Activation-induced microstructural refinement in Mg–Ni–Y alloys for rapid dehydrogenation and stable cycling

Rapid hydrogen exchange in compacted Mg-based materials is essential for extending their application beyond loose powders. In this work, Mg–Ni–Y alloy compacts were prepared by casting, mechanical filing and powder pressing to investigate the relationship between microstructural evolution and hydrogen sorption performance. The initial alloy consisted of Mg, Mg 2 Ni and a minor 18R-type long-period stacking ordered (LPSO) phase. Following activation, the LPSO phase was no longer detected, and the dehydrogenated material exhibited a Mg matrix containing finely dispersed Mg 2 Ni particles and YH 2 nanoparticles. The activated material released 5.5 wt.% H 2 within 4.5 min at 300 °C and 4.5 wt.% H 2 within 40 min at 240 °C. Johnson–Mehl–Avrami–Kolmogorov fitting combined with Arrhenius analysis yielded an apparent desorption activation energy of 95.5 kJ mol −1 . Hydrogen capacity retention reached 98.2% after 30 cycles, with largely unchanged sorption kinetics. Post-cycling XRD and TEM analyses revealed a stable dehydrogenated phase assemblage and no obvious coarsening of the dispersed secondary phases in the examined regions. These findings highlight the association between microstructural preservation and sustained hydrogen sorption performance, providing guidance for designing Mg-based hydrogen-storage materials through the formation and stabilization of finely dispersed multiphase microstructures.