Friction Stir Spot Weldability of AA7075-T6 Sheets with a Pinless Tool Providing Enhanced Stirring Effect

The automotive and aerospace industries have explored alternative welding methods, such as friction stir welding (FSW) and its derivation, friction stir spot welding (FSSW). Welding parameters and tool shoulder designs influence material flow dynamics and stirring during the FSSW process. The current study uses a newly manufactured pinless tool to focus on the FSSW of 3-mm-thick AA7075-T6 aluminum sheets, which were joined using a pinless tool with a concave shape of three grooves for improved flow characteristics. The experiments explore the impact of welding parameters on the weld quality. Tensile tests, macroscopic examination, fracture surface analysis, and microhardness tests were performed. The geometric characteristics of hook shape and effective weld width substantially affected the tensile shear load (TSL). Tensile test findings and changes in effective weld width with welding parameters reveal that low rotational speed, high penetration depth, and dwell time parameters can result in a high TSL. Microhardness profiles reveal that the stir zone (SZ) exhibits the highest hardness values, reaching 27% above the base material hardness. The heat-affected zone (HAZ) shows the lowest hardness values. Fracture surface morphology analysis reveals different fracture modes in high and low TSL specimens.