Silicon (Si) is an inevitable impurity element in the AZ31 alloy. In this study, the Si impurity was detected mainly as fine Mg₂Si particles dispersed widely within the central region of the Mg₁₇Al₁₂ phase. During the solidification process, the Mg₂Si particle precipitates at about 565 °C, before the Mg₁₇Al₁₂ phase of 186 °C, potentially acting as the heterogeneous nucleation core for the Mg₁₇Al₁₂ phase. The orientation relationship between Mg₂Si and Mg₁₇Al₁₂ was investigated using the Edge-to-Edge matching model (E2EM) calculations, which showed a misfit of only 0.1 %. This low misfit suggests that Mg₂Si can serve as a heterogeneous nucleation site for Mg₁₇Al₁₂. The surface and interface structures of Mg₂Si (220) and Mg₁₇Al₁₂ (332) were constructed, and then investigated through the first-principles calculation. The theoretical results indicate that Mg and Al are easily adsorbed on the surface of Mg₂Si, with Al showing higher adsorption energy than Mg. Furthermore, the interface between Mg₂Si and Mg₁₇Al₁₂ exhibits favorable thermodynamic stability. Combined with experiments and theoretical calculations, it is confirmed that the Mg₂Si particles, formed due to the Si impurity, provide effective heterogeneous nucleation sites for the Mg₁₇Al₁₂ phase.

中文翻译：

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揭示 Mg17Al12 对商用 AZ31 合金中杂质 Mg2Si 颗粒的非均相形核机制


硅 （Si） 是 AZ31 合金中不可避免的杂质元素。在本研究中，Si 杂质主要以广泛分散在 Mg₁₇Al₁₂ 相中心区域内的细小 Mg₂Si 颗粒的形式进行检测。在凝固过程中，Mg₂Si 颗粒在大约 565 °C 时析出，然后是 186 °C 的 Mg₁₇Al₁₂ 相，可能充当 Mg₁₇Al₁₂ 相的非均相形核核心。使用边到边匹配模型 （E2EM） 计算研究了 Mg₂Si 和 Mg₁₇Al₁₂ 之间的取向关系，结果显示失配仅为 0.1%。这种低失配表明 Mg₂Si 可以作为 Mg₁₇Al₁₂ 的异质成核位点。构建了 Mg₂Si （220） 和 Mg₁₇Al₁₂ （332） 的表面和界面结构，然后通过第一性原理计算进行了研究。理论结果表明，Mg 和 Al 很容易吸附在 Mg₂Si 的表面，其中 Al 的吸附能高于 Mg。此外，Mg₂Si 和 Mg₁₇Al₁₂ 之间的界面表现出良好的热力学稳定性。结合实验和理论计算，证实由于 Si 杂质形成的 Mg₂Si 颗粒为 Mg₁₇Al₁₂ 相提供了有效的非均相成核位点。