Reduction in Heavy Rare Earth Diffusion Sources in Sintered Nd-Fe-B Magnets via Grain Boundary Diffusion of Dy70Ce70−xCu30

This study investigates the effect of Ce on the diffusion behavior of Dy-Cu alloys. The addition of Ce reduces the diffusion source melting point and promotes the formation of low-melting alloy phases, benefiting the diffusion behavior. The diffusion source with 10 wt.% of Ce shows the best magnetic performance, the coercivity of the magnet increases from 18.47 kOe to 23.60 kOe, and the incremental coercivity reaches 5.13 kOe. Ce diffusion improves the utilization of Dy, enhances diffusion uniformity, and promotes coercivity improvement. Ce also optimizes and regulates grain boundary phase structure distribution, consistent with magnetic property changes. Dy70Cu30 with an excessive thick shell layer wastes Dy and reduces utilization, while Dy60Ce10Cu30 has a relatively thin and uniform shell layer. Ce mainly distributes in the intergranular phase region, promoting Dy diffusion from the intergranular phase to form a shell layer. Excessive Ce can distort the magnet’s crystal structure, hindering magnetic property improvement. This study provides insights into optimizing the diffusion process and improving the Dy-Cu alloy.