on weld joint morphology, microstructure, and mechanical properties, pointed out that the morphologies of welded joints differed significantly among the modes. Circular oscillation achieved the maximum weld penetration, the finest columnar grains, and the largest equiaxed grain area, resulting in significantly superior joint mechanical properties [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. However, most existing research focuses on the influence of single process parameters or other metallic materials. Systematic studies on OLAHW for 2507 SDSS remain relatively scarce, particularly comparative studies on the effects of different welding processes (LBW, GMAW, LAHW, OLAHW) on the weld formation, microstructure, and properties. The regulatory mechanisms of oscillation parameters (frequency, amplitude) in OLAHW on the duplex phase balance and corrosion resistance of 2507 SDSS have not been clearly defined, and the optimization of relevant process parameters lacks theoretical support.\u003c/p\u003e \u003cp\u003eBased on the aforementioned research status, this study used 2507 SDSS as the research object and systematically conducted welding experiments using four processes: LBW, GMAW, LAHW, and OLAHW. It focused on investigating the influence laws of key hybrid welding parameters (laser power, welding current, welding speed, heat source spacing) and oscillation parameters (frequency \u003cem\u003ef\u003c/em\u003e, amplitude \u003cem\u003eA\u003c/em\u003e) on weld formation (penetration, width), microstructure (grain size, phase ratio, harmful phase content), mechanical properties (microhardness, tensile strength, elongation), and electrochemical corrosion performance (corrosion potential, corrosion current density, passivation range). By revealing the internal relationship of \"beam oscillation - molten metal flow - microstructure evolution - performance response\" in OLAHW, the optimal welding process scheme for 2507 SDSS was identified, providing a theoretical basis and technical reference for the welding engineering application of this material in harsh environments.\u003c/p\u003e"},{"header":"2 Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Base material and filler wire\u003c/h2\u003e \u003cp\u003eRolled 2507 SDSS plates with dimensions of 200 mm \u0026times;70 mm \u0026times; 6 mm were used as the base metal. The welding wire was ER2594 with a diameter of 1.2 mm, which was specifically designed in composition to match the high chromium, molybdenum, and nitrogen content of 2507 SDSS, aiming to compensate for element burn-off during welding and promote austenite formation to maintain the required duplex phase balance and corrosion resistance of the weld metal. The specific chemical compositions were shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Before welding, the plates were mechanically polished, followed by cleaning with anhydrous ethanol to remove surface oxides and oil stains, ensuring process stability and weld quality.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eChemical composition of 2507 SDSS and ER 2594 (wt.%)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"11\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaterial\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMn\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCr\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eMo\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eP\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eS\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eCu\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c11\"\u003e \u003cp\u003eN\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2507\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.018\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e25.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e7.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e3.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e0.26\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eER2594\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.017\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e24.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e8.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e3.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e0.21\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Welding system and evaluation modes\u003c/h2\u003e \u003cp\u003eThe experiment adopted a laser-arc hybrid welding system as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a), primarily consisting of a 3 kW fiber laser (wavelength 1064 nm), a digital GMAW power source, and a beam oscillation module. The laser beam was transmitted via optical fiber, and then entered the beam oscillation system, where it was driven by oscillating motors to perform periodic oscillations along preset trajectories in the X-Y plane, finally focusing on the workpiece surface with a spot diameter of approximately 1 mm.\u003c/p\u003e \u003cp\u003eDuring welding, a cooperative mode with the arc leading and the laser trailing was adopted. The GMAW torch was tilted backward, and the laser beam was tilted forward, maintaining angles of 70\u0026deg; and 80\u0026deg; with the workpiece surface, respectively. The distance between them varied according to the experimental design, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(b). High-purity argon was used as the shielding gas, with flow rates set at 20 L/min for both the arc and laser.\u003c/p\u003e \u003cp\u003eBased on the principle of single-variable control, 18 groups of welding experiments were systematically designed on the basis of benchmark parameters (laser power 2.5 kW, current 250 A, welding speed 20 mm/s, heat source spacing 2 mm, oscillation off), covering four processes: LBW, GMAW, LAHW, and OLAHW. In the OLAHW experiments, the laser beam adopted a linear oscillation mode, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(c). The effects of oscillation frequency (100\u0026ndash;500 Hz) and oscillation width (1\u0026ndash;5 mm) on weld formation and organizational properties were specifically studied. Detailed welding parameters are listed in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eParameters of welding process\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNo.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eProcess\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLaser power (kW)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCurrent (A)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eVoltage (V)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eWelding\u003c/p\u003e \u003cp\u003eSpeed (mm/s)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eInter-beam Distance (mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eOscillating\u003c/p\u003e \u003cp\u003eFrequency (Hz)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eOscillating width (mm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLBW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGMAW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e20.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e300\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e30.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e300\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e300\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e300\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAfter welding, X-ray non-destructive testing was used to analyze internal defects such as porosity. Sampling was performed according to the scheme shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Metallographic specimens of the weld cross-section were obtained by wire electrical discharge machining. After etching with Beraha's reagent (20 ml HCl\u0026thinsp;+\u0026thinsp;80 ml H₂O\u0026thinsp;+\u0026thinsp;1 g K₂S₂O₅), a stereomicroscope and optical microscope (OM) were used to observe the macrostructure and microstructure. Electron backscatter diffraction (EBSD) was employed to analyze grain morphology and phase distribution, with an operating voltage of 20 kV and a step size of 0.5 \u0026micro;m.