Hydrogen storage performance and phase transformations in as-cast and extruded Mg-Ni-Gd-Y-Zn-Cu alloys

Abstract

Thermal-mechanical processing of magnesium-based materials is an effective method to tailor the hydrogen storage performance. In this study, Mg-Ni-Gd-Y-Zn-Cu alloys were prepared by Direct Chill (DC) casting, with and without extrusion process. The influences of microstructure evolution, introduced by DC casting and thermal-mechanical processing, on the hydrogen storage performance of Mg-Ni-Gd-Y-Zn-Cu alloys were comprehensively explored, using analytical electron microscopy and in-situ synchrotron powder X-ray diffraction. The result shows that the extruded alloy yields higher hydrogen absorption capacity and faster hydrogen ab/desorption kinetics. As subjected to extrusion processing, the α-Mg grains in the microstructure were significantly refined and a large number of 14H type long-period stacking ordered (LPSO) phases appeared on the α-Mg matrix. After activation, there were more nanosized Gd hydride/Mg2Ni intermetallics and finer chips. These modifications synergistically enhance the hydrogen storage properties. The findings have implications for the alloy design and manufacturing of magnesium-based hydrogen storage materials with the advantages of rapid mass production and anti-oxidation.