Effect of Mg content on Cu precipitation behavior in Al-Cu-Mg ternary alloy by molecular dynamics simulation

To analyze the mechanism of the Mg content on Cu precipitation in Al-Cu-Mg ternary alloy, the microstructure evolution of Al-5%Cu, Al-5%Cu-1%Mg and Al-5%Cu-2%Mg alloys during the solidification process was investigated by both the molecular dynamics simulation and solidification experiment methods. The simulated results demonstrate that the introduction of Mg accelerates atomic diffusion. And as the Mg content increases, more large-sized Cu agglomerates are formed in the solidified tissue, due to the Mg plays a connecting role in the process of Cu agglomerate formation. It is also found that the introduction of Mg results in the development of more FCC phases in the final tissue. The experimental results show that Cu elements are concentrated in the Al crystal boundaries, and the degree of Cu enrichment increases with the level of Mg content. The physical phase analysis shows that the final organization is primarily composed of the Al phase and Al2Cu phase, and both phases increase slightly with a higher Mg rate. The consistency between experimental and simulation results was verified by a comparative discussion of the Cu agglomerated and precipitated phases. It provides a theoretical basis for improving Al-Cu-Mg alloys' performance enhancement and structural optimization.