\u003c/p\u003e \u003cp\u003eMechanical property tests included: transverse and longitudinal microhardness mapping was performed using a Vickers hardness tester (load 500 gf, dwell time 15 s) along the paths shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b). Tensile tests were conducted at room temperature at a rate of 1 mm/min, and the fracture morphology was observed using a scanning electron microscopy (SEM) to analyze the fracture mechanism.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results and discussions","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Weld bead formation\u003c/h2\u003e \u003cp\u003eFigures \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e present the weld surface morphology, cross-sectional macrostructure, X-ray non-destructive testing results, and weld formation for the four welding processes (LBW, GMAW, LAHW, OLAHW). Macrostructure analysis revealed significant differences in penetration depth, weld width, and formation quality among the different processes.\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e3.1.1 Comparison of weld formation\u003c/h2\u003e \u003cp\u003eIn terms of weld surface morphology (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea-d), the LBW weld surface was the brightest and continuous, with a width of only 2.72 mm, exhibiting typical laser welding characteristics. The GMAW weld surface had slightly lower glossiness, with a width reaching 5.19 mm, showing the typical wide weld characteristic of arc welding. The LAHW weld surface appeared dark gray, with the width increasing to 6.05 mm; whereas the OLAHW weld surface was the darkest, with the maximum width of 7.02 mm, indicating that beam oscillation significantly altered molten pool flow and thermal distribution uniformity.\u003c/p\u003e \u003cp\u003eComparison of weld cross-sectional morphology found that the LBW weld was flat-shaped, characterized by a large weld width and a small penetration, and belonged to heat conduction welding. The GMAW weld was bowl-shaped, with the shallowest penetration (1.05 mm) but the widest HAZ, reflecting its high heat input characteristic. The LAHW weld achieved better coordination between penetration depth (1.72 mm) and weld width, demonstrating the synergistic enhancement effect of laser and arc. OLAHW, through the stirring action of beam oscillation, achieved the maximum penetration depth (1.81 mm), with the most ideal molten pool morphology.\u003c/p\u003e \u003cp\u003eX-ray non-destructive testing results showed varying characteristics of porosity and undercut defect distributions for different processes. Welds from the LBW and GMAW showed no obvious defects. In LAHW, when laser power was too low (2.0 kW) or current was too small (200 A), the fluidity and existence time of the molten pool were insufficient, exacerbating the tendency for porosity and undercut formation. In OLAHW, when oscillation frequency was too low (100 Hz) or amplitude too small (1 mm), the stirring effect was weak, which was not conducive to gas escape and prone to porosity.\u003c/p\u003e \u003cp\u003eBy comparing welds under different parameters, it was found that minor changes in process parameters significantly affected formation quality. OLAHW under the optimal oscillation parameters (\u003cem\u003ef\u003c/em\u003e\u0026thinsp;=\u0026thinsp;300 Hz, \u003cem\u003eA\u003c/em\u003e\u0026thinsp;=\u0026thinsp;3 mm) had the most ideal weld formation, featuring the best coordination between weld penetration and width, the fewest defects, and fully demonstrated the significant advantages of beam oscillation technology in improving weld formation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e3.1.2 Influence mechanism of process parameters on weld formation\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, by systematically comparing weld dimensions (penetration, width) under different process parameters, clearly reveals the influence of each parameter on weld formation. Within the laser power range of 2.0\u0026ndash;3.0 kW, the penetration and width did not increase monotonically with power but instead showed a trend of first decreasing and then increasing (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). The mechanism was as follows: increased power enhanced the laser-induced plasma, which guided and compressed the arc, but excessively strong plasma also shielded the incident laser energy [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Before reaching the critical power threshold, the shielding effect was dominant, resulting in insufficient laser energy effectively used for deep penetration; beyond the threshold, the laser energy density was sufficient to penetrate the plasma, the deep penetration effect was enhanced, and the synergistic effect reached the best.\u003c/p\u003e \u003cp\u003eWhen the welding current was in the range of 200\u0026ndash;300 A, the increase in current directly led to higher total heat input and a wider arc action range, thereby significantly increasing penetration and width (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). More importantly, the increased arc plasma had a \"dilution\" effect on the laser-induced plasma, reducing its shielding effect on the laser, thereby improving the absorption efficiency of the base metal for laser energy and achieving a \"1\u0026thinsp;+\u0026thinsp;1\u0026gt;2\" synergistic enhancement effect [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eWhen the welding speed increased from 15 mm/s to 25 mm/s, the linear energy density decreased, leading to a significant decrease in penetration and width (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec). In the high-speed range (20\u0026ndash;25 mm/s), the penetration decrease rate slowed down, which proved a key advantage of the LAHW process: it could adopt a higher welding speed while maintaining the same penetration, thereby improving production efficiency and reducing total heat input.\u003c/p\u003e \u003cp\u003eThe inter-beam distance directly controls the strength of the synergistic interaction between the laser and arc. At a distance of 0 mm, the laser directly passed through the arc center, leading to arc instability and excessive expansion, forming a wide and shallow weld. At distances of 2\u0026ndash;4 mm, the synergistic effect was strongest, with the laser's stabilizing and compressing effect on the arc being most significant, resulting in the most concentrated energy and thus a narrower weld width. When the distance increased to 6 mm, the two heat sources operated almost independently, the synergistic effect disappeared, and the weld morphology resembled that of single GMAW.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e3.1.3 Effect of beam oscillation parameters on weld formation\u003c/h2\u003e \u003cp\u003eIn OLAHW, at low oscillation frequencies (100\u0026ndash;200 Hz), the oscillation period was long, equivalent to a slowly moving \"linear heat source\", leading to energy dispersion. The weld penetration and width were even smaller than those without oscillation (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee) [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. At medium frequency (300 Hz), the oscillation produced the best regulatory effect. At this point, intense periodic stirring enhanced internal convection within the molten pool, efficiently transferring heat to the bottom of the pool, while avoiding excessive energy dispersion, thus achieving the maximum penetration (1.81 mm). At high frequency (500 Hz), the laser beam scanning speed was extremely fast, transforming its heat source character from a \"point heat source\" to a \"surface heat source\", preheating the workpiece over a large area, resulting in a significant decrease in energy density, so the penetration decreased. At the same time, the intense stirring effect violently pushed the liquid metal to the edge of the molten pool, causing a sharp increase in weld width (to 9.27 mm).\u003c/p\u003e \u003cp\u003eWhen the oscillation amplitude increased (from 1 mm to 3 mm), the intensity and range of molten pool stirring were enhanced, which was more conducive to heat transfer to the depth direction, so the penetration and width increased synchronously (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef). However, when the amplitude was too large (5 mm), the laser beam scanning path was too long, and the energy density and residence time per unit area decreased again, leading to limited penetration growth and even a decrease in weld width.