Revealing joining mechanism in refill friction stir spot welding of AZ31 magnesium alloy to galvanized DP600 steel

The application of magnesium (Mg) inevitably involves dissimilar welding with steel. A novel solid state spot method, refill friction stir (refill FSSW), was utilized to weld AZ31 Mg alloy galvanized DP600 Although Mg/Fe is an immiscible system, defect-free welds high strength were successfully obtained in a wide parameter window. results microstructure, interfacial reactions, and mechanical properties are reported reveal the underlying joining mechanism. Due melting Zn coating subsequent Mg-Zn eutectic intermetallic compounds detected within welds. Heterogeneous reactions occur along Mg/steel interface, relationship between structure fracture behavior investigated. mechanism associated Fe-Al layer: 1) presence beneficial for achieving high-quality steel, it protects interface from oxidation contributes brazing weld; 2) Al present reacts Fe, resulting growth layer, which diffusion bonding interface. overall clearly show that FSSW competitive method