Effects of Rotational Speed on Microstructure and Mechanical Properties of Friction Stir Spot-Welded AA6082-T6/AA1050 Dissimilar Lap Joints

Abstract

In this study, the macrostructure and mechanical characteristics of friction stir spot-welded (FSSWed) dissimilar lap joints between AA6082-T6 and AA1050 were investigated as a function of rotational speed. The FSSW procedure was carried out with a constant dwell time of 4 s and rotating speeds of 500, 700, and 900 rpm. The results showed that the heat input and maximum peak temperature increased by increasing the rotational speed, which improved material flow and wider bonding area between the upper and lower sheets. Microhardness measurements in the stir zone indicated an increase in higher value at lower rotational speeds, increasing from 86.9 HV at 900 rpm to 102.3 HV at 500 rpm, due to enhanced material flow, plastic deformation and re-precipitation of strengthening phases. Tensile-shear tests revealed a non-linear relationship between rotational speed and joint strength, with a maximum load of 4.58 kN at 500 rpm. Fracture analysis showed a shift from ductile fracture at lower speeds to a mix of ductile and smooth fracture features at higher speeds, indicating changes in the failure mechanism.