Mn-Al-C alloy is well known as a material for anisotropic magnets containing no expensive elements such as rare earth element or Co. The Mn-Al-C magnets show excellent performance in terms of high strength, good machinability, good corrosion resistance, etc. Mn-Al-C alloy magnet has been fabricated by the gas atomized powder extrusion process since 1989.
The magnetic properties of Mn-Al-C alloy extruded from gas atomized powder depend on the solidification rate of powder during atomization. Two exothermic peaks were observed at 760K and 820K by differential thermal analysis of gas atomized powder. Two exothermic peaks indicate that the ε→τ phase transformation occured in the different Mn content regions of ε phase. In this work, we investigated the phase transformation behaviors of gas atomized powder below 723K. It was found that in the first stage of ε→ τ transformation, ε→ε'→ τ transformation occurred with the activation energy of Q=277kJ/mole. The effects of Ni addition on ε→τ transformation were investigated between 673K and 723K. The activation energy was not affected by Ni addition, but small addition of Ni reduced the frequency factor.