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采用XRD、SEM和DSC等手段对Sr、Ca复合添加后的AZ31镁合金中合金相的类别进行了鉴别。结果表明,Ca与Mg元素在基体中形成了Mg2Ca合金相,并不是形成生成焓更低的Al2Ca。随着Ca含量的增加,基体中Mg2Ca合金相的含量增加,当Ca含量增加至0.6%(质量分数)时,基体中出现了带状析出相,并且在Mg2Ca合金相中发现了Sr元素的存在。利用合金相形核理论论证了基体中出现Mg2Ca而不是Al2Ca的原因,计算结果表明虽然Al2Ca的生成焓比较低,但是形核时产生的化学自由能变较大。且Al2Ca合金相的弹性模量与镁基体差异太大,其形核所产生的弹性应变能比Mg2Ca大,所以阻碍了Al2Ca在AZ31基体中形成。
The types of alloy phases in AZ31 magnesium alloy after the addition of Sr and Ca were identified by means of XRD, SEM and DSC. The results show that Ca2 + and Mg2 + form Mg2Ca phase in the matrix, but not Al2Ca with lower enthalpy of formation. With the increase of Ca content, the content of Mg2Ca alloy phase in the matrix increases. When Ca content increases to 0.6% (mass fraction), a banded precipitation phase appears in the matrix, and the presence of Sr element is found in the Mg2Ca alloy phase . The reason why Mg2Ca instead of Al2Ca occurs in the matrix is demonstrated by the alloy nucleation theory. The calculated results show that although the formation enthalpy of Al2Ca is relatively low, the chemical free energy produced during nucleation becomes larger. And Al2Ca alloy phase elastic modulus and magnesium matrix difference is too large, the elastic deformation of its nucleation than Mg2Ca, which hindered Al2Ca AZ31 matrix formed.