Bi，Sb合金化对AZ91镁合金组织、性能影响机理研究

利用大角重位点阵模型建立了AZ91镁合金α相［0001］对称倾斜晶界原子结构模型，应用实空间的连分数方法计算了Mg合金的总结构能，合金元素引起的环境敏感镶嵌能及原子间相互作用能，讨论了主要合金元素Al及Bi，Sb在AZ91中的合金化行为.计算结果表明，Al，Bi，Sb固溶于α相内或晶界区使总结构能都降低，起到固溶强化作用；合金元素在AZ91α相内趋于均匀分布，在晶界区易占位于三角椎上部.AZ91镁合金中加入Bi或Sb时，Bi或Sb比Al容易偏聚于晶界，从而抑制了Al在晶界的偏聚，促进基体中连续的Mg₁₇Al₁₂相的析出，提高AZ91合金室温性能； AZ91合金中(α相内和晶界区)主要合金元素Al和微加元素Bi，Sb都能够形成有序相Mg₁₇Al₁₂，Mg₃Bi₂或Mg₃Sb₂，且在晶界区形成的量大.Bi，Sb加入AZ91合金中，由于Bi，Sb抑制Al在晶界的偏聚，晶界区主要析出相为Mg₃Bi₂或Mg₃Sb₂，提高镁合金高温性能. 关键词： 电子理论 合金化 晶界偏聚 镁合组织与性能

A study on the mechanism of the influence of Bi, Sb alloying on microstructure and properties of AZ91 magnesium alloy

The atomic structure model of symmetric ［0001］tilt boundary of α phase in AZ91 magnesium alloy was set up by using the concept of coincidence-site lattice (CSL). The total structure energies of α matrix and grain boundary (GB), the environment sensitive embedding energies (E_ESE) and the interaction energies of Al, Bi and Sb were calculated by using recursion method. The alloying behaviour of Al, Bi, Sb in AZ91 magnesium alloy was discussed. Calculation results show that the total structure energies of α matrix and grain boundary (GB) are decreased due to the presence of Al, Bi or Sb, which suggests AZ91 alloy is strengthened due to solid solution strengthening. Alloying elements tend to be distributed uniformly in α matrix, and are apt to occupy the top sites of the trigonal prism formed by Mg in the GB core. The aggregation of Bi or Sb to GBs,being easier than Al, suppresses the aggregation of Al, which accelerates the formation of continuous precipitates, improves the high temperature properties. The major alloying element Al and the additional elements Bi or Sb in small amounts can form the ordered phases in AZ91 alloys: Mg_１７Al_１２, Mg₃Bi₂ and Mg_３Sb_２, respectively, and the quantity of the ordered phase is greater in GBs than in α(Mg) matrix. Bi or Sb additions to AZ91 retards the aggregation of Al, and Mg₃Bi₂ or Mg_３Sb_２ precipitates along boundaries greatly improve the high temperature properties.