Effect of Tool Rotation Rate on Microstructure and Mechanical Behavior of Friction Stir Spot-Welded Al/Cu Composite

In this study, the friction stir spot welding of Al/Cu composite produced by accumulative roll-bonding process was performed using a triangular pin with no features. The influence of tool rotation rate on the microstructure, surface hardness, and tensile shear strength was examined. The results indicated that the weld made at lower tool rotation rate was not bonded because there was no intermixing between the upper and lower sheets. The maximum shear failure load increased with the increasing tool rotation rate, and reached a maximum value at 1400 rpm, which can be ascribed to the increasing area and effective length (d) of stir zone (SZ). The experimental observations showed the presence of the intermetallic compounds (Al₂Cu and AlCu₃) in the SZ. It was concluded that the intermetallic compounds, accompanied by the material crushing, increased the hardness of the SZ.