Abstract:The process of mechanically assisted hydriding and subsequent thermal dehydriding was proposed to produce nanocrystalline Mg and Mg alloy powders using pure Mg and Mg-5.5%Zn-0.6%Zr (mass fraction) (ZK60 Mg) alloy as the starting materal. The hydriding was achieved by room-temperature reaction milling in hydrogen. The dehydriding was carried out by vacuum annealing of the as-milled powders. The microstructure and morphology of both the as-milled and subsequently dehydrided powders were characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM), respectively. The results show that, by reaction milling in hydrogen, both Mg and ZK60 Mg alloy can be fully hydrided to form nanocrystalline MgH₂ with an average grain size of 10 nm. After subsequent thermal dehydriding at 300 ˚C, the MgH₂ can be turned into Mg again, and the newly formed Mg grains are nanocrystallines, with an average grain size of 25 nm.

Key words: Mg; Mg alloy; hydriding; dehydriching; hydrogen treatment; nanocrystalline