Influence of welding parameters on macrostructural and thermomechanical properties in micro friction stir spot welded under high-speed tool rotation

An investigation of micro friction stir spot welding (μFSSW) of 0.42-mm-thick AA1100 sheets has been performed under high-speed tool rotation. This study aimed to determine the effect of the plunge rate and dwell time on the thermal history and the axial force during the welding process, and also optimizing plunge rate and dwell time to obtain the good result of the weld joint strength. Thermal histories and axial force histories during μFSSW experiments were obtained. Both showed that increasing the dwell time has no significant effect on increasing the maximum temperature at the center of the weld and the axial force. The plunge rates were the major cause of the hardening and softening of the material in the plunging stage. However, the tensile shear test results indicate that the dwell time plays a major role in increasing the tensile shear strength, while the plunge rate has a minor effect on the tensile strength. The macrostructural observation was also performed to study the hook formation and stirred zone width of μFSSW. Furthermore, the correlation of the hook shape to failure propagation has been carried out.