利用固体与分子经验电子理论(EET),计算分析了Al-Er合金的价电子结构.计算了不同温度下Er在基体铝中的平衡固溶度,同时结合界面前的溶质原子再分配原理,研究了在凝固过程中溶质原子Er的分配问题.结果表明:在Al_3-Er晶胞中最强Al-Er共价键的共价电子数为0.35798,表明Al-Er之间存在强烈的相互作用,在合金凝固过程中存在较大的形成金属间化合物Al_3-Er的趋势.固溶体中3种晶胞中最强键键能的关系为:E~(Er)＞E~(Al-Er)＞E~(Al).因此Er元素的加入可以提高Al基体的结合强度,从而提高合金的抗高温性能.Er在基体铝中平衡固溶度很低,共晶温度928 K下铒的固溶度仅为0.017%,平衡分配系数K约为0.0028＜＜1,运用shell模型计算表明当铒含量很低的情况下,凝固过程溶体中也会存在较大的成分过冷,随着凝固过程的进行,固液界面铒原子偏聚与铝结合生成Al3 Er,起到异质形核的作用,细化了铸态晶粒组织.
The valence electron structure of Al-Er alloys were calculated according to the empirical electron theory in solid(EET).And equilibrium solubility of Er in pure Al at different temperatures,distribution problem of solute atom Er during the solidification was analyzed based on the redistribution mechanism in the interface.The results demonstrated that the cov~ence electron number of the strongest bond in Al_3Er cell was 0.35798,which indicated that there was a strong interaction between Al atoms and Er atoms.So Al and Er would tended to form the Al_3Er phase.The relationship of the strongest bond energy in crystal cell of solid was E~(Er)＞E~(Al-Er)＞E~(Al).As a result,the strength and high temperature resistance ofpure Al was improved.The equilibrium solubility of Er in pure Al was as low as 0.017%at the eutectic temperature.and the equilibrium solid-liquid partition coefficient K=0.0028 which Was far less than 1.According to Sheil model,a great composition supercooling would occur even though the content of Er Was very low,the Al_3Er phase formed in the solid-liquid interface when the content of Er was up to the eutectic composition.Thus Al_3 Er phase acted as heterogeneous nuclear which was firstly crystallized in alloy to make grains refine remarkably.
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