On Dy-M (M = Al, Ni, and Cu) diffusion sources for enhancing coercivity and corrosion resistance of Nd-Fe-B magnets

Abstract

Dy based alloys have been widely employed as the grain boundary diffusion (GBD) sourcesfor Nd-Fe-B magnets. To reveal the design principle of these alloys, we carried out a systematic investigation on the magnetic properties, microstructure evolution, and corrosion behavior of grain boundary diffused (Nd,Pr)-Fe-B based sintered magnets using Dy 100-x Al x , Dy 100-x Ni x , and Dy 100-x Cu x (x = 0, 10, 20, 30, 40, at.%) alloys as the diffusion sources. It is found that Dy 90 Al 10 , Dy 80 Ni 20 , and Dy 80 Cu 20 alloys exhibit the highest coercivity enhancements of 429 kA/m, 334 kA/m, and 183 kA/m, respectively, in each series of alloys due to their relatively high Dy content and low melting point. The superior performance of Al-containing diffusion source originates from the facilitated formation of continuous grain boundary phases (GBPs) during diffusion and the high Dy diffusion efficiency. All diffused magnets exhibited improved corrosion resistance compared to the initial magnet. The results indicate that the non-rare earth elements can modify the electrode potentials of both main phase and grain boundaries, while simultaneously optimizing the composition and distribution of intergranular phases. Notably, Dy-Al and Dy-Ni diffused magnets show better corrosion resistance performance than Dy-Cu in the GBD process diffused magnets. This work provides critical insights for designing highperformance diffusion sources to achieve high comprehensive performance in GBD treated Nd-Fe-B magnets.