Microstructure and magnetic properties of Mn-Al-C permanent magnets produced by various techniques

Bulk Mn52Al46C2 in τ-phase was prepared by vacuum induction melting and used as precursor for the production bulk permanent magnets by suction casting and hot-extrusion. Part of the precursor alloy was mechanically milled into a τ-phase powder and used as precursor for production of samples by electron beam melting, hot-compaction and high pressure torsion processes. The microstructure and magnetic properties of all samples were investigated and correlated. It was found that the mechanical deformation enhances coercivity, up to 0.58 T, while the absence of this strain is beneficial for magnetization. Among the observed techniques, hot extrusion and high pressure torsion have shown promising possibilities to further develop Mn-Al-C as permanent magnets. However, it should be taken into account the challenges related to design a proper processing window for hot extrusion and the limitation of HPT regarding the absence of texture.