Effects of the materials processing on the hydrogen absorption properties of MmNi(5) type alloys

The effects of heat treating conditions on the hydrogen absorption characteristics of low-cost cobalt-free Mm(Al-Mn-Fe-Ni-Cu)(5+x) alloys were investigated. The alloys were prepared by induction melting and water cooling and thermally treated at temperatures between 1153 and 1353 K in vacuo. For the stoichiometric alloy of Mm(Al-Mn-Fe-Ni-Cu)(5), brittleness was increased abruptly by heat treatment at temperatures above 1300 K; however, electrochemical deterioration was not much influenced by the thermal treatment conditions. For over-stoichiometric alloys a segregation into an iron-rich secondary phase could be seen after a heat treatment at 1153 K. The segregation disappeared and a single phase was attained in an alloy prepared at 1353 K. The hydrogen absorption characteristics were, therefore, strongly dependent on the thermal treatment conditions.