Hook formation and mechanical properties of friction spot welding in alloy 6061-T6

A series of welds were produced at various processing parameters in friction spot welded of AA6061-T6 to investigate hook formation and mechanical properties. Two different types of hook defect were identified based on the locations, which were closely associated to the plunge depth. The weld strength had a negative correlation with the hook height. An increase in rotational speed, joining time or plunge depth increased the hook height and resulted in lower weld strength. Increasing plunge depth might also bring a positive effect of weld strength as a result of increased effective shear area.