Effects of Gd/Y Ratio on the Microstructures and Mechanical Properties of Cast Mg–Gd–Y–Zr Alloys

Three Mg–xGd–yY–0.5Zr (x + y=13, wt%) alloys were prepared by sand casting to investigate the effects of Gd/Y ratio on the microstructures and mechanical properties. The results show that Gd/Y ratio had little influence on the grain size and the phase constitution of the microstructures. However, the volume fraction of the second phase Mg₂₄(Gd, Y)₅ in as-cast state increased, while that of the cubic phase (Y, Gd)H₂ in as-solutionized state almost unchanged with the decrease of Gd/Y ratio. The uniaxial tension tests of the three alloys show that for both as-solutionized and as-aged states, the yield strength was slightly increased but the ductility was apparently decreased with the decrease of Gd/Y ratio from 3.33 to 1.17. It was thought that Gd and Y atoms in Mg matrix have approximate solute strengthening effect but different adverse effect on ductility, which should be responsible for the mechanical properties difference for the three alloys.