Clarifying the effects of La and Ce in the grain boundary diffusion sources on sintered NdFeB magnets

Abstract

(La,Ce)–Al–Cu alloys with different La/Ce ratios were employed as the diffusion sources for grain boundary diffusion of sintered NdFeB magnets. The coercivity changed from 990 kA m−1 to 984, 1021 and 1031 kA m−1 after diffusion by (La x Ce1−x )–Al–Cu alloys with La/Ce ratio (x) of 0, 0.5 and 1, respectively. Varied magnetic properties resulted from different effects of La and Ce on the microstructure, in particular the formation and amount of the REFe2 phase. REFe2 phase formed after diffusion deteriorated the magnetic properties but improved the wettability between grain boundary and main phase. After (La,Ce)–Al–Cu alloys diffusion, the corrosion resistance was reduced but the mechanical properties were improved. The underlying mechanisms have been discussed in this paper.