Anisotropic bulk rare-earth-free Mn-Al-(C) magnets prepared under high-stress and large-strain conditions

Fabricating anisotropic bulk rare-earth (RE)-free magnets with both crystallographic texture and refined grains is a difficult task. In this paper, an anisotropic bulk Mn-Al-(C) RE-free magnet with a (00 l) crystallographic texture was fabricated using the confined deformation under high-stress and large-strain conditions during the phase transformation from hexagonal ε-phase to tetragonal τ-phase. XRD patterns and TEM images of the magnets revealed that the τ-phase with grain sizes of 150–200 nm is the predominant phase and that the magnets exhibit a (00 l) texture perpendicular to the pressure direction. The deformed magnets have an obvious magnetic anisotropy and enhanced remanence perpendicular to the pressure direction due to the texture formation. The effects of deformation temperature (T_d) and time (t) on microstructures and magnetic properties of these magnets were investigated, and optimal magnetic properties, with a coercivity of 239 kA/m (3 kOe) and energy product of 14.5 kJ/m³ (1.82 MGOe), were obtained at T_d = 550 °C and t = 60 s. Our work is of importance for future development of high-performance anisotropic bulk RE-free magnets.