Abstract
Bulk Mn-Al-C magnets have been prepared by hot-compaction, microwave sintering and hot-deformation. Powders of Mn53.5Al44.5C2 alloy in the ε-phase produced by high energy ball milling have been used as precursor for the hot-compacted and microwave sintered magnets. Hot-deformed magnets were produced from alloy pieces in the τ-phase. The hot-compacted magnet exhibits magnetization, remanence and coercivity of 50 emu/g, 28 emu/g and 3.3 kOe, respectively. Microwave sintered magnet shows a maximum magnetization of 94 emu/g, remanence of 30 emu/g and coercivity of 1.1 kOe. The best magnetic properties are obtained in hot-deformed magnets with magnetization, remanence, coercivity and energy product of 82 emu/g, 50 emu/g, 2.2 kOe and 1.8 MGOe, respectively. Hot-deformed magnets exhibit texture with the highest degree of texture obtained 0.26. It is found that the pressure applied during compaction/deformation favors coercivity.
Highlights
Volatile rare-earth (RE) metal prices, environmental concerns involving the RE-metal extraction, and geopolitical issues joined by the large coercivity (Hc) gap existing between alnico/ferritebased magnets and RE-based magnets created a need to reinvestigate the Mn-Al based magnets, first reported by Koch et al in 1960, for the development of a non-rare earth magnet competing with the medium performance Nd-Fe-B magnets.[1,2,3]
The X-ray diffraction (XRD) patterns of the heat-treated powder show peaks belonging to τ, β- and γ2-phases and sharper peaks indicating grain growth and stress relief, that cause an increase in magnetization after the heat-treatment
The Mn53.5Al44.5C2 alloy powder produced by high energy ball milling in ε-phase was used as precursor for the hot-compaction and microwave sintering
Summary
Volatile rare-earth (RE) metal prices, environmental concerns involving the RE-metal extraction, and geopolitical issues joined by the large coercivity (Hc) gap existing between alnico/ferritebased magnets and RE-based magnets created a need to reinvestigate the Mn-Al based magnets, first reported by Koch et al in 1960, for the development of a non-rare earth magnet competing with the medium performance Nd-Fe-B magnets.[1,2,3] The hard-magnetic properties in Mn-Al alloy system originate from the L10 τ-phase with high anisotropy field of ∼40 kOe, a relatively high saturation magnetization of ∼96 emu/g and Curie temperature > 300 ◦C.1–3. The Mn-Al magnet with best properties so far was produced by Matsushita Electrical Industrial company (Mr = 6.1 kG, Hc = 3.2 kOe, (BH)max ∼7 MGOe) by hot extrusion/swaging.[4] the performance improvement as compared to the ferrite magnets was not sufficient to justify the cost of the manufacturing. Have explored different techniques (hot-compaction, microwave sintering and hot-deformation) to produce Mn-Al based bulk magnets with improved properties
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