Effect of surface oxide layers in solid-state welding of aluminium alloys – review

This review sheds novel insights on the residual oxide behaviour of solid-state weld joints of aluminium alloys. Understanding the influence of oxides on the aluminium surface before and during welding, its impact on the weld structure and possible solutions for reducing its impact were addressed. The solid-state techniques most relevant to the transportation sector namely, diffusion bonding, friction stir spot welding and ultrasonic welding were surveyed, analysed and reviewed. During this analysis, the implication of the presence of oxides on aluminium substrate affecting the metallurgical characteristics of the weld joints was reviewed. Visible defects such as voids, delamination, kissing bond and hook defects, and problems associated with these defects were analysed and few suggestions are made to partially overcome these issues. Abbreviations: AS, Advancing side; CDRX, Continuous dynamic recrystallisation; CFSSW, Conventional friction stir spot welding; DB, Diffusion bonding; EDS, Energy-dispersive spectroscopy; e-TEM, Environmental transmission electron microscopy; FSW, Friction stir welding; FFSSW, Flat friction stir spot welding; FSSW, Friction stir spot welding; IPDB, Impulse pressuring diffusion bonding; IPADB, Impulse pressure-assisted diffusion bonding; PLT-FSSW, Pinless tool friction stir spot welding; PFSSW, Protrusion friction stir spot welding; RFSSW, Refill friction stir spot welding; RS, Retreating side; RZ, Recrystallised zone; SEM, Scanning electron microscopy; TEM, Transmission electron microscopy; TWI, The Welding Institute; USW, Ultrasonic welding; WFI, Weld faying interface; WFSSW, Walking friction stir spot welding; XPS, X-Ray Photoelectron Spectroscopy