Effect of Sn microalloying on microstructure and mechanical properties of Mg-11Gd-1Zn-0.5Zr alloy

The effect of Sn microalloying on the microstructure and mechanical properties of the Mg-Gd-Zn-Zr alloy has been systematically investigated. The grain size of the cast alloy was found to be coarse. The two alloys were mainly composed of α-Mg and (Mg, Zn)3Gd phases, and the addition of 0.5 % Sn also caused a small amount of Sn3Gd5 phases to appear. In the subsequent homogenization heat treatment at 500 °C, adding Sn promoted the formation of many lamellar 14H-LPSO phases. After undergoing three rounds of hot rolling, the Sn-containing alloy exhibited a refined grain size and a significant reduction in the volume fraction of twins, mainly due to the particle-stimulated nucleation (PSN) mechanism and the inhibiting effect of LPSO on twins. In addition, the ultimate tensile strength (UTS) of the alloy (380 ± 1 MPa) was significantly increased by the addition of Sn, although the age hardening effect was prolonged. The high strength was attributed to the dispersion distribution of fine chain-like β′ structure, which was conductive to the movement of pinning basal dislocations.