Effect of Laser Beam Power on AA6082 Plates Joined by Wobbling Mode Remote Laser Welding

Effect of Laser Beam Power on AA6082 Plates Joined by Wobbling Mode Remote Laser Welding | 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 Laser Beam Power on AA6082 Plates Joined by Wobbling Mode Remote Laser Welding UĞUR AVCI, Pasquale Franciosa This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3983654/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 The advancement of technology has led to an increased need for new materials, which has necessitated the development of new joining techniques. With the adaptation of advanced automation technology, remote laser welding, which has become increasingly widespread, has facilitated the joining of desired complex structures. In this context, the determination of the laser beam power, which is the locomotive of the welding parameters, before the joining process has played an important role in the weld quality. In this study, 2 mm thick AA6082 plates were joined with a wobling mode remote laser welding system using 4 kW, 3 kW and 2.5 kW laser beam powers. Except for the laser beam power, other parameters were optimized by preliminary studies. The welding process was performed in circular oscillation mode and the time-dependent motion of the laser beam was calculated in advance. The seam geometry, microstructure and hardness properties of the weld line initial, middle and end regions of each joining plate were investigated. As a result of the investigations, full penetration was achieved in the joints made with 4 kW and 3 kW laser powers, but the use of 4kW laser power reduced the weld quality. As a result of using 2.5 kw laser power, full penetration was not achieved and porosity formations were observed. In addition, seam geometry values, HAZ distance and compound dimensions close to the fusion line decreased and weld zone element values changed with decreasing laser power. The transformation in structural and elemental values caused regional hardness changes. Remote laser welding wobbling mode weld geometry microstructure hardness 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 1. Introduction Today, laser welding as a non-contact process has many advantages over fusion welding processes. The high energy density maintains a deep penetrating weld pool and ensures that joining through the thickness of the materials is done quickly in a single pass. The resulting low energy input minimizes the need for rework and produces a small heat-affected zone (HAZ) with limited residual stresses and distortion [ 1 ]. In this way, the amount of energy required for welding is reduced, the welding speed is increased and unnecessary thermal load is not applied to areas outside the joining zone of the material. As a result of the balanced cooling in the weld zone, the formation of beneficial fine solidification microstructures and limited HAZ grain growth is observed. In this context, the ability to focus the laser beam to a small spot and position it numerically allows precise control over weld seam position and chemistry, even when different joint tolerances are demanded. Capital costs are significantly higher than in conventional arc processes, but this can be offset by increased productivity, product quality and production flexibility [ 2 ]. Accordingly, the use of laser welding has grown in popularity in recent years and ushered in a new era of technology due to its easy automation, high welding speeds, high power density, narrow HAZ, high weld seam depth and low thermal distortion [ 3 ][ 4 ]. Technological advances have paved the way for remote controlled laser welding (RLW) applications, taking conventional laser welding one step further. RLW processes are performed from a remote location by means of a laser beam emitted from a scanner mounted on the arm of an industrial robot [ 5 ]. This application, which can operate at higher speeds than conventional spot welding applications, has provided the ability to create a non-contact joint in a fraction of a second, without the need for filler wire and shielding gas atmosphere [ 6 ][ 7 ] [ 8 ]. Due to these highly advantageous properties, RLW has been widely used in various industries such as automobile manufacturing, shipbuilding, bridge construction, electric vehicles and lightweight structures [ 9 ][ 10 ]. In particular, demands such as weight reduction, improving fuel efficiency, and reducing vehicle emissions have led to increased interest in laser welding for joining aluminum alloy sheets [ 11 ] [ 12 ]. It is known that 6XXX series aluminum alloys containing Mg and Si as the main alloying elements have good extrusion, weldability rolling capabilities in general, as well as good corrosion resistance, especially in atmospheric environments. The low cost of 6XXX alloys is especially significant to the aerospace industry, that relies heavily on the more expensive 2XXX and 7XXX alloys [ 13 ]. The microstructure of 6XXX series aluminum alloys consists of coarse elongated α-Al grains in the rolling direction and Mg-Si rich clusters [ 14 , 15 ]. Mg 2 Si, present as an intermetallic compound in the alloy system and has strength enhancing properties [ 16 ]. In this context, these alloys can be age-hardenad and thus their microstructure can improve during the welding process [ 17 ]. In addition to these positive properties, the fact that 6XXX series aluminum alloys maintain their surface brightness after anodization ensures that the amount of commercial use is increasing day by day [ 18 ]. AA6082 is of interest for bridges, truck guardrails, shipbuilding industry, bicycle manufacturing, rivets, mining equipment, automotive industry due to its easy formability, high weld quality and low cost [ 19 ]. However, during the welding process, the heat-affected zone (HAZ) of the joint can be softened due to microstructural transformation, ultimately affecting the mechanical properties of the HAZ. Therefore, reducing the extent of HAZ softening in the 6082-T6 aluminum alloy is crucial for enhancing joint performance [ 20 ]. In this context, laser welding has recently been preferred for joining AA6082. However, aluminium alloys are one of the most challenging metals to be welded by laser, because of their high surface reflectivity, low molten viscosity and inherent oxide layer [ 21 ]. Also in laser welding, heating and cooling rates can lead to changes in chemical composition, microstructures and residual stresses at melting and HAZs. These changes can lead to the formation of defects and affect the weld quality. In other words, the mechanical properties and corrosion resistance of the weld may deteriorate due to the appearance of phase transformations and defects such as porosity, cracking, element loss and oxidation within the weld. As is well known, oscillatory motion in welded joints is used to obtain a coaxial grain structure and to optimize the local solidification rate [ 22 ]. Laser beam oscillation at frequencies of several 100 Hz is generally known to stabilize laser welding processes. Studies have shown that circular beam oscillation produces finer grains and more homogeneously distributed dentrite structures in the weld zone compared to other oscillation mechanisms [ 23 ]. In the light of the researches carried out, it is of great importance to determine the laser power parameter in order to achieve the desired weld quality in the joining of AA6082 alloy with RLW, which has a wide range of applications. In this context, it has been known that the applied power has a great effect on the microstructure of the weld zone and HAZ zone and a comprehensive study is needed to clearly demonstrate this effect. In the present study, the wobling mode stages with circular oscillation will be defined and relationship between laser power and microstructure change will be revealed. 2. Material and Methods In this study, AA6082 alloy plates with dimensions of 60x40x2 mm 3 were used. The nominal chemical composition of AA6082 alloy according to the standard was presented in Table 1 . The joining process was performed with the ARM FL 10000 remote laser welding system and Precitec Weld Master welding head shown in Fig. 1 a. The system data during welding included a collimation length of 158 mm, a focusing length of 176 mm and fiber diameters of 110 µm and 320 µm for the core and ring, respectively. The surface cleaned plates were placed on the clamping platform with overlapping weld configuration (25 mm) and prepared for RLW with wobbling mode as shown in Fig. 1 b. In order to be able to observe the weld start and end shape, a gap of 5 mm was left on both sides of the plates and the joining was carried out between 5 and 55 mm along the x -axis with reference to point O . Table 1 Chemical composition of the EN AW-6082 [ 24 ] Si Mg Fe Mn Cr Zn Cu Al Content (wt%) 0.70–1.30 0.60–1.20 max. 0.50 0.40-1.00 max. 0.25 max. 0.20 max. 0.10 balance The AA6082 plates were joined by the circular oscillation path configuration shown in Fig. 2 . In this configuration, the frequency ( f ) to 100 Hz, the x and y amplitude ( A x , A y ) to 0.5 mm and the welding feed rate ( v x ) to 50 mm.s − 1 . was set. In circular oscillation, the laser beam moves in both circular and x -direction. In this framework, these two motions have two velocity parameters. The speed of the circular motion is known as the tangential velocity and is denoted by Vt . The number of circular revolutions made in one second is defined as the frequency value. The speed of movement in the x direction is known as v x and the ratio of this value to the frequency value gives the overlap ( O l ) measure. The periode is the time during which a circular motion is performed and is denoted by T . The total diameter of the circle is A. There is a relationship between these values as exhibited in Equations 1–3. $$f=\frac{{V}_{t}}{\pi .A} \left(Hz\right) \left(1\right)$$ $$T= \frac{1}{f} \left(s\right) \left(2\right)$$ $${O}_{l}= \frac{{v}_{x}}{f} \left(mm\right) \left(3\right)$$ As a result of the calculations made according to the given equations, the O l value was found to be 0.5 mm. As a result of the oscillation repeating over time, each passage distance of the laser from the x-axis (center of welding) is 0.25 mm. Given that the fiber laser ring diameter is 0.32 mm, the laser spots are in contact with each other in the x-axis along the oscillation path. In addition, due to the oscillation pattern, the + y region of the plate (I.zone) has a more intense laser spot contact, while the -y region (II. zone) has less laser spot contact than the other region. As a result, it is observed that more intense heat transfer will occur in I.zone of the plates. As long as there is no movement in the x direction, the laser will only move in a circular motion. When this motion is divided into regions, a semicircle is formed in I. and II.zones separately. However, once the movement in the x-direction starts, the patterns in I. and II. zones are evaluated separately. The total displacement distance in the x direction from the origin (O) is found by summing the displacement A for the semicircular motion and the velocity-dependent displacement in the x direction. In this context, the total displacement in x direction of the I. zone pattern ( I x =1.25 mm) is found by Eq. 4. Where t sc is time (s), which defines the time required for a semicircle and is found by Eq. 5. $${I}_{x}=A+{v}_{x}.{t}_{sc} \left(mm\right) \left(4\right)$$ $${t}_{sc}=\frac{T}{2} \left(\text{s}\right) \left(5\right)$$ The pattern in II. zone has a completely different formation compared to the pattern in I. zone. The circular motion in II. zone is in the – x direction. The total displacement distance in the x direction from O in II. zone is found by subtracting the displacement A for the semicircular motion and the velocity-dependent displacement in the x direction. In this context, the total displacement in the x direction ( IIx = 0.75 mm ) of II. zone pattern is found by Eq. 6. $${II}_{x}=A-{v}_{x}.