Abstract:The phase equilibria and compositions in Mg-rich side at 300 °C were investigated in Mg−Zn−Ca ternary system through the equilibrated alloy method by using scanning electron microscopy, electron probe microanalysis, X-ray diffraction and transmission electron microscopy. The results show that two ternary compounds T₁ and T₂ can be in equilibrium with the Mg-based solid solution in Mg−Zn−Ca system. T₁ phase is a linear compound with the composition region (molar fraction) of 15% Ca, 20.5%−48.9% Zn and balanced Mg at 300 °C. Its hexagonal structure parameters decrease with increasing Zn content, i.e. a=0.992−0.945 nm, c=1.034−1.003 nm. T₂ phase has hexagonal structure with the composition region of 26.4%−28.4% Mg, 63.2%−65.5% Zn and 7.1%−8.4% Ca. At 300 °C, the solubility of Zn in the Mg-based solid solution increases for the addition of Ca, the maximum solubility of Zn is 3.7%. Three-phase fields consisting of a-Mg+Mg₂Ca+T₁, a-Mg+T₁+T₂, a-Mg+T₂+MgZn and MgZn+T₂+Mg₂Zn₃ exist in the Mg−Zn−Ca system at 300 °C.

Key words: Mg-Zn-Ca system; ternary compound; structure; composition; phase equilibrium