Abstract:β？(Mg₅Al₂Si₄) phase is the main strengthening phase in 6000-series aluminum alloys. The effect of Cu-doping on the geometrical structure, the phase stability and the electronic properties of β？(Mg₅Al₂Si₄) phase were investigated by using projector augmented wave method and the generalized gradient approximation based on density functional theory. The results show that the calculated equilibrium lattice parameters of β？ phase are in good agreement with available experimental results. After Cu incorporates into β？ phase, the cell shape changes slightly and the cell volume decreases. Various doping contents and doping sites result in various geometrical properties of Cu-doped structures, which then impacts the lattice mismatch between β？ and Al matrix. The structures in which Cu atoms replace both Mg1 and Al atoms, or only replace Al atoms are easier to form in the alloys, while it is harder to form in the alloys for the structures, in which Cu atoms only replace Mg1 atoms, which is supported by experimental results. The analysis of electronic structures shows that the phase stability of the Cu-doped structures Mg_5-xAl_2-ySi₄Cu_x+y is closely related to the pseudo gap near the Fermi level.

Key words: first-principles; 6000-series aluminum alloys; strengthening β？ phase; phase structure stability; Cu-doping