Phase transitions and hard magnetic properties for rapidly solidified MnAl alloys doped with C, B, and rare earth elements

MnAl alloys are attractive candidates to potentially replace rare earth hard magnets because of their superior mechanical strength, reasonable magnetic properties, and low cost. In this study, the phase transitions and magnetic properties of melt spun Mn(55)Al(45) based alloys doped with C, B, and rare earth (RE) elements were investigated. As-spun Mn-Al, Mn-Al-C, and Mn-Al-C-RE ribbons possessed a hexagonal epsilon crystal structure. Phase transformations between the epsilon and the L1(0) (tau) phase are of interest. The epsilon -> tau transformation occurred at similar to 500 A degrees C and the reversed tau A -> A epsilon transformation was observed at similar to 800 A degrees C. Moderate carbon addition promoted the formation of the desired hard magnetic L1(0) tau-phase and improved the hard magnetic properties. The Curie temperature T (C) of the tau phase is very sensitive to the C concentration. Dy or Pr doping in MnAlC alloy had no significant effect on T (C). Pr addition can slightly improve the magnetic properties of MnAlC alloy, especially J(S). Doping B could not enhance the magnetic properties of MnAl alloy since B is not able to stabilize either the epsilon phase or the L1(0) hard magnetic tau phase.