Shigehiko Arai1 and Mitsuru Nagakura1
1Faculty of Engineering, University of Meiji, Kawasaki
A new processing for MnBi permanent magnets was studied. Mn-Bi specimens were obtained by the following processes:
(1) cast into metal mould → magnetic annealing (1 hr at 300°C, 5 kOe) → swaging → magnetic annealing (1 hr at 300°C, 5 kOe), and
(2) cast into metal mould → swaging → magnetic annealing (1 hr at 300°C, 5 kOe).
It was found that the specimens obtained by the process (2) showed desirable magnetic properties for parmanent magnets. In this process, swaging reduced the MnBi compounds to fine particles and caused an increase in coercive force. The following heat treatment in a magnetic field improved the value of 4 π I10K and 4 π Ir without any decrease in coercive force. The value of maximum magnetic energy product was 6.1 MGOe in a 40 at%Mn-Bi alloy swaged to 92% reduction.
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