Microstructure of as-cast Mg-4.2Zn-0.8Y (at.%) alloys containing Gd

Mg-Zn-Y is a high performance magnesium ternary alloy with high specific strength. A second rare earth element Gd with different content was added into Mg-4.2Zn-0.8Y (at.%) alloys to investigate the effect of Gd addition on the microstructure and mechanical properties. In the as cast alloys, the following phases have been identified: in the Gd-free alloy, an H phase (hcp, a=0.918nm, c=0.95nm), W phase (fcc, a=0.682nm) and icosahedral quasicrystalline phases (i-phase). With 0.5at.% Gd and 1 at.% Gd, W phase, long-period stacking ordered phase (LPSO phase) and i-phase were observed. The coexistence of i-phase and LPSO phase was observed after Gd addition. As the content of Gd increased, the grain size decreased, the volume fractions of second phases increased, and the hardness of the as-cast alloys increased.