Prospect of developing Nd-Fe-B-type magnet with high electrical resistivity

Nd-Fe-B-type magnet is exclusively used as a rotor magnet in the traction motor of hybrid electric vehicle (HEV) and electric vehicle (EV), but its overly high operating temperature is a lingering problem attached to the magnet. The major cause of the high operating temperature is eddy current, which is readily generated in the highly conductive metallic magnet under alternating magnetic field from stator ripple. In this article, temperature rise in the Nd-Fe-B-type magnet with varying electrical resistivity under alternating magnetic field is discussed with the intention of highlighting the importance of enhancing the electrical resistivity for reducing the operating temperature of the Nd-Fe-B-type rotor magnet. Temperature rise in the Nd-Fe-B-type magnet (dielectric salt-added die-upset magnet) with high electrical resistivity is noticeably lower compared to the magnet (commercial sintered rotor magnet) with lower electrical resistivity, substantiating the theory that enhancing the electrical resistivity in the rotor magnet is fairly effective for suppressing the over-rise of its operating temperature during operation. Die-upset process is revealed to be particularly pertinent for the fabrication of highly dense salt-added magnet with high electrical resistivity. Graphic abstract