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eComprehensive analysis indicated that process parameters macroscopically influence weld dimensions by controlling the total heat input and laser-arc synergistic effect, whereas beam oscillation parameters (frequency, amplitude) achieve micro-regulation of weld formation by altering the energy distribution state and molten pool fluid dynamics behavior. The optimal oscillation parameters (300 Hz, 3 mm in this study) achieved the best balance between energy concentration and molten pool stirring, resulting in a weld with deep penetration and favorable morphology.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Microstructure characterization of the weld\u003c/h2\u003e \u003cp\u003eUsing OM, EBSD, and grain size statistical analysis (Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e), the influence laws of different welding processes on the microstructural evolution of 2507 SDSS welds were systematically revealed, clarifying the differences in microstructure morphology, phase ratio, and grain size under various processes.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e3.2.1 Microstructure of the base metal\u003c/h2\u003e \u003cp\u003eThe 2507 SDSS base metal had a typical duplex microstructure, consisting of nearly equal proportions of ferrite (α phase, dark area in OM image) and austenite (γ phase, bright area in OM image), where the γ phase was uniformly distributed in the α phase matrix in island or strip form (Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a-c)). EBSD grain size statistics showed that the average grain size of the α phase was 8.6 \u0026micro;m, and the average grain size of the γ phase was 4.4 \u0026micro;m (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(d)). The microstructure was uniform and fine, providing a benchmark for subsequent comparison of weld microstructure and properties.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e3.2.2 Weld microstructure morphology\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the microstructures of the 2507 SDSS weld fusion line and center under four welding processes (LBW, GMAW, LAHW, OLAHW). LBW, with its low heat input and extremely high cooling rate, resulted in the α phase growing directionally from the fusion line towards the weld center, forming coarse columnar grains (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a1)). Its HAZ width was the narrowest, but slight grain coarsening of the α phase still occurred within the HAZ. The diffusion-based phase transformation of the γ phase in the weld was significantly inhibited, and only a small amount of discontinuous grain boundary austenite (GBA) was formed at the α phase grain boundaries, with the GBA morphology conforming to the contours of the α phase grains (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a2)). This led to a significantly high α phase content (\u0026gt;\u0026thinsp;80%) in the weld zone, resulting in a severe imbalance in the duplex phase ratio.\u003c/p\u003e \u003cp\u003eGMAW had high heat input and slow cooling rate, providing sufficient time for γ phase nucleation and growth. The weld contained numerous coarse GBA and feathery WA growing perpendicular to the fusion line. Its HAZ width was the widest, and grains were severely coarsened, becoming a weak performance area (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(b1)). There was a small amount of IGA in the weld, which contained less Cr, Mo, and N elements than GBA, leading to reduced material toughness, increased brittleness, and decreased fatigue strength and corrosion resistance [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn LAHW, the laser-arc synergistic effect resulted in a weld cooling rate intermediate between LBW and GMAW. Its HAZ width was also intermediate, and the degree of grain coarsening was weaker than in GMAW (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(c1)) [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. The GBA in the weld was slenderer, the WA content was significantly reduced compared to GMAW, and the IGA content increased markedly, appearing as acicular/particulate dispersions within the α phase (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(c2)). The microstructure was significantly improved, and the degree of duplex phase ratio imbalance was alleviated compared with LBW.\u003c/p\u003e \u003cp\u003eOLAHW introduced periodic beam oscillation, which enhanced the convection of liquid metal and made the temperature distribution more uniform in the molten pool. Its HAZ width was narrower than that of LAHW, and there was no obvious grain coarsening phenomenon (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e (d1)). The α phase grains in the weld were finer, providing more nucleation sites for the γ phase, leading to the formation of numerous fine IGA particles, appearing as acicular/particulate dispersions within the α phase (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(d2)). The GBA became slenderer and more discontinuous, the proportion of WA further reduced, resulting in the optimal microstructure.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e3.2.3 Quantitative analysis of grain and phase distribution\u003c/h2\u003e \u003cp\u003eQuantitative analysis of grain size and phase distribution in the welds of the four processes was performed using EBSD Inverse Pole Figure (IPF) maps and phase maps (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e), with results summarized in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eDue to the excessively fast cooling rate of LBW welds, the duplex phase ratio was seriously imbalanced, only a small amount of discontinuous GBA was distributed at the α grain boundaries. The α and γ grain sizes of GMAW welds were 18.4 \u0026micro;m and 6.7 \u0026micro;m respectively, the duplex phase ratio was the most balanced, but the microstructure was coarse, and there was more WA, affecting the microstructure uniformity. LAHW achieved grain refinement and phase ratio optimization through synergistic effect. The α and γ grain sizes in the weld were 16.2 \u0026micro;m and 5.3 \u0026micro;m respectively, the contents of GBA and WA decreased, and the IGA content increased significantly. By virtue of the molten pool stirring effect of beam oscillation, OLAHW obtained the most ideal microstructure: the finest α phase grains (14.6 \u0026micro;m), with the γ phase predominantly in the form of uniformly dispersed IGA, and a relatively balanced duplex phase ratio, laying a microstructural foundation for performance enhancement.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAverage grain size phase ratio of the weld bead under different welding processes\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProcess\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSize of α (\u0026micro;m)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSize of γ (\u0026micro;m)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRatio of α (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRatio of γ (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e51.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e48.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLBW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e36.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e94.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e6.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGMAW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e18.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e37.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e62.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e16.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e60.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e39.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e14.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e62.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e37.