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

Abstract

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 exists between nugget rotation and lap shear failure load. Maximum lap shear failure loads of 4.0 kN and 2.1 kN are obtained in pinless and conical pin welds at the optimum welding parameter combinations of 1500 rpm – 0.8 mm – 8 s and 1400 rpm – 0.43 mm – 4 s, respectively.