Effect of heat treatment on mechanical properties and corrosion resistance of Directed Energy Deposition-Arc 2319 Al alloy

Effect of heat treatment on mechanical properties and corrosion resistance of Directed Energy Deposition-Arc 2319 Al alloy | 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 Effect of heat treatment on mechanical properties and corrosion resistance of Directed Energy Deposition-Arc 2319 Al alloy Fenglei Cao, Aiping Liu, Dianlong Wang, Zhen Tan, Liwei Wang, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7155152/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract In this study, homogenization + solution aging treatments were applied to Directed Energy Deposition-Arc (DED-Arc) 2319 Al alloy components. The impact of the heat treatment and their influence on microstructure evolution, mechanical properties and corrosion resistance was analyzed. A number of acicular strengthening phases θ′ (Al 2 Cu) and θ″ (Al 2 Cu) were precipitated by heat treatment. The hardness increased from 73.9 HV (as-deposited state) to 148.0 HV in the aged state. Similarly, the ultimate tensile strength (UTS) in longitudinal direction increased from 254.3 MPa (deposited state) to 371.7 MPa in aged state. The transverse UTS of the samples increased from 257.2 MPa in the deposited state to 383.1 MPa in the aged state. The results of both electrochemical and intergranular corrosion (IGC) tests indicate that heat treatment can enhance the corrosion resistance of the alloy by promoting the dissolution of the secondary phase and the diffusion of elements. Directed Energy Deposition-Arc (DED-Arc) 2319 Al alloy Homogenizing treatment Solution aging treatment Electrochemical testing Intergranular corrosion (IGC) Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 Figure 20 Figure 21 1 Introduction The 2319 aluminum (Al) alloy boasts excellent mechanical properties, including low density, high specific strength, superior weldability and formability, making it ideal for a number of applications [ 1 – 3 ]. However, traditional manufacturing methods for Al alloys face significant challenges such as inefficiency, and difficulty in producing complex components [ 4 – 5 ]. Additive Manufacturing (AM) technology overcomes these drawbacks with its exceptional flexibility, high material utilization, near-net-shape forming, and ability to create parts with intricate geometries [ 6 – 7 ]. However, this technology has limitations affecting its widespread applications. For instance, the occurrence of complex thermal cycling during material deposition can lead to high residual stresses, compositional segregation, anisotropic microstructures, poor mechanical properties, and inadequate corrosion resistance [ 8 – 9 ]. Consequently, post-treatment processes are necessary to address these issues, particularly to improve mechanical properties and corrosion resistance. Homogenization + solution aging heat treatment is a common post-treatment method for casting Al alloys [ 10 – 12 ], but there are similar heat treatment studies for Al alloys deposited using Directed Energy Deposition-Arc (DED-Arc) [ 13 – 14 ]. DED-Arc is a technology that use welding arc as a heat source to deposit metal wire or power source layer by layer. These treatments can promote elemental diffusion and secondary phase evolution, thereby improving the mechanical properties and corrosion resistance of the formed parts [ 10 – 14 ]. Controlling the secondary phase evolution by heat treatment is an important mechanism to improve the mechanical properties of Al-Cu alloys. Cai et al. [ 13 ] investigated the effect of different heat treatment processes on the mechanical properties of DED-Arc 2219 Al alloy components. The direct aging treatment had little effect on the properties of DED-Arc 2219 Al alloy, and the Vickers hardness value of the alloy was only increased by about 10%. The hardness of the DED-Arc 2219 Al alloy increased considerably after solution + aging treatments but still did not match the hardness values of the cast alloy. Finally, a combination of homogenization + solution + aging treatments was employed at DED-Arc 2219 Al alloy to achieve the hardness (143.5 HV) of the cast + aged 2219 Al alloy. Zhou et al. [ 14 ] found that DED-Arc 2219 Al alloy exhibited a good combination of strength and plasticity after homogenization + solution aging heat treatment, and its mechanical properties were superior to those of pre-deformed compression Al-Cu alloy. Compared with the T6 heat treatment (solution treated at high temperatures and then artificially aged at a certain temperature), the additional homogenization treatment prefabricated more Al 3 Zr dispersions, which indirectly promoted the transformation of the θ″ phase to the θ′ phase and significantly reduced the plastic anisotropy. In addition, homogenization + solution + aging heat treatments of the alloy enhanced the thermal stability and mechanical properties of DED-Arc 2219 alloy. Wang et al. [ 15 ] investigated the strengthening mechanism of T6 heat treatment for in-situ rolled DED-Arc Al-Cu alloys. During T6 heat treatment, most of the eutectic structures with continuous or semi-continuous distribution at grain boundaries dissolved into the matrix. Some undissolved θ and a high density of acicular θ′ phases appeared inside the grains. After T6 treatment, the ultimate tensile strength (UTS) and yield strength (YS) of the alloy reached 454.4 ± 23.8 MPa and 356.6 ± 17.1 MPa, respectively, which was mainly due to precipitation strengthening. Controlling the elemental distribution by heat treatment can enhance the corrosion resistance of Al-Cu alloys. Chen et al. [ 16 ] investigated the effect of homogenization + aging treatments on the corrosion behavior of Al-Cu-Li alloys. The high concentration of Cu often leads to the precipitation of more secondary phase during homogenization of the alloy, which is more uniformly dispersed within the alloy after aging. The corrosion potential increases with aging time, enhancing the corrosion resistance of the alloy. Sun et al. [ 17 ] used homogenization + solution aging heat treatments to strengthen Sr-containing 2024 Al alloy. The 2024 Al alloy matrix housed intermetallic phases after artificial aging, which contributed to diffusion strengthening. In addition, Sr inhibited the growth of Cu-rich second-phase particles and increased the amount of Cu in the matrix. The increased Cu content in the matrix further improved the corrosion resistance and strength of the alloy. Li et al. [ 18 ] investigated the effect of different aging treatments on the mechanical behavior, microstructural characteristics and corrosion behavior of rotary friction welded AA2024 joints. After artificial and long-term natural aging treatments, the tensile strength and corrosion resistance of the joints was uniform at different locations. After artificial aging, the Cu present in the intracrystalline and grain boundaries are uniformly distributed, reducing the tendency of intergranular corrosion (IGC). In summary, heat treatment of Al alloys, such as homogenization, solution and aging treatments have a positive impact in enhancing the mechanical properties and corrosion resistance [ 13 – 18 ]. However, the high thermal conductivity of Al challenges the heat treatment of large components due to difficulties in maintaining temperature control [ 9 – 10 ]. During heat treatment processes, the diffusion coefficient, solid solution solubility, and nucleation barriers of metallic materials are constantly changing. The evolution of microstructure is gradual and complex, which makes the extent of heat treatment often difficult to control [ 12 – 13 ]. Therefore, there is a need to incorporate a slow and multi-stage heat treatment process for Al alloys. For example, in order to obtain finer second-phase particles, Zhang et al. [ 19 ] used double-stage homogenization instead of single-stage homogenization for Al-Mg-Zn-Sc-Zr alloy, and Vandersluis et al. [ 20 ] used double-stage solution instead of single-stage solution treatment for B319 Al alloy. Cai et al. [ 13 ] and Zhou et al. [ 14 ] included homogenization before solution + aging treatments, which refined the secondary phase particles, reducing the anisotropy and improving the thermal stability and mechanical properties of the alloy. So far, the homogenization + solution aging heat treatments have been predominantly employed to improve the mechanical properties of Al-Cu alloys, and relatively little research has been done on corrosion resistance. Several reports have demonstrated that homogenization [ 21 ], solution treatment [ 9 ], aging [ 22 ], homogenization + aging [ 16 ], and solution + aging [ 23 ] treatments can enhance the corrosion resistance of Al-Cu alloys. Additionally, homogenization + solution aging treatment involves a gradual heating, which is expected to improve the mechanical properties and corrosion resistance of Al-Cu alloys [ 13 – 14 ]. Currently, homogenization + solution aging treatments are mostly used in DED Arc 2219 Al alloy in Al-Cu alloy series. 2319 Al alloy chosen in this study has a similar composition to 2219 Al alloy, and is employed in a wide range of applications and relatively cheaper than 2319 Al alloy. In this study, an in-depth investigation was carried out on the effects of homogenization + solution + aging treatments on the microstructural characteristics and the evolution of the secondary phase in DED-Arc 2319 Al alloy. The effect of the heat treatments on the mechanical behavior and the corrosion resistance was also investigated. 2. Experiments and methods A 2319 Al alloy welding wire with a diameter of 1.2 mm was selected as the filler material, and 5083 Al alloy with a size of 200 mm × 100 mm × 10 mm was used as the forming substrate. The chemical composition of the wire and substrate are shown in Table 1 . The surface of the substrate was subjected to a deep cleaning treatment to remove oil and other impurities. Initially, the substrate was immersed in a NaOH solution (concentration of 5%) at 50°C for 10 min, followed by a cold-water rinse. Subsequently, the substrate was dipped in 30% HNO 3 solution for 30 s. Finally, it was cleaned with hot water (at 50°C) and dried. The surface of the substrate was then sanded using an abrasive wheel until smooth, and then cleaned with acetone before metal deposition. The DED-Arc system employs CMT welding, where the welding current is 115 A, and the wire feeding speed is 0.5m/min. Argon gas (purity of 99.99% and a flow rate of 20 L/min) was used to prevent the impurity gases from entering the molten pool and also to avoid porosity defects during the DED-Arc process. Table 1 Chemical composition of the welding wire and substrate (wt. %). Alloys Cu Mg Si Fe Zn Mn ER2319 5.8–6.8 0.02 0.2 0.3 0.1 0.2–0.4 5083 0.07 3.75 0.09 0.20 0.04 0.49 The dimensions of the DED-Arc samples are ~ 240 mm in length, ~ 14 mm in width and ~ 105 mm in height, respectively (Figs. 1 a and b). Straight walls were cut and machined into small blocks (10 mm × 5 mm × 10 mm) for heat treatment (homogenization + solution + aging) and characterization purposes (Fig. 1 b). Figure 2 shows the schematic representations of different heat treatments undertaken in the current study. All heat treatments were carried out in a muffle furnace with a temperature accuracy of ± 1°C. Double-stage homogenization treatments were performed in two conditions, i.e., 460℃ − 480℃ for 8h and 520℃ − 530℃ for 24h, and an optimal double-stage homogenization temperature and time were selected by observing the microstructure changes [ 17 – 18 , 23 – 24 ]. Based on the chosen double-stage homogenization treatment, solution treatment (535℃ − 545℃ for 0.5–2 h) and aging treatment (160℃ − 180℃ for 24 h) were trialed and then optimized. The heating rate of homogenization and solution treatment was set at 10℃/min, while the heating rate of aging treatment was 5℃/min. After homogenization and solution treatments, samples were cooled to 20 ± 5℃ by water quenching, and after aging treatment, samples were air-cooled to 20 ± 5℃. The microstructures were observed and analyzed using a Leica DMi8 optical microscopy (OM) and a QUANTA FEG 450 scanning electron microscopy (SEM). The hardness tests were carried out at 100 different points with 0.5 mm apart on the XZ surface and the average value was taken (Fig. 1 b). Three tensile tests of YZ surface (Fig. 1 c) were carried out (Tensile rate-0.5 mm/min & strain rate-6×10 − 4 s − 1 ) in each condition and an average value was taken into consideration. The phase transition temperature of the deposited alloy and the degree of dissolution of the eutectic phase after homogenization were analyzed using a SDT-Q600 differential scanning calorimeter (DSC). The heating rate of DSC test was 20 K/min. Two sets of corrosion tests, i.e., electrochemical and intergranular corrosion (IGC) were included in this study. The electrochemical tests were performed using a standard three-electrode system with a saturated calomel electrode (SCE) and platinum sheet for the reference electrode and counter electrode, respectively. The working electrodes were DED-Arc 2319 Al alloy in different conditions (i.e., as-deposited, homogenized, solution treated and aged) with a working area of 0.25 cm 2 . After connecting the specimens with copper wires, the non-working surface was encapsulated and protected using resin, and the surface of the working electrode was ground and polished. The electrochemical test medium was 3.5 wt.