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e3.2.4 Microstructure evolution mechanism\u003c/h2\u003e \u003cp\u003eWelding processes dominated the microstructure evolution path by regulating thermal cycles and molten pool fluid dynamics behavior, and the core mechanisms could be divided into two aspects:\u003c/p\u003e \u003cp\u003eCooling rate dominated phase transformation behavior: the LBW cooling rate far exceeded the critical value for the diffusion-based phase transformation of the γ phase, forming a high proportion of α phase structure, leading to duplex phase ratio imbalance [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. GMAW, with high heat input and slow cooling, promoted γ phase nucleation and growth but easily caused grain coarsening and WA formation, and sufficient element diffusion led to grain boundary segregation [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. LAHW and OLAHW had cooling rates intermediate between LBW and GMAW, providing sufficient time for γ phase precipitation while avoiding excessive grain coarsening.\u003c/p\u003e \u003cp\u003eMolten pool flow regulated microstructure homogeneity: OLAHW, through periodic beam oscillation, enhanced molten pool convection, broke the directional growth trend of α phase columnar grains in traditional welding, increased nucleation sites, and promoted the formation of equiaxed grains and IGA [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Simultaneously, the oscillation action homogenized the chemical composition of the molten pool, reduced micro-segregation of elements like Cr, Mo, and N, avoided local phase transformation abnormalities due to compositional inhomogeneity, and achieved dual optimization of \"grain refinement\u0026thinsp;+\u0026thinsp;compositional homogenization\".\u003c/p\u003e \u003cp\u003eIn summary, OLAHW, leveraging the synergistic effect of \"moderate cooling rate\u0026thinsp;+\u0026thinsp;forced molten pool convection\", outperformed the other processes in terms of grain refinement, phase ratio control, and compositional homogeneity, providing an ideal microstructural foundation for the enhancement of mechanical properties and corrosion resistance of the weld.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Mechanical properties and corrosion resistance\u003c/h2\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003e3.3.1 Microhardness test\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows the microhardness distribution of weld zones under four welding processes (LBW, GMAW, LAHW, OLAHW). In the transverse hardness distribution (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(a)), the LBW weld had the highest microhardness, reaching 342.3 HV\u003csub\u003e0.5\u003c/sub\u003e, which was higher than its HAZ hardness (325.3 HV\u003csub\u003e0.5\u003c/sub\u003e). This was because the extremely fast cooling rate of LBW inhibited austenite precipitation, forming a high proportion of ferrite, leading to weld hardening. The GMAW weld hardness was 283.2 HV\u003csub\u003e0.5\u003c/sub\u003e, between LAHW and OLAHW, and lower than its HAZ hardness (296.0 HV\u003csub\u003e0.5\u003c/sub\u003e). High heat input and slow cooling coarsened the weld microstructure, and generated a large amount of GBA and WA with low hardness, leading to weld softening. Its HAZ had a higher ferrite proportion and relatively higher hardness. The LAHW weld hardness was 297.6 HV\u003csub\u003e0.5\u003c/sub\u003e, higher than OLAHW. Its moderate cooling rate promoted finer GBA and more acicular IGA, balancing strength and toughness, and avoiding excessive hardening of LBW and excessive softening of GMAW. The OLAHW weld had the lowest hardness of 272.4 HV\u003csub\u003e0.5\u003c/sub\u003e, which was close to the HAZ hardness (279.8 HV\u003csub\u003e0.5\u003c/sub\u003e) and the most matched with the base metal hardness (274.1 HV\u003csub\u003e0.5\u003c/sub\u003e). Beam oscillation strengthened molten pool stirring, significantly promoted austenite transformation, especially increased IGA content, which mainly softened the weld and made the hardness closer to the base metal.\u003c/p\u003e \u003cp\u003eIn the longitudinal hardness distribution (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(b)), the central region of the LBW weld maintained a high average hardness (345.1 HV\u003csub\u003e0.5\u003c/sub\u003e), reflecting the microstructure inhomogeneity caused by rapid cooling. The central hardness of the GMAW weld was generally low (average 279.1 HV\u003csub\u003e0.5\u003c/sub\u003e) with large fluctuations, and the peak value (298.5 HV\u003csub\u003e0.5\u003c/sub\u003e) appeared in the HAZ. This was consistent with the characteristics of HAZ grain coarsening and weld microstructure softening. The central hardness distribution of the LAHW weld was relatively uniform with a narrow fluctuation range (270\u0026ndash;287 HV\u003csub\u003e0.5\u003c/sub\u003e). The laser-arc synergistic effect created a balanced thermal process, refined the microstructure, and promoted uniform austenite precipitation, reducing hardness differences. The central hardness distribution of the OLAHW weld was the flattest, with the lowest overall hardness value (average 275.6 HV\u003csub\u003e0.5\u003c/sub\u003e). Beam oscillation made the weld microstructure highly uniform, providing the weld with better plasticity and crack resistance.\u003c/p\u003e \u003cp\u003eCombining transverse and longitudinal hardness data, the hardness differences among the four processes essentially represented the relationship of \"thermal cycle - microstructure evolution - hardness response\". The cooling rate dominated the hardness foundation: LBW rapid cooling \u0026rarr; high ferrite \u0026rarr; high hardness; GMAW slow cooling \u0026rarr; coarsened structure\u0026thinsp;+\u0026thinsp;austenite \u0026rarr; low hardness; LAHW and OLAHW intermediate cooling \u0026rarr; balanced phase composition \u0026rarr; medium hardness. Beam oscillation optimized hardness uniformity: OLAHW, through periodic beam oscillation, not only adjusted the phase composition but also eliminated microstructure segregation through molten pool stirring, making the weld and HAZ hardness tend to be consistent and approach the base metal hardness, laying the foundation for enhanced comprehensive mechanical properties.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e \u003ch2\u003e3.3.2 Mechanical tensile test\u003c/h2\u003e \u003cp\u003eRoom temperature tensile tests were conducted to test the properties of welded joints under four welding processes (LBW, GMAW, LAHW, OLAHW), with results shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The tensile strength of all process joints was equivalent to or slightly higher than that of the base metal (823.7\u0026thinsp;\u0026plusmn;\u0026thinsp;9 MPa), meeting the engineering strength requirements. However, each process showed significant differences in yield strength, elongation, and fracture location, reflecting the profound influence of different thermal processes on properties.\u003c/p\u003e \u003cp\u003eDue to the extremely high cooling rate, the LBW weld had a ferrite content exceeding 80%. Although it exhibited the highest tensile strength (842.8\u0026thinsp;\u0026plusmn;\u0026thinsp;13 MPa) and relatively high yield strength (693.3\u0026thinsp;\u0026plusmn;\u0026thinsp;4 MPa), its plasticity was severely degraded, with an elongation of only 16.9\u0026thinsp;\u0026plusmn;\u0026thinsp;1%. During tensile testing, plastic deformation concentrated in the relatively softer base metal region, leading to fracture located in the base metal (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e (a)), exhibiting a characteristic of \"weld hard and brittle - base metal weak\" performance imbalance.\u003c/p\u003e \u003cp\u003eGMAW, with high heat input and slow cooling, promoted austenite precipitation (relatively balanced duplex phase ratio), contributing to improved plasticity, with an elongation (23.3\u0026thinsp;\u0026plusmn;\u0026thinsp;2%) second only to the base metal and OLAHW. However, severe grain coarsening in the HAZ made it a performance weak zone, initiating fracture, demonstrating a defect of \"good weld plasticity - insufficient HAZ strength\".