Mg-Zn-Ca系富Mg区域三元化合物及其固态相平衡

TERNARY COMPOUNDS AND RELATIVE PHASE EQUILIBRIA IN THE Mg-RICH SIDE OF THE Mg-Zn-Ca SYSTEM

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T_1和T_2.其中化合物T_1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=0.995-0.945nm,c=1.036-1.003nm.T_2相的成分范围为:Mg 27.1-29.3,Zn 62.1-64.4和Ca7.6-9.0;也为六方结构,晶格常数a=1.475nm和c=0.879nm.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+Mg_2Ca+T_1,α-Mg+T_1+T_2,α-Mg+T_2+MgZn,MgZn+T_2+Mg_2Zn_3和α-Mg+Mg_7Zn_3+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 T_1 and T_2 in equilibrium with the Mg-based solid solution in the Mg-Zn-Ca system.T_1 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 T_2 phase is Mg 27.1—29.3,Zn 62.1—64.4 and Ca 7.6—9.0.T_2 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 theα-Mg solid solution,but the solubility of Zn in theα-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 ofα-Mg＋Mg_2Ca＋T_1,α-Mg＋T_1＋T_2,α-Mg＋T_2＋MgZn,MgZn＋T_2＋Mg_2Zn_3 andα-Mg＋Mg_7Zn_3＋MgZn in the Mg-Zn-Ca system,respectively.