% NaCl solution with a pH = 6.0. Before the test, the working electrode was immersed in the electrolyte, and the electrochemical test was performed after the stabilization of real-time potential. The electrochemical test outputs included polarization curves and electrochemical impedance spectroscopy (EIS). Electrochemical impedance spectroscopy (EIS) is widely used to study the corrosion behavior and the continuous evolution of the corrosion resistance of the material under test [ 25 – 26 ]. IGC tests were performed on DED-Arc 2319 Al alloy specimens in as-deposited and heat-treated conditions, three specimens were tested from each condition. The IGC test solution comprised of: 10 mL of H 2 O 2 solution at 30% concentration, 57 g of NaCl, and 1 L of distilled or deionized water. The IGC tests were carried out under constant temperature at 35 ± 2℃. The specimens were suspended in the solution for 6h and utmost care was taken to avoid samples touching one another. The corroded specimens were rinsed in alcohol and blown dry. 3. Development of heat treatment process parameters 3.1 Optimization of homogenization treatment process parameters To avoid overburning during the heat treatment process and to establish a reasonable temperature range for the heat treatment, the dissolution degree of the secondary phase and the melting point of the non-equilibrium eutectic phase were investigated by DSC. Figure 3 shows the DSC curve of the as-deposited 2319 Al alloy. The temperature of the endothermic peak refers to the melting temperature of non-equilibrium eutectic phase with a low melting point of ~ 546°C (also known as the overburning temperature) along with the melting point of the alloy, ~ 651°C. The first stage of the double-stage homogenization treatment of 2XXX Al alloys has a temperature time range of 440°C- 480°C at 8 h. The second stage of the double-stage homogenization treatment of DED-Arc 2319 Al alloy in the as-deposited state ranges from 520°C to 530°C (below the overcooking temperature of 546°C) with a holding time of 24 h. Therefore, six double-stage homogenization regimes of 440°C/8 h + 520°C/24 h, 440°C/8 h + 530°C/24 h, 460°C/8 h + 520°C/24 h, 460°C/8 h + 530°C/24 h, 480°C/8 h + 520°C/24 h and 480°C/8 h + 530°C/24 h were designed. Based on Fig. 4 , when the temperature of the first stage homogenization is low (440°C), a small amount of incomplete dissolution of the eutectic phase still occurs, and part of the dendritic microstructure remains at the grain boundaries (Figs. 4 b and c). At the first stage homogenization temperature, i.e., 480°C, there is less residual dendritic microstructure at the grain boundaries, as shown in Figs. 4 (f) and (g). During the second stage of the homogenization, there was an increased dissolution of the eutectic phase, with a uniform microstructure, and the grain boundaries were clear without any overheating or overburning phenomena (Fig. 4 g). 3.1 Optimization of solution treatment process parameters By analyzing the DSC curves of DED-Arc 2319 Al alloy in the as-deposited state, the solution treatment temperature range was determined to be 535℃-545℃. Three solution treatment temperatures (535°C, 540°C and 545°C) and holding times (0.5 h, 1 h, 1.5 h and 2 h) were trailed to optimize the parameters. With an increase in solutionizing temperature and the extension of time, the solubility of residual phase increases and enters the matrix. At a solution temperature of 535°C, a large number of residual phases remained undissolved in the intralayer columnar and interlayer fine-crystalline structures of the treated DED-Arc 2319 Al alloy (Figs. 5 a-d). When the temperature was raised to 540°C, the grain boundaries became clearer and the precipitated phases in the intralayer and the interlayer zones were more dissolved (Figs. 5 e-h), and this effect was pronounced when the holding time was raised to 2 h (Fig. 5 h). There was hardly any distinct changes in the microstructures, when the temperature was raised to 545°C for the same holding time of 2h. The degree of grain boundary clarity and the dissolution effect of precipitated phases were comparable to that of the earlier condition-540°C/2 h. However, there was a melting phenomenon of low-melting-point eutectic phases and the formation of a remelting pellet (black arrow) in the process of cooling [ 27 ] (Fig. 5 l). Therefore, the optimal solutionizing condition is 540°C/2 h because there was an almost complete dissolution of the precipitated phases at the grain boundaries of the intralayer and interlayer regions. 3.2 Formulation of aging process parameters Optimum aging conditions were determined based on the tensile tests of the aged specimens under different aging temperatures and time. Prior to that the samples subjected to double stage homogenization (480℃/8h + 530℃/24h) and solution treatment (540℃/8h) specimens (Fig. 6 ). Longitudinal tensile tests of YZ surface (parallel to the building direction Z axis) were performed for two different aging conditions, i.e., A. constant aging temperature (175℃) and variable time (6, 12, 18, 24, 30 & 36 h) & variable aging temperatures (160, 165, 170, 175 and 180℃) and B. constant time (24 h) (Figs. 6 a and b). Table 2 shows the longitudinal tensile strength and elongation of DED-Arc 2319 Al alloy at different aging temperatures and times. Table 2 Longitudinal UTS and elongation of DED-Arc 2319 Al alloy at different aging parameters (temperature and time). double-stage homogenization Solution Aging UTS/MPa Elongation /% Temperature/℃ Time/h / / / / 254.30 13.10 480℃/8h + 530℃/24h 540℃/2h 160 24 281.39 9.52 165 315.50 9.31 170 347.24 8.03 175 371.69 5.89 180 343.65 5.77 175 6 279.90 9.51 12 316.50 8.90 18 343.90 7.12 24 371.69 5.89 30 351.06 4.58 36 344.44 4.39 From Fig. 6 and Table 2 , the as-deposited DED-Arc 2319 Al alloy displayed the lowest UTS of 254.30 MPa, and the highest elongation of 13.10%. whereas after double-stage homogenization and solution aging treatments, the UTS are both significantly increased, and the elongation decreased significantly. The maximum UTS of 371.69 MPa was achieved at an aging condition of 175°C/24 h. An increase in aging temperature (180°C) and time (> 24 h), resulted in a simultaneous decrease in UTS and elongation. 4. Results and discussion The effect of heat treatment (homogenization + solution aging) on the microstructural characteristics of DED-Arc 2319 Al alloy were analyzed. Advanced characterization techniques were used to characterize the second phase and elements before and after heat treatment. Figure 7 shows a SEM image of the secondary phase evolution in as-deposited and heat-treated conditions of the DED-Arc 2319 Al alloy. There is a eutectic phase segregation at the grain boundaries of the as-deposited DED-Arc 2319 Al alloy, and some discrete distribution of rods and particles of the second phase θ within the grain, (Fig. 7 a). After homogenization, a vast majority of the low melting point eutectic phases (at grain boundaries and within the grains) were broken down and dissolved, and the remaining high melting point secondary phase θ was uniformly distributed within the grains (Fig. 7 (b). The solution treatment further increased the dissolution of the undissolved secondary phase θ from the homogenization treatment (Fig. 7 c). After aging, the remaining secondary phase θ precipitated out and distributed within the grains (Fig. 7 d). An in-depth observation on the secondary phase evolution was conducted using TEM analysis (Fig. 8 ). Large disc-shaped black particles (Fig. 8 a) are the eutectic phase in the as-deposited state. During homogenization, these particles were broken down and uniformly distributed as small particles of θ phase in the Al matrix (Fig. 8 b). This phenomenon was further enhanced during the solution treatment (Fig. 8 c). After ageing, many fine needle-like strengthening phases θ′ and θ″ were precipitated within the Al matrix (Fig. 8 d). In addition, small disk-like dispersed phases were not dissolved during the heat treatment process, and these dispersed phases are often detrimental for mechanical behavior, however, they can act as nucleation sites for the precipitation of the reinforcing phases (θ′ and θ″) [ 8 – 9 ]. A high-resolution transmission microscopy was employed to characterize the morphology and lattice variations in the secondary phase (Fig. 9 ). Figure 9 (a) identified the θ phase microscopic morphology and the spacing of the θ phase lattice stripes to be 0.1299 nm. Both θ′ and θ″ phases are needle-like structures with short rod-like profiles. The size of θ′ and θ″ phases are ~ 150 nm and ~ 15 nm, respectively. Similarly, the θ′ and θ″ phase lattice stripe spacings were 0.2907 nm and 0.2127 nm, respectively (Figs. 9 b and c). The lattice stripe spacing of the Al matrix was 0.2052 nm, and among the secondary phases, only the θ″ phase and the Al matrix are completely coherent. TEM-EDS technique was employed to study the elemental distribution and compositional analysis on the secondary phases (Fig. 10 ). In the as-deposited state, the composition of the eutectic phases was found to be θ (Al 2 Cu) + T (Al 12 CuMn 2 ) + α (Al) along with low levels of Cu and Mn segregations were observed in the Al matrix (Fig. 10 a). This could be due to the homogenization treatment, which promotes the dissolution of eutectic phases, reducing Cu and Mn segregation, and thereby promoting a uniform distribution of elements in the matrix (Fig. 10 b). The solution treatment further enhances the dissolution of the remaining second phase θ (Al 2 Cu) and Cu into the Al matrix, forming a supersaturated solid solution (Fig. 10 c). However, the concentration of Cu in the Al matrix decreases after aging, and many fine needle-like reinforced phases θ′ and θ″ are precipitated (Fig. 10 d). Additionally, a number of reinforcing phases θ′ and θ″ precipitate around the disk-shaped structures. 4.2 Effect of heat treatment on mechanical properties 4.2.1 Effect of heat treatment on bulk hardness From Fig. 11 , the bulk hardness of DED-Arc 2319 Al alloy in the as-deposited state is 73.9 HV. Homogenization and solution treatments decreased the bulk hardness to 52.7 HV and 49.6 HV, respectively. Both the treatments dissolve both the low and high smelting point eutectic phases resulting in a gradual decrease in the bulk hardness of the as-deposited alloy. However, after aging, the bulk hardness was significantly increased to 148 HV. After aging, a number of needle-like reinforcing phases are precipitated to increase the bulk hardness of the alloy. 4.2.2 Effect of heat treatment on tensile properties in longitudinal and transverse direction: The longitudinal tensile (parallel to the building direction Z axis) UTS of DED-Arc 2319 Al alloy in the as-deposited state in Fig. 12 was 254.3 MPa. This was decreased to ~ 180 MPa after both homogenization and solution treatments. As expected, the aging treatment improved the UTS to 371.7 MPa. After homogeneous solution treatment, the elongation of the alloy was increased by dissolving the second phase (~ 13% ~ 16.6%). After aging treatment, the Cu segregation and precipitation in the matrix decreased the elongation of the alloy (~ 5.9%). Fracture analysis was conducted on the tensile specimens from as-deposited and different heat-treated conditions (Fig. 13 ). In Fig. 13 (a), the tensile fracture of the as deposited specimen was distributed with fine and dense dimples, along with hard and brittle eutectic phase particles in the center of the dimples, indicating a ductile mode of fracture. Compared with the as-deposited state, the alloy has larger and deeper dimples at the fracture after the homogenization and solution treatments, which exhibits typical ductile fracture characteristics (Figs. 13 b and c). Larger dimples and minimal θ phase observed in the fractured surface improved plasticity. On other hand, a brittle fracture was observed in aged tensile specimen, consisting of several tearing ridges and presence of a brittle secondary phase at the fracture sites. This leads to increased strength and reduced plasticity after aging (Fig. 13 d). Tensile properties in transverse direction (perpendicular to the building direction Z axis) exhibited a similar trend to that in longitudinal direction (Fig. 14 ). The UTS of the as deposited specimen (i.e., 257.2 MPa) decreased after homogenization and solution heat treatments (i.e., ~ 184 MPa). After aging, the UTS was increased to ~ 380 MPa. Homogenization and solution treatments improved the elongation from ~ 14% to ~ 17% as expected, while the aging treatment decreased the elongation to 8.9%. Fractured surface analysis revealed similar features and fracture modes in both transverse and longitudinal directions. In the as deposited condition, the fractured samples contained a dense distribution of small dimples and brittle secondary phases (Fig. 15 a). Large and deep dimples were observed at the fractured surfaces post homogenization and solution treatments (Figs. 15 b and c), along with tearing ridges after aging treatment (Fig. 15 d). 