Mg-Gd-Y system phase diagram calculation and experimental clarification

Phase equilibrium of the Mg-Gd-Y system in Mg-rich corner was calculated in detail by phase diagram calculation software Pandat and thermodynamic database for Mg alloys. The calculated phase diagrams were compared with the key experimental results of DSC analysis for the alloys Mg-1 wt%Gd-7 wt%Y and Mg-5 wt%Gd-2 wt%Y. The solidification and precipitation process of the newly developed alloy Mg-12 wt%Gd-4 wt%Y-0.6 wt%Zr were analyzed. The detailed comparison strongly supports the reliability of the selected thermodynamic description based on the results of thermodynamic calculation. It is clarified that when the Mg-1Gd-7Y alloy ends its solidification and cools down continuously, the second phase Mg₂₄Y₅ firstly precipitated from solid solution of magnesium and then the GdMg₅ phase precipitated at relative lower temperature. But for Mg-5Gd-2Y alloy, the precipitation sequence of Mg₂₄Y₅ and GdMg₅ are in reverse order. Referring the calculated Mg-Gd-Y system phase diagrams, the suitable thermal mechanical processing and heat-treatment processes of newly designed and developed alloy Mg-12 wt%Gd-4 wt%Y-0.6 wt%Zr has been done.