\u003c/p\u003e \u003cp\u003eThe LAHW weld, influenced by the laser-arc synergistic effect, had a cooling rate intermediate between LBW and GMAW. The austenite content increased, but the distribution uniformity was general. The joint performance was intermediate: tensile strength 835.1\u0026thinsp;\u0026plusmn;\u0026thinsp;10 MPa, yield strength 724.3\u0026thinsp;\u0026plusmn;\u0026thinsp;4 MPa, elongation 19.6\u0026thinsp;\u0026plusmn;\u0026thinsp;3%. The fracture location was in the weld zone, reflecting the constraint on plasticity due to insufficient microstructural homogeneity in the weld.\u003c/p\u003e \u003cp\u003eOLAHW introduced beam oscillation, enhancing molten pool stirring, achieving grain refinement and dispersed austenite distribution (predominantly intragranular austenite). The joint plasticity significantly improved, with elongation reaching 24.8\u0026thinsp;\u0026plusmn;\u0026thinsp;2% (second only to the base metal); tensile strength 815.8\u0026thinsp;\u0026plusmn;\u0026thinsp;10 MPa, yield strength 688.2\u0026thinsp;\u0026plusmn;\u0026thinsp;5 MPa, showing the highest match with base metal properties. The fracture location returned to the base metal, indicating that the weld and HAZ achieved a balanced performance with synergistic optimization of \"strength-plasticity\".\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDetailed tensile test results\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTensile specimen\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTensile strength (MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eYield strength (MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDuctility (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eFracture location\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBase metal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e823.7\u0026thinsp;\u0026plusmn;\u0026thinsp;9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e677.2\u0026thinsp;\u0026plusmn;\u0026thinsp;6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e26.3\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1-LBW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e842.8\u0026thinsp;\u0026plusmn;\u0026thinsp;13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e693.3\u0026thinsp;\u0026plusmn;\u0026thinsp;4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e16.9\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eBM\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2-GMAW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e833.2\u0026thinsp;\u0026plusmn;\u0026thinsp;11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e741.8\u0026thinsp;\u0026plusmn;\u0026thinsp;9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e23.3\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eHAZ\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4-LAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e835.1\u0026thinsp;\u0026plusmn;\u0026thinsp;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e724.3\u0026thinsp;\u0026plusmn;\u0026thinsp;4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e19.6\u0026thinsp;\u0026plusmn;\u0026thinsp;3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eWB\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e15-OLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e815.8\u0026thinsp;\u0026plusmn;\u0026thinsp;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e688.2\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e24.8\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eBM\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eObservation of the tensile fracture surfaces via SEM (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e) revealed that all four processes exhibited ductile fracture characteristics (visible dimples), but there were significant differences in dimple morphology and associated features. The LBW fracture surface had uneven dimple sizes, with local cleavage planes visible, indicating limited plastic deformation capacity during fracture, consistent with the hard and brittle characteristics caused by the high ferrite proportion, and matching the lowest elongation test result. The GMAW fracture surface had a larger number of dimples, but some dimple bottoms contained second-phase particles (nitrides or carbides precipitated during welding). These particles became nucleation sites for microcavities during tensile deformation. Although the elongation was not significantly reduced, it reflected the micro segregation problem caused by slow cooling. The LAHW fracture surface showed cleavage steps and cleavage planes, with a lower dimple density than GMAW and OLAHW, indicating poorer plastic deformation capacity, consistent with the inhomogeneous austenite distribution and insufficient microstructural homogeneity in the weld. The OLAHW fracture surface was covered by a large number of uniformly deep, densely arranged equiaxed dimples, without obvious cleavage characteristics or second-phase particle aggregation, indicating that microcavities could fully grow and coalesce during tensile deformation, reflecting excellent plastic deformation capacity, directly corresponding to its refined and uniform microstructural characteristics.\u003c/p\u003e \u003cp\u003eIn summary, the correlation between tensile properties and fracture morphology indicated that the \"strength-plasticity\" balance of 2507 SDSS welded joints depended on the process's ability to regulate the microstructure. Specifically, through the dual effects of \"grain refinement\u0026thinsp;+\u0026thinsp;austenite dispersion\", OLAHW solved the problems of insufficient plasticity of LBW, weak HAZ of GMAW, and inhomogeneous microstructure of LAHW, achieving the optimal mechanical properties matching the base metal.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section3\"\u003e \u003ch2\u003e3.3.3 Corrosion resistance\u003c/h2\u003e \u003cp\u003ePotentiodynamic polarization tests were conducted to evaluate the electrochemical corrosion behavior of welds and base metal in a 3.5% NaCl solution at room temperature (simulating marine corrosion environment). The polarization curves were shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e. The extracted results of key electrochemical parameters (self-corrosion potential \u003cem\u003eE\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e, breakdown potential \u003cem\u003eE\u003c/em\u003e\u003csub\u003eb\u003c/sub\u003e, passivation interval \u003cem\u003e∆E\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e, self-corrosion current density \u003cem\u003eI\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e) were shown in Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cem\u003eE\u003c/em\u003e \u003csub\u003ecorr\u003c/sub\u003e reflected the thermodynamic stability of the material in the corrosion environment. The higher the value, the more difficult the material was to corrode. \u003cem\u003eI\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e was a direct indicator of the corrosion rate. The lower the value, the slower the corrosion rate [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. The \u003cem\u003eE\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e of the LBW weld was higher than that of the base metal, but the \u003cem\u003eI\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e was about 1.8 times that of the base metal. Its higher \u003cem\u003eE\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e was due to the rapid cooling inhibiting the precipitation of harmful phases, but the high proportion of ferrite (\u0026gt;\u0026thinsp;80%) still led to a higher corrosion rate than the base metal. The \u003cem\u003eE\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e of the GMAW weld was lower than that of the base metal, and the \u003cem\u003eI\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e was about 4.5 times that of the base metal. High heat input and slow cooling promoted the precipitation of Cr and Mo elements at grain boundaries to form Cr-rich carbides, leading to Cr-depleted zones at grain boundaries, which became corrosion active sites and significantly accelerated the corrosion process. The \u003cem\u003eE\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e of the LAHW weld was lower than that of the base metal, and the \u003cem\u003eI\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e was about 2.0 times that of the base metal. Although the laser-arc synergistic effect optimized the cooling rate, the lack of molten pool stirring led to element segregation, and the corrosion rate was significantly higher than that of the base metal. The OLAHW weld had the highest \u003cem\u003eE\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e among all tested samples, and the \u003cem\u003eI\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e was only slightly lower than that of the base metal, indicating that the introduction of beam oscillation significantly improved the electrochemical stability of the weld and reduced the corrosion rate.