4.3 Effect of heat treatment on corrosion resistance 4.3.1 Electrochemical corrosion behaviour Corrosion properties of the alloys were studied using electrochemical corrosion tests. Figure 16 (a) shows the polarization curves for the as-deposited state (black curve), homogenization (red curve), solution (blue curve) and aging treatment (green curve). There are two sections in each polarization curve, i.e., anodic Tafel curve (the curve to the right of the spike) and the cathodic Tafel curve (the curve to the left of the spike). The hydrogen precipitation in aqueous solution occurs in the cathodic reaction stage, while the dissolution of Al occurs in the anodic reaction stage. The shift between cathodic and anodic reaction phases is related to the internal corrosion potential of the alloy [ 28 ]. As the internal corrosion potential of the alloy increases, the corrosion product film (Al 2 O 3 ) ruptures in response to the sharply increasing anodic current, and when the corrosion potential reaches a threshold value, rapid anodic Al dissolution occurs. At these breakdown potentials, homogenized, solution and aging treated specimens have similar anodic kinetics. Figure 16 (b) shows the EIS results of specimens in different conditions (as deposited and heat treated). The corrosion resistance of the specimen in the corrosive solution can be expressed by the capacitive arc resistance diameter in the electrical impedance meter. As the capacitive arc resistance diameter increases, the corrosion resistance of the specimen improves [ 28 ]. Alloys in the as-deposited state have the smallest arc diameter indicating a relatively poor corrosion resistance. While the heat-treated conditions revealed an increased arc diameter indicating an improved corrosion resistance. The corrosion potential (E corr ) and corrosion current density (I corr ) were calculated by extrapolation. Horizontal and vertical coordinates of the slopes of cathodic and anodic curves indicate the corrosion potential and current density, respectively. As shown in Table 3 , the highest corrosion potential (-0.556 V vs SCE) was observed for the solution treated specimens, followed by aging (-0.664 V vs SCE) and homogenization treatments, (-0.712 V vs SCE), whereas the lowest corrosion potential was observed for the as-deposited specimens (-0.826 V vs SCE). Based on the thermodynamic system, corrosion potential can reflect the trend of corrosion, the lower the corrosion potential, the more susceptible the material to corrosion. Table 3 Tafel fitting data for DED-Arc 2319 Al alloy in as-deposited and different heat treated conditions. E corr (V vs. SCE) I corr (A/cm 2 ) As-deposited -0.826 -4.3891 Homogenization -0.712 -6.3526 Solution -0.556 -6.3726 Aging -0.664 -6.0755 The effect of electrochemical testing on the surface morphology of the specimens before and after heat treatment were analyzed. SEM tests were performed to investigate the micro-morphology after corrosion. From Fig. 17 (a), three types of corrosion, i.e., pitting, IGC, and exfoliation corrosion, occur sequentially in the as-deposited state DED-Arc 2319 Al alloy. With the deepening of pits around the secondary phase, grain boundary pitting connects to form IGC, creating corrosion channels, followed by exfoliation corrosion. Figure 17 (b) shows the corrosion morphology after homogenization treatment, where pitting phenomenon was more serious. However, this phenomenon (pitting) was less severe in solution treated conditions (Fig. 17 c). After aging treatment, Cu segregation and secondary phase growth occurred in the alloy, resulting in pitting corrosion and a slight IGC phenomenon, with no exfoliation corrosion (Fig. 17 d). This clearly indicates that heat treatments can enhance the corrosion resistance of DED-Arc 2319 Al alloy by regulating the evolution of the secondary phase. The thickness of corrosion layer after electrochemical testing were analyzed (Fig. 18 ). Depending on the thickness of the corrosion layer, the corrosion resistance of the alloy is determined. In general, heat-treated samples revealed better corrosion resistance than the as-deposited specimen. As deposited specimens displayed the poorest corrosion resistance with a thick corrosive layer (717 µm), followed by aged (553 µm), homogenized (258 µm) and solution treated specimens (128 µm). As the eutectic phase in the as-deposited state is segregated at the grain boundaries, it leads to the formation of a number of wide IGC channels after electrochemical corrosion, leading to an increased thickness of the corrosion layer (717 µm Fig. 18 a). After homogenization and solution treatments, the eutectic and the secondary phases dissolved sequentially, with no IGC channels to be formed. The maximum thickness of the corrosion layers after homogenization and solution treatments were 258 µm and 128 µm, respectively, (Figs. 18 b and c). The aged specimens contains several secondary phases (θ, θ′ and θ″), which acted as sources for pitting during electrochemical corrosion. Meanwhile, the secondary phase at the grain boundary led to an increase in the IGC channels with a maximum corrosion layer depth of 553 µm (Fig. 18 d). 4.3.1 Intergranular corrosion (IGC) The effect of heat treatment on the IGC of DED-Arc 2319 Al alloy was investigated and SEM was used to characterize the morphology of the secondary phases (Fig. 19 ). The eutectic phase in the as-deposited state was segregated at the grain boundaries, forming reticulated IGC channels and exacerbating IGC (Fig. 19 a). However, the homogenization treatment has dissolved the eutectic phase at the grain boundaries and promotes a uniform distribution of the second phase within the grain, hindering the development of pitting corrosion into IGC, (Fig. 19 b). Solution treatment has promoted a full dissolution of the secondary phase, reducing the source of pitting, thereby eliminating the formation of IGC and enhancing the resistance of the alloy to pitting and IGC (Fig. 19 c). After aging treatment, the secondary phase increased in size, forming fewer IGC channels, (Fig. 19 d). Compared with the as-deposited condition, the aging state alloy does not have IGC channels, which also slows down the IGC process and improves the IGC resistance of the alloy. An EDS characterization was undertaken to analyze the elemental distribution after IGC tests for different conditions (Fig. 20 ). The major alloying element, Cu plays a major role in affecting IGC in all conditions. In Fig. 20 (a), there is Cu segregation at the grain boundaries of the alloy, and IGC channels are formed in the region of high concentration of Cu near the intergranular area, which reduces the IGC resistance of the alloy. Homogenization and solution treatments eliminated the segregation of Cu at grain boundaries, and the source of pitting corrosion was reduced preventing the formation of IGC channels (Figs. 20 b and c). A small amount of Cu segregation is observed after aging, and there are fewer IGC channels (Fig. 20 d). The IGC resistance of the specimens was further analyzed by comparing the thickness of the IGC layers. The as deposited condition revealed the most severe and thickest corrosion layer, ~ 162 µm (Fig. 21 a). The depth of the IGC layer was relatively shallow for the homogenized and solution-treated alloys, at 25 µm and 11 µm, respectively (Figs. 21 b and c). The IGC layer of the alloy after aging was 68 µm (Fig. 21 d). Compared with the as-deposited condition, there are fewer internal pitting sources and IGC channels in the aged alloy, indicating a relatively improved corrosion performance in aged conditions. 5. Conclusions The effect of a series of heat treatment procedures (i.e., homogenization, solution treatment and aging) on the microstructural characteristics, mechanical properties and corrosion behavior of DED-Arc 2319 Al alloy was investigated. The main conclusions are as follows: (1) Homogenization treatment promoted the dissolution of the low melting point eutectic phase and dendritic structures in DED-Arc 2319 Al alloy, thereby eliminating the segregation of Cu and Mn, and enhancing the homogeneity of the microstructure. The solution treatment was responsible the dissolution of the remaining high melting point secondary phase θ, prompting a complete dissolution of Cu and the formation of supersaturated solid solution. A number of needle-like reinforced phases θ′ and θ″ were precipitated within the Al matrix after aging. Additionally, the relationship between the θ′ and the Al matrix was investigated and found to be semi-coherent, while there was also a coherent relationship between θ″ phase and the Al matrix. (2) The effect of heat treatment had a significant impact on the mechanical properties on DED-Arc 2319 Al alloy. For instance, homogenization + solution aging treatments increased the hardness of DED-Arc 2319 Al alloy from 73.9 HV in the as-deposited state to 148.0 HV in aged state. The longitudinal UTS was increased from 254.3 MPa in the as-deposited state to 371.7 MPa after the heat treatment, and the transverse UTS was increased from 257.2 MPa in the as-deposited state to 383.1 MPa. The longitudinal elongation was 13.1% in as-deposited state, increased to 15.9% and 16.3% after double-stage homogenization and solution treatments, respectively, and this decreased to 5.9% after aging treatment. Elongation (in transverse direction) was 13.9% in as-deposited, which increased to 16.8% and 17.5% after double-stage homogenization and solution treatments, respectively, and this decreased to 8.9% after aging treatment. (3) Heat-treated specimens displayed improved corrosion resistance than the as-deposited specimen. Pitting, intergranular and exfoliation corrosion were observed in DED-Arc as-deposited state 2319 Al alloy specimens after electrochemical corrosion testing. Only pitting corrosion occurred in homogenized, and solution treated specimens. Meanwhile, pitting and intergranular corrosion occurred in the aged specimens. The thickness of the electrochemical corrosion layer decreased from 717 µm in the as-deposited state to 553 µm in the aged state. Pitting and intergranular corrosion were observed in the as-deposited state specimens after IGC testing. Homogenization, solution and aging treated specimens showed only pitting. The depth of the IGC layer was reduced from 162 µm in the as-deposited state to 68 µm in the aged state. Declarations Data availability The data that support the findings of this study are avail-able on request from the corresponding author, [L.W.W.]. Author contribution All authors contributed to the study conception and design. Material preparation, data collection, and analysis were performed by Fenglei Cao, Zhen Tan, and Yunfeng Yao; The project funds come from Liwei Wang and Aiping Liu; Dianlong Wang, Zhimin Liang, Shaohui Chen, and Changjiang Tian participated in the project management process; Balaji Narayanaswamy completed the editing and proofreading of the manuscript. The first draft of the manuscript was written by Fenglei Cao and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Declaration of interest statement The authors declare that we have no known any competing financial interests or personal relationships with other people or organizations that could have appeared to inappropriately influence the work reported in this paper. Fundings This work was supported by National Natural Science Foundation of China (Grant No. 52475343), Central Guidance for Local Scientific and Technological Development Funding Projects (Grant No. 246Z1015G) and Natural Science Foundation of Hebei Province (Grant No. E2024208049). References Y.H. Peng, C.L. Liu, G. Lin, G.H. Fan, Microstructures and cryogenic mechanical properties of spray deposited 2195 Al-Cu-Li alloy with different heat treatments, Mater. Sci. Eng. A. 895 (2024) 146173. https://doi.org/10.1016/j.msea.2024.146173 L. Zhang, S.T. Wang, H.X. Wang, J. Wang, W.Z. Bian, Mechanical properties and microstructure revolution of vibration assisted wire arc additive manufacturing 2319 aluminum alloy, Mater. Sci. Eng. 