Microstructure evolution during heat treatment and mechanical properties of Mg-2.49Nd-1.82Gd-0.19Zn-0.4Zr cast alloy

Microstructure evolution during heat treatment and mechanical properties of Mg-2.49Nd-1.82Gd-0.19Zn-0.4Zr cast alloy were investigated experimentally in different stages of heat treatment process. As-cast alloy was found to be consisting of dendritic α(Mg) grains, interdendritic α(Mg) + Mg12Nd eutectic. Within α(Mg) grains, needle-like Mg12Nd phase, quadrate-like Mg5Gd phase and α(Zr) particles were also observed. After a solution treatment at 515 °C for 18 h, α(Mg) + Mg12Nd eutectic was almost dissolved into α(Mg) grain, but a new Zn2Zr3 phase was observed within α(Mg) grains and along grain boundaries. After an aged treatment at 205 °C for 18 h, more dispersed interdendritic Mg12Nd precipitates, coarsened Zn2Zr3 and rod-shaped metastable precipitates of β″(Mg3Nd) and β′(Mg7Nd) were observed within α(Mg) grains. The ultimate tensile strength and the yield strength of the experimental alloy after the aged treatment were measured to be 287 MPa and 206 MPa at room temperature, 240 MPa and 175 MPa at 200 °C, and 220 MPa and 165 MPa at 250 °C, respectively. The improved mechanical properties were also discussed based on the observed microstructure evolution.