\u003c/p\u003e \u003cp\u003e \u003cem\u003e∆E\u003c/em\u003e \u003csub\u003ep\u003c/sub\u003e represented the ability of the material to resist pitting corrosion after forming a passive film. The wider the interval, the stronger the pitting corrosion resistance [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. The base metal performed the best, reflecting the excellent pitting corrosion resistance of its original duplex structure. The LBW weld had the narrowest \u003cem\u003e∆E\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e. Although there was no obvious element segregation, the excessive ferrite led to inhomogeneous composition of the passive film, resulting in the weakest pitting corrosion resistance. The \u003cem\u003e∆E\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e of GMAW and LAHW welds were slightly narrowed, reflecting the damage to the integrity of the passive film caused by improper heat input control or inhomogeneous microstructure. The \u003cem\u003e∆E\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e of the OLAHW weld was only minimally smaller than that of the base metal, indicating that after grain refinement and uniform phase distribution by beam oscillation, the stability of the weld passive film was close to that of the base metal.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eExtracted data from the polarization curves\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eE\u003csub\u003ecorr\u003c/sub\u003e (mV vs. SSE)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eE\u003csub\u003eb\u003c/sub\u003e (mV vs. SSE)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e∆E\u003csub\u003ep\u003c/sub\u003e (mV vs. SSE)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eI\u003csub\u003ecorr\u003c/sub\u003e (nA/cm\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-415\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1011.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1426.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e153.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLBW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-398\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e896.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1294.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e273.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGMAW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-478\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e875.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1353.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e685.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-458\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e925.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1383.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e311.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOLAHW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-384\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1016.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1400.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e143.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe differences in corrosion resistance among the four processes were essentially a chain effect of \"welding thermal cycle - molten pool behavior - microstructure - corrosion response\", and the core regulatory mechanisms could be summarized into two points:\u003c/p\u003e \u003cp\u003eThe first was the balance of phase ratio and suppression of harmful phase. The corrosion resistance of 2507 SDSS depended on a balanced α/γ ratio (industrial requirement γ\u0026thinsp;\u0026ge;\u0026thinsp;30%). LBW rapid cooling led to insufficient γ phase precipitation (\u0026lt;\u0026thinsp;20%), while GMAW slow cooling, although achieving balanced phase ratio, induced coarse WA, both of which damaged the microstructure stability. Through \"moderate cooling rate\u0026thinsp;+\u0026thinsp;beam oscillation stirring\", OLAHW promoted the dispersed precipitation of IGA while suppressing the formation of WA, forming an ideal balanced α/γ structure, laying the structural foundation for corrosion resistance [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe second was microstructure homogeneity and element segregation control. In OLAHW, beam oscillation strengthened molten pool convection, effectively breaking the directional growth of α phase columnar grains, achieving grain refinement (the average size of α phase was 14.6 \u0026micro;m, the finest among the four processes), and increasing the nucleation sites of the passive film [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. It also significantly homogenized the molten pool composition, alleviating micro-segregation of key corrosion-resistant elements like Cr and Mo, avoiding the formation of local Cr-depleted zones, thereby ensuring a uniform and dense passive film. This was directly manifested as excellent electrochemical performance: \"high \u003cem\u003eE\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e, low \u003cem\u003eI\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e, wide \u003cem\u003e∆E\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e\".\u003c/p\u003e \u003cp\u003eIn summary, OLAHW, through the synergistic regulation of molten pool behavior and microstructure evolution by beam oscillation, significantly improved the \"phase imbalance\" of LBW, the \"element segregation\" of GMAW, and the \"microstructural inhomogeneity\" of LAHW. This resulted in weld corrosion resistance not only superior to the other three processes but also matching that of the base metal, providing key technical support for the engineering application of 2507 SDSS in harsh corrosive environments.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"4 Conclusions","content":"\u003cp\u003eThis study systematically compared the effects of four processes (LBW, GMAW, LAHW, and OLAHW) on the weld formation, microstructure evolution, mechanical properties, and corrosion resistance of 2507 SDSS, and the following conclusions were drawn:\u003c/p\u003e \u003cp\u003e(1) The process synergistic effect determined the weld formation quality, and beam oscillation achieved formation optimization. LAHW combined the synergistic advantages of laser and arc, resulting in weld penetration depth and width superior to single heat source processes. After introducing beam oscillation (OLAHW), under suitable parameters (frequency 300 Hz, amplitude 3 mm), the molten pool flow and thermal distribution were further optimized, achieving relatively large penetration (1.81 mm), the best formation quality, and the lowest defect rate.\u003c/p\u003e \u003cp\u003e(2) Cooling rate and molten pool flow synergistically regulate the microstructure, constructing the optimal morphological structure. LAHW, through the laser-arc synergistic effect, regulated the cooling rate, promoted IGA precipitation, and alleviated the duplex phase imbalance, but the lack of molten pool stirring led to insufficient microstructural homogeneity. OLAHW, through the dual action of \"moderate cooling rate\u0026thinsp;+\u0026thinsp;forced molten pool convection,\" broke the directional growth of α phase columnar grains, promoted uniform dispersion of the γ phase, significantly suppressed WA formation, and constructed the optimal microstructure of \"fine-grained α phase\u0026thinsp;+\u0026thinsp;dispersed IGA\".