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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-7155152","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":512180283,"identity":"ef3dc85e-49e5-4ef1-84e4-0210459958ae","order_by":0,"name":"Fenglei Cao","email":"","orcid":"","institution":"Hebei University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Fenglei","middleName":"","lastName":"Cao","suffix":""},{"id":512180284,"identity":"71e85ef7-ff25-44ff-af72-4d091a36bcbd","order_by":1,"name":"Aiping Liu","email":"","orcid":"","institution":"Hebei University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Aiping","middleName":"","lastName":"Liu","suffix":""},{"id":512180285,"identity":"246e3dcb-ab39-4bea-a471-9f4cfc0fb7e6","order_by":2,"name":"Dianlong Wang","email":"","orcid":"","institution":"Yanshan University","correspondingAuthor":false,"prefix":"","firstName":"Dianlong","middleName":"","lastName":"Wang","suffix":""},{"id":512180286,"identity":"edbbe31f-312f-4a1c-9547-3d2588d6f3d7","order_by":3,"name":"Zhen Tan","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA2UlEQVRIie3PoQvCQBTH8ScHt3JofaJs/8KBMP1zbgxmURAsF4YIiga1WvZPzGY8EJbObtRi1iKGBbc1y7YoeN/8+8B7ACbT74aMEmhchQxrAgUDu2nNCb/qpDaRPZsp2r4tSfXa2Z9i8kjRW6F/l96cQmu9EaWkEQUTUCwngXvxjl1AfY5LCemMOCjMiciIpsBxXE5oQXhOhq+JtyLVhBVEYI8y7UItgp3sF63QptZ2ikInrPIXJ/JjkOmMOQvr8HzL0G6td+Ukq//+urRqnsfrjEwmk+mf+wDHKEMRG7yyIwAAAABJRU5ErkJggg==","orcid":"","institution":"Hebei University of Science and Technology","correspondingAuthor":true,"prefix":"","firstName":"Zhen","middleName":"","lastName":"Tan","suffix":""},{"id":512180287,"identity":"327cd9de-58c2-4f51-8329-60ec49c27661","order_by":4,"name":"Liwei Wang","email":"","orcid":"","institution":"Hebei University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Liwei","middleName":"","lastName":"Wang","suffix":""},{"id":512180288,"identity":"4e29e8cf-72f4-4554-88e9-de31ce4652b6","order_by":5,"name":"Zhimin Liang","email":"","orcid":"","institution":"Hebei University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Zhimin","middleName":"","lastName":"Liang","suffix":""},{"id":512180289,"identity":"be047b82-8f9c-4550-a839-530211a2d5b3","order_by":6,"name":"Shaohui Chen","email":"","orcid":"","institution":"beijing aeronautical technology research center","correspondingAuthor":false,"prefix":"","firstName":"Shaohui","middleName":"","lastName":"Chen","suffix":""},{"id":512180290,"identity":"4f11397e-1368-4dee-88ac-a8e9063d4e94","order_by":7,"name":"Changjiang Tian","email":"","orcid":"","institution":"Shijiazhuang Haishan industrial development company","correspondingAuthor":false,"prefix":"","firstName":"Changjiang","middleName":"","lastName":"Tian","suffix":""},{"id":512180291,"identity":"74b43dd8-44dc-4920-a516-1876f7937936","order_by":8,"name":"Yunfeng Yao","email":"","orcid":"","institution":"Hebei University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Yunfeng","middleName":"","lastName":"Yao","suffix":""},{"id":512180292,"identity":"f273d5c4-10f5-4220-9656-b53aacf2038d","order_by":9,"name":"Balaji Narayanaswamy","email":"","orcid":"","institution":"university of sydeny","correspondingAuthor":false,"prefix":"","firstName":"Balaji","middleName":"","lastName":"Narayanaswamy","suffix":""}],"badges":[],"createdAt":"2025-07-18 07:49:21","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7155152/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7155152/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":91457341,"identity":"0b119d19-df77-46fd-99a9-f2af252c7796","added_by":"auto","created_at":"2025-09-16 16:35:06","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1157684,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of DED-Arc 2319 Al alloy sample location and size: (a) Macroscopic image of the as-deposited DED-Arc2319 Al alloy; 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(b) 440°C/8 h+520°C/24 h; (c) 440°C/8 h+530°C/24 h; (d) 460°C/8 h+520°C/24 h; (e) 460°C/8 h+530°C/24 h; (f) 480°C/8 h+520°C/24 h; (g) 480℃/8 h+530℃/24 h.\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7155152/v1/63c31bc90f67bb61c3230c44.jpeg"},{"id":91457490,"identity":"55c3f6e3-6a03-43bf-9346-edace8e019b0","added_by":"auto","created_at":"2025-09-16 16:36:08","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":5639688,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of solution treatment temperature and time on the microstructure of DED-Arc 2319 Al alloy: (a) 535°C/0.5h; (b) 535°C/1h; (c) 535°C/1.5h; (d) 535°C/2h; (e) 540°C/0.5h; (f) 540°C/1h; (g) 540°C/1.5h; (h) 540°C/2h; (i) 545°C/0.5h; (j) 545°C/1h; (k) 545°C/1.5h; (l) 545°C/2h.\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7155152/v1/45f05b7ff7efa5ac048ff7e8.jpeg"},{"id":91458392,"identity":"81bdcf50-8d34-410f-aa29-b59615552558","added_by":"auto","created_at":"2025-09-16 16:43:06","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":282282,"visible":true,"origin":"","legend":"\u003cp\u003eLongitudinal stress-strain curves of DED-Arc 2319 Al alloy under different aging conditions: (a) Variation with temperature; (b) Variation with time.\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7155152/v1/e9e0d77473695adc97542bb3.jpeg"},{"id":91457343,"identity":"fe8ab783-c972-4385-9400-6478f254fc37","added_by":"auto","created_at":"2025-09-16 16:35:06","extension":"jpeg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":633973,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of the secondary phase evolution of DED-Arc 2319 Al alloy in as-deposited and different heat treated conditions: (a) As-deposited state; (b) Homogenization; (c) Solution; (d) Aging.\u003c/p\u003e","description":"","filename":"floatimage7.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7155152/v1/0681b282903d3bd8e4dee369.jpeg"},{"id":91457412,"identity":"a778c477-27a3-4edd-aa57-84024f394c87","added_by":"auto","created_at":"2025-09-16 16:35:41","extension":"jpeg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":673428,"visible":true,"origin":"","legend":"\u003cp\u003eTEM images of the evolution of the secondary phase of DED-Arc 2319 Al alloy in as-deposited and different heat treated conditions: (a) as-deposited state; (b) homogenization; (c) solution; (d) aging.\u003c/p\u003e","description":"","filename":"floatimage8.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7155152/v1/4167d6c539d35d28ae0d6c61.jpeg"},{"id":91458966,"identity":"cdfa7e43-b5b4-4383-a454-e72ce5a34e3e","added_by":"auto","created_at":"2025-09-16 16:51:06","extension":"jpeg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":2179830,"visible":true,"origin":"","legend":"\u003cp\u003eMicro-morphology and lattice striations of different secondary phases of DED-Arc 2319 Al alloy: (a) θ phase; (b) θ′ phase; (c) θ″ phase.\u003c/p\u003e","description":"","filename":"floatimage9.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7155152/v1/d36a7339b33e9fbe6dd25b8e.jpeg"},{"id":91457352,"identity":"86180e67-8f74-4af3-84ff-080393ae089f","added_by":"auto","created_at":"2025-09-16 16:35:06","extension":"jpeg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":3070547,"visible":true,"origin":"","legend":"\u003cp\u003eElemental distribution of DED-Arc 2319 Al alloy in as-deposited and different heat treated conditions: (a) As-deposited state; (b) Homogenization; (c) Solution; (d) Aging.\u003c/p\u003e","description":"","filename":"floatimage10.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7155152/v1/677736fd4ee73d5ffb6f8fcc.jpeg"},{"id":91457348,"identity":"89595c6c-a9f7-4e2d-a4cf-437bfa561ba0","added_by":"auto","created_at":"2025-09-16 16:35:06","extension":"jpeg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":697719,"visible":true,"origin":"","legend":"\u003cp\u003eBulk hardness of DED-Arc 2319 Al alloy in as-deposited and different heat treated conditions.\u003c/p\u003e","description":"","filename":"floatimage11.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7155152/v1/f6b3da6f9f782e49613dedae.jpeg"},{"id":91458388,"identity":"b78538c8-c5a3-4212-8592-4cdc6f98515d","added_by":"auto","created_at":"2025-09-16 16:43:06","extension":"jpeg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":1058773,"visible":true,"origin":"","legend":"\u003cp\u003eLongitudinal tensile properties of DED-Arc 2319 Al alloy in as-deposited and different heat treated conditions.\u003c/p\u003e","description":"","filename":"floatimage12.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7155152/v1/b9f045ad18997def4aadab9b.jpeg"},{"id":91458967,"identity":"b46f923d-9c33-42b6-81cb-7f4e7adc9874","added_by":"auto","created_at":"2025-09-16 16:51:06","extension":"jpeg","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":1018216,"visible":true,"origin":"","legend":"\u003cp\u003eLongitudinal tensile fracture morphology of DED-Arc 2319 Al alloy in as-deposited and different heat treated conditions: (a) As-deposited state; (b) Homogenization; (c) Solution; (d) Aging.\u003c/p\u003e","description":"","filename":"floatimage13.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7155152/v1/66d19c22f445d1fd2f26b255.jpeg"},{"id":91460502,"identity":"49f321fb-b35f-429a-ab34-b850abde641f","added_by":"auto","created_at":"2025-09-16 17:07:06","extension":"jpeg","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":1043566,"visible":true,"origin":"","legend":"\u003cp\u003eTransverse tensile properties of DED-Arc 2319 Al alloy in as-deposited and different heat treated conditions.\u003c/p\u003e","description":"","filename":"floatimage14.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7155152/v1/c08f6aad70e86ca3bdc6f390.jpeg"},{"id":91458971,"identity":"82f36514-25a4-4fb9-bd54-2ca799257c44","added_by":"auto","created_at":"2025-09-16 16:51:06","extension":"jpeg","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":1051953,"visible":true,"origin":"","legend":"\u003cp\u003eTransverse tensile fracture morphology of DED-Arc 2319 Al alloy in as-deposited and different heat treated conditions: (a) As-deposited state; (b) Homogenization; (c) Solution; (d) Aging.\u003c/p\u003e","description":"","filename":"floatimage15.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7155152/v1/d9ba9421739a3fc8242fbb8e.jpeg"},{"id":91457353,"identity":"a5265373-0972-4b8f-865d-972c48fd5941","added_by":"auto","created_at":"2025-09-16 16:35:06","extension":"jpeg","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":326470,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Polarization curves and (b) EIS before and after electrochemical testing of DED-Arc 2319 Al alloy.\u003c/p\u003e","description":"","filename":"floatimage16.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7155152/v1/37adbccf5a2e1e0fb81c4823.jpeg"},{"id":91457365,"identity":"5d6dae2f-e338-49fb-b4ef-c98327052a96","added_by":"auto","created_at":"2025-09-16 16:35:07","extension":"jpeg","order_by":17,"title":"Figure 17","display":"","copyAsset":false,"role":"figure","size":1140155,"visible":true,"origin":"","legend":"\u003cp\u003eSurface morphology of DED-Arc 2319 Al alloy before and after electrochemical testing: (a) As-deposited state; (b) Homogenization; (c) Solution; (d) Aging.\u003c/p\u003e","description":"","filename":"floatimage17.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7155152/v1/eed088231478c03cbc38900f.jpeg"},{"id":91457367,"identity":"54b56846-bdfc-496c-b3b0-58c4fe5c2704","added_by":"auto","created_at":"2025-09-16 16:35:07","extension":"jpeg","order_by":18,"title":"Figure 18","display":"","copyAsset":false,"role":"figure","size":1195967,"visible":true,"origin":"","legend":"\u003cp\u003eThickness of corrosion layer before and after electrochemical testing of DED-Arc 2319 Al alloy: (a) As-deposited state; (b) Homogenization; (c) Solution; (d) Aging\u003c/p\u003e","description":"","filename":"floatimage18.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7155152/v1/6d897a13c3af2cadd27dd501.jpeg"},{"id":91458399,"identity":"9fb5b593-e697-4e25-9c67-5fbfbed6e37e","added_by":"auto","created_at":"2025-09-16 16:43:07","extension":"jpeg","order_by":19,"title":"Figure 19","display":"","copyAsset":false,"role":"figure","size":1070998,"visible":true,"origin":"","legend":"\u003cp\u003eSurface morphology of DED-Arc 2319 Al alloy before and after IGC testing: (a) As-deposited state; (b) Homogenization; (c) Solution; (d) Aging.\u003c/p\u003e","description":"","filename":"floatimage19.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7155152/v1/fca02b9438e7015244a1cb50.jpeg"},{"id":91458405,"identity":"030e2e76-80f1-46e0-960a-14cac825ee15","added_by":"auto","created_at":"2025-09-16 16:43:07","extension":"jpeg","order_by":20,"title":"Figure 20","display":"","copyAsset":false,"role":"figure","size":2926920,"visible":true,"origin":"","legend":"\u003cp\u003eSurface element distribution before and after IGC testing of DED-Arc 2319 Al alloy: (a) As-deposited state; (b) Homogenization; (c) Solution; (d) Aging.\u003c/p\u003e","description":"","filename":"floatimage20.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7155152/v1/b66102df1ba0751c2abb6776.jpeg"},{"id":91458401,"identity":"72aadbaf-a205-4549-be79-f327b32806c3","added_by":"auto","created_at":"2025-09-16 16:43:07","extension":"jpeg","order_by":21,"title":"Figure 21","display":"","copyAsset":false,"role":"figure","size":828680,"visible":true,"origin":"","legend":"\u003cp\u003eDepth of corrosion layer before and after IGC testing of DED-Arc 2319 Al alloy: (a) As-deposited state; (b) Homogenization; (c) Solution; (d) Aging.\u003c/p\u003e","description":"","filename":"floatimage21.