Fabrication of a Metal Bonded Fe3B/Nd2Fe14B Permanent Magnet from AZ31 Magnesium Alloy Scraps

Abstract

The heat-resisting temperature of a conventional bonded magnet produced by combining a magnetic powder and a resin or a rubber is limited to about 150°C. A new type of metal bonded magnet was fabricated using AZ31 magnesium alloy powder and Nd-Fe-B -base magnetic powder to improve the heat-resisting temperature of the bonded magnet. The AZ31 magnesium powder was produced by pulverizing scrap generated by machining. An isotropic Fe3B/Nd2Fe14B nano-composite powder was used as the magnetic material. The mixed powder was formed by closed-die compaction and extrusion at 240∼350°C. The magnetic properties and mechanical strength of the formed metal bonded magnet were investigated. Also, bonded magnets were fabricated using bonding materials such as brazing and conventional resin powders, and the magnetic properties were compared with that of the magnet produced using AZ31 powder. It was found that the magnetic properties of the bonded magnet could be determined by the product of the density of the bonded magnet and the mass ratio of the magnetic powder, namely, the mass content of the magnetic powder per unit volume (dimensions Mg·m-3) regardless of the kind of the bonding material that was used. The maximum mixing ratio of the magnetic powder that satisfied the criterion of 15MPa strength for the splitting tensile strength test was 85 mass%, and the mass content of the magnetic powder per unit volume was 3.47Mg·m-3.