Microstructure and mechanical properties of Mg–Gd–Y–Zn–Zr alloy after resistance butt welding

This study employed resistance butt welding (RBW) technology to join the rods of an Mg–9Gd–3Y–1Zn–0.3Zr alloy, and the resultant microstructural transformations and mechanical properties of the welded joints were investigated. In the weld zone (WZ), a network of bright eutectic phases, predominantly consisting of (Mg, Zn)₃(Gd, Y), formed along the grain boundaries. The heat-affected zone (HAZ) contained both the (Mg, Zn)₃(Gd, Y) phase and gray Long-Period Stacking Ordered (LPSO) phase, with the bright eutectic phases adhering predominantly to the edges of the LPSO phase. The base material zone (BMZ) retained its striated LPSO structure. The average grain size in the welded area post-welding was approximately 3.33 μm, which was essentially unchanged from the pre-weld size of 2.41 μm. According to the base material to the weld zone, the crystallographic orientation transitioned from an extrusion direction (ED)∥<0001> texture to a dual-textured orientation of ED∥<01-10> and ED∥<−12-10>. The ultimate tensile strength (UTS) and yield strength (YS) of the base material were 349.67±6.65 and 288.67±2.51 MPa, respectively, slightly decreasing in the welded specimens to 308.33±6.02 and 278.67±4.5 MPa. Given the minimal change in grain size, a notable fine-grain strengthening effect was observed post-welding, allowing the mechanical properties of the welded samples to reach 96.54% of the unwelded base material. However, the presence of the (Mg, Zn)₃(Gd, Y) phase at the weld significantly reduced ductility, with the elongation (EL) decreasing from 8.83% to 3.03%, while correspondingly increasing the strength of the weld zone.