Effect of mole ratio of Y to Zn on phase constituent of Mg-Zn-Zr-Y alloys

The phase constituent evolution of Mg-Zn-Y-Zr alloys with the mole ratio of Y to Zn both in the as-cast and as-annealed states at the Mg-rich corner was investigated by XRD and SEM/EDS analysis and was further explained from the ternary phase diagram calculation. The results show that the formation of the secondary phases in Mg-Zn-Y-Zr alloys firmly depends on the mole ratio of Y to Zn, and X (Mg12YZn)-phase, W (Mg3Y2Zn3)-phase and I (Mg3YZn6)-phase come out in sequence as the ratio of Y to Zn decreases. The mole ratios of Y to Zn with the corresponding phase constituent are suggested quantitatively as follows: the phase constituent is a-Mg + I when the mole ratio of Y to Zn is about 0.164; a-Mg + I +W when the mole ratio of Y to Zn is in the range of 0.164-0.33;a-Mg +W when the mole ratio of Y to Zn is about 0.33; a-Mg +W+X when the mole ratio of Y to Zn is in the range of 0.33-1.32; and a-Mg +X when the mole ratio of Y to Zn is about 1.32. The results also offer a guideline for alloy selection and alloy design in Mg-Zn-Y-Zr system.