Process technology, properties, and microstructure of hot rolled rare earth-transition metal-boron permanent magnets

Permanent magnets were produced by rolling ingots with the three compositio ns: Nd17Fe76.5B5Cu1.5, Nd17-1Fe74Nb1B6.7Cu1.2, and Pr17Fe76.5B5Cu1.5. Rolli ng temperatures were 750, 850, and 950 degrees C, and the specimens were su bsequently heat treated. The microstructure was very homogeneous and the gr ain size exhibited an inverse correlation with rolling temperature. A fine microstructure corresponded to high coercivity levels, and the highest valu e of this magnetic property was achieved by the praesodymium containing mag net. High temperature heat treatment was deleterious to the coercivity of t he neodymium containing magnets but the opposite was observed for the praes odymium magnets. Although, as a rule, the heat treatment did not affect the remanence, this magnetic property increased noticeably for the praesodymiu m magnet. As for the magnetic alignment or texture, X-ray diffraction showe d that it was increased by hot rolling compared with the as cast ingot. The degree of magnetic texture was increased by deformation but was also favou red by a previously existing highly developed and well oriented lath micros tructure. MST/3906