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7155152/v1/60e811a4b49394bb94c59f76.jpeg"},{"id":91816706,"identity":"c5acadb6-f2b9-420b-9398-a97274def01c","added_by":"auto","created_at":"2025-09-22 06:52:41","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":31494402,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7155152/v1/de249109-4724-4234-ac1e-acceca5c0724.pdf"}],"financialInterests":"","formattedTitle":"Effect of heat treatment on mechanical properties and corrosion resistance of Directed Energy Deposition-Arc 2319 Al alloy","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eThe 2319 aluminum (Al) alloy boasts excellent mechanical properties, including low density, high specific strength, superior weldability and formability, making it ideal for a number of applications [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. However, traditional manufacturing methods for Al alloys face significant challenges such as inefficiency, and difficulty in producing complex components [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Additive Manufacturing (AM) technology overcomes these drawbacks with its exceptional flexibility, high material utilization, near-net-shape forming, and ability to create parts with intricate geometries [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. However, this technology has limitations affecting its widespread applications. For instance, the occurrence of complex thermal cycling during material deposition can lead to high residual stresses, compositional segregation, anisotropic microstructures, poor mechanical properties, and inadequate corrosion resistance [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Consequently, post-treatment processes are necessary to address these issues, particularly to improve mechanical properties and corrosion resistance. Homogenization\u0026thinsp;+\u0026thinsp;solution aging heat treatment is a common post-treatment method for casting Al alloys [\u003cspan additionalcitationids=\"CR11\" citationid=\"CR11\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e12\u003c/span\u003e], but there are similar heat treatment studies for Al alloys deposited using Directed Energy Deposition-Arc (DED-Arc) [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. DED-Arc is a technology that use welding arc as a heat source to deposit metal wire or power source layer by layer. These treatments can promote elemental diffusion and secondary phase evolution, thereby improving the mechanical properties and corrosion resistance of the formed parts [\u003cspan additionalcitationids=\"CR11 CR12 CR13\" citationid=\"CR11\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eControlling the secondary phase evolution by heat treatment is an important mechanism to improve the mechanical properties of Al-Cu alloys. Cai et al. [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e13\u003c/span\u003e] investigated the effect of different heat treatment processes on the mechanical properties of DED-Arc 2219 Al alloy components. The direct aging treatment had little effect on the properties of DED-Arc 2219 Al alloy, and the Vickers hardness value of the alloy was only increased by about 10%. The hardness of the DED-Arc 2219 Al alloy increased considerably after solution\u0026thinsp;+\u0026thinsp;aging treatments but still did not match the hardness values of the cast alloy. Finally, a combination of homogenization\u0026thinsp;+\u0026thinsp;solution\u0026thinsp;+\u0026thinsp;aging treatments was employed at DED-Arc 2219 Al alloy to achieve the hardness (143.5 HV) of the cast\u0026thinsp;+\u0026thinsp;aged 2219 Al alloy. Zhou et al. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e14\u003c/span\u003e] found that DED-Arc 2219 Al alloy exhibited a good combination of strength and plasticity after homogenization\u0026thinsp;+\u0026thinsp;solution aging heat treatment, and its mechanical properties were superior to those of pre-deformed compression Al-Cu alloy. Compared with the T6 heat treatment (solution treated at high temperatures and then artificially aged at a certain temperature), the additional homogenization treatment prefabricated more Al\u003csub\u003e3\u003c/sub\u003eZr dispersions, which indirectly promoted the transformation of the θ\u0026Prime; phase to the θ\u0026prime; phase and significantly reduced the plastic anisotropy. In addition, homogenization\u0026thinsp;+\u0026thinsp;solution\u0026thinsp;+\u0026thinsp;aging heat treatments of the alloy enhanced the thermal stability and mechanical properties of DED-Arc 2219 alloy. Wang et al. [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e15\u003c/span\u003e] investigated the strengthening mechanism of T6 heat treatment for in-situ rolled DED-Arc Al-Cu alloys. During T6 heat treatment, most of the eutectic structures with continuous or semi-continuous distribution at grain boundaries dissolved into the matrix. Some undissolved θ and a high density of acicular θ\u0026prime; phases appeared inside the grains. After T6 treatment, the ultimate tensile strength (UTS) and yield strength (YS) of the alloy reached 454.4\u0026thinsp;\u0026plusmn;\u0026thinsp;23.8 MPa and 356.6\u0026thinsp;\u0026plusmn;\u0026thinsp;17.1 MPa, respectively, which was mainly due to precipitation strengthening.\u003c/p\u003e\u003cp\u003eControlling the elemental distribution by heat treatment can enhance the corrosion resistance of Al-Cu alloys. Chen et al. [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e16\u003c/span\u003e] investigated the effect of homogenization\u0026thinsp;+\u0026thinsp;aging treatments on the corrosion behavior of Al-Cu-Li alloys. The high concentration of Cu often leads to the precipitation of more secondary phase during homogenization of the alloy, which is more uniformly dispersed within the alloy after aging. The corrosion potential increases with aging time, enhancing the corrosion resistance of the alloy. Sun et al. [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e17\u003c/span\u003e] used homogenization\u0026thinsp;+\u0026thinsp;solution aging heat treatments to strengthen Sr-containing 2024 Al alloy. The 2024 Al alloy matrix housed intermetallic phases after artificial aging, which contributed to diffusion strengthening. In addition, Sr inhibited the growth of Cu-rich second-phase particles and increased the amount of Cu in the matrix. The increased Cu content in the matrix further improved the corrosion resistance and strength of the alloy. Li et al. [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e18\u003c/span\u003e] investigated the effect of different aging treatments on the mechanical behavior, microstructural characteristics and corrosion behavior of rotary friction welded AA2024 joints. After artificial and long-term natural aging treatments, the tensile strength and corrosion resistance of the joints was uniform at different locations. After artificial aging, the Cu present in the intracrystalline and grain boundaries are uniformly distributed, reducing the tendency of intergranular corrosion (IGC).\u003c/p\u003e\u003cp\u003eIn summary, heat treatment of Al alloys, such as homogenization, solution and aging treatments have a positive impact in enhancing the mechanical properties and corrosion resistance [\u003cspan additionalcitationids=\"CR14 CR15 CR16 CR17\" citationid=\"CR14\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. However, the high thermal conductivity of Al challenges the heat treatment of large components due to difficulties in maintaining temperature control [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. During heat treatment processes, the diffusion coefficient, solid solution solubility, and nucleation barriers of metallic materials are constantly changing. The evolution of microstructure is gradual and complex, which makes the extent of heat treatment often difficult to control [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Therefore, there is a need to incorporate a slow and multi-stage heat treatment process for Al alloys. For example, in order to obtain finer second-phase particles, Zhang et al. [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e19\u003c/span\u003e] used double-stage homogenization instead of single-stage homogenization for Al-Mg-Zn-Sc-Zr alloy, and Vandersluis et al. [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e20\u003c/span\u003e] used double-stage solution instead of single-stage solution treatment for B319 Al alloy. Cai et al. [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e13\u003c/span\u003e] and Zhou et al. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e14\u003c/span\u003e] included homogenization before solution\u0026thinsp;+\u0026thinsp;aging treatments, which refined the secondary phase particles, reducing the anisotropy and improving the thermal stability and mechanical properties of the alloy.\u003c/p\u003e\u003cp\u003eSo far, the homogenization\u0026thinsp;+\u0026thinsp;solution aging heat treatments have been predominantly employed to improve the mechanical properties of Al-Cu alloys, and relatively little research has been done on corrosion resistance. Several reports have demonstrated that homogenization [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e21\u003c/span\u003e], solution treatment [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e9\u003c/span\u003e], aging [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e22\u003c/span\u003e], homogenization\u0026thinsp;+\u0026thinsp;aging [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e16\u003c/span\u003e], and solution\u0026thinsp;+\u0026thinsp;aging [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e23\u003c/span\u003e] treatments can enhance the corrosion resistance of Al-Cu alloys. Additionally, homogenization\u0026thinsp;+\u0026thinsp;solution aging treatment involves a gradual heating, which is expected to improve the mechanical properties and corrosion resistance of Al-Cu alloys [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Currently, homogenization\u0026thinsp;+\u0026thinsp;solution aging treatments are mostly used in DED Arc 2219 Al alloy in Al-Cu alloy series. 2319 Al alloy chosen in this study has a similar composition to 2219 Al alloy, and is employed in a wide range of applications and relatively cheaper than 2319 Al alloy. In this study, an in-depth investigation was carried out on the effects of homogenization\u0026thinsp;+\u0026thinsp;solution\u0026thinsp;+\u0026thinsp;aging treatments on the microstructural characteristics and the evolution of the secondary phase in DED-Arc 2319 Al alloy. The effect of the heat treatments on the mechanical behavior and the corrosion resistance was also investigated.\u003c/p\u003e"},{"header":"2. Experiments and methods","content":"\u003cp\u003eA 2319 Al alloy welding wire with a diameter of 1.2 mm was selected as the filler material, and 5083 Al alloy with a size of 200 mm \u0026times; 100 mm \u0026times; 10 mm was used as the forming substrate. The chemical composition of the wire and substrate are shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The surface of the substrate was subjected to a deep cleaning treatment to remove oil and other impurities. Initially, the substrate was immersed in a NaOH solution (concentration of 5%) at 50\u0026deg;C for 10 min, followed by a cold-water rinse. Subsequently, the substrate was dipped in 30% HNO\u003csub\u003e3\u003c/sub\u003e solution for 30 s. Finally, it was cleaned with hot water (at 50\u0026deg;C) and dried. The surface of the substrate was then sanded using an abrasive wheel until smooth, and then cleaned with acetone before metal deposition. The DED-Arc system employs CMT welding, where the welding current is 115 A, and the wire feeding speed is 0.5m/min. Argon gas (purity of 99.99% and a flow rate of 20 L/min) was used to prevent the impurity gases from entering the molten pool and also to avoid porosity defects during the DED-Arc process.\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 the welding wire and substrate (wt. %).\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"7\"\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=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAlloys\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"6\" nameend=\"c7\" namest=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCu\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eMg\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eSi\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eFe\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003eZn\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003eMn\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eER2319\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e5.8\u0026ndash;6.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.2\u0026ndash;0.4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e5083\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.07\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3.75\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.09\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.04\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.49\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 dimensions of the DED-Arc samples are ~\u0026thinsp;240 mm in length, ~\u0026thinsp;14 mm in width and ~\u0026thinsp;105 mm in height, respectively (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea and b). Straight walls were cut and machined into small blocks (10 mm \u0026times; 5 mm \u0026times; 10 mm) for heat treatment (homogenization\u0026thinsp;+\u0026thinsp;solution\u0026thinsp;+\u0026thinsp;aging) and characterization purposes (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the schematic representations of different heat treatments undertaken in the current study. All heat treatments were carried out in a muffle furnace with a temperature accuracy of \u0026plusmn;\u0026thinsp;1\u0026deg;C. Double-stage homogenization treatments were performed in two conditions, i.e., 460℃ \u0026minus;\u0026thinsp;480℃ for 8h and 520℃ \u0026minus;\u0026thinsp;530℃ for 24h, and an optimal double-stage homogenization temperature and time were selected by observing the microstructure changes [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Based on the chosen double-stage homogenization treatment, solution treatment (535℃ \u0026minus;\u0026thinsp;545℃ for 0.5\u0026ndash;2 h) and aging treatment (160℃ \u0026minus;\u0026thinsp;180℃ for 24 h) were trialed and then optimized. The heating rate of homogenization and solution treatment was set at 10℃/min, while the heating rate of aging treatment was 5℃/min. After homogenization and solution treatments, samples were cooled to 20\u0026thinsp;\u0026plusmn;\u0026thinsp;5℃ by water quenching, and after aging treatment, samples were air-cooled to 20\u0026thinsp;\u0026plusmn;\u0026thinsp;5℃.