High-energy cast Pr-Fe-B magnets

Abstract

A new process has been developed to produce high-energy bulk Pr-Fe-B magnets directly from the melt without the handling of magnetic powder or powderlike ribbons. The process mainly consists of only three steps—casting/hot pressing/annealing—and minimizes the oxygen contamination of magnets. A typical composition of cast alloy is Pr17 Fe76.5 B5 Cu1.5 . Using this type of alloy, a magnetic alignment is easily introduced by hot pressing. Copper plays two important roles: high coercivity and excellent magnetic alignment are achieved simultaneously by the addition of copper. Magnetic properties of hot-pressed Pr17 Fe76.5 B5 Cu1.5 magnets are as follows: Br=12.5 kG, i Hc =10.0 kOe, and (BH)max =36.2 MGOe. The cast alloy of this composition also has an i Hc of 7.4 kOe and a (BH)max of 8.8 MGOe after annealing at 1000 °C for 24 h. The steep rise in the initial magnetization curve indicates a type of nucleation-controlled coercivity mechanism.