Dry and wet milling comparison of Nd-Fe-B magnets based on strip cast alloys

Abstract

In this work, the influence of milling medium was investigated in order to achieve high energy-product Nd-Fe-B magnets, mostly by the remanence improvement related to the obtention of monocrystalline particles during milling. Nd-Fe-B alloy made by strip-casting process were used as starting material, which exhibits refined grain structure and demands special attention during milling in relation to coarse-grained, conventionally cast alloys. It was found that by using liquid medium during ball milling process, the mean particle size decreased, as well as the size distribution, which improved the particle alignment and hence the remanence in the sintered magnet. Texture was quantified by magnetic characterization based on reference isotropic magnets made in same conditions, and microstructure development was evaluated by optical microscopy. Moreover, after post-sintering treatment, the coercivity increased 20% compared to as sintered state without changing the remanence, providing an anisotropic magnet with high coercivity.