The impact of processing parameters on the properties of Zn-bonded Nd–Fe–B magnets

Abstract

We report on the effect of loading factor and pressure on the density and the magnetic properties of Zn-bonded Nd–Fe–B magnets produced by pulsed-electric-current sintering (PECS). The idea behind this study is to fabricate bonded magnets with a metallic binder in order for the bonded magnet to operate at temperatures higher than 180°C: the current upper-limit for polymer-bonded magnets. These composites are made of hard-magnetic powder in the form of melt-spun ribbons bonded with the low-melting-point metal Zn. The binder additions were varied from 10 to 30wt%, and pressures of 50 and 500MPa were applied. The high-pressure mode with 20wt% Zn resulted in a 24% increase of Jr, compared to the low-pressure mode. The magnetic measurements revealed a maximum remanence of 0.64T for 10wt% Zn, while the coercivity is largely unaffected by the processing conditions. The density of the composites was up to 7.0g/cm3, corresponding to 94% of the theoretical density. Compared to commercial polymer-bonded magnets, the Zn-bonded counterparts exhibit a slightly lower Jr, but the coercivity is retained. We show that there is a minor diffusion of Zn into the Nd–Fe–B, forming a 1μm thin transition layer, but it does not harm the magnetic properties. These metal-bonded Nd–Fe–B magnets are ideal for use in high-temperature automotive applications like under-the-hood sensors and other magnet-based devices that are close to the engine.