Sr、Ca复合添加对AZ31镁合金中合金相的影响

Effect of Sr and Ca Compound Alloying on the Phase of the AZ31 Magnesium Alloy

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 phase in the AZ31 with Sr and Ca compound addition were analyzed by X-ray diffraction, scanning electron microscope and differential scanning calorimeters.The results show that the Ca and Mg form the Mg2Ca instead of Al2 Ca though it has the lower enthalpies of formation.The amount of the Mg2Ca is increased with the Ca addition increasing.The banding-shaped phase has been observed in the matrix when the content of Ca is greater than 0.6 wt% and the Sr have been found in the Mg2Ca.The Mg2Ca occurrence in the matrix has been demonstrated by the nuclear theory of phase.Although the formation enthalpy of Al2 Ca is lower than that of Mg2Ca, the molar free energy of Al2 Ca nucleation and the elastic strain energy are larger than those of Mg2Ca for the Al2 Ca elasticity modulus is larger than the magnesium matrix.So the Mg2Ca has the higher probability than Al2 Ca occurring in the AZ31 matrix.