Correlation of Shear Texture Evolution and Microstructural Development with the Formability of Dissimilar Friction Stir Welded AA6061 and AA5754 Sheets at Various Strain Paths

The development of normal shear texture in the friction stir welding (FSW) process is primarily influenced by high strain, strain rate, and temperature due to the tool's stirring action, where the shear plane aligns with the tool pin surface. These shear textures impact the forming limits during the stretch forming of welded blanks, yet limited research has explored this effect. In this study, dissimilar FSW was performed on 1.5 mm thick AA6061 and AA5754 alloy sheets using various process parameters. The tailor-welded blanks subsequently underwent a limit dome height test in uniaxial, plane strain, and biaxial strain paths. Strain path curves were developed from the deformation initiation to the fracture onset using a digital image correlation technique integrated with the hydraulic press. Failures in uniaxial and plane strain paths occurred in the thermo-mechanically affected zone, while in the biaxial strain path, failure locations were at the weld center for all specimens. Shear texture in these regions was analyzed before and after deformation using EBSD characterization. The minor strain in the biaxial strain path was unusually low for specimens welded at 1250 rpm - 50 mm/min and 1400 rpm - 75 mm/min which was correlated with localized thinning at limited punch travel. This peculiarity was attributed to a high-intensity C texture and lack of B texture near failure regions. Grain orientation spread maps indicated more recrystallized and less misoriented grains in biaxial specimens compared to other strain paths, explaining the lower deformation from the as-welded state. IPF maps and corresponding ODF textures were determined from 2 to 3 Taylor factor partitioning near failure regions, revealing that uniaxial deformation slip system activation was driven by cube and H textures. However, the intense cube texture had negatively affected the slip system activity during biaxial stretching.