Microstructure and mechanical properties of semi-continuous cast Mg-Gd-Y-Zr alloy

Semi-continuous cast Mg-8Gd-3Y-0.4Zr (wt%) alloy in different conditions was systematically investigated in its microstructure and mechanical properties. β phase and eutectic compounds were observed in the as-cast alloy. β phase and most of the eutectic compounds were dissolved into the matrix and Y-rich phase was precipitated during the homogenization. Extreme grain refinement and slight precipitation took place in the extrusion of the alloy. β′ phase precipitates were observed and studied in the peak-aged alloy. Effective strengthening modes were used to predict the strength and the results are consistent with the experiment. The results suggest that solution strengthening and grain boundary strengthening are the main strengthening factors of the as-extruded alloy, while β′ phase is the biggest strengthening contributor of the as peak-aged alloy.