Microstructure Evolution of Mg-Sn-Y Alloy Solidified under High Pressure and Temperature Gradient

The microstructures of Mg-1Sn-2.5Y (wt%) alloys solidified under high pressures were investigated. In addition, a mathematical model was established to analyze the effects of solidification pressure and cooling rate on the average grain size. The results show that the alloy was solidified under high pressure and temperature gradient using the cooling rate difference in the high pressure chamber, resulting in the formation of the outer equiaxed zone, the columnar zone, and the equiaxed zone in the sample. With an increase in the solidification pressure, the columnar-to-equiaxed transition was inhibited in Mg-1Sn-2.5Y alloy. In the outer fine equiaxed zone and the columnar zone, the solubility of Sn in the Mg matrix increased with an increase in solidification pressure. The average secondary dendrite arm spacing decreased from 14-17 mu m under 1 GPa to 9-11 mu m under 1.5 GPa. Increases in pressure and cooling rate resulted in a reduction in average grain size.