Abstract: With the aim to evaluation of the substituent effects of Mg, Ag, Si on the Al-Cu alloy, the structural stabilities, electronic and mechanical properties of AlCu₃ alloy and the substituted structures Al₇Cu₂₄X and Al₈Cu₂₃X (X=Mg, Ag, Si) in Al or Cu sites were explored by first-principles calculations. The computational results show that the X (X=Mg, Ag, Si) substitution have minimal influence on the AlCu₃ crystal structure, and the three doped elements tend to replace the position of Cu atoms. All Al₇Cu₂₄X and Al₈Cu₂₃X (X=Mg, Ag, Si) satisfy the criteria of thermodynamical and mechanical stabilities, so Al₇Cu₂₄X and Al₈Cu₂₃X (X=Mg, Ag, Si) alloys exhibit high structural stabilities. The density of states and charge density differences demonstrate that all doped Al₇Cu₂₄X and Al₈Cu₂₃X (X=Mg, Ag, Si) structures still maintain noticeably metallic characteristics of the AlCu₃ alloy. The valence electron orbitals of Cu 3d provide dominant contributions to the total density of states of the AlCu₃ intermetallic compounds, and the doped Si and Mg atoms have slight effect on the AlCu₃ alloy, while the Ag atom enhances the interatomic bonding on account of the existence of electrons in 4d orbitals. The mechanical properties indicate that the doped Mg atom effectively improves the ductility and plasticity of the AlCu₃ alloy, and Mg, Ag and Si doped structures are ductile materials with anisotropy. Therefore, the alloying with Mg, Ag and Si doping improves the hardness and deformation resistance of AlCu₃ alloy, which could effectively improve the mechanical properties.

Key words: intermetallic compounds, AlCu₃ alloy, electronic structure, mechanical properties, first-principles calculations