Abstract
The MnAl alloy is most succesfully melted in an alumina crucible by a high frequency induction furnace under argon atmosphere. The alloy containing 68 to 70 wt% Mn exhibits the highest saturation magnetization in this system. The ferromagnetic phase (π-phase) can be prepared by quenching and subsequent tempering. The adequate quenching temperature is 1100°C to 1150°C. When the quenched MnAl is tempered at a temperature not exceeding 500°C, its saturation magnetization increases with time and approaches a common limiting value. The higher the temperature is, the faster it reaches the limit. For example, at 500°C, the limiting value is attained within a few tens of minutes. Although the specimen tempered above 500°C loses its magnetic properties after a very rapid increase in saturation magnetization, the peak value is rather higher than the limiting value in the lower temperature tempering. The X-ray diffraction and microstructure show that the ferromagnetic phase thus obtained is entirely the same as that obtained by Kono’s “controlled cooling”.
