Calculation and Simulation of the Mechanical Properties and Surface Structures for η′ Precipitate in Al-Zn-Mg-Cu Alloys

Existing experiments have shown that in Al-Zn-Mg-Cu alloys, solute Cu, when substituting for Al atoms, can enter the interior of η′ precipitate, changing its composition significantly, but the mechanical properties of the η′ compound containing dissolved Cu has not yet been explored. In this study, we conducted a theoretical prediction to investigate the effect of dissolved Cu on the mechanical properties of the η′ compound (Al4Mg2Zn3). The results indicate that Cu, substituted for Al, tends to reduce the volume, increase the hardness, and raise the Debye temperature of the η′ crystal. Although dissolved Cu weakly increases the brittleness of the crystal, the η′ still retains its ductile nature. Additionally, we simulated the surface structure of the (0001) surface and discovered that there are five distinct surface terminations, namely Al1, Al2, Mg1, Mg2, and Zn. Exact calculations reveal that the surface energies of different terminations are influenced not only by the electronic structure of the surface atoms but also by the distance between the surface layer and the sub-surface layer of the corresponding surface supercell.