\u003c/p\u003e \u003cp\u003e(3) Mechanical properties matching the base metal were achieved, solving the \"strength-plasticity\" imbalance problem. The OLAHW weld had the lowest hardness and the most uniform distribution. Its tensile strength reached 815.8 MPa, and its elongation reached 24.8%, showing the closest match to the base metal properties. The tensile fracture surface was covered with dense and uniform equiaxed dimples, with no obvious cleavage planes or aggregation of second-phase particles, indicating excellent plasticity and crack propagation resistance.\u003c/p\u003e \u003cp\u003e(4) Beam oscillation enhanced corrosion resistance, enabling applicability in harsh corrosive environments. OLAHW, through grain refinement, increased passive film nucleation sites, while homogenizing the distribution of corrosion-resistant elements like Cr and Mo, avoiding the formation of local Cr-depleted zones, and ensuring a dense passive film. This resulted in the weld exhibiting the highest corrosion potential, the lowest corrosion current density, and a passivation range close to that of the base metal, representing the optimal corrosion resistance.\u003c/p\u003e \u003cp\u003eIn summary, OLAHW, through the synergistic regulation of process parameters and oscillation parameters, outperformed the other processes in terms of grain refinement, phase ratio control, and compositional homogeneity. It achieved synergistic improvement in weld formation, mechanical properties, and corrosion resistance. The regulatory principle of \"beam oscillation - molten pool flow - microstructure evolution - performance response\" provided direct technical reference for the engineering welding of 2507 SDSS and theoretical guidance for the optimization of welding processes for other stainless steels.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eCompeting Interests\u003c/h2\u003e \u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis work was supported by the Shandong Provincial Natural Science Foundation [grant number ZR2023ME139], Central Guiding Local Technology Development Funding Projects [grant number YDZX2024113].\u003c/p\u003e\u003ch2\u003eAuthor Contributions\u003c/h2\u003e \u003cp\u003e \u003cb\u003eJianxin Wang\u003c/b\u003e: Writing \u0026ndash; original draft, Data curation. \u003cb\u003eZhaorong Sun\u003c/b\u003e: Formal analysis, Resources. \u003cb\u003eChuantai Yu\u003c/b\u003e: Investigation, Visualization. \u003cb\u003eWang Zheng\u003c/b\u003e: Methodology. \u003cb\u003eRan Zong\u003c/b\u003e: Writing \u0026ndash; review \u0026amp; editing, Supervision.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThis work was supported by the Shandong Provincial Natural Science Foundation [grant number ZR2023ME139], Central Guiding Local Technology Development Funding Projects [grant number YDZX2024113].\u003c/p\u003e\u003ch2\u003eData availability\u003c/h2\u003e \u003cp\u003eData will be made available on request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eChen H, Cui H, Ma G et al (2026) Mechanical and corrosion behavior of oscillating laser beam welded 2507 super duplex stainless steel: Synergistic effects of acidic seawater and strain states. J Mater Sci Technol 251:227\u0026ndash;240. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jmst.2025.07.010\u003c/span\u003e\u003cspan address=\"10.1016/j.jmst.2025.07.010\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCui S, Shi Y, Cui Y, Zhu T (2019) The influence of microstructure and chromium nitride precipitations on the mechanical and intergranular corrosion properties of K-TIG weld metals. Constr Build Mater 210:71\u0026ndash;77. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.conbuildmat.2019.03.212\u003c/span\u003e\u003cspan address=\"10.1016/j.conbuildmat.2019.03.212\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFellicia DM, Sutarsis, Kurniawan BA et al (2017) Study of sigma phase in duplex SAF 2507. Iop Conf Ser: Mater Sci Eng 202:012039. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1088/1757-899X/202/1/012039\u003c/span\u003e\u003cspan address=\"10.1088/1757-899X/202/1/012039\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVinoth Jebaraj A, Ajaykumar L, Deepak CR, Aditya KVV (2017) Weldability, machinability and surfacing of commercial duplex stainless steel AISI2205 for marine applications \u0026ndash; A recent review. J Adv Res 8:183\u0026ndash;199. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jare.2017.01.002\u003c/span\u003e\u003cspan address=\"10.1016/j.jare.2017.01.002\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVerma J, Taiwade RV (2017) Effect of welding processes and conditions on the microstructure, mechanical properties and corrosion resistance of duplex stainless steel weldments\u0026mdash;a review. J Manuf Processes 25:134\u0026ndash;152. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jmapro.2016.11.003\u003c/span\u003e\u003cspan address=\"10.1016/j.jmapro.2016.11.003\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChu Q, Yang D, Chang Z et al (2024) Investigation on microstructure evolution, mechanical properties and corrosion resistance of dual phase stainless steel joints welded by GTAW and SAW methods. Int J Press Vessels Pip 209:105183. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ijpvp.2024.105183\u003c/span\u003e\u003cspan address=\"10.1016/j.ijpvp.2024.105183\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAcherjee B (2018) Hybrid laser arc welding: State-of-art review. Opt Laser Technol 99:60\u0026ndash;71. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.optlastec.2017.09.038\u003c/span\u003e\u003cspan address=\"10.1016/j.optlastec.2017.09.038\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHao K, Gao Z, Huang J et al (2023) Comparisons of laser and laser-arc hybrid welded carbon steel with beam oscillation. Opt Laser Technol 157:108787. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.optlastec.2022.108787\u003c/span\u003e\u003cspan address=\"10.1016/j.optlastec.2022.108787\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQi K, Li R, Wang G, Sun Z (2019) Structure and mechanical properties of laser-MIG hybrid welded SAF 2507 super duplex stainless steel joints. Int J Mod Phys B 33:1940037. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1142/S021797921940037X\u003c/span\u003e\u003cspan address=\"10.1142/S021797921940037X\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSu R, Li H, Chen H et al (2024) Stability analysis and porosity inhibition mechanism of oscillating laser-arc hybrid welding process for medium-thick plate TC4 titanium alloy. Opt Laser Technol 174:110569. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.optlastec.2024.110569\u003c/span\u003e\u003cspan address=\"10.1016/j.optlastec.2024.110569\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMa C, Chen B, Meng Z et al (2023) Characteristic of keyhole, molten pool and microstructure of oscillating laser TIG hybrid welding. Opt Laser Technol 161:109142. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.optlastec.2023.109142\u003c/span\u003e\u003cspan address=\"10.1016/j.optlastec.2023.109142\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen C, Zhou H, Wang C et al (2021) Laser welding of ultra-high strength steel with different oscillating modes. J Manuf Processes 68:761\u0026ndash;769. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jmapro.2021.06.004\u003c/span\u003e\u003cspan address=\"10.1016/j.jmapro.2021.06.004\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGao M, Zeng XY, Hu QW (2006) Effects of welding parameters on melting energy of CO2 laser\u0026ndash;GMA hybrid welding. Sci Technol Weld Join 11:517\u0026ndash;522. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1179/174329306X148138\u003c/span\u003e\u003cspan address=\"10.1179/174329306X148138\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMeng Y, Gao M, Zeng X (2018) Effects of arc types on the laser-arc synergic effects of hybrid welding. Opt Express 26:14775. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1364/OE.26.014775\u003c/span\u003e\u003cspan address=\"10.1364/OE.26.014775\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShi L, Jiang L, Gao M (2022) Numerical research on melt pool dynamics of oscillating laser-arc hybrid welding. Int J Heat Mass Transf 185:122421. