Influence of the ECAP and HEBM processes and the addition of Ni catalyst on the hydrogen storage properties of AZ31-x Ni (x=0,2,4) alloy

Abstract

In this work, the hydrogen sorption properties of AZ31 magnesium alloys with various additions of nickel (Ni) (i.e., Ni (X = 0, 2, 4) wt.%) were investigated. Cast ingots with different AZ31/NiP compositions were fabricated using a gravitating mechanical stir casting (GMSC) method. Two different processes, namely, equal channel angular pressing (ECAP) and high energy ball milling (HEBM) were performed to improve its hydrogen storage properties. The particle size of the sample powders were measured by laser diffraction analysis. The microstructures, powder morphologies, and phase transformation were characterized by optical microscopy (OM), scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis. The hydrogen sorption kinetics were measured by a Sievert's type apparatus. The results showing the impact of the ECAP and HEBM processes on the hydrogen storage properties were compared. The AZ31-4 Ni ECAP processed sample showed a maximum hydrogen storage capacity of 7.0 wt.% at 2322 s with complete desorption of all the hydrogen in less than 5 min at a temperature of 375 °C. On the other hand, the pure AZ31 alloy which was treated with the HEBM process showed the maximum hydrogen capacity of 6.5 wt.% at 2393 s with desorption of all the hydrogen within 6 min. In addition, the activation energy, as illustrated by the Kissinger plot, revealed that the activation energy of the ECAP processed AZ31-4 Ni was 104.73 (KJ/mol), obviously lower than the material processed by HEBM and pure MgH2.