Discovery of Mg₃Zn₂ Intermetallic Phase in the Mg-Zn System Enabled by Neuroevolution Potentials

Magnesium-zinc (Mg-Zn) alloys derive much of their mechanical strength from the formation and evolution of intermetallic compounds. However, the Mg-rich and intermediate compositional regimes remain insufficiently resolved structurally, hindering a comprehensive and phase-consistent understanding of phase stability and its role in microstructural strengthening. Here, we develop a high-accuracy neuroevolution potential (NEP) for the Mg-Zn system by integrating an active-learning strategy with the CALYPSO structure-search method, enabling systematic exploration of complex configurational phase space with near-first-principles accuracy. Extensive NEP-assisted structure searches reproduce all experimentally established Mg-Zn intermetallic phases and predict a previously unreported thermodynamically stable Mg₃Zn₂ phase with P4₂/mnm symmetry, together with a metastable I4/mcm-Mg₂Zn phase. Mg₃Zn₂ is a plausible candidate constituent phase, as a selected simulated X-ray diffraction feature is consistent with an unassigned peak previously reported in multiphase Mg-Zn alloys. Additionally, Mg₃Zn₂ exhibits superior thermal robustness, retaining higher strength and hardness at elevated temperatures compared with the widely studied MgZn₂. These results demonstrate the effectiveness of NEP-assisted structure prediction in resolving hidden intermetallic phases and establishing systematic structure-property relationships in chemically complex alloy systems.