The Y1-xMgxNi 2.1 (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) alloys were prepared by the sintering method. XRD, EPMA, and Sieverts’methods were used to study the influence of Mg partial substitution of Y on the alloys phase structure and hydrogen storage properties. It was found that with the increase of Mg substitution, the (Y, Mg)Ni2 phase abundance increases and the total amount of (Y, Mg)Ni3 and (Y, Mg)2Ni7 phases first increases and then decreases. The Mg content in the (Y, Mg)Ni2 phase is higher than that in the (Y, Mg)Ni 3 and (Y, Mg)2Ni7 phases. The stable hydrogen absorption capacity first increases and then decreases. When x = 0.1, the maximum stable hydrogen absorption is 1.55 wt.%. The increase of Mg content in the (Y, Mg)Ni 2 phase and the presence of the (Y, Mg)Ni3 and (Y, Mg)2Ni 7 phases in the alloys can suppress the capacity decay. When x ≥ 0.2, no significant changes in phase structure are observed, and the capacity decay rate is less than 5%. The PCT curve shows that with the increase of Mg content, the plateau pressure and hydrogen absorption capacity of the (Y, Mg)Ni2 phase gradually increase. When x ≥ 0.4, the PCT curves of the alloy transform into a single plateau for hydrogen absorption and desorption
