Prediction of Mg-Zn binary intermetallics from first-principles calculations: Stoichiometries, crystal structures, mechanical and electronic properties

Magnesium-based alloys, as the lightest metallic structural materials, have great potential for applications in the aerospace and automotive industries. Among these, Mg-Zn alloys have received considerable attention due to their significant precipitation strengthening effects. Although extensive experimental and theoretical studies have been conducted to investigate the crystal structures and mechanical properties of precipitates in Mg-Zn alloys, there remains considerable debate about the exact stoichiometry and crystal structures of these precipitates. In this study, the thermodynamic stability, crystal structure, mechanical properties, and electronic structure of intermetallic phases in the Mg-Zn binary system are systematically explored using the variable-composition evolutionary algorithm (USPEX) combined with first-principles calculations. Over 1,700 possible crystal structures were generated by USPEX, and their formation energies were calculated. Four thermodynamically stable phases (Mg2Zn, MgZn, Mg4Zn7, and MgZn2) and one metastable phase (MgZn4) were found. The addition of Zn can significantly enhance the bulk, shear, and Young’s moduli of Mg–Zn intermetallics relative to pure Mg, with MgZn4 showing the highest shear and Young’s moduli. Bader charge and density of states analysis reveal significant charge transfer from Mg to Zn, indicating the ionic bonding and metallic nature in the Mg-Zn system. The results of this study not only confirm the stoichiometries and crystal structures of Mg-Zn intermetallics but also provide theoretical insights into the strengthening mechanisms of Mg-Zn alloys and for the design of new high-performance alloys.