| Summary: | 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 Al<sub>2</sub>Cu (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 Al<sub>2</sub>CuMg<sub>X</sub> phase change with the concentration of Mg doping (X = 2, 4, 6, and 8). The cohesive energy calculation and electronic structure analysis show that Al<sub>2</sub>CuMg<sub>6</sub> has a high structural stability. The criterion based on elastic constants indicates that Al<sub>2</sub>CuMg<sub>2</sub>, Al<sub>2</sub>CuMg<sub>4</sub>, and Al<sub>2</sub>CuMg<sub>8</sub> have a brittle tendency and show strong anisotropy of mechanical properties, while Al<sub>2</sub>CuMg<sub>6</sub> shows better comprehensive mechanical properties. The thermodynamic analysis results based on the quasi-harmonic Debye model show that the Al<sub>2</sub>CuMg<sub>6</sub> precipitated phase has good stability at high temperatures and pressure.
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