Abstract Alien elemental segregation can pronouncedly change the grain boundary properties. Systematic first-principles calculations were performed to investigate the Mg and Cu segregation behavior at Σ5 (210)[001] symmetrical tilt grain boundary (STGB) in Al. The mechanical properties of Mg or Cu containing Σ5 (210)[001] STGBs were probed by combining a canonical Griffith fracture model with an ab-initio tensile test method. It is found that both Mg and Cu have a large driving force to segregate to Al grain boundaries, with Mg preferentially segregating at symmetric substitutional core sites and Cu at interstitial hollow sites at the grain boundary. Interestingly, Al Σ5 (210)[001] is shown to possess a stronger sink strength of Cu impurities than Mg. Both Mg and Cu segregation leads to a grain boundary expansion and a significant decrease of the grain boundary energy. Calculations show that Mg segregation leads to embrittlement of the STGB, contrary to the cohesion enhancing effect of Cu solutes on Al grain boundaries. The Mg induced embrittlement is due to a combination of “structural effect” ‒ (grain boundary expansion) and “chemical effect” ‒ (charge density depletion). The strengthening effect of Cu solutes lies in the creation of new Cu-Al bonds across the grain boundary, which is considered as a strong contribution to the grain boundary cohesion, thereby increasing its resistance against intergranular cleavage. This work demonstrates how a fundamental theoretical understanding on the atomic and electronic level can rationalize mechanical properties of alloys at the macroscopic scale.

中文翻译：

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Mg、Cu的偏析及其对Al Σ5(210)[001]对称倾斜晶界强度的影响

摘要 外来元素偏析可以显着改变晶界特性。进行了系统的第一性原理计算以研究 Al 中 Σ5 (210)[001] 对称倾斜晶界 (STGB) 处的 Mg 和 Cu 偏析行为。通过将典型格里菲斯断裂模型与 ab-initio 拉伸试验方法相结合，探索了含有 Σ5 (210)[001] STGB 的 Mg 或 Cu 的机械性能。发现 Mg 和 Cu 都有很大的偏析驱动力偏析到 Al 晶界，其中 Mg 优先偏析在对称置换核心位置，而 Cu 偏析在晶界的间隙空心位置。有趣的是，Al Σ5 (210)[001] 显示出比 Mg 具有更强的 Cu 杂质沉降强度。Mg和Cu的偏析都导致晶界扩大和晶界能的显着降低。计算表明，Mg 偏析导致 STGB 脆化，这与 Cu 溶质对 Al 晶界的内聚力增强作用相反。Mg 引起的脆化是由于“结构效应”（晶界膨胀）和“化学效应”（电荷密度耗尽）的组合。Cu 溶质的强化作用在于在晶界上产生新的 Cu-Al 键，这被认为是对晶界内聚力的重要贡献，从而增加了其对晶间解理的抵抗力。这项工作展示了原子和电子水平上的基本理论理解如何在宏观尺度上合理化合金的机械性能。