The mechanical properties and failure process of 2 mm-thick 5052 Al and 6 mm-thick 2A12 Al fabricated by refill friction stir spot-welding were investigated. The hooks were bent respectively downwards and upwards at plunge depths smaller and larger than the upper plate thickness. The joint area of the lap interface and bearing thickness of the upper plate were related to the hook direction. The tensile shear failure load was affected by structural characteristics and hardness of the joints. Stress concentration occurred in the hook and strain expanded with the hook during fracture. There were two fracture modes: shear fracture and shear plug fracture, where both cracks passed through the hook and fracture morphology of the hook was less plastic.

In this study, the refill friction stir processing (RFSP) method was utilised to repair a exit-hole defect located at the end of the friction stir welding (FSW) joints in 7475 aluminium alloy plate. The morphology, macroscopic defects, and mechanical properties of the repaired joints were investigated. The results demonstrate that the exit-hole was successfully refilled after RFSP. Material flow caused the refill voids, annular grooves, and un-stirred material defects. The maximum strength reached 415 Mpa, equal to 105% of the base defect-free weld. The mechanical properties of repaired joint were largely influenced by the stir zone (SZ) boundary and un-stirred material defects.