Microstructural characteristics and mechanical properties of the dissimilar friction-stir butt welds between an Al–Mg alloy and A316L stainless steel

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In this research, dissimilar butt joining of an Al–Mg alloy (AA5083) to austenitic stainless steel (A316L) by using friction-stir welding (FSW) process was examined. FSW parameters and joint design were optimized, owning to achieve the best joint strength. The processed FSWs at the optimized traverse speeds of 16, 20, and 25 mm/min with the sound surface appearance were considered for further cross-sectional investigations, microstructural characterizations, and mechanical testings. In situ reactions at the interface of Al–Mg alloy and stainless steel during FSW processes were studied by using field emission-scanning electron microscopy (FE-SEM) and line-scan energy-dispersive X-ray spectroscopy (EDS) analysis. As expected from the monitored thermal histories during FSW joining, the features indicating the formation of tunneling like defects were observed at low heat inputs (low w/v ratios). Moreover, some discontinuous thin intermetallic layers (with the thickness of ∼0.5 μm) were formed at the joint interface at the expressed processing conditions. Mechanical performances of the prepared dissimilar joints were assessed during transverse tensile loading and Vickers indentation micro-hardness testing. The joint strength ratio to the ultimate tensile strength (UTS) of the weakest base metal (BM) was improved up to ∼93 %, as all of the dissimilar FSWs failed from the Al–Mg base alloy, with a Vickers hardness enhancement of ∼460 % at the interface.