Abstract
Nd-Fe-B-type die-upset magnet with high electrical resistivity was prepared by doping of eutectic DyF3–LiF salt mixture. Mixture of melt-spun Nd-Fe-B flakes (MQU-F: Nd13.6Fe73.6Co6.6Ga0.6B5.6) and eutectic binary (DyF3–LiF) salt (25 mol% DyF3 – 75 mol% LiF) was hot-pressed and then die-upset. By adding the eutectic salt mixture (> 4 wt%), electrical resistivity of the die-upset magnet was enhanced to over 400 μΩ.cm compared to 190 μΩ.cm of the un-doped magnet. Remarkable enhancement of the electrical resistivity was attributed to homogeneous and continuous coverage of the interface between flakes by the easily melted eutectic salt dielectric mixture. It was revealed that active substitution of the Nd atoms in neighboring flakes by the Dy atoms from the added (DyF3–LiF) salt mixture had occurred during such a quick thermal processing of hot-pressing and die-upsetting. This Dy substitution led to coercivity enhancement in the die-upset magnet doped with the eutectic (DyF3–LiF) salt mixture. Coercivity and remanence of the die-upset magnet doped with (DyF3–LiF) salt mixture was as good as those of the DyF3-doped magnet.
Highlights
High performance Nd-Fe-B-type magnet is essentially used in the traction motor of HEV, EV and wind turbine generator.[1,2] Because of its high operating temperature (≈ 200 ◦C), the Nd-FeB-type magnet for those applications definitely needs to have high room temperature coercivity
As eddy current is inversely proportional to electrical resistivity of a material, enhancing the electrical resistivity of magnet would be a useful approach for suppressing the excessive heating
Electrical resistivity of the die-upset Nd-Fe-B-type magnet was remarkably enhanced by doping with eutectic (DyF3–LiF) salt mixture
Summary
High performance Nd-Fe-B-type magnet is essentially used in the traction motor of HEV, EV and wind turbine generator.[1,2] Because of its high operating temperature (≈ 200 ◦C), the Nd-FeB-type magnet for those applications definitely needs to have high room temperature coercivity. High operating temperature of the magnet is due to the excessive heating mostly caused by an eddy current,[3,4,5,6] which is generated by alternating slot field coming from armature in the motor. As eddy current is inversely proportional to electrical resistivity of a material, enhancing the electrical resistivity of magnet would be a useful approach for suppressing the excessive heating. Doping technique using dielectric RF3 (R = heavy rare earth) has been investigated extensively for die-upset Nd-Fe-B-type magnet as an effective means of enhancing the electrical resistivity and coercivity. An attempt was made to enhance electrical resistivity and to improve performance of the Nd-Fe-B-type die-upset magnet by doping with eutectic DyF3–LiF salt mixture
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