\u003c/p\u003e\u003cp\u003eThe microstructures were observed and analyzed using a Leica DMi8 optical microscopy (OM) and a QUANTA FEG 450 scanning electron microscopy (SEM). The hardness tests were carried out at 100 different points with 0.5 mm apart on the XZ surface and the average value was taken (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). Three tensile tests of YZ surface (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec) were carried out (Tensile rate-0.5 mm/min \u0026amp; strain rate-6\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) in each condition and an average value was taken into consideration. The phase transition temperature of the deposited alloy and the degree of dissolution of the eutectic phase after homogenization were analyzed using a SDT-Q600 differential scanning calorimeter (DSC). The heating rate of DSC test was 20 K/min.\u003c/p\u003e\u003cp\u003eTwo sets of corrosion tests, i.e., electrochemical and intergranular corrosion (IGC) were included in this study. The electrochemical tests were performed using a standard three-electrode system with a saturated calomel electrode (SCE) and platinum sheet for the reference electrode and counter electrode, respectively. The working electrodes were DED-Arc 2319 Al alloy in different conditions (i.e., as-deposited, homogenized, solution treated and aged) with a working area of 0.25 cm\u003csup\u003e2\u003c/sup\u003e. After connecting the specimens with copper wires, the non-working surface was encapsulated and protected using resin, and the surface of the working electrode was ground and polished. The electrochemical test medium was 3.5 wt.% NaCl solution with a pH\u0026thinsp;=\u0026thinsp;6.0. Before the test, the working electrode was immersed in the electrolyte, and the electrochemical test was performed after the stabilization of real-time potential. The electrochemical test outputs included polarization curves and electrochemical impedance spectroscopy (EIS). Electrochemical impedance spectroscopy (EIS) is widely used to study the corrosion behavior and the continuous evolution of the corrosion resistance of the material under test [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. IGC tests were performed on DED-Arc 2319 Al alloy specimens in as-deposited and heat-treated conditions, three specimens were tested from each condition. The IGC test solution comprised of: 10 mL of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e solution at 30% concentration, 57 g of NaCl, and 1 L of distilled or deionized water. The IGC tests were carried out under constant temperature at 35\u0026thinsp;\u0026plusmn;\u0026thinsp;2℃. The specimens were suspended in the solution for 6h and utmost care was taken to avoid samples touching one another. The corroded specimens were rinsed in alcohol and blown dry.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"3. Development of heat treatment process parameters","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Optimization of homogenization treatment process parameters\u003c/h2\u003e\u003cp\u003eTo avoid overburning during the heat treatment process and to establish a reasonable temperature range for the heat treatment, the dissolution degree of the secondary phase and the melting point of the non-equilibrium eutectic phase were investigated by DSC. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the DSC curve of the as-deposited 2319 Al alloy. The temperature of the endothermic peak refers to the melting temperature of non-equilibrium eutectic phase with a low melting point of ~\u0026thinsp;546\u0026deg;C (also known as the overburning temperature) along with the melting point of the alloy, ~\u0026thinsp;651\u0026deg;C. The first stage of the double-stage homogenization treatment of 2XXX Al alloys has a temperature time range of 440\u0026deg;C- 480\u0026deg;C at 8 h. The second stage of the double-stage homogenization treatment of DED-Arc 2319 Al alloy in the as-deposited state ranges from 520\u0026deg;C to 530\u0026deg;C (below the overcooking temperature of 546\u0026deg;C) with a holding time of 24 h. Therefore, six double-stage homogenization regimes of 440\u0026deg;C/8 h\u0026thinsp;+\u0026thinsp;520\u0026deg;C/24 h, 440\u0026deg;C/8 h\u0026thinsp;+\u0026thinsp;530\u0026deg;C/24 h, 460\u0026deg;C/8 h\u0026thinsp;+\u0026thinsp;520\u0026deg;C/24 h, 460\u0026deg;C/8 h\u0026thinsp;+\u0026thinsp;530\u0026deg;C/24 h, 480\u0026deg;C/8 h\u0026thinsp;+\u0026thinsp;520\u0026deg;C/24 h and 480\u0026deg;C/8 h\u0026thinsp;+\u0026thinsp;530\u0026deg;C/24 h were designed.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eBased on Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, when the temperature of the first stage homogenization is low (440\u0026deg;C), a small amount of incomplete dissolution of the eutectic phase still occurs, and part of the dendritic microstructure remains at the grain boundaries (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb and c). At the first stage homogenization temperature, i.e., 480\u0026deg;C, there is less residual dendritic microstructure at the grain boundaries, as shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e (f) and (g). During the second stage of the homogenization, there was an increased dissolution of the eutectic phase, with a uniform microstructure, and the grain boundaries were clear without any overheating or overburning phenomena (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Optimization of solution treatment process parameters\u003c/h2\u003e\u003cp\u003eBy analyzing the DSC curves of DED-Arc 2319 Al alloy in the as-deposited state, the solution treatment temperature range was determined to be 535℃-545℃. Three solution treatment temperatures (535\u0026deg;C, 540\u0026deg;C and 545\u0026deg;C) and holding times (0.5 h, 1 h, 1.5 h and 2 h) were trailed to optimize the parameters.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eWith an increase in solutionizing temperature and the extension of time, the solubility of residual phase increases and enters the matrix. At a solution temperature of 535\u0026deg;C, a large number of residual phases remained undissolved in the intralayer columnar and interlayer fine-crystalline structures of the treated DED-Arc 2319 Al alloy (Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea-d). When the temperature was raised to 540\u0026deg;C, the grain boundaries became clearer and the precipitated phases in the intralayer and the interlayer zones were more dissolved (Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee-h), and this effect was pronounced when the holding time was raised to 2 h (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eh). There was hardly any distinct changes in the microstructures, when the temperature was raised to 545\u0026deg;C for the same holding time of 2h. The degree of grain boundary clarity and the dissolution effect of precipitated phases were comparable to that of the earlier condition-540\u0026deg;C/2 h. However, there was a melting phenomenon of low-melting-point eutectic phases and the formation of a remelting pellet (black arrow) in the process of cooling [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e27\u003c/span\u003e] (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003el). Therefore, the optimal solutionizing condition is 540\u0026deg;C/2 h because there was an almost complete dissolution of the precipitated phases at the grain boundaries of the intralayer and interlayer regions.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Formulation of aging process parameters\u003c/h2\u003e\u003cp\u003eOptimum aging conditions were determined based on the tensile tests of the aged specimens under different aging temperatures and time. Prior to that the samples subjected to double stage homogenization (480℃/8h\u0026thinsp;+\u0026thinsp;530℃/24h) and solution treatment (540℃/8h) specimens (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). Longitudinal tensile tests of YZ surface (parallel to the building direction Z axis) were performed for two different aging conditions, i.e., A. constant aging temperature (175℃) and variable time (6, 12, 18, 24, 30 \u0026amp; 36 h) \u0026amp; variable aging temperatures (160, 165, 170, 175 and 180℃) and B. constant time (24 h) (Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea and b). Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the longitudinal tensile strength and elongation of DED-Arc 2319 Al alloy at different aging temperatures and times.\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\u003eLongitudinal UTS and elongation of DED-Arc 2319 Al alloy at different aging parameters (temperature and time).\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\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=\"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\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003edouble-stage homogenization\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eSolution\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003eAging\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eUTS/MPa\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eElongation /%\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eTemperature/℃\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eTime/h\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e/\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e/\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\u003e/\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e254.30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e13.10\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"10\" rowspan=\"11\"\u003e\u003cp\u003e480℃/8h\u0026thinsp;+\u0026thinsp;530℃/24h\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\" morerows=\"10\" rowspan=\"11\"\u003e\u003cp\u003e540℃/2h\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e160\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003e24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e281.39\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e9.52\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e165\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e315.50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e9.31\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e170\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e347.24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e8.03\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e175\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e371.69\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e5.89\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e180\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e343.65\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e5.77\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\" morerows=\"5\" rowspan=\"6\"\u003e\u003cp\u003e175\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e279.90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e9.51\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e316.50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e8.90\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e343.90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e7.12\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e371.69\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e5.89\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e351.06\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e4.58\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e36\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e344.44\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e4.39\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\u003eFrom Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the as-deposited DED-Arc 2319 Al alloy displayed the lowest UTS of 254.30 MPa, and the highest elongation of 13.10%. whereas after double-stage homogenization and solution aging treatments, the UTS are both significantly increased, and the elongation decreased significantly. The maximum UTS of 371.69 MPa was achieved at an aging condition of 175\u0026deg;C/24 h. An increase in aging temperature (180\u0026deg;C) and time (\u0026gt;\u0026thinsp;24 h), resulted in a simultaneous decrease in UTS and elongation.\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Results and discussion","content":"\u003cp\u003eThe effect of heat treatment (homogenization\u0026thinsp;+\u0026thinsp;solution aging) on the microstructural characteristics of DED-Arc 2319 Al alloy were analyzed. Advanced characterization techniques were used to characterize the second phase and elements before and after heat treatment. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e shows a SEM image of the secondary phase evolution in as-deposited and heat-treated conditions of the DED-Arc 2319 Al alloy. There is a eutectic phase segregation at the grain boundaries of the as-deposited DED-Arc 2319 Al alloy, and some discrete distribution of rods and particles of the second phase θ within the grain, (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea). After homogenization, a vast majority of the low melting point eutectic phases (at grain boundaries and within the grains) were broken down and dissolved, and the remaining high melting point secondary phase θ was uniformly distributed within the grains (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(b). The solution treatment further increased the dissolution of the undissolved secondary phase θ from the homogenization treatment (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ec). After aging, the remaining secondary phase θ precipitated out and distributed within the grains (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ed).