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 alpha(Mg) grains, interdendritic alpha(Mg) + Mg12Nd eutectic. Within alpha(Mg) grains, needle-like Mg12Nd phase, quadrate-like Mg5Gd phase and alpha(Zr) particles were also observed. After a solution treatment at 515 degrees C for 18 h, alpha(Mg) + Mg12Nd eutectic was almost dissolved into alpha(Mg) grain, but a new Zn2Zr3 phase was observed within alpha(Mg) grains and along grain boundaries. After an aged treatment at 205 degrees C for 18 h, more dispersed interdendritic Mg12Nd precipitates, coarsened Zn2Zr3 and rod-shaped metastable precipitates of beta ''(Mg3Nd) and beta'(Mg7Nd) were observed within alpha(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 degrees C, and 220 MPa and 165 MPa at 250 degrees C, respectively. The improved mechanical properties were also discussed based on the observed microstructure evolution. (C) 2015 Elsevier Inc. All rights reserved.