Die-upset PrCo5-type magnets: Enhanced coercivities

Abstract

Rare-earth–cobalt alloys have been melt spun, yielding ribbons whose major phase was the hexagonal PrCo5 phase. Fully dense hot-pressed magnets with essentially isotropic magnetic properties have been formed by consolidating the ribbons at high temperatures and pressures. The hot-pressed precursor was then subjected to hot deformation or die upsetting, thereby inducing partial alignment of the c axis along the press direction. The resulting magnets had remanences approaching ∼75% of the saturation magnetization of the hexagonal PrCo5 phase. Three approaches were used to optimize the coercivity of the die-upset magnets: (i) replacing small amounts of cobalt with carbon; (ii) partially substituting samarium for the praseodymium; and (iii) high-temperature heat treatment followed by a thermal quench. Coercivities near ∼20 kOe were achieved with thermally quenched die-upset (Pr0.6Sm0.4)18Co81C magnets, while maintaining remanences above 8 kG.