\u003c/p\u003e\u003cp\u003eAn in-depth observation on the secondary phase evolution was conducted using TEM analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). Large disc-shaped black particles (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea) are the eutectic phase in the as-deposited state. During homogenization, these particles were broken down and uniformly distributed as small particles of θ phase in the Al matrix (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eb). This phenomenon was further enhanced during the solution treatment (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ec). After ageing, many fine needle-like strengthening phases θ\u0026prime; and θ\u0026Prime; were precipitated within the Al matrix (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ed). In addition, small disk-like dispersed phases were not dissolved during the heat treatment process, and these dispersed phases are often detrimental for mechanical behavior, however, they can act as nucleation sites for the precipitation of the reinforcing phases (θ\u0026prime; and θ\u0026Prime;) [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eA high-resolution transmission microscopy was employed to characterize the morphology and lattice variations in the secondary phase (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(a) identified the θ phase microscopic morphology and the spacing of the θ phase lattice stripes to be 0.1299 nm. Both θ\u0026prime; and θ\u0026Prime; phases are needle-like structures with short rod-like profiles. The size of θ\u0026prime; and θ\u0026Prime; phases are ~\u0026thinsp;150 nm and ~\u0026thinsp;15 nm, respectively. Similarly, the θ\u0026prime; and θ\u0026Prime; phase lattice stripe spacings were 0.2907 nm and 0.2127 nm, respectively (Figs.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eb and c). The lattice stripe spacing of the Al matrix was 0.2052 nm, and among the secondary phases, only the θ\u0026Prime; phase and the Al matrix are completely coherent.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eTEM-EDS technique was employed to study the elemental distribution and compositional analysis on the secondary phases (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e). In the as-deposited state, the composition of the eutectic phases was found to be θ (Al\u003csub\u003e2\u003c/sub\u003eCu)\u0026thinsp;+\u0026thinsp;T (Al\u003csub\u003e12\u003c/sub\u003eCuMn\u003csub\u003e2\u003c/sub\u003e) + α (Al) along with low levels of Cu and Mn segregations were observed in the Al matrix (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ea). This could be due to the homogenization treatment, which promotes the dissolution of eutectic phases, reducing Cu and Mn segregation, and thereby promoting a uniform distribution of elements in the matrix (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003eb). The solution treatment further enhances the dissolution of the remaining second phase θ (Al\u003csub\u003e2\u003c/sub\u003eCu) and Cu into the Al matrix, forming a supersaturated solid solution (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ec). However, the concentration of Cu in the Al matrix decreases after aging, and many fine needle-like reinforced phases θ\u0026prime; and θ\u0026Prime; are precipitated (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ed). Additionally, a number of reinforcing phases θ\u0026prime; and θ\u0026Prime; precipitate around the disk-shaped structures.\u003c/p\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e4.2 Effect of heat treatment on mechanical properties\u003c/h2\u003e\u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\u003ch2\u003e4.2.1 Effect of heat treatment on bulk hardness\u003c/h2\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFrom Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e, the bulk hardness of DED-Arc 2319 Al alloy in the as-deposited state is 73.9 HV. Homogenization and solution treatments decreased the bulk hardness to 52.7 HV and 49.6 HV, respectively. Both the treatments dissolve both the low and high smelting point eutectic phases resulting in a gradual decrease in the bulk hardness of the as-deposited alloy. However, after aging, the bulk hardness was significantly increased to 148 HV. After aging, a number of needle-like reinforcing phases are precipitated to increase the bulk hardness of the alloy.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\u003ch2\u003e4.2.2 Effect of heat treatment on tensile properties in longitudinal and transverse direction:\u003c/h2\u003e\u003cp\u003eThe longitudinal tensile (parallel to the building direction Z axis) UTS of DED-Arc 2319 Al alloy in the as-deposited state in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e was 254.3 MPa. This was decreased to ~\u0026thinsp;180 MPa after both homogenization and solution treatments. As expected, the aging treatment improved the UTS to 371.7 MPa. After homogeneous solution treatment, the elongation of the alloy was increased by dissolving the second phase (~\u0026thinsp;13% ~ 16.6%). After aging treatment, the Cu segregation and precipitation in the matrix decreased the elongation of the alloy (~\u0026thinsp;5.9%).\u003c/p\u003e\u003cp\u003eFracture analysis was conducted on the tensile specimens from as-deposited and different heat-treated conditions (Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e). In Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e(a), the tensile fracture of the as deposited specimen was distributed with fine and dense dimples, along with hard and brittle eutectic phase particles in the center of the dimples, indicating a ductile mode of fracture. Compared with the as-deposited state, the alloy has larger and deeper dimples at the fracture after the homogenization and solution treatments, which exhibits typical ductile fracture characteristics (Figs.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003eb and c). Larger dimples and minimal θ phase observed in the fractured surface improved plasticity. On other hand, a brittle fracture was observed in aged tensile specimen, consisting of several tearing ridges and presence of a brittle secondary phase at the fracture sites. This leads to increased strength and reduced plasticity after aging (Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003ed).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eTensile properties in transverse direction (perpendicular to the building direction Z axis) exhibited a similar trend to that in longitudinal direction (Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e14\u003c/span\u003e). The UTS of the as deposited specimen (i.e., 257.2 MPa) decreased after homogenization and solution heat treatments (i.e., ~\u0026thinsp;184 MPa). After aging, the UTS was increased to ~\u0026thinsp;380 MPa. Homogenization and solution treatments improved the elongation from ~\u0026thinsp;14% to ~\u0026thinsp;17% as expected, while the aging treatment decreased the elongation to 8.9%.\u003c/p\u003e\u003cp\u003eFractured surface analysis revealed similar features and fracture modes in both transverse and longitudinal directions. In the as deposited condition, the fractured samples contained a dense distribution of small dimples and brittle secondary phases (Fig.\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e15\u003c/span\u003ea). Large and deep dimples were observed at the fractured surfaces post homogenization and solution treatments (Figs.\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e15\u003c/span\u003eb and c), along with tearing ridges after aging treatment (Fig.\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e15\u003c/span\u003ed).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e4.3 Effect of heat treatment on corrosion resistance\u003c/h2\u003e\u003cdiv id=\"Sec12\" class=\"Section3\"\u003e\u003ch2\u003e4.3.1 Electrochemical corrosion behaviour\u003c/h2\u003e\u003cp\u003eCorrosion properties of the alloys were studied using electrochemical corrosion tests. Figure\u0026nbsp;\u003cspan refid=\"Fig16\" class=\"InternalRef\"\u003e16\u003c/span\u003e(a) shows the polarization curves for the as-deposited state (black curve), homogenization (red curve), solution (blue curve) and aging treatment (green curve). There are two sections in each polarization curve, i.e., anodic Tafel curve (the curve to the right of the spike) and the cathodic Tafel curve (the curve to the left of the spike). The hydrogen precipitation in aqueous solution occurs in the cathodic reaction stage, while the dissolution of Al occurs in the anodic reaction stage. The shift between cathodic and anodic reaction phases is related to the internal corrosion potential of the alloy [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. As the internal corrosion potential of the alloy increases, the corrosion product film (Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) ruptures in response to the sharply increasing anodic current, and when the corrosion potential reaches a threshold value, rapid anodic Al dissolution occurs. At these breakdown potentials, homogenized, solution and aging treated specimens have similar anodic kinetics.\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig16\" class=\"InternalRef\"\u003e16\u003c/span\u003e(b) shows the EIS results of specimens in different conditions (as deposited and heat treated). The corrosion resistance of the specimen in the corrosive solution can be expressed by the capacitive arc resistance diameter in the electrical impedance meter. As the capacitive arc resistance diameter increases, the corrosion resistance of the specimen improves [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Alloys in the as-deposited state have the smallest arc diameter indicating a relatively poor corrosion resistance. While the heat-treated conditions revealed an increased arc diameter indicating an improved corrosion resistance.\u003c/p\u003e\u003cp\u003eThe corrosion potential (E\u003csub\u003ecorr\u003c/sub\u003e) and corrosion current density (I\u003csub\u003ecorr\u003c/sub\u003e) were calculated by extrapolation. Horizontal and vertical coordinates of the slopes of cathodic and anodic curves indicate the corrosion potential and current density, respectively. As shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, the highest corrosion potential (-0.556 V vs SCE) was observed for the solution treated specimens, followed by aging (-0.664 V vs SCE) and homogenization treatments, (-0.712 V vs SCE), whereas the lowest corrosion potential was observed for the as-deposited specimens (-0.826 V vs SCE). Based on the thermodynamic system, corrosion potential can reflect the trend of corrosion, the lower the corrosion potential, the more susceptible the material to corrosion.\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\u003eTafel fitting data for DED-Arc 2319 Al alloy in as-deposited and different heat treated conditions.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"3\"\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\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 (V vs. SCE)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eI\u003csub\u003ecorr\u003c/sub\u003e (A/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\u003eAs-deposited\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e-0.826\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-4.3891\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eHomogenization\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e-0.712\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-6.3526\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSolution\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e-0.556\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-6.3726\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAging\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e-0.664\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-6.0755\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\u003e\u003c/p\u003e\u003cp\u003eThe effect of electrochemical testing on the surface morphology of the specimens before and after heat treatment were analyzed. SEM tests were performed to investigate the micro-morphology after corrosion. From Fig.\u0026nbsp;\u003cspan refid=\"Fig17\" class=\"InternalRef\"\u003e17\u003c/span\u003e(a), three types of corrosion, i.e., pitting, IGC, and exfoliation corrosion, occur sequentially in the as-deposited state DED-Arc 2319 Al alloy. With the deepening of pits around the secondary phase, grain boundary pitting connects to form IGC, creating corrosion channels, followed by exfoliation corrosion. Figure\u0026nbsp;\u003cspan refid=\"Fig17\" class=\"InternalRef\"\u003e17\u003c/span\u003e(b) shows the corrosion morphology after homogenization treatment, where pitting phenomenon was more serious. However, this phenomenon (pitting) was less severe in solution treated conditions (Fig.\u0026nbsp;\u003cspan refid=\"Fig17\" class=\"InternalRef\"\u003e17\u003c/span\u003ec). After aging treatment, Cu segregation and secondary phase growth occurred in the alloy, resulting in pitting corrosion and a slight IGC phenomenon, with no exfoliation corrosion (Fig.