AI 中文总结
本研究通过GDOES实验和DFT计算，揭示了增材制造Al-Mg-Si-Zr合金近表面Mg富集源于强偏析驱动力和氧吸附促进的扩散，为理解其表面化学提供了原子尺度机制。
AI 中文摘要
增材制造铝合金的表面化学性质对其耐腐蚀性和与外部材料的连接性能起着关键作用。本研究采用辉光放电发射光谱（GDOES）深度剖析技术，表征了激光粉末床熔融（PBF-LB/M）工艺制备的Al-Mg-Si-Zr合金的近表面元素组成。测量结果显示，近表面区域（延伸至约10微米，与表面粗糙度的特征尺度一致）存在显著的Mg富集，同时氧浓度增加，而Al、Si和Zr在更深处趋于稳定的类体相水平。为了在原子尺度上理解这一现象，基于密度泛函理论（DFT）的第一性原理计算在低指数Al表面上进行。计算结果表明，Mg表面偏析存在强烈的热力学驱动力，扩散能差范围约为-0.30 eV至-0.41 eV，而Zr则表现出明显倾向于保留在基体内部。空位迁移计算进一步表明，完全的结构弛豫显著降低了Mg的迁移势垒至低于Si的水平，这使得Mg扩散在动力学上极为有利。此外，吸附的表面氧极大地促进了Mg向表面扩散的趋势，将Mg的扩散能差降低至多达-3.0 eV。这促进了局部重构的Mg-O-Al配位前驱体结构的形成，并伴随电子局域函数分析所显示的局部电子转移。
英文摘要
The surface chemistry of additively manufactured aluminum alloys plays a critical role in corrosion resistance and joining with external materials. In this work, the near-surface elemental composition of a laser powder bed fusion (PBF-LB/M) processed Al-Mg-Si-Zr alloy was characterized by glow discharge optical emission spectroscopy GDOES depth profiling. The measurements reveal pronounced Mg enrichment within the near-surface region extending to approximately 10 μm, consistent with the characteristic scale of surface roughness, together with an increase in oxygen concentration, whereas Al, Si, and Zr approach stable bulk-like levels at greater depths. To understand this observation on the atomic scale, first-principles calculations based on density functional theory (DFT) were performed on low-index Al surfaces. The calculated results show a strong thermodynamic driving force for Mg surface segregation, with diffusion energy differences ranging from approximately -0.30 eV to -0.41 eV, while Zr exhibits a pronounced preference for remaining in the bulk matrix. Vacancy migration calculations further demonstrate that full structural relaxation substantially reduces the migration barrier for Mg to below that of Si, which makes Mg diffusion kinetically highly favorable. Moreover, the presence of adsorbed surface oxygen dramatically promotes the tendency of Mg to diffuse toward the surface, which lowers the diffusion energy difference of Mg to as much as -3.0 eV. This promotes the formation of a locally reconstructed Mg-O-Al coordinated precursor structure accompanied by localized electron transfer shown by an electron localization function analysis.
Comments14 pages, 6 figures
