Abstract: The La-Mg-Ni system (PuNi₃-type) hydrogen storage alloys La₂Mg(Ni_0.85Co_0.15)₉B_x (x = 0, 0.1, 0.2) were prepared by casting and rapid quenching. The microstructures and electrochemical cycling stabilities of the as-cast and quenched alloys were determined and measured. The effects of boron content and quenching rate on the microstructures and electrochemical cycling stabilities of the alloys were investigated. The results show that the as-cast and quenched alloys are composed of the (La, Mg)Ni₃ phase (PuNi₃-type structure), the LaNi₅ phase and the LaNi₂ phase. A trace of the Ni₂B phase exists in the as-cast alloys containing boron, and after the as-cast alloys are quenched when quenching rate is more than 15m/s, the Ni₂B phase in the alloys nearly disappears. The relative amount of each phase in the alloys changes with the variety of the quenching rate. The addition of boron enhances the cycle stability of the as-cast and quenched alloys, but the mechanism is completely different. The cycle lives of the as-quenched alloys increase with the increasing quenching rate, but the improvement of the rapid quenching treatment on the cycling stability of La-Mg-Ni system hydrogen storage alloys is very limited.

Key words: La-Mg-Ni system electrode alloy; rapid quenching technology; microstructure; cycling stability