Mechanical properties and failure analysis of refill friction stir spot-welded 5052/2A12 joints

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.