{t}_{sc} \left(mm\right) \left(6\right)$$ Equations 7 and 8 present the time-dependent displacements in x directions for I. zone and II. zone, respectively. In the context, Equations 9 present the time-dependent displacements in y directions for I. and II. zone. It should be noted that the formulations created are obtained for only one circular motion. Where Xt and Yt are functions of time t as independent variables, which respectively represent the horizontal and vertical coordinates of the beam spot in the coordinate system. As a result of the calculations, the time-dependent displacement graphs of the beam spot in x and y directions for a circular motion is given in Fig. 3 . $$Xt={v}_{x} . t+\frac{A }{2}-\left(\frac{A}{2}\text{cos}\left(2\pi .t.f\right)\right) \left(7\right)$$ $$Xt=Ix-\left(\frac{A }{2}+\left(\frac{A}{2}\text{cos}\left(2\pi .t.f\right)\right)\right){-(v}_{x} .( t-{t}_{sc})\left) \right(8)$$ $$Yt=\frac{A }{2}sin\left(2\pi .t.f\right) \left(9\right)$$ Since the study focuses on the effect of laser power, laser powers of 4 kW, 3 kW and 2.5 kW were used during the experimental studies and other parameters were kept constant. The welding parameters applied are presented in Table 2 . In addition, no welding wire and no shielding gas were used in the joining process. Table 2 Welding parameters Laser Power (kW) Welding speed (feed rate) (mm.sn − 1 ) Frequency (Hz) Amplitude value for Ax-Ay (mm) Plate thicknes (mm) Sample 1 4 50 100 0.5 2 Sample 2 3 50 100 0.5 2 Sample 3 2.5 50 100 0.5 2 After the welding performance, the welded plates were cut 15 mm in x direction and 20 mm in y direction for microstructure and hardness examinations. Thus, specimens were obtained for separate examination of the initial, middle and end zones of the weld line. After hot mounting process, the cut samples were ground with 320 grit SiC abrasive under 5N and then polished with 9 and 3 µm solutions respectively. Barker solution (200 ml HBF4 + 800 ml H 2 O) was used for etching. The microstructure of the samples was examined with Nickon Eclipse LV150N microscope. SM-7800F Schottky Field Emission Scanning Electron Microscope was used for SEM images, EDX and EBSD analysis. Finally, microhardness measurements were performed with Wilson VH1150 under 300gf for 15 seconds. An indentation range of 250 µm was used for each test measurement. The hardness test specimens were evaluated with measurements taken on 4 different lines: surface line, center line, root line and vertical line. 3. Results and Discussion 3.1. Weld geometry and microstructure The weld bead and weld root surfaces of AA6082 plates joined with different laser beam powers are shown in Fig. 4 a-f. In the joining process performed with 4 kW laser power, an incomplete filled groove (IFG) was observed on the weld bead surface (Fig. 4 a), while high root reinforcement (RR) and undercutting caused by excessive penetration was detected on the weld root surface (Fig. 4 b). Reducing the laser beam power to 3 kW significantly reduced IFG and undercut defects on the weld bead surface (Fig. 4 c), while resulting in lower of RR formation on the weld root surface (Fig. 4 d). In the joining process using 2.5 kW laser power, no significant defects were observed on both the weld bead surface (Fig. 4 d) and the weld root surface (Fig. 4 e) by visual inspection. In addition, incomplete fusion was detected at the weld initial and end points in all plates joined with different laser power. The seam geometric models prepared by utilizing the cross-sectional images of the plates joined with different laser powers to determine the weld cross-sectional dimensions are presented in Fig. 5 . In Figs. 6a-d, the cross-sectional images of the seams in different zones of the plate joined with 4 kW laser power are presented. As shown in Fig. 6a, the weld cracks appeared at the initial of the weld line, above the weld seam. These cracks, known as solidification cracks, were caused by the high heat input and progressed from the seam surface to the center depending on the cooling rate (residual stresses) [ 25 , 26 ]. During the welding process, the initial region of the weld line is exposed to continuous heat input (post-heating) and therefore the cooling rate along the weld line is low [ 27 ]. The continuous heat input and slow cooling created a wider and more downwardly directed seam compared to other weld lines. The weld geometry shows the formation of a 0.78 mm deep IFG and 1.26 mm RR in the weld initiation zone. Since high laser power causes undercutting in the root area, the root width (RW) size is in the range of 3.11–2.77 mm. In other seam measurements, the seam width (SW) was 4.50 mm, while the mid-seam width (Mid.SW) and minimum seam width (Min.SW) were 3.37 mm and 2.46 mm, respectively. Figure 6b shows a cross-sectional image of the seam in the middle zone of the weld line. The laser beam reached the center of the weld line after about 50 circular movements. Thus, a localized preheating occurs before the welding process takes place. The heat generated before welding, combined with the heat input during the welding process, caused a higher temperature melting compared to the previous region. In this context, the high cooling rate of the weld seam increased further, and as a result, the crack formation that appeared in the initial region of the weld line appeared longitudinally in the z direction in the middle zone of the weld line. The high cooling rate directed the seam upward (IFG = 0.57, RR = 0.74) and accordingly the seam widths decreased (SW = 3.92 mm, Max.SW = 4.06 mm, Mid.SW = 3.21 mm, Min. SW = 2.48 mm). The undercut formation in the root zone became more pronounced (RW = 2.99–2.10 mm). Figure 6d shows the microstructure image of the rectangular area covering the HAZ and fusion zone (FZ). The HAZ near the fusion line has compounds of different sizes (≈ 16µm) containing the elements AA6082. Some grain coarsening was observed at the edge of the fusion line, but no significant grain orientation was detected. As it progressed from the fusion line to FZ, clustered coarse grain (CG) regions were observed as a result of uneven solidification. Especially considering the grain size distribution around the crack, it was revealed that crack formation occurred due to residual stress in the FZ. In the cross-sectional view of the end region of the weld line shown in Fig. 6c, the crack density increased due to rapid cooling of the surface. The zone was preheated due to heat input from previous weld lines, but exhibited faster solidification after the welding process than the other zones, especially on the surface. This resulted in less deep but more intense crack formation compared to the middle zone. The high preheating did not lead to a large change in seam dimensions, although it directed the seam slightly downward compared to the middle weld region (SW = 3.94 mm, Max.SW = 3.98 mm, Mid.SW = 3.18 mm, Min.SW = 2.41 mm, IFG = 0.61 mm, RR = 0.98 mm). The undercut defect remains, but its effects have been reduced (RW = 2.94–2.18). Table 3 presents the seam geometry dimensions of the different weld zones for 4 kw laser power, it is clearly identified that the largest seam size is obtained in the initial zone of the weld line. Except for the initial zone values in the Table 3, the seam geometries of the other welding zones comply with ISO 13919-1 and ISO 13919-2 standards. Finally, under the influence of 4 kW laser power, weld distortion occurred in all regions, but the most pronounced weld distortion was in the weld initial zone. This is evident from the fact that the bottom weld plates are not aligned with each other in Figure 3a. Table 3 Seam geometry dimensions of different weld zones for 4 kW laser power 4 kW Laser Power Max.SW (mm) SW (mm) Mid.SW (mm) Min.SW (mm) IFG (mm) RR (mm) RW (mm) Int. Zone - 4.50 3.37 2.46 0.78 1.26 3.11–2.77 Mid.Zone 4.06 3.92 3.21 2.48 0.57 0.74 2.99–2.10 End Zone 3.98 3.94 3.18 2.41 0.61 0.98 2.94–2.18 The cross-sectional images of the seams in different regions of the plate joined with 3 kW laser power and the microstructure of some regions of the middle zone of weld line are shown in Fig. 7 a-g. In the weld cross-section images presented in Fig. 7 a-c, it was observed that the formation of solidification cracks was significantly eliminated by decreasing the laser power. Table 4 presents the seam geometry dimensions of different welding zones for 3 kW laser power. The seam dimensions show that low heat input reduces the weld width dimensions. Furthermore, the IFG and RR dimensions were reduced for all zones of the weld line and no undercut formation was observed on the root surface. Figures 7 d and 7 e show optical microscope images of the HAZ and FZ of the middle zone weld line, respectively. The decrease in laser power caused an increase in the proportion of the compund distribution in the HAZ and a grain orientation (columnar dentrites) from the FZ towards the fusion line. The morphology of the grains was affected by the solid-liquid interfacial ratio as well as structural supercooling [ 28 ]. At high laser power, the compounds in the HAZ were coarser but more sparse, whereas with decreasing laser power and the associated increase in cooling rate, the compounds became finer but more dispersed (≈ 11.5µm). However, coarse compounds and precipitates are not present in the FZ. The precipitates dissolve during welding due to the high temperature and do not have time to regenerate [ 29 ]. In rare cases, the appearance of coarse-grained phase (CGP) in the FZ region is possible due to slow cooling, but especially the FZ center contains equiaxed dentrites (Fig. 7 e). Figures 7 f and 7 g show SEM images of HAZ - FZ and FZ - HAZ zone transitions, respectively. Due to the overlap welding position, the short plate area close to the weld zone in the + y direction (Fig. 1 b) was subjected to heat accumulation, resulting in the reduction of precipitates and compounds in the HAZ due to heat treatment, as shown in Fig. 7 g. With the circular oscillation configuration, which is more effective in the + y direction, the heat treatment was even more effective in this region. Table 4 Seam geometry dimensions of different weld zones for 3 kW laser power 3 kW Laser Power Max.SW (mm) SW (mm) Mid.SW (mm) Min.SW (mm) IFG (mm) RR (mm) RW (mm) Int. Zone - 3.29 2.25 1.82 0.33 0.55 1.70 Mid.Zone - 2.96 2.13 1.86 0.28 0.63 1.87 End Zone - 2.91 2.68 1.88 0.41 0.52 1.93 Figure 8 a-e shows cross-sectional images of the seams in different regions of the plate joined with 2.5 kW laser power. The full seam penetration could not be achieved by reducing the laser power, therefore face reinforcement (FR) was used instead of IFG value and lack of penetration (LP) was used instead of RR value for weld geometry evaluation. Table 5 presents the seam geometry dimensions of the different weld zones for 2.5 kW laser power. Although the seam penetration (SP) values increased towards the end region of the weld line, in general all seam dimensions had values close to each other. In addition, low laser power caused the formation of pores. The bubbles formed at the tip of the keyhole are carried into the molten pool by the flow of molten metal and the keyhole expands and deepens, then the bubbles formed in the keyhole, which undergo severe expansion and contraction, also expand and are retained in the weld zone as large pores [ 30 ]. With 4 kW and 3 kW laser powers, the joints were fully penetrated, so that pore formation was largely unnoticeable. This is due to the complete penetration of the keyhole tip into the workpiece so that the bubbles were directed out of the base cavity [ 31 ]. Table 5 Seam geometry dimensions of different weld zones for 2.5 kW laser power 2.5 kW Laser Power SP (mm) SW (mm) Mid.SW (mm) Min.SW (mm) FR (mm) LP (mm) RW (mm) Int. Zone 3.44 2.70 1.95 1.91 0.11 0.61 1.49 Mid.Zone 3.54 2.72 1.95 1.74 0.11 0.48 1.48 End Zone 3.65 2.83 1.93 1.69 0.15 0.41 1.51 Figure 8 d-e shows HAZ - FZ and FZ - HAZ microstructure images of the initial zone of the weld line. The columnar dentrites were formed in the direction of the arrow towards the fusion line from both edges of the FZ with the effect of the cooling rate. Furthermore the low laser power caused sudden cooling and the post heating process did not reach a sufficient level for this zone during the rest of the welding process. Insufficient time for pore expulsion increased the pore density. The reason for the decrease in porosity towards the end of the weld line is the natural preheating that occurs during the welding process. Natural preheating is a process that can help reduce porosity in processes without full penetration. 