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ijheatmasstransfer.2021.122421\u003c/span\u003e\u003cspan address=\"10.1016/j.ijheatmasstransfer.2021.122421\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGeng S, Sun J, Guo L, Wang H (2015) Evolution of microstructure and corrosion behavior in 2205 duplex stainless steel GTA-welding joint. J Manuf Processes 19:32\u0026ndash;37. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jmapro.2015.03.009\u003c/span\u003e\u003cspan address=\"10.1016/j.jmapro.2015.03.009\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang S-H, Chiu P-K, Yang J-R, Fang J (2006) Gamma (γ) phase transformation in pulsed GTAW weld metal of duplex stainless steel. Mater Sci Engineering: A 420:26\u0026ndash;33. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.msea.2006.01.028\u003c/span\u003e\u003cspan address=\"10.1016/j.msea.2006.01.028\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMohammed G, Ishak M, Aqida S, Abdulhadi H (2017) Effects of heat input on microstructure, corrosion and mechanical characteristics of welded austenitic and duplex stainless steels: A review. Metals 7:39. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/met7020039\u003c/span\u003e\u003cspan address=\"10.3390/met7020039\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang H-S (2005) Effect of welding variables on cooling rate and pitting corrosion resistance in super duplex stainless weldments. Mater Trans 46:593\u0026ndash;601. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.2320/matertrans.46.593\u003c/span\u003e\u003cspan address=\"10.2320/matertrans.46.593\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eK\u0026ouml;se C, Topal C (2022) Texture, microstructure and mechanical properties of laser beam welded AISI 2507 super duplex stainless steel. Mater Chem Phys 289:126490. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.matchemphys.2022.126490\u003c/span\u003e\u003cspan address=\"10.1016/j.matchemphys.2022.126490\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGe C, Meng Y, Xie Y et al (2024) Microstructures and mechanical properties of laser-arc hybrid welded high-strength aluminum alloy through beam oscillation. J Mater Res Technol 32:3015\u0026ndash;3024. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jmrt.2024.08.144\u003c/span\u003e\u003cspan address=\"10.1016/j.jmrt.2024.08.144\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang Y, Yang C, Zhao L, Zhang J (2021) Study on the electrochemical corrosion behavior of 304 stainless steel in chloride ion solutions. Int J Electrochem Sci 16:210251. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.20964/2021.02.01\u003c/span\u003e\u003cspan address=\"10.20964/2021.02.01\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhao Y, Wang Y, Tang S et al (2019) Edge cracking prevention in 2507 super duplex stainless steel by twin-roll strip casting and its microstructure and properties. J Mater Process Technol 266:246\u0026ndash;254. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jmatprotec.2018.11.010\u003c/span\u003e\u003cspan address=\"10.1016/j.jmatprotec.2018.11.010\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZheng J, Hu X, Pan C et al (2018) Effects of inclusions on the resistance to pitting corrosion of S32205 duplex stainless steel. Mater Corros 69:572\u0026ndash;579. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/maco.201709723\u003c/span\u003e\u003cspan address=\"10.1002/maco.201709723\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMoura VS, Lima LD, Pardal JM et al (2008) Influence of microstructure on the corrosion resistance of the duplex stainless steel UNS S31803. Mater Charact 59:1127\u0026ndash;1132. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.matchar.2007.09.002\u003c/span\u003e\u003cspan address=\"10.1016/j.matchar.2007.09.002\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRalston KD, Birbilis N (2010) Effect of grain size on corrosion: A review. Corrosion 66. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.5006/1.3462912\u003c/span\u003e\u003cspan address=\"10.5006/1.3462912\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. 075005-1-075005\u0026ndash;13\u003c/span\u003e\u003c/li\u003e \u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"the-international-journal-of-advanced-manufacturing-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jamt","sideBox":"Learn more about [The International Journal of Advanced Manufacturing Technology](https://www.springer.com/journal/170)","snPcode":"170","submissionUrl":"https://submission.nature.com/new-submission/170/3","title":"The International Journal of Advanced Manufacturing Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"2507 Super Duplex Stainless Steel, Laser-Arc Hybrid Welding, Microstructure, Mechanical Properties, Corrosion Resistance","lastPublishedDoi":"10.21203/rs.3.rs-8819933/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8819933/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eTo address the challenge of uncontrollable welded joint quality in the application of 2507 Super Duplex Stainless Steel (2507 SDSS) in high-performance industrial fields, this study systematically compared the effects of four welding processes - Laser Beam Welding (LBW), Gas Metal Arc Welding (GMAW), Laser-Arc Hybrid Welding (LAHW), and Oscillating Laser-Arc Hybrid Welding (OLAHW) - on the weld formation, microstructure, mechanical properties, and corrosion resistance of 2507 SDSS. Special focus was placed on exploring the regulatory mechanisms of hybrid welding process parameters (laser power, welding current, welding speed, heat source spacing) and oscillation parameters (oscillation frequency, oscillation amplitude). The results indicated that, compared with single-heat-source LBW and GMAW, LAHW achieved optimized cooling rate (between LBW and GMAW) through the laser-arc synergistic effect, promoted the dispersed precipitation of austenite, and significantly improved mechanical properties and corrosion resistance. The further introduction of beam oscillation in OLAHW enhanced molten pool agitation and improved thermal distribution homogeneity. This not only resulted in the greatest penetration depth but also achieved grain refinement, significantly suppressed the formation of Widmanst\u0026auml;tten austenite (WA), and increased the intragranular austenite content (IGA). The OLAHW welds exhibited properties equivalent to or even superior to the base metal in terms of microhardness, tensile strength, elongation, and corrosion resistance. This study revealed the regulatory mechanism of OLAHW on the weld quality of 2507 SDSS, providing key technical support for the selection of welding processes and parameters for this material in harsh environments such as marine and chemical industries.\u003c/p\u003e","manuscriptTitle":"Study on the mechanism of laser-arc hybrid welding in improving the weld quality of 2507 super duplex stainless steel","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-11 07:58:49","doi":"10.21203/rs.3.rs-8819933/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewersInvited","content":"","date":"2026-05-01T08:23:41+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-02-10T13:21:23+00:00","index":"","fulltext":""},{"type":"submitted","content":"The International Journal of Advanced Manufacturing Technology","date":"2026-02-08T02:43:59+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"the-international-journal-of-advanced-manufacturing-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jamt","sideBox":"Learn more about [The International Journal of Advanced Manufacturing Technology](https://www.springer.com/journal/170)","snPcode":"170","submissionUrl":"https://submission.nature.com/new-submission/170/3","title":"The International Journal of Advanced Manufacturing Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"01e82ee5-7bc1-46b1-bd28-9d9d173afecb","owner":[],"postedDate":"May 11th, 2026","published":true,"recentEditorialEvents":[{"type":"reviewersInvited","content":"","date":"2026-05-01T08:23:41+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-11T07:58:50+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-11 07:58:49","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8819933","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8819933","identity":"rs-8819933","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}