Effect of applied pressure on microstructures of squeeze cast Mg-15Gd-1Zn-0.4Zr alloy

Microstructural evolution of Mg-15Gd-1Zn-0.4Zr (GZ151K, wt%) alloys, cast under 0 MPa (gravity cast) and 6 MPa (squeeze cast), were comparatively studied. It is found that the grain size of squeeze cast GZ151K alloy with applied stress 6 MPa is much smaller than that of the gravity cast counterpart. Moreover, the squeezing pressure hinders the transition from β' precipitates to β1 precipitates during subsequent aging process, leading to reduced volume fraction of β1 precipitates in the squeeze cast alloy. Thus, the relatively lower volume fraction of β1 precipitates in the squeeze cast GZ151K results in higher hardness increment and stronger precipitation hardening effect.