3.2. Microstructure analysis Figure 9 a-e shows the microstructure analysis results of the FZ center in the middle region of the weld line for 3 kW. As a result of the EDS mapping analysis of the microstructure image presented in Fig. 9 a, it was determined that in the FZ region, besides Al, Si (Fig. 9 b) and Cu (Fig. 9 c) were dominant in the dark and light colored structure, respectively. Considering the high melting point of Si, it is an expected result that Si is dominant in the FZ element distribution in the process of melting and re-solidification in a short time. In Fig. 9 d, elemental analysis was performed within the rectangular areas determined for spectrum 1 and the presence of 95.46 wt.% Al, 1.79 wt.% Cu and 1.36 wt.% Si elements as well as Mn, Mg and Fe elements below 1 wt.% were determined. In spectrum 2 analyses representing light-colored structures, the presence of compound formation with 70.47 wt.% Cu, 16.25 wt.% Al, 9.40 wt.% Zn, 3.56 wt.% Si and 0.33 wt.% Mg was determined. Figure 10 a-e shows the microstructure analysis results of the HAZ in the middle region of the weld line for 3 kW. As a result of the EDS mapping analysis of the microstructure image presented in Fig. 10 a, it was determined that Si (Fig. 10 b) and Cu (Fig. 10 c) were dominant in HAZ as in FZ. The compounds with Si and Cu elements in this region are not dentritic because they are under the influence of heat treatment. As a result of the analysis of the dark compounds in Fig. 10 d (spectrum 3), 60.13 wt.% Al, 30.05 wt.% Si, 8.56 wt.% Cu and 1.25 wt.% Mg were determined. As a result of the analysis of the yellow compounds presented in Fig. 10 e (spectrum 4), 45.18 wt.% Cu, 39.55 wt.% Al, 10.71 wt.% Fe and 4.55 wt.% Si were determined. For a clearer understanding of the microstructural change in the HAZ region with decreasing laser power, the HAZ region selected for the 3kW laser power examination was also selected for 2.5 kW laser power The results of the HAZ microstructure analysis of the plate joined with 2.5 kW laser power are shown in Fig. 11 a-e. As the laser power decreased, the average size of Al compounds with high Si content in the HAZ decreased gradually and the average size of these compounds was calculated as 10 µm at 2.5 kW laser power. The average size of the compounds with similar content in the base metal is 7.7 µm and in this context, it can be said that increasing the laser power causes the compound coarsening in the HAZ. In the EDS mapping analysis of the region shown in Fig. 11 a, it is observed that Cu particle size is smaller but dispersed while Si particles are larger but not dispersed (Fig. 11 b-c). Spectrum analyses (Fig. 11 d-e) from the points identified in the HAZ near the fusion boundary revealed that the Si content in the compound decreased when the 3 kW laser power was compared to the HAZ. Figure 12 a-e shows the microstructure analysis results of the seam root in the middle region of the weld line for 2.5 kW. As a result of the spectrum analysis performed (Fig. 12 b) on the seam root image presented in Fig. 12 a, it was determined that the compounds containing Al, Cu, Si and Mg elements together are concentrated in the seam root region towards the bottom of the FZ. Figure 12 c-e mapping analysis shows that Al, Mg, Si and Cu elements form clustered compounds in this region. Since the low heat input 200 µm upwards from the bottom FZ point could not form a clear liquefaction form and also since a rapid cooling occurred in this region, it is estimated that compound clusters may have occurred. The high aggregation amounts are about 30 µm in size and are observed at the edges of the root curvature formation. 3.3. Microhardness The hardness measurements of the plates joined with different laser powers were performed with the hardness test model shown in Fig. 13 . For hardness testes, specimens belonging to the initial zone of the weld line, which was determined to have minimum weld defects in general after microstructure examinations, were used. Each hardness measurement line was established at a distance of 250 µm from the nearest plate surface. Thus, the changes in the weld seam and surrounding areas were observed. Figure 14 a-d shows the hardness graphs of the weld joints performed with 4kW laser power. Since the longest solidification time is at the center ( O ) of the horizontal hardness lines, a decrease in hardness is observed towards the center of the FZ. However, the hardness in the center decreases dramatically for joints made with high laser power. The FZ exhibits a melting followed by solidification and high laser power will increase the melting area. This phenomenon will lead to slow solidification in the center of the FZ and rapid solidification at the edges of the region close to the fusion line. Figure 14 a-b shows the graphs of the surface and center hardness lines on the top weld plate. The hardness value at center O was 75 HV at surface line and 58 HV at center line. Furthermore, the hardness value increased towards the fusion line and reached the maximum hardness value (≈ 93 HV) and the hardness pattern was similar for both hardness lines. The hardness of the base metal was in the range 105 HV − 120 HV. In this context, although it was possible to reach the base metal from the HAZ at a distance of 6 mm in the - y direction, this was not possible in the + y direction. The inability to reach the hardness of the base metal in the + y direction is due to the fact that the weld plate ends too close to the weld zone and this zone is softened by the heat treatment effect. In the root line graph in Fig. 14 c, the hardness properties changed direction due to the overlap plate position and the base metal hardness was not reached in the - y direction. The vertical line graph in Fig. 14 d shows the hardness values of the weld seam from top to bottom. Depending on the cooling rate, the hardness value decreases towards the center, while the hardness values increase towards the bead and root surface. In the vertical hardness line, the highest hardness is observed in the root region (88 HV − 94 HV). In the hardness graphs of the welded joints with 3 kW laser power presented in Figs. 15 a-d, the effects of reduced heat input were observed. In this context, the hardness distribution at the fusion center on the surface hardness line continued in the range of 74 HV − 80 HV for about 2 mm (Fig. 15 a). Thus, it can be said that solidification occurs in the surface line in a similar time period and crack formation is prevented. As the fusion line was approached, the hardness reached in the range of 85 HV − 88 HV. Although the hardness decreased up to 78 HV in the HAZ near the fusion line in the -y direction, the hardness increased to 110 HV towards the base metal. In the + y direction, the HAZ hardness after the fusion line reached from 82 HV to 93 HV, but the hardness of the base metal could not be reached at a distance of 6 mm from the center. The hardness pattern at the center line (Fig. 15 b) is similar to the hardness pattern of the welded joint performed with 4 kW laser power, except for the fusion center hardness increase. While a slight increase in hardness was noted in the root line, base metal was reached in the + y and -y directions (Fig. 15 c). The lower RW size in the seam geometry and the lower temperature in this region reduced the effect of the heat treatment and, accordingly, the HAZ distance. The increase in hardness at the root line was also determined in the vertical hardness line pattern and the hardness range was 75 HV − 118 HV (Fig. 15 d). Figures 16 a-d show the hardness patterns of the welded joints obtained by reducing the laser power to 2.5 kW. The hardness patterns of the horizontal lines showed the formation of boundaries between the HAZ and the base metal. The low laser power resulted in a low HAZ distance and the FZ hardness and HAZ hardness close to the fusion line were close to each other. At a distance of 1.5 mm from the fusion center of the surface hardness line in Fig. 16 a, the hardness range was 78 HV- 84 HV. The hardness reached the range of 90 HV − 93 HV close to the + y and -y fusion lines. The estimated HAZ distance is about 2.75 mm in the -y direction and about 4 mm in the + y direction. Despite a slight decrease in hardness values, a similar formation is observed in the center hardness line presented in Fig. 16 b. In the root hardness line graph presented in Fig. 16 c, the hardness value in the fusion region is in the range of 83 HV – 88 HV. Although HAZ softening was observed in the short area close to the weld zone (in the - y direction) on the bottom plate, the hardness gradually increased from the FZ to the base metal as soon as the HAZ zone in the + y direction was crossed. The vertical hardness line values shown in Fig. 16 d are in the range of 78 HV- 86 HV. Considering the specimens joined with different laser power, a balanced hardness was determined in the FZ at 2.5 kW laser power. 4. Conclusion In the presented study, AA6082 plates were joined in overlap weld configuration using wobling mode RLW at different laser beam powers. The seam geometries, microstructures and hardness properties were evaluated by dividing the weld joints into initial, middle and final zones and the following results were obtained. In the joining processes performed at 4 kW and 3 kW laser beam powers where full penetration was achieved, incomplete filled groove and root reinforcement with decreasing values were observed on the bead and root surfaces of the welded plates with decreasing laser power. The face reinforcement was observed at 2.5 kW laser beam power, where full penatrayon was not achieved. For each laser beam power value, the seam geometry changed in different zones of the weld line. For each laser beam power value, the seam geometry changed in different zones of the weld line. The ratio of power and average seam width between the determined zones is 4 kW/4.12 mm, 3 kW/3.05 mm and 2.5 kW/2.75 mm. The circular oscillation path is designed for the laser beam center to move a total of 1 mm in the y-axis for each circular movement (Ay = 0.5) and the beam contact distance range in the y-axis is determined as 1.32 mm by adding the laser beam ring dimension value. Considering the measured seam widths, it is observed that the effect of the laser beam power on the welding process will be improved by using it with the correct oscillation path. Microstructural investigations of the initial, middle and end zones of the welded plates revealed that the variation in laser beam power affects the structural formation phenomena of each zone. Since the laser beam power is converted into a heat source during the joining process, the plates were subjected to heat treatment before, during or after welding. As a result, weld zones with different cooling rates exhibited different structural properties. The cooling rate was evaluated differently for full penetration and non-full penetration welding processes. Considering the crack formation between the zones under the influence of 4kW laser beam power, the post sintering of the weld initial zone reduced the crack formation, but the high laser beam power caused undercutting in all regions. With the choice of 3 kW laser beam power, crack formation and undercutting defects were minimized. In the full non-penetrated joining process with 2.5 kW, while pore formations were observed, it was determined that the end zone of weld line, which was subjected to pre-sintering between the zones, had the minimum pore level. Microstructure analysis of the weld zones generally revealed that Si and Cu elements were dominant in the FZ, except Al. While no significant change was observed in the dentritic structure and compound contents in FZs with full penetration, the presence of compound clusters dominated by Cu and Si elements in the seam root region in the welding process without full penetration was determined. In the HAZ region close to the fusion line, compounds containing Al, Si, Cu and Mg were detected, while the compound sizes changed in direct proportion to the laser power. After the welding process with full penetration, the hardness decreased in the center of the FZ zone due to the effect of cooling rate, but the hardness increased from the surface to the root zone. In the welding process without full penetration, the hardness value in the entire FZ zone was in the range of 81–88 HV. Due to the overlap welding configuration, since one edge of the joined plates was very close to the welding center, at high laser powers, this region was affected by heat treatment and the base metal could not be detected. As the laser power decreased, HAZ and base metal boundaries could be detected. At 2.5 kW laser beam power, the average HAZ width was 3 mm. Declarations Conflict of interest I wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome. I further confirm that there are no other persons who satisfied the criteria for authorship but are not listed. Acknowledgements This research was supported by The Scientific and Technological Research Council of Turkey (TUBITAK) with the project numbered TUBITAK2219/1059B192202722. 