Additive manufacturing of Mn-Al permanent magnets via laser powder bed fusion

Permanent magnet materials based on Mn demonstrate high potential to fill the gap between lower-performance bonded ferrites and high-performance magnets based on rare-earth elements. Mn-Al permanent magnets were processed into bulk via the laser powder bed fusion (LPBF) technique. Gas-atomized Mn54Al46 precursor particulates were fused into cube-shaped magnets of the high-temperature epsilon phase with similar to 93 % bulk density. A 450 degrees C anneal for 30 min transformed the epsilon phase into largely the ferromagnetic tau phase. The magnetic properties were compared to an as-cast reference bulk Mn54Al46 sample prepared from epsilon phase via the same heat treatment. The LPBF sample exhibited a finer grain size, a similar to 45 % gain in coercivity, and higher remanence due to grain elongation and a weak <001>(tau) texture parallel to the printing direction. Despite the loss of density, the LPBF sample had a similar to 70 % improvement in (BH)(max) compared to the as-cast bulk reference sample. The success of this process demonstrates that the LPBF technique is a viable method to densify the metastable Mn-Al tau phase from particulate into bulk while retaining a fine grain size, developing magnetic anisotropy, and preventing phase decomposition. Optimal properties of the LPBF magnet were M-r = 41 Am-2/kg, H-ci = 129 kA/m, and (BH)(max) = 7.2 kJ/m(3) along the print direction.