Microstructure and Mechanical Properties of Semi-Solid Die Casting Mg–5Zn–2Gd–0.6Zr Alloy

The microstructure and mechanical properties of Mg–5Zn–2Gd–0.6Zr under different processes (permanent mold casting, semi-solid metal (SSM) die casting, and T6 heat treatment after SSM die casting) were investigated using SEM, XRD and tensile mechanical tests. The results demonstrated that Mg–5Zn–2Gd–0.6Zr alloy was composed of α-Mg, quasicrystal I phase (Mg3Zn6Gd) and W phase (Mg3Zn3Gd2). Compared to permanent casting specimens, the microstructure and mechanical properties of Mg–5Zn–2Gd–0.6Zr alloy could be significantly improved by the SSM die casting process, where non-dendrite and spheroidal crystal structures were formed. After SSM die casting, the second phase exhibited a continuous reticular morphology and precipitated along the grain boundaries. The average grain size was 56.4 μm with a shape factor of 0.81. As a result, the mechanical properties were remarkably reinforced, with a tensile strength of 233 MPa and an elongation rate of 9.8