Research of Mm(NiMnAlCu)4.9Co0.2 hydrogen storage alloys prepared by cast and rapidly quenched

The rapidly quenched treatment produced significant effects on the electrochemical characteristics of Mm(NiMnAlCu)4.9Co0.2 alloy. It made the activation capability and the discharge capacity decrease, while the cycle stability improved and the degree of the effects increased with increase of the quenching rate. The results of X-ray diffraction analysis showed that the structures of the main phase and secondary phase of Mm(NiMnAlCu)4.9Co0.2 alloy are both of the CaCu5 type, but the lattice constants of two structures have a little difference. The amount of the secondary phase in the as-quenched alloy is very little, and rapidly quenched treatment made the structure of the alloy more homogeneous. The lattice constants of the main phase of the as-quenched alloy are larger than that of the as-cast one. Amorphous and crystal co-exist in the alloy with quenching rate of 15 m/s. The Co content was reduced from 10.0 wt.% to 2.8 wt.% through suitable rapidly quenched treatment, and it is not necessary to add other expensive elements in the alloy.