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Elsevier B.V., pp 478–487 Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 01 Mar, 2024 Reviewers invited by journal 28 Feb, 2024 Editor invited by journal 27 Feb, 2024 Editor assigned by journal 26 Feb, 2024 First submitted to journal 22 Feb, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-3983654","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":275582089,"identity":"791a0f48-ab23-48cd-aaf2-d0d8cb0b02bb","order_by":0,"name":"UĞUR 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Centre","correspondingAuthor":false,"prefix":"","firstName":"Pasquale","middleName":"","lastName":"Franciosa","suffix":""}],"badges":[],"createdAt":"2024-02-24 02:50:32","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3983654/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3983654/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":52023641,"identity":"347e862c-5bbc-4b5c-b13c-8d808c12950d","added_by":"auto","created_at":"2024-03-05 15:32:18","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":672344,"visible":true,"origin":"","legend":"\u003cp\u003eExperimental setup\u003cstrong\u003e, \u003c/strong\u003ea) laser welding system view, b) \u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eoverlap weld schematic 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displalecement in x direction, b) displacement in y direction\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3983654/v1/4ed9eb824fb601fde8edde47.png"},{"id":52023651,"identity":"fd2809b5-3c89-4c62-87ae-bccec4676a42","added_by":"auto","created_at":"2024-03-05 15:32:18","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":676321,"visible":true,"origin":"","legend":"\u003cp\u003eWeld bead and weld root surfaces of AA6082 plates joined with different laser power values, a) 4 kW-weld bead surface, b) 4 kW-weld root surface, c) 3 kW-weld bead surface, d) 3 kW-weld root surface, e) 2.5 kW-weld bead surface, f) 2.5 kW-weld root surface\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3983654/v1/a844245cf3631b0166a3dfb9.png"},{"id":52024458,"identity":"8a47dd99-84b3-423f-a2a7-ca5c7de67127","added_by":"auto","created_at":"2024-03-05 15:40:18","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":114947,"visible":true,"origin":"","legend":"\u003cp\u003eSeam cross-section geometric models of plates joined with different laser powers\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3983654/v1/afff76b8309e47128af872e5.png"},{"id":52023654,"identity":"974c18f0-5160-4c70-a5dd-a26b422dc6fc","added_by":"auto","created_at":"2024-03-05 15:32:19","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":2093441,"visible":true,"origin":"","legend":"\u003cp\u003eSeam cross sections of different weld zones for 4 kW laser power, a) initial zone of weld line, b) middle zone of weld line, c) end zone of weld line, d) middle zone HAZ and fusion 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15:32:19","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":1777165,"visible":true,"origin":"","legend":"\u003cp\u003eSeam cross sections of different weld zones for 2.5 kW laser power, a) initial zone of weld line, b) middle zone of weld line, c) end zone of weld line, d) initial zone HAZ – FZ microstructure, e) initial zone FZ – HAZ microstructure\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-3983654/v1/efa23121324a9e0f405506e2.png"},{"id":52023668,"identity":"18ec4e84-d3ff-445e-8845-18b9536ca1b5","added_by":"auto","created_at":"2024-03-05 15:32:19","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":615959,"visible":true,"origin":"","legend":"\u003cp\u003eThe microstructure analysis results of the FZ center in the middle region of the weld line for 3 kW, a) FZ analysis region, b-c) EDS mapping analysis, d-e) EDS spectrum 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11","display":"","copyAsset":false,"role":"figure","size":626711,"visible":true,"origin":"","legend":"\u003cp\u003eThe microstructure analysis results of the HAZ in the middle region of the weld line for 2.5 kW, a) HAZ analysis region, b-c) EDS mapping analysis, d-e) EDS spectrum analysis graphs\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-3983654/v1/b07f8aa93913d7331c8d31b0.png"},{"id":52023672,"identity":"ded51f81-032d-4c42-8562-8e6e09dfe9cb","added_by":"auto","created_at":"2024-03-05 15:32:20","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":746007,"visible":true,"origin":"","legend":"\u003cp\u003eThe microstructure analysis results of the seam root in the middle region of the weld line for 2.5 kW, a) seam root analysis region, b) EDS spectrum analysis graph, c-e) EDS mapping 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root line, d) vertical line\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-3983654/v1/d7122b6554cee6a86a872ff2.png"},{"id":52023644,"identity":"73bea4e6-3bec-46a0-8299-8aabd60821c5","added_by":"auto","created_at":"2024-03-05 15:32:18","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":144142,"visible":true,"origin":"","legend":"\u003cp\u003eThe hardness graphs of the weld joints performed with 3 kW laser power, a) surface line, b) center line, c) root line, d) vertical line\u003c/p\u003e","description":"","filename":"15.png","url":"https://assets-eu.researchsquare.com/files/rs-3983654/v1/ec70c4f1c1e314df8ff9776b.png"},{"id":52023643,"identity":"3b9be667-3467-45a8-a329-2ea46b00dfe7","added_by":"auto","created_at":"2024-03-05 15:32:18","extension":"png","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":160831,"visible":true,"origin":"","legend":"\u003cp\u003eThe hardness graphs of the weld joints performed with 2.5 kW laser power, a) surface line, b) center line, c) root line, d) vertical line\u003c/p\u003e","description":"","filename":"16.png","url":"https://assets-eu.researchsquare.com/files/rs-3983654/v1/147665bc2ba3005007af9e0c.png"},{"id":52025546,"identity":"93f6b08d-7d2c-4b8f-bf99-831c56c16f13","added_by":"auto","created_at":"2024-03-05 15:48:21","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":9302859,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3983654/v1/c3118a3a-e7a5-49c1-b278-d6c78da66bf6.pdf"}],"financialInterests":"","formattedTitle":"Effect of Laser Beam Power on AA6082 Plates Joined by Wobbling Mode Remote Laser Welding","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eToday, laser welding as a non-contact process has many advantages over fusion welding processes. The high energy density maintains a deep penetrating weld pool and ensures that joining through the thickness of the materials is done quickly in a single pass. The resulting low energy input minimizes the need for rework and produces a small heat-affected zone (HAZ) with limited residual stresses and distortion [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. In this way, the amount of energy required for welding is reduced, the welding speed is increased and unnecessary thermal load is not applied to areas outside the joining zone of the material. As a result of the balanced cooling in the weld zone, the formation of beneficial fine solidification microstructures and limited HAZ grain growth is observed. In this context, the ability to focus the laser beam to a small spot and position it numerically allows precise control over weld seam position and chemistry, even when different joint tolerances are demanded. Capital costs are significantly higher than in conventional arc processes, but this can be offset by increased productivity, product quality and production flexibility [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Accordingly, the use of laser welding has grown in popularity in recent years and ushered in a new era of technology due to its easy automation, high welding speeds, high power density, narrow HAZ, high weld seam depth and low thermal distortion [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e][\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTechnological advances have paved the way for remote controlled laser welding (RLW) applications, taking conventional laser welding one step further. RLW processes are performed from a remote location by means of a laser beam emitted from a scanner mounted on the arm of an industrial robot [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. This application, which can operate at higher speeds than conventional spot welding applications, has provided the ability to create a non-contact joint in a fraction of a second, without the need for filler wire and shielding gas atmosphere [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e][\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Due to these highly advantageous properties, RLW has been widely used in various industries such as automobile manufacturing, shipbuilding, bridge construction, electric vehicles and lightweight structures [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e][\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. In particular, demands such as weight reduction, improving fuel efficiency, and reducing vehicle emissions have led to increased interest in laser welding for joining aluminum alloy sheets [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIt is known that 6XXX series aluminum alloys containing Mg and Si as the main alloying elements have good extrusion, weldability rolling capabilities in general, as well as good corrosion resistance, especially in atmospheric environments. The low cost of 6XXX alloys is especially significant to the aerospace industry, that relies heavily on the more expensive 2XXX and 7XXX alloys [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The microstructure of 6XXX series aluminum alloys consists of coarse elongated α-Al grains in the rolling direction and Mg-Si rich clusters [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Mg\u003csub\u003e2\u003c/sub\u003eSi, present as an intermetallic compound in the alloy system and has strength enhancing properties [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. In this context, these alloys can be age-hardenad and thus their microstructure can improve during the welding process [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. In addition to these positive properties, the fact that 6XXX series aluminum alloys maintain their surface brightness after anodization ensures that the amount of commercial use is increasing day by day [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAA6082 is of interest for bridges, truck