Effect of residual Alclad on friction stir spot welds of AA2219 alloys

Abstract This paper aims to determine the role of in-nugget/residual Alclad in the friction stir spot welds of 1.6 mm thick Alclad AA2219 aluminum alloy via an assessment of microstructure, mechanical properties and fracture modes of welds. Alclad redistribution/dispersion within the stir zone of the alloy is varied by using different tool profiles (pinless and conical pin tools) and welding parameter combinations. The results reveal that a pinless tool facilitates the retention of Alclad within the weld's effective joint line/width while no substantial residual Alclad is observed in the effective bonded width of a conical pin weld. The increase in tool depth improves the weld strength of a pinless weld. The fracture morphology of a pinless weld is influenced by the in-nugget Alclad content. Interfacial fracture with midpoint defect, interfacial fracture and nugget pull-out are the fracture modes of pinless welds while a conical pin weld fails by circumferential nugget shear failure. A direct correlation ...