Effect of Different Grain Boundary Diffusion Alloys on Magnetic Properties of Dy-Free Sintered NdFeB Magnet

Dy-free sintered magnets were fabricated by blending Neo powder with different grain boundary diffusion (GBD) alloy powders. Cu, CeAl, and CeAlCu have a negative effect on $\mathrm{H}_{\text{cj}}$ of magnets, while PrAlCu and AlCuGa have a positive effect. PrAlCu alloy achieves the best magnetic properties among all of the GBD alloys. With increasing PrAlCu from 0–10 wt.%, $\mathrm{H}_{\text{cj}}$ of the magnets gradually increases from the original 14.5 kOe to 19.2 kOe. The magnet with 7.5 wt.% PrAlCu obtains a $\mathrm{H}_{\text{cj}}$ of 18 $\text{kOe}$ and $(\text{BH})_{\max}$ of 39.1MGOe. It is found that Pr and Cu in PrAlCu alloy are mainly distributed at the grain boundary and triple junctions, leading to a reduced coupling among grains, thus an enhanced $\mathrm{H}_{\text{cj}}$. The grain boundary engineering by adding an appropriate alloy is an effective method to improve $\mathrm{H}_{\text{cj}}$ of Dy-free magnets.