Mn-Al-C for permanent magnets (invited)

Mn-Al-C alloy for permanent magnets has merit for several reasons: a) carbon stabilizes the metallurgical phases, deformation temperature is high enough for plastic transformation to produce anisotropic τ-phase efficiently; b) useful magnetic energy exceeds the best hexaferrites; the alloy can be more efficient than Alnico 8 and some other high-cobalt materials; c) Mn sources are more widely distributed and the metal is much less costly to obtain than cobalt. Carbon control and tooling life are key factors to obtain a commercial product. Micrographs illustrate the metallurgical phases. Although Mn-Al-C has a lower temperature coefficient for magnetic flux changes than the hexaferrites, its maximum use will be limited to 100–125 °C. Certain energy-efficient electric motors could be an important application.