Influences of Y Additions on the Hot Tearing Susceptibility of Mg-1.5wt.%Zn Alloys

Abstract

The influences of Y (0.2, 2 and 4 wt.%) additions on the hot tearing behaviour of Mg‑1.5Zn alloys were investigated using a constrained rod casting (CRC) apparatus equipped with a load cell and data acquisition system. The initiation of hot tearing was monitored during CRC experiments. It corresponds to a drop in load on the hot tearing curves. The experimental results indicate that, the hot tearing susceptibility defined by the total crack volume, which was measured by the wax penetration method, decreases with increasing the content of Y at a mould temperature of 250 °C. The reduced susceptibility is attributed to the effect of Y on the solidification behaviour: it shortens the freezing range and reduces the grain size. The highest susceptibility is observed for Mg-1.5Zn-0.2Y alloy. It is caused by its coarse microstructure and relatively larger solidification range. In contrast, the lowest susceptibility is observed for Mg-1.5Zn-4Y alloy with a small equiaxed grain microstructure. In addition, the healing of hot cracks by the subsequent refilling of the remained liquid at the later stage of solidification is also beneficial for the alleviation of hot tearing susceptibility in Mg-1.5Zn-4Y alloy.