利用SEM, EPMA, XRD和TEM对Mg-Zn-Ca系富Mg区域三元化合物的成分、结构及其相平衡进行了研究. 结果表明, Mg-Zn-Ca系富Mg区域存在2个可与镁基固溶体相平衡的三元化合物T1和T2. 其中化合物T1为线性化合物, 成分(原子分数, %, 下同)为: Ca约16, Zn 16.8-49.5, Mg余量; 晶体结构为六方结构, 晶格常数随Zn含量的增大而减小, a=0.995-0.945 nm, c=1.036-1.003 nm. T2相的成分范围为: Mg 27.1-29.3, Zn 62.1-64.4和Ca 7.6-9.0; 也为六方结构, 晶格常数 a=1.475 nm和c=0.879 nm. 335 ℃时, Zn的加入并未使得镁基固溶体对Ca的溶解度降低, 但Ca元素提高了Zn在镁基固溶体中的溶解度, Zn达到4.6. 335 ℃时, Mg-Zn-Ca系相图富Mg区域存在着三相区α-Mg+Mg2Ca+T1, α-Mg+T1+T2, α-Mg+T2+MgZn, MgZn+T2+Mg2Zn3和 α-Mg+Mg7Zn3+MgZn.
The structure, composition range and phase equilibria of the ternary compounds in Mg-rich side of the Mg-Zn-Ca system have been investigated by SEM, EPMA, XRD and TEM. It has been shown that there exist two ternary compounds T1 and T2 in equilibrium with the Mg-based solid solution in the Mg-Zn-Ca system. T1 phase is a linear compound with hexagonal structure, whose structure parameters decrease with the Zn content, i.e. a=0.995-0.945 nm, c=1.036-1.003 nm. Its composition region (atomic fraction, %) is Ca about 16, Zn 16.8-49.5 and balanced Mg. The composition region of the T2 phase is Mg 27.1-29.3, Zn 62.1-64.4 and Ca 7.6-9.0. T2 phase also has the hexagonal structure, whose structure parameters are a=1.475 nm and c=0.879 nm. At 335 ℃, the dissolution of Zn has not decreased the solubility of Ca in the α-Mg solid solution, but the solubility of Zn in the α-Mg solid solution increases with the dissolution of Ca, and the maximum solubility of Zn is 4.6. At 335 ℃, there are five three--phase fields consisting of α-Mg+Mg2Ca+T1, α-Mg+T1+T2, α-Mg+T2+MgZn, MgZn+T2+Mg2Zn3 and α-Mg+Mg7Zn3+MgZn in the Mg-Zn-Ca system, respectively.
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