\u0026nbsp;\u003cspan refid=\"Fig17\" class=\"InternalRef\"\u003e17\u003c/span\u003ed). This clearly indicates that heat treatments can enhance the corrosion resistance of DED-Arc 2319 Al alloy by regulating the evolution of the secondary phase.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe thickness of corrosion layer after electrochemical testing were analyzed (Fig.\u0026nbsp;\u003cspan refid=\"Fig18\" class=\"InternalRef\"\u003e18\u003c/span\u003e). Depending on the thickness of the corrosion layer, the corrosion resistance of the alloy is determined. In general, heat-treated samples revealed better corrosion resistance than the as-deposited specimen. As deposited specimens displayed the poorest corrosion resistance with a thick corrosive layer (717 \u0026micro;m), followed by aged (553 \u0026micro;m), homogenized (258 \u0026micro;m) and solution treated specimens (128 \u0026micro;m). As the eutectic phase in the as-deposited state is segregated at the grain boundaries, it leads to the formation of a number of wide IGC channels after electrochemical corrosion, leading to an increased thickness of the corrosion layer (717 \u0026micro;m Fig.\u0026nbsp;\u003cspan refid=\"Fig18\" class=\"InternalRef\"\u003e18\u003c/span\u003ea). After homogenization and solution treatments, the eutectic and the secondary phases dissolved sequentially, with no IGC channels to be formed. The maximum thickness of the corrosion layers after homogenization and solution treatments were 258 \u0026micro;m and 128 \u0026micro;m, respectively, (Figs.\u0026nbsp;\u003cspan refid=\"Fig18\" class=\"InternalRef\"\u003e18\u003c/span\u003eb and c). The aged specimens contains several secondary phases (θ, θ\u0026prime; and θ\u0026Prime;), which acted as sources for pitting during electrochemical corrosion. Meanwhile, the secondary phase at the grain boundary led to an increase in the IGC channels with a maximum corrosion layer depth of 553 \u0026micro;m (Fig.\u0026nbsp;\u003cspan refid=\"Fig18\" class=\"InternalRef\"\u003e18\u003c/span\u003ed).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section3\"\u003e\u003ch2\u003e4.3.1 Intergranular corrosion (IGC)\u003c/h2\u003e\u003cp\u003eThe effect of heat treatment on the IGC of DED-Arc 2319 Al alloy was investigated and SEM was used to characterize the morphology of the secondary phases (Fig.\u0026nbsp;\u003cspan refid=\"Fig19\" class=\"InternalRef\"\u003e19\u003c/span\u003e). The eutectic phase in the as-deposited state was segregated at the grain boundaries, forming reticulated IGC channels and exacerbating IGC (Fig.\u0026nbsp;\u003cspan refid=\"Fig19\" class=\"InternalRef\"\u003e19\u003c/span\u003ea). However, the homogenization treatment has dissolved the eutectic phase at the grain boundaries and promotes a uniform distribution of the second phase within the grain, hindering the development of pitting corrosion into IGC, (Fig.\u0026nbsp;\u003cspan refid=\"Fig19\" class=\"InternalRef\"\u003e19\u003c/span\u003eb). Solution treatment has promoted a full dissolution of the secondary phase, reducing the source of pitting, thereby eliminating the formation of IGC and enhancing the resistance of the alloy to pitting and IGC (Fig.\u0026nbsp;\u003cspan refid=\"Fig19\" class=\"InternalRef\"\u003e19\u003c/span\u003ec). After aging treatment, the secondary phase increased in size, forming fewer IGC channels, (Fig.\u0026nbsp;\u003cspan refid=\"Fig19\" class=\"InternalRef\"\u003e19\u003c/span\u003ed). Compared with the as-deposited condition, the aging state alloy does not have IGC channels, which also slows down the IGC process and improves the IGC resistance of the alloy.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAn EDS characterization was undertaken to analyze the elemental distribution after IGC tests for different conditions (Fig.\u0026nbsp;\u003cspan refid=\"Fig20\" class=\"InternalRef\"\u003e20\u003c/span\u003e). The major alloying element, Cu plays a major role in affecting IGC in all conditions. In Fig.\u0026nbsp;\u003cspan refid=\"Fig20\" class=\"InternalRef\"\u003e20\u003c/span\u003e(a), there is Cu segregation at the grain boundaries of the alloy, and IGC channels are formed in the region of high concentration of Cu near the intergranular area, which reduces the IGC resistance of the alloy. Homogenization and solution treatments eliminated the segregation of Cu at grain boundaries, and the source of pitting corrosion was reduced preventing the formation of IGC channels (Figs.\u0026nbsp;\u003cspan refid=\"Fig20\" class=\"InternalRef\"\u003e20\u003c/span\u003eb and c). A small amount of Cu segregation is observed after aging, and there are fewer IGC channels (Fig.\u0026nbsp;\u003cspan refid=\"Fig20\" class=\"InternalRef\"\u003e20\u003c/span\u003ed).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe IGC resistance of the specimens was further analyzed by comparing the thickness of the IGC layers. The as deposited condition revealed the most severe and thickest corrosion layer, ~ 162 \u0026micro;m (Fig.\u0026nbsp;\u003cspan refid=\"Fig21\" class=\"InternalRef\"\u003e21\u003c/span\u003ea). The depth of the IGC layer was relatively shallow for the homogenized and solution-treated alloys, at 25 \u0026micro;m and 11 \u0026micro;m, respectively (Figs.\u0026nbsp;\u003cspan refid=\"Fig21\" class=\"InternalRef\"\u003e21\u003c/span\u003eb and c). The IGC layer of the alloy after aging was 68 \u0026micro;m (Fig.\u0026nbsp;\u003cspan refid=\"Fig21\" class=\"InternalRef\"\u003e21\u003c/span\u003ed). Compared with the as-deposited condition, there are fewer internal pitting sources and IGC channels in the aged alloy, indicating a relatively improved corrosion performance in aged conditions.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eThe effect of a series of heat treatment procedures (i.e., homogenization, solution treatment and aging) on the microstructural characteristics, mechanical properties and corrosion behavior of DED-Arc 2319 Al alloy was investigated. The main conclusions are as follows:\u003c/p\u003e\u003cp\u003e(1) Homogenization treatment promoted the dissolution of the low melting point eutectic phase and dendritic structures in DED-Arc 2319 Al alloy, thereby eliminating the segregation of Cu and Mn, and enhancing the homogeneity of the microstructure. The solution treatment was responsible the dissolution of the remaining high melting point secondary phase θ, prompting a complete dissolution of Cu and the formation of supersaturated solid solution. A number of needle-like reinforced phases θ\u0026prime; and θ\u0026Prime; were precipitated within the Al matrix after aging. Additionally, the relationship between the θ\u0026prime; and the Al matrix was investigated and found to be semi-coherent, while there was also a coherent relationship between θ\u0026Prime; phase and the Al matrix.\u003c/p\u003e\u003cp\u003e(2) The effect of heat treatment had a significant impact on the mechanical properties on DED-Arc 2319 Al alloy. For instance, homogenization\u0026thinsp;+\u0026thinsp;solution aging treatments increased the hardness of DED-Arc 2319 Al alloy from 73.9 HV in the as-deposited state to 148.0 HV in aged state. The longitudinal UTS was increased from 254.3 MPa in the as-deposited state to 371.7 MPa after the heat treatment, and the transverse UTS was increased from 257.2 MPa in the as-deposited state to 383.1 MPa. The longitudinal elongation was 13.1% in as-deposited state, increased to 15.9% and 16.3% after double-stage homogenization and solution treatments, respectively, and this decreased to 5.9% after aging treatment. Elongation (in transverse direction) was 13.9% in as-deposited, which increased to 16.8% and 17.5% after double-stage homogenization and solution treatments, respectively, and this decreased to 8.9% after aging treatment.\u003c/p\u003e\u003cp\u003e(3) Heat-treated specimens displayed improved corrosion resistance than the as-deposited specimen. Pitting, intergranular and exfoliation corrosion were observed in DED-Arc as-deposited state 2319 Al alloy specimens after electrochemical corrosion testing. Only pitting corrosion occurred in homogenized, and solution treated specimens. Meanwhile, pitting and intergranular corrosion occurred in the aged specimens. The thickness of the electrochemical corrosion layer decreased from 717 \u0026micro;m in the as-deposited state to 553 \u0026micro;m in the aged state. Pitting and intergranular corrosion were observed in the as-deposited state specimens after IGC testing. Homogenization, solution and aging treated specimens showed only pitting. The depth of the IGC layer was reduced from 162 \u0026micro;m in the as-deposited state to 68 \u0026micro;m in the aged state.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are avail-able on request from the corresponding author, [L.W.W.].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contribution\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors contributed to the study conception and design. Material preparation, data collection, and analysis were performed by Fenglei Cao, Zhen Tan, and Yunfeng Yao;\u0026nbsp;The project funds come from Liwei Wang and Aiping Liu; Dianlong Wang, Zhimin Liang, Shaohui Chen, and Changjiang Tian participated in the project management process; Balaji Narayanaswamy completed the editing and proofreading of the manuscript. The first draft of the manuscript was written by Fenglei Cao and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of interest statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that we have no known any competing financial interests or personal relationships with other people or organizations that could have appeared to inappropriately influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFundings\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by National Natural Science Foundation of China (Grant No. 52475343), Central Guidance for Local Scientific and Technological Development Funding Projects (Grant No. 246Z1015G) and Natural Science Foundation of Hebei Province (Grant No. E2024208049).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eY.H. Peng, C.L. Liu, G. Lin, G.H. 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Perform. 27 (2018) 5926-5937. https://doi.org/10.1007/s11665-018-3694-y\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"welding-in-the-world","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"witw","sideBox":"Learn more about [Welding in the World](https://www.springer.com/journal/40194)","snPcode":"40194","submissionUrl":"https://www.editorialmanager.com/witw/","title":"Welding in the World","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Directed Energy Deposition-Arc (DED-Arc) 2319 Al alloy, Homogenizing treatment, Solution aging treatment, Electrochemical testing, Intergranular corrosion (IGC)","lastPublishedDoi":"10.21203/rs.3.rs-7155152/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7155152/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn this study, homogenization\u0026thinsp;+\u0026thinsp;solution aging treatments were applied to Directed Energy Deposition-Arc (DED-Arc) 2319 Al alloy components. The impact of the heat treatment and their influence on microstructure evolution, mechanical properties and corrosion resistance was analyzed. A number of acicular strengthening phases θ\u0026prime; (Al\u003csub\u003e2\u003c/sub\u003eCu) and θ\u0026Prime; (Al\u003csub\u003e2\u003c/sub\u003eCu) were precipitated by heat treatment. The hardness increased from 73.9 HV (as-deposited state) to 148.0 HV in the aged state. Similarly, the ultimate tensile strength (UTS) in longitudinal direction increased from 254.3 MPa (deposited state) to 371.7 MPa in aged state. The transverse UTS of the samples increased from 257.2 MPa in the deposited state to 383.1 MPa in the aged state. The results of both electrochemical and intergranular corrosion (IGC) tests indicate that heat treatment can enhance the corrosion resistance of the alloy by promoting the dissolution of the secondary phase and the diffusion of elements.\u003c/p\u003e","manuscriptTitle":"Effect of heat treatment on mechanical properties and corrosion resistance of Directed Energy Deposition-Arc 2319 Al alloy","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-16 16:35:01","doi":"10.21203/rs.3.rs-7155152/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2025-09-17T10:53:13+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-09-09T01:13:49+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Welding in the World","date":"2025-08-22T08:24:34+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-08-01T14:18:05+00:00","index":"","fulltext":""},{"type":"submitted","content":"Welding in the World","date":"2025-07-30T22:02:39+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"welding-in-the-world","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"witw","sideBox":"Learn more about [Welding in the World](https://www.springer.com/journal/40194)","snPcode":"40194","submissionUrl":"https://www.editorialmanager.com/witw/","title":"Welding in the World","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"75bfa541-3e32-4441-b2c8-18647393deee","owner":[],"postedDate":"September 16th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-13T05:57:11+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-16 16:35:01","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7155152","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7155152","identity":"rs-7155152","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}