Coercivity enhancement of sintered Nd-Fe-B magnets by grain boundary diffusion with Pr80–x Al x Cu20 alloys

A grain boundary diffusion (GBD) process with Pr80 – x Al x Cu20 (x = 0, 10, 15, 20) low melting point alloys was applied to commercial 42M sintered Nd–Fe–B magnets. The best coercivity enhancement of a diffused magnet was for the Pr65Al15Cu20 GBD magnet, from 16.38 kOe to 22.38 kOe. Microstructural investigations indicated that increase in the Al content in the diffusion source can form a continuous grain boundary (GB) phase, optimizing the microstructure to enhance the coercivity. The coercivity enhancement is mainly due to the formation of a continuous GB phase to separate the main phase grains. Exchange decoupling between the adjacent main phase grains is enhanced after the GBD process. Meanwhile, the introduction of Al can effectively promote the infiltration of Pr into the magnet, 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 use of rare-earth resources by partial replacement of rare-earth elements with non-rare-earth elements in the diffusion source.