La和Nd是镁合金中常用的稀土添加元素, 为了帮助理解它们在Mg合金中的强化机制, 应用第一原理计算方法, 研究了Mg-La和Mg-Nd二元合金的相稳定性. 计算结果表明, Mg-La和Mg-Nd合金在Mg12RE和Mg3RE之间的平衡相分别为Mg17La2和Mg41Nd5; La和Nd在Mg中的溶解度大小差别较大, 表明二者在镁合金中产生强化的机理不同; Mg3Nd具有比Mg12La更大的弹性模量, 因而具有更好的强化效果.
The applications of magnesium alloys in automobile industry are limited by their poor high-temperature creep resistance, which can be effectively improved by rare earth (RE) elements addition. In general, rare earth elements are introduced as mixtures of various kinds of metals, and all of the elements are considered to behave in the same way. In practice, various rare earth elements may act differently in magnesium alloys. La and Nd are the two elements usually added to magnesium alloys. In this paper, first-principles calculations are made to investigate the phase stability of Mg-La and Mg-Nd binary alloy systems. In addition, the solubility of La and Nd in Mg is discussed and the elastic constants of the strengthening phases in Mg-La and Mg-Nd alloys are calculated. The equilibrium phases between Mg12RE and Mg3RE are Mg17La2 and Mg41Nd5 for Mg-La and Mg-Nd systems respectively. The difference of calculated solubility for La and Nd in Mg indicates the distinct strengthening mechanism for these two alloy systems. Mg3Nd is predicted to have larger elastic moduli and a better strengthening effect than Mg$_{12}$La.
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