guardrails, shipbuilding industry, bicycle manufacturing, rivets, mining equipment, automotive industry due to its easy formability, high weld quality and low cost [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. However, during the welding process, the heat-affected zone (HAZ) of the joint can be softened due to microstructural transformation, ultimately affecting the mechanical properties of the HAZ. Therefore, reducing the extent of HAZ softening in the 6082-T6 aluminum alloy is crucial for enhancing joint performance [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. In this context, laser welding has recently been preferred for joining AA6082. However, aluminium alloys are one of the most challenging metals to be welded by laser, because of their high surface reflectivity, low molten viscosity and inherent oxide layer [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Also in laser welding, heating and cooling rates can lead to changes in chemical composition, microstructures and residual stresses at melting and HAZs. These changes can lead to the formation of defects and affect the weld quality. In other words, the mechanical properties and corrosion resistance of the weld may deteriorate due to the appearance of phase transformations and defects such as porosity, cracking, element loss and oxidation within the weld. As is well known, oscillatory motion in welded joints is used to obtain a coaxial grain structure and to optimize the local solidification rate [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Laser beam oscillation at frequencies of several 100 Hz is generally known to stabilize laser welding processes. Studies have shown that circular beam oscillation produces finer grains and more homogeneously distributed dentrite structures in the weld zone compared to other oscillation mechanisms [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn the light of the researches carried out, it is of great importance to determine the laser power parameter in order to achieve the desired weld quality in the joining of AA6082 alloy with RLW, which has a wide range of applications. In this context, it has been known that the applied power has a great effect on the microstructure of the weld zone and HAZ zone and a comprehensive study is needed to clearly demonstrate this effect. In the present study, the wobling mode stages with circular oscillation will be defined and relationship between laser power and microstructure change will be revealed.\u003c/p\u003e"},{"header":"2. Material and Methods","content":"\u003cp\u003eIn this study, AA6082 alloy plates with dimensions of 60x40x2 mm\u003csup\u003e3\u003c/sup\u003e were used. The nominal chemical composition of AA6082 alloy according to the standard was presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The joining process was performed with the ARM FL 10000 remote laser welding system and Precitec Weld Master welding head shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea. The system data during welding included a collimation length of 158 mm, a focusing length of 176 mm and fiber diameters of 110 \u0026micro;m and 320 \u0026micro;m for the core and ring, respectively. The surface cleaned plates were placed on the clamping platform with overlapping weld configuration (25 mm) and prepared for RLW with wobbling mode as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb. In order to be able to observe the weld start and end shape, a gap of 5 mm was left on both sides of the plates and the joining was carried out between 5 and 55 mm along the \u003cem\u003ex\u003c/em\u003e-axis with reference to point \u003cem\u003eO\u003c/em\u003e.\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 EN AW-6082 [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMg\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFe\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMn\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCr\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eZn\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCu\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eAl\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eContent (wt%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.70\u0026ndash;1.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.60\u0026ndash;1.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003emax. 0.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.40-1.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003emax. 0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003emax. 0.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003emax. 0.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ebalance\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 AA6082 plates were joined by the circular oscillation path configuration shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. In this configuration, the frequency ( \u003cem\u003ef\u003c/em\u003e ) to 100 Hz, the \u003cem\u003ex\u003c/em\u003e and \u003cem\u003ey\u003c/em\u003e amplitude ( \u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, \u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u003cem\u003ey\u003c/em\u003e\u003c/sub\u003e ) to 0.5 mm and the welding feed rate ( \u003cem\u003ev\u003c/em\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e ) to 50 mm.s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. was set. In circular oscillation, the laser beam moves in both circular and \u003cem\u003ex\u003c/em\u003e-direction. In this framework, these two motions have two velocity parameters. The speed of the circular motion is known as the tangential velocity and is denoted by \u003cem\u003eVt\u003c/em\u003e. The number of circular revolutions made in one second is defined as the frequency value. The speed of movement in the \u003cem\u003ex\u003c/em\u003e direction is known as \u003cem\u003ev\u003c/em\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e and the ratio of this value to the frequency value gives the overlap (\u003cem\u003eO\u003c/em\u003e\u003csub\u003e\u003cem\u003el\u003c/em\u003e\u003c/sub\u003e) measure. The periode is the time during which a circular motion is performed and is denoted by \u003cem\u003eT\u003c/em\u003e. The total diameter of the circle is A. There is a relationship between these values as exhibited in Equations 1\u0026ndash;3.\u003c/p\u003e \u003cp\u003e \u003cdiv id=\"Equa\" class=\"Equation\"\u003e \u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$f=\\frac{{V}_{t}}{\\pi .A} \\left(Hz\\right) \\left(1\\right)$$\u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Equb\" class=\"Equation\"\u003e \u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$T= \\frac{1}{f} \\left(s\\right) \\left(2\\right)$$\u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Equc\" class=\"Equation\"\u003e \u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$${O}_{l}= \\frac{{v}_{x}}{f} \\left(mm\\right) \\left(3\\right)$$\u003c/div\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003eAs a result of the calculations made according to the given equations, the \u003cem\u003eO\u003c/em\u003e\u003csub\u003e\u003cem\u003el\u003c/em\u003e\u003c/sub\u003e value was found to be 0.5 mm. As a result of the oscillation repeating over time, each passage distance of the laser from the x-axis (center of welding) is 0.25 mm. Given that the fiber laser ring diameter is 0.32 mm, the laser spots are in contact with each other in the x-axis along the oscillation path. In addition, due to the oscillation pattern, the +\u0026thinsp;y region of the plate (I.zone) has a more intense laser spot contact, while the -y region (II. zone) has less laser spot contact than the other region. As a result, it is observed that more intense heat transfer will occur in I.zone of the plates.\u003c/p\u003e \u003cp\u003eAs long as there is no movement in the \u003cem\u003ex\u003c/em\u003e direction, the laser will only move in a circular motion. When this motion is divided into regions, a semicircle is formed in I. and II.zones separately. However, once the movement in the x-direction starts, the patterns in I. and II. zones are evaluated separately. The total displacement distance in the x direction from the origin (O) is found by summing the displacement A for the semicircular motion and the velocity-dependent displacement in the \u003cem\u003ex\u003c/em\u003e direction. In this context, the total displacement in \u003cem\u003ex\u003c/em\u003e direction of the I. zone pattern ( \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e =1.25 mm) is found by Eq.\u0026nbsp;4. Where \u003cem\u003et\u003c/em\u003e\u003csub\u003e\u003cem\u003esc\u003c/em\u003e\u003c/sub\u003e is time (s), which defines the time required for a semicircle and is found by Eq.\u0026nbsp;5.\u003cdiv id=\"Equd\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equd\" name=\"EquationSource\"\u003e\n$${I}_{x}=A+{v}_{x}.{t}_{sc} \\left(mm\\right) \\left(4\\right)$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Eque\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Eque\" name=\"EquationSource\"\u003e\n$${t}_{sc}=\\frac{T}{2} \\left(\\text{s}\\right) \\left(5\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe pattern in II. zone has a completely different formation compared to the pattern in I. zone. The circular motion in II. zone is in the \u0026ndash; \u003cem\u003ex\u003c/em\u003e direction. The total displacement distance in the \u003cem\u003ex\u003c/em\u003e direction from O in II. zone is found by subtracting the displacement A for the semicircular motion and the velocity-dependent displacement in the \u003cem\u003ex\u003c/em\u003e direction. In this context, the total displacement in the x direction ( \u003cem\u003eIIx\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.75 mm \u003cem\u003e)\u003c/em\u003e of II. zone pattern is found by Eq.\u0026nbsp;6.\u003cdiv id=\"Equf\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equf\" name=\"EquationSource\"\u003e\n$${II}_{x}=A-{v}_{x}.{t}_{sc} \\left(mm\\right) \\left(6\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eEquations\u0026nbsp;7 and 8 present the time-dependent displacements in \u003cem\u003ex\u003c/em\u003e directions for I. zone and II. zone, respectively. In the context, Equations 9 present the time-dependent displacements in \u003cem\u003ey\u003c/em\u003e directions for I. and II. zone. It should be noted that the formulations created are obtained for only one circular motion. Where \u003cem\u003eXt\u003c/em\u003e and \u003cem\u003eYt\u003c/em\u003e are functions of time \u003cem\u003et\u003c/em\u003e as independent variables, which respectively represent the horizontal and vertical coordinates of the beam spot in the coordinate system. As a result of the calculations, the time-dependent displacement graphs of the beam spot in x and y directions for a circular motion is given in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003cdiv id=\"Equg\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equg\" name=\"EquationSource\"\u003e\n$$Xt={v}_{x} . t+\\frac{A }{2}-\\left(\\frac{A}{2}\\text{cos}\\left(2\\pi .t.f\\right)\\right) \\left(7\\right)$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equh\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equh\" name=\"EquationSource\"\u003e\n$$Xt=Ix-\\left(\\frac{A }{2}+\\left(\\frac{A}{2}\\text{cos}\\left(2\\pi .t.f\\right)\\right)\\right){-(v}_{x} .( t-{t}_{sc})\\left) \\right(8)$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equi\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equi\" name=\"EquationSource\"\u003e\n$$Yt=\\frac{A }{2}sin\\left(2\\pi .t.f\\right) \\left(9\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSince the study focuses on the effect of laser power, laser powers of 4 kW, 3 kW and 2.5 kW were used during the experimental studies and other parameters were kept constant. The welding parameters applied are presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. In addition, no welding wire and no shielding gas were used in the joining process.