Influence of Mg Doping on the Structure and Mechanical Properties of Al2Cu Precipitated Phase by First-Principles Calculations

Al-Cu-Mg high-strength alloys are widely used in industrial production because of their excellent mechanical performance and good machining properties. In this study, first-principles calculations based on density functional theory were carried out to investigate the influence of Mg doping on the structural stability and mechanical properties of the Al₂Cu (θ) precipitated phase in Al-Cu-Mg alloys. The results show that the structural stability, electronic structure, bulk modulus, mechanical anisotropy, and thermodynamic properties of the precipitated Al₂CuMg_X phase change with the concentration of Mg doping (X = 2, 4, 6, and 8). The cohesive energy calculation and electronic structure analysis show that Al₂CuMg₆ has a high structural stability. The criterion based on elastic constants indicates that Al₂CuMg₂, Al₂CuMg₄, and Al₂CuMg₈ have a brittle tendency and show strong anisotropy of mechanical properties, while Al₂CuMg₆ shows better comprehensive mechanical properties. The thermodynamic analysis results based on the quasi-harmonic Debye model show that the Al₂CuMg₆ precipitated phase has good stability at high temperatures and pressure.