Coercivity enhancement of sintered Nd-Fe-B magnets by grain boundary diffusion with Pr_80-xAl_xCu₂₀ alloys

Abstract In this work, grain boundary diffusion (GBD) process with Pr 80-x Al x Cu 20 (x=0, 10, 15, 20) low melt-point alloys was applied to the commercial 42M sintered Nd-Fe-B magnets. The best coercivity enhancement of diffused magnet is the Pr 65 Al 15 Cu 20 GBD magnet, from 16.38 kOe to 22.38 kOe. Microstructural investigations indicated that increment of Al content in the diffusion source can form the continuous grain boundary (GB) phase clearly, optimizing the microstructure to enhance coercivity. The coercivity enhancement is mainly due to the formation of continuous GB phase to separate the main phase grains. The exchange decoupling between the adjacent main phase grains is enhanced after the GBD process. Meanwhile, the introduction of Al can promote Pr infiltrate into the magnet effectively which increases the diffusion rate of rare-earth elements within a certain range. This work provides a feasible method to enhance coercivity and reduce the usage of the rare-earth resource by replacing partial rare-earth element with non-rare-earth elements in the diffusion source.