\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\u003eWelding parameters\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=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLaser Power (kW)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eWelding speed (feed rate)\u003c/p\u003e \u003cp\u003e(mm.sn\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFrequency\u003c/p\u003e \u003cp\u003e(Hz)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAmplitude value\u003c/p\u003e \u003cp\u003efor Ax-Ay\u003c/p\u003e \u003cp\u003e(mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003ePlate thicknes\u003c/p\u003e \u003cp\u003e(mm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAfter the welding performance, the welded plates were cut 15 mm in x direction and 20 mm in y direction for microstructure and hardness examinations. Thus, specimens were obtained for separate examination of the initial, middle and end zones of the weld line. After hot mounting process, the cut samples were ground with 320 grit SiC abrasive under 5N and then polished with 9 and 3 \u0026micro;m solutions respectively. Barker solution (200 ml HBF4\u0026thinsp;+\u0026thinsp;800 ml H\u003csub\u003e2\u003c/sub\u003eO) was used for etching. The microstructure of the samples was examined with Nickon Eclipse LV150N microscope. SM-7800F Schottky Field Emission Scanning Electron Microscope was used for SEM images, EDX and EBSD analysis. Finally, microhardness measurements were performed with Wilson VH1150 under 300gf for 15 seconds. An indentation range of 250 \u0026micro;m was used for each test measurement. The hardness test specimens were evaluated with measurements taken on 4 different lines: surface line, center line, root line and vertical line.\u003c/p\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1. Weld geometry and microstructure\u003c/h2\u003e\n \u003cp\u003eThe weld bead and weld root surfaces of AA6082 plates joined with different laser beam powers are shown in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea-f. In the joining process performed with 4 kW laser power, an incomplete filled groove (IFG) was observed on the weld bead surface (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea), while high root reinforcement (RR) and undercutting caused by excessive penetration was detected on the weld root surface (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb). Reducing the laser beam power to 3 kW significantly reduced IFG and undercut defects on the weld bead surface (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ec), while resulting in lower of RR formation on the weld root surface (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ed). In the joining process using 2.5 kW laser power, no significant defects were observed on both the weld bead surface (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ed) and the weld root surface (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ee) by visual inspection. In addition, incomplete fusion was detected at the weld initial and end points in all plates joined with different laser power. The seam geometric models prepared by utilizing the cross-sectional images of the plates joined with different laser powers to determine the weld cross-sectional dimensions are presented in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003eIn Figs.\u0026nbsp;6a-d, the cross-sectional images of the seams in different zones of the plate joined with 4 kW laser power are presented. As shown in Fig.\u0026nbsp;6a, the weld cracks appeared at the initial of the weld line, above the weld seam. These cracks, known as solidification cracks, were caused by the high heat input and progressed from the seam surface to the center depending on the cooling rate (residual stresses) [\u003cspan class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e]. During the welding process, the initial region of the weld line is exposed to continuous heat input (post-heating) and therefore the cooling rate along the weld line is low [\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e]. The continuous heat input and slow cooling created a wider and more downwardly directed seam compared to other weld lines. The weld geometry shows the formation of a 0.78 mm deep IFG and 1.26 mm RR in the weld initiation zone. Since high laser power causes undercutting in the root area, the root width (RW) size is in the range of 3.11\u0026ndash;2.77 mm. In other seam measurements, the seam width (SW) was 4.50 mm, while the mid-seam width (Mid.SW) and minimum seam width (Min.SW) were 3.37 mm and 2.46 mm, respectively.\u003c/p\u003e\n \u003cp\u003eFigure 6b shows a cross-sectional image of the seam in the middle zone of the weld line. The laser beam reached the center of the weld line after about 50 circular movements. Thus, a localized preheating occurs before the welding process takes place. The heat generated before welding, combined with the heat input during the welding process, caused a higher temperature melting compared to the previous region. In this context, the high cooling rate of the weld seam increased further, and as a result, the crack formation that appeared in the initial region of the weld line appeared longitudinally in the z direction in the middle zone of the weld line. The high cooling rate directed the seam upward (IFG\u0026thinsp;=\u0026thinsp;0.57, RR\u0026thinsp;=\u0026thinsp;0.74) and accordingly the seam widths decreased (SW\u0026thinsp;=\u0026thinsp;3.92 mm, Max.SW\u0026thinsp;=\u0026thinsp;4.06 mm, Mid.SW\u0026thinsp;=\u0026thinsp;3.21 mm, Min. SW\u0026thinsp;=\u0026thinsp;2.48 mm). The undercut formation in the root zone became more pronounced (RW\u0026thinsp;=\u0026thinsp;2.99\u0026ndash;2.10 mm). Figure\u0026nbsp;6d shows the microstructure image of the rectangular area covering the HAZ and fusion zone (FZ). The HAZ near the fusion line has compounds of different sizes (\u0026asymp;\u0026thinsp;16\u0026micro;m) containing the elements AA6082. Some grain coarsening was observed at the edge of the fusion line, but no significant grain orientation was detected. As it progressed from the fusion line to FZ, clustered coarse grain (CG) regions were observed as a result of uneven solidification. Especially considering the grain size distribution around the crack, it was revealed that crack formation occurred due to residual stress in the FZ.\u003c/p\u003e\n \u003cp\u003eIn the cross-sectional view of the end region of the weld line shown in Fig.\u0026nbsp;6c, the crack density increased due to rapid cooling of the surface. The zone was preheated due to heat input from previous weld lines, but exhibited faster solidification after the welding process than the other zones, especially on the surface. This resulted in less deep but more intense crack formation compared to the middle zone. The high preheating did not lead to a large change in seam dimensions, although it directed the seam slightly downward compared to the middle weld region (SW\u0026thinsp;=\u0026thinsp;3.94 mm, Max.SW\u0026thinsp;=\u0026thinsp;3.98 mm, Mid.SW\u0026thinsp;=\u0026thinsp;3.18 mm, Min.SW\u0026thinsp;=\u0026thinsp;2.41 mm, IFG\u0026thinsp;=\u0026thinsp;0.61 mm, RR\u0026thinsp;=\u0026thinsp;0.98 mm). The undercut defect remains, but its effects have been reduced (RW\u0026thinsp;=\u0026thinsp;2.94\u0026ndash;2.18).\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cp\u003eTable 3 presents the seam geometry dimensions of the different weld zones for 4 kw laser power, it is clearly identified that the largest seam size is obtained in the initial zone of the weld line. Except for the initial zone values in the Table 3, the seam geometries of the other welding zones comply with ISO 13919-1 and ISO 13919-2 standards. Finally, under the influence of 4 kW laser power, weld distortion occurred in all regions, but the most pronounced weld distortion was in the weld initial zone. This is evident from the fact that the bottom weld plates are not aligned with each other in Figure 3a.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n \u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n \u003ctable id=\"Tab4\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eSeam geometry dimensions of different weld zones for 4 kW laser power\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth colspan=\"9\" align=\"left\"\u003e\n \u003cp\u003e4 kW Laser Power\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMax.SW (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSW (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMid.SW (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMin.SW (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eIFG (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003eRR (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRW\u003c/p\u003e\n \u003cp\u003e(mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eInt. Zone\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e3.11\u0026ndash;2.77\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMid.Zone\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e2.99\u0026ndash;2.10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEnd Zone\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e2.94\u0026ndash;2.18\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003eThe cross-sectional images of the seams in different regions of the plate joined with 3 kW laser power and the microstructure of some regions of the middle zone of weld line are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ea-g. In the weld cross-section images presented in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ea-c, it was observed that the formation of solidification cracks was significantly eliminated by decreasing the laser power. Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e presents the seam geometry dimensions of different welding zones for 3 kW laser power. The seam dimensions show that low heat input reduces the weld width dimensions. Furthermore, the IFG and RR dimensions were reduced for all zones of the weld line and no undercut formation was observed on the root surface. Figures\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ed and \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ee show optical microscope images of the HAZ and FZ of the middle zone weld line, respectively. The decrease in laser power caused an increase in the proportion of the compund distribution in the HAZ and a grain orientation (columnar dentrites) from the FZ towards the fusion line. The morphology of the grains was affected by the solid-liquid interfacial ratio as well as structural supercooling [\u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e]. At high laser power, the compounds in the HAZ were coarser but more sparse, whereas with decreasing laser power and the associated increase in cooling rate, the compounds became finer but more dispersed (\u0026asymp;\u0026thinsp;11.5\u0026micro;m). However, coarse compounds and precipitates are not present in the FZ. The precipitates dissolve during welding due to the high temperature and do not have time to regenerate [\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e]. In rare cases, the appearance of coarse-grained phase (CGP) in the FZ region is possible due to slow cooling, but especially the FZ center contains equiaxed dentrites (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ee). Figures\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ef and \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eg show SEM images of HAZ - FZ and FZ - HAZ zone transitions, respectively. Due to the overlap welding position, the short plate area close to the weld zone in the +\u0026thinsp;y direction (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eb) was subjected to heat accumulation, resulting in the reduction of precipitates and compounds in the HAZ due to heat treatment, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eg. With the circular oscillation configuration, which is more effective in the +\u0026thinsp;y direction, the heat treatment was even more effective in this region.