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

Abstract

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 ε phase with ∼93 % bulk density. A 450 °C anneal for 30 min transformed the ε phase into largely the ferromagnetic τ phase. The magnetic properties were compared to an as-cast reference bulk Mn54Al46 sample prepared from ε phase via the same heat treatment. The LPBF sample exhibited a finer grain size, a ∼45 % gain in coercivity, and higher remanence due to grain elongation and a weak <001>τ texture parallel to the printing direction. Despite the loss of density, the LPBF sample had a ∼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 τ 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 Mr = 41 Am2/kg, Hci = 129 kA/m, and (BH)max = 7.2 kJ/m3 along the print direction.