Similar and Dissimilar Micro Friction Stir Welding of Magnesium and Aluminium Alloys

Abstract

Micro friction stir welding (µFSW) — a variant of FSW — is a solid-state process intended to join thin materials with thicknesses equal to or lower than 1 mm. In general, friction stir welding (FSW) of bulk materials results in superior joints compared to conventional fusion-based welding techniques. However, if the same is true for friction stir welded thin material joints remains an open research question. In this study, micro friction stir welding of AZ31 magnesium and 6061 aluminium in similar and dissimilar configurations is carried out. Joining of light metal alloys ratio such as AZ31 and 6061, due to their high strength to weight ratio, is attractive in general and especially in thin cross-sections owing to their application in miniaturized structures. The microstructure and mechanical properties of the resulting joints are studied as a function of process parameters and tool designs. The research demonstrated µFSW can be successfully applied to produce defect-free dissimilar welds between AZ31 Mg and 6061 Al alloys having a thickness of 500 µm. The resulting joints showed mechanical interlocking between Al and Mg with the presence of finger-like projections in the SZ. Metallurgical interlocking was also observed between AZ31 and 6061 with the presence of aluminium and magnesium-rich intermetallic compounds (Al₃Mg₂ and Al₁₂Mg₁₇), along with grain refinement in the stir zone. Tensile testing on the ultra-thin µFSWed joint revealed joint efficiency of 54.5% w.r.t AZ31 base material. Under tensile loading, fracture initiated towards the AZ31 side along the interface of the stir zone and thermomechanically affected zone owing to the presence of brittle intermetallic compounds. The results from the present research have great potential applications in various industries including transportation and electronics.