Influence of optimized FSW process parameters on the mechanical and metallurgical properties of AA7075-T6 alloy at parallel and off-axis weld orientations

Abstract This study investigates the mechanical characteristics of optimized friction stir welding (FSW) process parameters for joining similar AA-7075-T651 alloy. Nine unique combinations of FSW process parameters were tested, involving three rotational and traverse speeds, while maintaining a tool tilt angle of 2°. Tensile specimens were obtained from each plate at two weld orientations: 0° (parallel) and 30° (off-axis) with the rolling texture. The results show that the ultimate tensile strength (UTS) of the 0° specimens is higher compared to the 30° specimens. For the 30° specimens, UTS was found to be directly proportional to the rotational speed at a fixed traverse speed. In contrast, for the 0° specimens, UTS decreased at the highest rotational speed. Microstructural analysis reveals that the 0° weld orientation features smaller, equiaxed crystals, indicating uniform recrystallization and enhanced material flow, which improves strength. In contrast, the 30° orientation displays larger, elongated crystals, suggesting less effective recrystallization and anisotropic stress distribution. Joints fabricated at 1500 rpm show improved stress distribution and reduced residual stresses, leading to enhanced mechanical properties. Conversely, joints made at 1200 rpm exhibit lower tensile strength, highlighting the significant impact of rotational speed on residual stresses and mechanical properties.