The Effect of Tool Rotation Speed on Local and Global Mechanical Behavior of Friction Stir Spot Welded (FSSW) AA7075-T6 Aluminum Alloy Sheets

 Abstract — This investigation focused on the impact of tool rotation speed on the mechanical and metallurgical characteristics of friction stir spot welded (FSSW) AA7075-T6 aluminum alloy sheets. To achieve this, aluminum alloy plates were joined using FSSW with four distinct welding parameters consisting of rotation speeds of 725, 1000, 1500 and 1800 rpm and a constant insertion depth of 3.2 mm. To evaluate the mechanical properties and strain field evolution of the welded joint AA7075, a lap shear and digital image correlation (DIC) tests were conducted. In the spot-welded specimens, the highest tensile strength value (2200 N) was found in plates welded at a tool rotation speed of 1500 rpm. The results from a hardness distribution indicate that the thermomechanical affected zone (TMAZ) is the softest area in the weldment, and the fracture typically occurs in this region. The results from DIC clearly show that the strain was heterogeneously distributed across the specimen, mainly due to the microstructural changes in the welded zone.