The protium absorption properties of Mg-Al-Cu, Mg-Al-Ni, and Mg-Al-Si alloys have been investigated in conjunction with microstructures and the phases present. The alloys were prepared by a flux-melting technique. Mg-Al-Cu as-cast alloys were found to consist of Mg, MgAlCu, and Mg17Al12 phases. In addition to the Mg phase, the Mg17Al12 phase also contributed to the protium absorption by undergoing a disproportionation reaction. The protium absorption capacity of these Mg-Al-Cu alloys ranged from 2.2 to 4.6 mass% at 623 K, and was found to be controlled by the amount of Mg and Mg17Al12 phases present. For the Mg-25Al-5Ni and Mg-25Al-5Si as-cast alloys, Mg and Mg17Al12 phases were found to be present. In addition, a Mg2Si phase was observed in the Mg-25Al-5Si alloy. The protium absorption capacities of the Mg-25Al-5Ni and Mg-25Al-5Si alloys were 3.6 and 3.9 mass%, respectively. Unlike the Mg-Al-Cu alloys, the Mg17Al12 phase in Mg-Al-Ni and Mg-Al-Si alloys partially remained even after protium absorption. This difference in disproportionation behavior seems to be due to the small amount of solute elements in the Mg17Al12 phase, and/or to the microstructure.
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