Magnetic Properties of Nd-Fe-B Magnets Sintered after Compacting Spray Dried Powders in a Pulsed Magnetic Field

Abstract

Nd-Fe-B alloy powder was granulated by a spray drying method using an organic binder in order to improve the powder flowability during feeding and compacting. In this experiment, whether or not the degree of magnetic orientation of primary particles in granulated powders is raised by applying high intensity pulsed magnetic field in compacting was studied, in order to improve magnetic properties of sintered magnets. It was found that the orientation of particles (remanences) was improved remarkably by applying high intensity pulsed magnetic field in initial process of compaction of granulated powders, so that magnetic properties of magnets are superior to those of magnets when applying only static magnetic field in compacting. The observation of granulated powders after applying magnetic field shows that granulated powders were destructed more easily by such high intensity pulsed field. The orientation of primary particles in granulated powders depends strongly on the apparent density of powders when applying pulsed field. It was very effective for improving magnetic properties of magnets using granulated powders to apply pulsed field when powders fed in die cavity are free for orientation. By means of controlling the binding strength of binder and timing of pulsed magnetic field, magnetic characteristics of magnets using granulated powders became almost equal to that of magnet using raw powder.