Phase equilibria of low-Y side in Mg–Zn–Y system at 400 °C

Phase equilibrium relations of the Mg–Zn–Y system in the low-Y side at 400 °C were investigated by alloy-equilibrated method, combined with thermal analysis. The results show that there is a liquid phase which could be in equilibrium with an α-Mg solid solution and an icosahedral quasicrystal I phase in the low-Y side of the Mg–Zn–Y system at 400 °C. The liquid phase region originates from the binary Mg–Zn system and extends to 0.4 at%Y in the Mg–Zn–Y system. Besides, the hexagonal structure H phase, fcc W phase and LPSO phase (X phase) are in equilibrium with α-Mg. With Y/Zn (atomic ratio, the same as follows) increasing, there exist four three-phase regions consisting of I + liquid + α-Mg, I + H + α-Mg, H + W + α-Mg and W + X + α-Mg, respectively, in the low-Y side of the isothermal section at 400 °C. The two-phase region α-Mg + I phase exists between I + H + α-Mg and I + liquid + α-Mg. In this two-phase region, the Y/Zn ratio is in the range of 0.14–0.17; and a three-phase region of α-Mg + I phase + H phase appears when Y/Zn ratio comes up to 0.17–0.27. Not I but W phase is in equilibrium with α-Mg, when Y/Zn ratio > 0.27. The system is in liquid-state phase equilibrium, when Y/Zn ratio < 0.14.