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 degrees 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 alpha-Mg solid solution and an icosahedral quasicrystal I phase in the low-Y side of the Mg-Zn-Y system at 400 degrees 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 alpha-Mg. With Y/Zn (atomic ratio, the same as follows) increasing, there exist four three-phase regions consisting of I + liquid + alpha-Mg, I + H + alpha-Mg, H + W + alpha-Mg and W + X + alpha-Mg, respectively, in the low-Y side of the isothermal section at 400 degrees C. The two-phase region alpha-Mg + I phase exists between I + H + alpha-Mg and I + liquid + alpha-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 alpha-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 alpha-Mg, when Y/Zn ratio > 0.27. The system is in liquid-state phase equilibrium, when Y/Zn ratio < 0.14.