Dual‐Stage Heat Treatment for Enhanced Hydrogen Storage Properties of Mg−Ni−Y Alloys

ABSTRACT Mg−Ni−Y alloy is considered to be one of the most promising hydrogen storage materials, but its high dehydrogenation energy barrier hinders its practical application. A dual‐stage heat treatment (490°C × 4 h + 550°C × 4 h) is applied to optimize the microstructure and hydrogen storage performance of a vacuum‐melted Mg 94 Ni 3 Y 3 alloy. This process induces a two‐level phase transformation of the long‐period stacking ordered (LPSO) structure (18R + 14H→14H→18R), facilitating Ni/Y atom pre‐distribution via stacking fault recombination at 490°C and promoting a eutectic‐like reaction at 550°C. As a result, a large‐scale eutectic‐like structure composed of finely dispersed and uniformly interwoven Mg 2 Ni and LPSO phases is formed, characterized by a high density of phase boundaries. The optimization of the microstructure directly leads to the enhancement of hydrogen storage performance, as evidenced by a reduction in dehydrogenation activation energy from 139.7 to 113.5 kJ mol −1 and a decrease in enthalpy change from 85.8 to 71.7 kJ mol −1 . This work demonstrates a convenient microstructure regulation strategy, which is expected to advance Mg−Ni−Y alloys toward industrial applications.