The research of microstructure and mechanical properties of Mg-7Gd-3Y-1Nd-0.5Zn-0.5Zr (wt%) alloy

Microstructures and mechanical properties of Mg-7Gd-3Y-1Nd-0.5Zn-0.5Zr (wt%) alloy before and after homogenization at 520 °C were systematically studied. The results indicated that the microstructure of as-cast alloy mainly consisted of α-Mg, (Mg,Zn) 3 RE phase, Mg5 (RE, Zn) phase and some fine needle structures near the grain boundary; the (Mg, Zn) 3RE and Mg5 (RE, Zn) phases had a face centered cubic (fcc) structure and were isomorphous with β1 and β phases; the fine needle structures were an stacking fault. Heat treatment at 520 °C caused the dissolution of not only the (Mg, Zn) 3RE phase and Mg5 (RE, Zn) eutectic phases, but also the stacking fault into the α-Mg matrix; no long period stacking ordered (LPSO) phases were observed. The tensile test at room temperature suggested that the ultimate tensile strength (UTS), yield strength (YS) and elongation of the as-cast and as-homogenized were 170 MPa, 129 MPa and 238 MPa, 125 MPa, and the elongations were 3% and 12%, respectively. Fracture analysis of the as-cast alloys revealed that micro-cracks initiated in the grain boundary, which belonged to intergranular fracture, while the micro-cracks mainly appeared in the grain interior; the fracture mode was transgranular fracture after homogenization.