The effect of equal channel angular pressing on hydrogen storage properties of a eutectic Mg–Ni alloy

A multipass equal channel angular pressing (ECAP) technique was applied to as-cast eutectic MgNi alloy to refine its microstructure down to sub-micrometer size of Mg and Mg2Ni grains. This grain refinement was achieved after 10 ECAP passes. The Mg grains showed supersaturation in Ni, which was non-homogeneously distributed across the grains. All samples studied exhibited a gravimetric hydrogen storage capacity of about 6 wt.%. The pressure-composition isotherms for the hydrogenation of as-cast and ECAP processed alloys were determined. It was shown that equilibrium hydrogen desorption pressure increases with increasing number of ECAP passes, the alloy processed by 10 ECAP passes exhibiting approximately 50% pressure increase over its as-cast counterpart. The ECAP processed alloy exhibited an excellent hydrogen desorption kinetics, desorbing 5 wt.% of hydrogen in less than 5 min at the temperature lower than 573 K. It was also shown that in terms of hydrogen desorption pressure the ECAP treated MgNi alloy outperforms the alloys of similar composition nanostructured by alternative processing techniques.