Stability and Electronic Structure of Different Nanophases/Al Interfaces in Al–Cu–Li Alloys: A First-Principles Perspective

The mechanical performance of precipitation-strengthened aluminum alloys is governed by the interfacial stability and electronic configurations of precipitates. This study systematically investigated the stability and electronic structure of interfaces between the matrix and nanophases (δ'-Al₃Li, θ'-Al₂Cu, and T₁-Al₆Cu₄Li₃) in Al-Cu-Li alloys. The research was conducted by using first-principles calculations. The results indicate that the formation enthalpy of the T₁ phase was the lowest, rendering it the most thermodynamically stable. The δ' phase, with a low nucleation barrier, precipitates preferentially, while the T₁ phase gradually becomes the dominant equilibrium phase upon prolonged aging. Regarding surface energy, the δ'(001)-AlLi and T₁(001)-AlLi terminals exhibit significantly lower surface energies than other terminal configurations, suggesting a strong stability of the Li-terminal surfaces. The surface energy of the θ' phase was significantly influenced by Cu concentration in the matrix. Interface models with different terminals and stacking sequences exhibit distinct variations in interface energy and separation work. Specifically, the δ'(001)-AlLi (Bridge) interface in the Al/δ'/Al configuration displays the lowest interface energy and the highest separation work, indicating the optimal bonding strength. In the Al/θ'/Al and Al/T₁/Al interfaces, the presence of Cu-Al bonds significantly enhances the interface stability. The Al-Al and Cu-Al metallic bonds at the interface form strong interactions through high-charge-density regions, while the Al-Li interface, characterized by lower charge density, predominantly relies on van der Waals forces, resulting in weaker bonding. The shear modulus and hardness of the precipitate phases were significantly higher than those of the matrix; however, precipitates dominated by covalent bonds may reduce the material's ductility. This study provided theoretical insights into the optimization of precipitate phases and interface design in Al-Li alloys and highlights the crucial role of electronic rearrangement and bonding characteristics at the interface in the material strengthening mechanism.