低溶质浓度极限下Al-Mg合金的从头算高压相图
Ab initio High-Pressure Phase Diagrams of Al-Mg Alloys in the Low Solute Concentration Limit
AI总结：
该研究采用从头算方法计算了Al-Mg合金低压溶质极限下的高压相图，揭示了富Mg侧Al的固液分配随压力反转的新规律，对行星内部模型有重要意义。
AI中文摘要：
高压下二元合金相图对理解工程材料和行星内部的凝固与化学分异至关重要，但在极端条件下通过实验测定该相图的难度会显著增加。我们采用基于密度泛函理论的全从头算方法[J. Chem. Phys. 162, 184502 (2025)]，计算了Al-Mg体系从常压到150 GPa的稀极限相图。作为第一步，我们计算了纯面心立方（fcc）Al和纯六方最密堆积（hcp）/体心立方（bcc）Mg的熔化曲线，其中包含Mg的hcp-bcc相界和三相点，所有结果均与现有实验数据吻合良好。随后在两个组分极限下构建了二元相图：在富Al侧，Mg在整个压力范围内始终倾向于液态，且这种偏好随压缩单调增强；在富Mg侧，Al在常压下优先分配到液态，但在约60 GPa以上发生完全反转，当Mg基体从hcp转变为bcc后，Al转为倾向于固态。这种压力驱动的反转将富Mg共存场的拓扑结构从传统的向下倾斜相界反转为向上倾斜，对行星分异和内部化学分层模型具有直接意义。
英文摘要：
Binary alloy phase diagrams at high pressure are essential for understanding solidification and chemical partitioning in both engineered materials and planetary interiors, yet their experimental determination becomes increasingly challenging under extreme conditions. We apply a fully ab initio approach [J. Chem. Phys. 162, 184502 (2025)], based on density-functional theory, to compute the dilute-limit phase diagram of the Al-Mg system from ambient conditions up to 150 GPa. As a first step, we calculate the melting curves of pure fcc Al and pure hcp/bcc Mg, including the hcp-bcc phase boundary and triple point of Mg, all of which agree closely with available experimental data. The binary phase diagram is then constructed at both compositional extremes. On the Al-rich side, Mg consistently favours the liquid throughout the entire pressure range, with this preference strengthening monotonically under compression. On the Mg-rich side, Al partitions preferentially into the liquid at ambient pressure but undergoes a complete reversal above ~60 GPa, becoming solid-favouring as the Mg host transitions from hcp to bcc. This pressure-driven reversal inverts the topology of the Mg-rich coexistence field from a conventional downward-sloping to an upward-sloping phase boundary, and has direct implications for models of planetary differentiation and interior chemical stratification.
