The hydriding of as-cast Mg-5.5%Zn-0.6%Zr(ZK60 Mg)(mass fraction)alloy was achieved by room-temperature reaction milling in hydrogen,with the mechanical energy serving as the driving force for the process.The hydriding progress during milling was examined by hydrogen absorption measurement,and the microstructure change was characterized by X-ray diffraction analysis(XRD),scanning electron microscopy(SEM),and transmission electron microscopy(TEM),respectively.The results show that,by room-temperature reaction milling in hydrogen,the as-cast ZK60 Mg alloy can be fully hydrided to form a nanocrystalline MgH_(2) single-phase microstructure.In particular,the average grain size of the MgH_(2) phase obtained by room-temperature reaction milling in hydrogen for 16.2 h is about 8-10 nm,and the average particle size of the as-milled hydrided powders is 2-3μm.
In order to optimize the dehydriding process for producing nanocrystalline Mg alloy powders by hydriding-dehydriding treatment,nano-structured as-hydrided Mg-3%Al-1%Zn(AZ31 Mg)(mass fraction)alloy powders were thermally dehydrided at various temperatures from 275 to 375℃.The kinetics of hydrogen desorption was examined by hydrogen discharge measurement during dehydriding.The microstructure of the as-hydrided and the subsequently fully dehydrided alloy powders was investigated by X-ray diffraction analysis(XRD)and transmission electron microscopy(TEM),respectively.Both the desorption kinetics and the grain size of the alloy after complete dehydriding were found to be strongly dependent on the processing temperature.The higher the temperature,the faster the desorption,and the more significant the grain growth.When the desorption temperature was raised from 300 to 375℃,the time to achieve complete dehydriding was shortened from 190 to 20 min,and the average grain size increased correspondingly from 20 to 58 nm.
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℃,the MgH2 can be turned into Mg again,and the newly formed Mg grains are nanocrystallines,with an average grain size of 25 nm.