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n \u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n \u003ctable id=\"Tab5\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eSeam geometry dimensions of different weld zones for 3 kW laser power\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth colspan=\"8\" align=\"left\"\u003e\n \u003cp\u003e3 kW Laser Power\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMax.SW (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSW (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMid.SW (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMin.SW (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eIFG (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRR (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRW\u003c/p\u003e\n \u003cp\u003e(mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eInt. Zone\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.70\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMid.Zone\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.96\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.87\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEnd Zone\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.93\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003ea-e shows cross-sectional images of the seams in different regions of the plate joined with 2.5 kW laser power. The full seam penetration could not be achieved by reducing the laser power, therefore face reinforcement (FR) was used instead of IFG value and lack of penetration (LP) was used instead of RR value for weld geometry evaluation. Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e presents the seam geometry dimensions of the different weld zones for 2.5 kW laser power. Although the seam penetration (SP) values increased towards the end region of the weld line, in general all seam dimensions had values close to each other. In addition, low laser power caused the formation of pores. The bubbles formed at the tip of the keyhole are carried into the molten pool by the flow of molten metal and the keyhole expands and deepens, then the bubbles formed in the keyhole, which undergo severe expansion and contraction, also expand and are retained in the weld zone as large pores [\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e]. With 4 kW and 3 kW laser powers, the joints were fully penetrated, so that pore formation was largely unnoticeable. This is due to the complete penetration of the keyhole tip into the workpiece so that the bubbles were directed out of the base cavity [\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n \u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n \u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n \u003ctable id=\"Tab6\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eSeam geometry dimensions of different weld zones for 2.5 kW laser power\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth colspan=\"8\" align=\"left\"\u003e\n \u003cp\u003e2.5 kW Laser Power\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSP\u003c/p\u003e\n \u003cp\u003e(mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSW (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMid.SW (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMin.SW (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFR (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLP (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRW\u003c/p\u003e\n \u003cp\u003e(mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eInt. Zone\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.49\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMid.Zone\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.72\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.48\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEnd Zone\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.69\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.51\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003ed-e shows HAZ - FZ and FZ - HAZ microstructure images of the initial zone of the weld line. The columnar dentrites were formed in the direction of the arrow towards the fusion line from both edges of the FZ with the effect of the cooling rate. Furthermore the low laser power caused sudden cooling and the post heating process did not reach a sufficient level for this zone during the rest of the welding process. Insufficient time for pore expulsion increased the pore density. The reason for the decrease in porosity towards the end of the weld line is the natural preheating that occurs during the welding process. Natural preheating is a process that can help reduce porosity in processes without full penetration.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2. Microstructure analysis\u003c/h2\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003ea-e shows the microstructure analysis results of the FZ center in the middle region of the weld line for 3 kW. As a result of the EDS mapping analysis of the microstructure image presented in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003ea, it was determined that in the FZ region, besides Al, Si (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003eb) and Cu (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003ec) were dominant in the dark and light colored structure, respectively. Considering the high melting point of Si, it is an expected result that Si is dominant in the FZ element distribution in the process of melting and re-solidification in a short time. In Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003ed, elemental analysis was performed within the rectangular areas determined for spectrum 1 and the presence of 95.46 wt.% Al, 1.79 wt.% Cu and 1.36 wt.% Si elements as well as Mn, Mg and Fe elements below 1 wt.% were determined. In spectrum 2 analyses representing light-colored structures, the presence of compound formation with 70.47 wt.% Cu, 16.25 wt.% Al, 9.40 wt.% Zn, 3.56 wt.% Si and 0.33 wt.% Mg was determined.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003ea-e shows the microstructure analysis results of the HAZ in the middle region of the weld line for 3 kW. As a result of the EDS mapping analysis of the microstructure image presented in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003ea, it was determined that Si (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003eb) and Cu (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003ec) were dominant in HAZ as in FZ. The compounds with Si and Cu elements in this region are not dentritic because they are under the influence of heat treatment. As a result of the analysis of the dark compounds in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003ed (spectrum 3), 60.13 wt.% Al, 30.05 wt.% Si, 8.56 wt.% Cu and 1.25 wt.% Mg were determined. As a result of the analysis of the yellow compounds presented in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003ee (spectrum 4), 45.18 wt.% Cu, 39.55 wt.% Al, 10.71 wt.% Fe and 4.55 wt.% Si were determined.\u003c/p\u003e\n \u003cp\u003eFor a clearer understanding of the microstructural change in the HAZ region with decreasing laser power, the HAZ region selected for the 3kW laser power examination was also selected for 2.5 kW laser power The results of the HAZ microstructure analysis of the plate joined with 2.5 kW laser power are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003ea-e. As the laser power decreased, the average size of Al compounds with high Si content in the HAZ decreased gradually and the average size of these compounds was calculated as 10 \u0026micro;m at 2.5 kW laser power. The average size of the compounds with similar content in the base metal is 7.7 \u0026micro;m and in this context, it can be said that increasing the laser power causes the compound coarsening in the HAZ. In the EDS mapping analysis of the region shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003ea, it is observed that Cu particle size is smaller but dispersed while Si particles are larger but not dispersed (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003eb-c). Spectrum analyses (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003ed-e) from the points identified in the HAZ near the fusion boundary revealed that the Si content in the compound decreased when the 3 kW laser power was compared to the HAZ.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e12\u003c/span\u003ea-e shows the microstructure analysis results of the seam root in the middle region of the weld line for 2.5 kW. As a result of the spectrum analysis performed (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e12\u003c/span\u003eb) on the seam root image presented in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e12\u003c/span\u003ea, it was determined that the compounds containing Al, Cu, Si and Mg elements together are concentrated in the seam root region towards the bottom of the FZ. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e12\u003c/span\u003ec-e mapping analysis shows that Al, Mg, Si and Cu elements form clustered compounds in this region. Since the low heat input 200 \u0026micro;m upwards from the bottom FZ point could not form a clear liquefaction form and also since a rapid cooling occurred in this region, it is estimated that compound clusters may have occurred. The high aggregation amounts are about 30 \u0026micro;m in size and are observed at the edges of the root curvature formation.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3. Microhardness\u003c/h2\u003e\n \u003cp\u003eThe hardness measurements of the plates joined with different laser powers were performed with the hardness test model shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e13\u003c/span\u003e. For hardness testes, specimens belonging to the initial zone of the weld line, which was determined to have minimum weld defects in general after microstructure examinations, were used. Each hardness measurement line was established at a distance of 250 \u0026micro;m from the nearest plate surface. Thus, the changes in the weld seam and surrounding areas were observed.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e14\u003c/span\u003ea-d shows the hardness graphs of the weld joints performed with 4kW laser power. Since the longest solidification time is at the center (\u003cem\u003eO\u003c/em\u003e) of the horizontal hardness lines, a decrease in hardness is observed towards the center of the FZ. However, the hardness in the center decreases dramatically for joints made with high laser power. The FZ exhibits a melting followed by solidification and high laser power will increase the melting area. This phenomenon will lead to slow solidification in the center of the FZ and rapid solidification at the edges of the region close to the fusion line. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e14\u003c/span\u003ea-b shows the graphs of the surface and center hardness lines on the top weld plate. The hardness value at center \u003cem\u003eO\u003c/em\u003e was 75 HV at surface line and 58 HV at center line. Furthermore, the hardness value increased towards the fusion line and reached the maximum hardness value (\u0026asymp;\u0026thinsp;93 HV) and the hardness pattern was similar for both hardness lines. The hardness of the base metal was in the range 105 HV \u0026minus;\u0026thinsp;120 HV. In this context, although it was possible to reach the base metal from the HAZ at a distance of 6 mm in the - y direction, this was not possible in the +\u0026thinsp;y direction. The inability to reach the hardness of the base metal in the +\u0026thinsp;y direction is due to the fact that the weld plate ends too close to the weld zone and this zone is softened by the heat treatment effect. In the root line graph in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e14\u003c/span\u003ec, the hardness properties changed direction due to the overlap plate position and the base metal hardness was not reached in the - y direction. The vertical line graph in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e14\u003c/span\u003ed shows the hardness values of the weld seam from top to bottom. Depending on the cooling rate, the hardness value decreases towards the center, while the hardness values increase towards the bead and root surface. In the vertical hardness line, the highest hardness is observed in the root region (88 HV \u0026minus;\u0026thinsp;94 HV).\u003c/p\u003e\n \u003cp\u003eIn the hardness graphs of the welded joints with 3 kW laser power presented in Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e15\u003c/span\u003ea-d, the effects of reduced heat input were observed. In this context, the hardness distribution at the fusion center on the surface hardness line continued in the range of 74 HV \u0026minus;\u0026thinsp;80 HV for about 2 mm (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e15\u003c/span\u003ea). Thus, it can be said that solidification occurs in the surface line in a similar time period and crack formation is prevented. As the fusion line was approached, the hardness reached in the range of 85 HV \u0026minus;\u0026thinsp;88 HV. Although the hardness decreased up to 78 HV in the HAZ near the fusion line in the -y direction, the hardness increased to 110 HV towards the base metal. In the +\u0026thinsp;y direction, the HAZ hardness after the fusion line reached from 82 HV to 93 HV, but the hardness of the base metal could not be reached at a distance of 6 mm from the center. The hardness pattern at the center line (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e15\u003c/span\u003eb) is similar to the hardness pattern of the welded joint performed with 4 kW laser power, except for the fusion center hardness increase. While a slight increase in hardness was noted in the root line, base metal was reached in the +\u0026thinsp;y and -y directions (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e15\u003c/span\u003ec). The lower RW size in the seam geometry and the lower temperature in this region reduced the effect of the heat treatment and, accordingly, the HAZ distance. The increase in hardness at the root line was also determined in the vertical hardness line pattern and the hardness range was 75 HV \u0026minus;\u0026thinsp;118 HV (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e15\u003c/span\u003ed).\u003c/p\u003e\n \u003cp\u003eFigures \u003cspan class=\"InternalRef\"\u003e16\u003c/span\u003ea-d show the hardness patterns of the welded joints obtained by reducing the laser power to 2.5 kW. The hardness patterns of the horizontal lines showed the formation of boundaries between the HAZ and the base metal. The low laser power resulted in a low HAZ distance and the FZ hardness and HAZ hardness close to the fusion line were close to each other. At a distance of 1.5 mm from the fusion center of the surface hardness line in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e16\u003c/span\u003ea, the hardness range was 78 HV- 84 HV. The hardness reached the range of 90 HV \u0026minus;\u0026thinsp;93 HV close to the +\u0026thinsp;y and -y fusion lines. The estimated HAZ distance is about 2.75 mm in the -y direction and about 4 mm in the +\u0026thinsp;y direction. Despite a slight decrease in hardness values, a similar formation is observed in the center hardness line presented in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e16\u003c/span\u003eb. In the root hardness line graph presented in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e16\u003c/span\u003ec, the hardness value in the fusion region is in the range of 83 HV \u0026ndash; 88 HV. Although HAZ softening was observed in the short area close to the weld zone (in the - y direction) on the bottom plate, the hardness gradually increased from the FZ to the base metal as soon as the HAZ zone in the +\u0026thinsp;y direction was crossed. The vertical hardness line values shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e16\u003c/span\u003ed are in the range of 78 HV- 86 HV. Considering the specimens joined with different laser power, a balanced hardness was determined in the FZ at 2.5 kW laser power.\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn the presented study, AA6082 plates were joined in overlap weld configuration using wobling mode RLW at different laser beam powers. The seam geometries, microstructures and hardness properties were evaluated by dividing the weld joints into initial, middle and final zones and the following results were obtained.\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eIn the joining processes performed at 4 kW and 3 kW laser beam powers where full penetration was achieved, incomplete filled groove and root reinforcement with decreasing values were observed on the bead and root surfaces of the welded plates with decreasing laser power. The face reinforcement was observed at 2.5 kW laser beam power, where full penatrayon was not achieved. For each laser beam power value, the seam geometry changed in different zones of the weld line. For each laser beam power value, the seam geometry changed in different zones of the weld line. The ratio of power and average seam width between the determined zones is 4 kW/4.12 mm, 3 kW/3.05 mm and 2.5 kW/2.75 mm. The circular oscillation path is designed for the laser beam center to move a total of 1 mm in the y-axis for each circular movement (Ay\u0026thinsp;=\u0026thinsp;0.5) and the beam contact distance range in the y-axis is determined as 1.32 mm by adding the laser beam ring dimension value. Considering the measured seam widths, it is observed that the effect of the laser beam power on the welding process will be improved by using it with the correct oscillation path.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eMicrostructural investigations of the initial, middle and end zones of the welded plates revealed that the variation in laser beam power affects the structural formation phenomena of each zone. Since the laser beam power is converted into a heat source during the joining process, the plates were subjected to heat treatment before, during or after welding. As a result, weld zones with different cooling rates exhibited different structural properties. The cooling rate was evaluated differently for full penetration and non-full penetration welding processes. Considering the crack formation between the zones under the influence of 4kW laser beam power, the post sintering of the weld initial zone reduced the crack formation, but the high laser beam power caused undercutting in all regions. With the choice of 3 kW laser beam power, crack formation and undercutting defects were minimized. In the full non-penetrated joining process with 2.5 kW, while pore formations were observed, it was determined that the end zone of weld line, which was subjected to pre-sintering between the zones, had the minimum pore level.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eMicrostructure analysis of the weld zones generally revealed that Si and Cu elements were dominant in the FZ, except Al. While no significant change was observed in the dentritic structure and compound contents in FZs with full penetration, the presence of compound clusters dominated by Cu and Si elements in the seam root region in the welding process without full penetration was determined. In the HAZ region close to the fusion line, compounds containing Al, Si, Cu and Mg were detected, while the compound sizes changed in direct proportion to the laser power.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eAfter the welding process with full penetration, the hardness decreased in the center of the FZ zone due to the effect of cooling rate, but the hardness increased from the surface to the root zone. In the welding process without full penetration, the hardness value in the entire FZ zone was in the range of 81\u0026ndash;88 HV. Due to the overlap welding configuration, since one edge of the joined plates was very close to the welding center, at high laser powers, this region was affected by heat treatment and the base metal could not be detected. As the laser power decreased, HAZ and base metal boundaries could be detected. At 2.5 kW laser beam power, the average HAZ width was 3 mm.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eConflict of interest\u003c/h2\u003e \u003cp\u003eI wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome. I further confirm that there are no other persons who satisfied the criteria for authorship but are not listed.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThis research was supported by The Scientific and Technological Research Council of Turkey\u003c/p\u003e\n\u003cp\u003e(TUBITAK) with the project numbered TUBITAK2219/1059B192202722.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eTun\u0026ccedil;el O, Aydın H, \u0026Ccedil;etin Ş (2020) Microstructure and mechanical properties of similar and dissimilar laser welds of DP600 and DP1000 steel sheets used in the automotive industry. 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Elsevier B.V., pp 478\u0026ndash;487\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":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":"Remote laser welding, wobbling mode, weld geometry, microstructure, hardness","lastPublishedDoi":"10.21203/rs.3.rs-3983654/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3983654/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe advancement of technology has led to an increased need for new materials, which has necessitated the development of new joining techniques. With the adaptation of advanced automation technology, remote laser welding, which has become increasingly widespread, has facilitated the joining of desired complex structures. In this context, the determination of the laser beam power, which is the locomotive of the welding parameters, before the joining process has played an important role in the weld quality. In this study, 2 mm thick AA6082 plates were joined with a wobling mode remote laser welding system using 4 kW, 3 kW and 2.5 kW laser beam powers. Except for the laser beam power, other parameters were optimized by preliminary studies. The welding process was performed in circular oscillation mode and the time-dependent motion of the laser beam was calculated in advance. The seam geometry, microstructure and hardness properties of the weld line initial, middle and end regions of each joining plate were investigated. As a result of the investigations, full penetration was achieved in the joints made with 4 kW and 3 kW laser powers, but the use of 4kW laser power reduced the weld quality. As a result of using 2.5 kw laser power, full penetration was not achieved and porosity formations were observed. In addition, seam geometry values, HAZ distance and compound dimensions close to the fusion line decreased and weld zone element values changed with decreasing laser power. The transformation in structural and elemental values caused regional hardness changes.\u003c/p\u003e","manuscriptTitle":"Effect of Laser Beam Power on AA6082 Plates Joined by Wobbling Mode Remote Laser Welding","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-03-05 15:32:04","doi":"10.21203/rs.3.rs-3983654/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2024-03-01T08:11:11+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-02-28T08:23:19+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Welding in the World","date":"2024-02-27T21:00:33+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-02-26T06:38:57+00:00","index":"","fulltext":""},{"type":"submitted","content":"Welding in the World","date":"2024-02-23T03:44:21+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":"9cc82e1c-ba4c-4105-bd3a-3b28a1bef4f0","owner":[],"postedDate":"March 5th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-06-11T19:49:09+00:00","versionOfRecord":[],"versionCreatedAt":"2024-03-05 15:32:04","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3983654","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3983654","identity":"rs-3983654","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}