Optimized Microstructure and Improved Magnetic Properties of Pr-Dy-Al-Ga Diffused Sintered Nd-Fe-B Magnets

The grain boundary diffusion process (GBDP) has become an important technique in improving the coercivity and thermal stability of Dy-free sintered Nd-Fe-B magnets. The influence of Dy70Al10Ga20 and (Pr75Dy25)70Al10Ga20 alloys by the GBDP on sintered Nd-Fe-B magnets are investigated in this paper. After diffusing Dy70Al10Ga20 and (Pr75Dy25)70Al10Ga20 alloys, the coercivity (Hcj) of the magnets increased from 13.58 kOe to 20.10 kOe and 18.11 kOe, respectively. Meanwhile, the remanence of the magnets decreased slightly. The thermal stability of the diffused magnets was improved by the GBDP. The microstructure shows continuous Rare-earth-rich (RE-rich) grain boundary phases and (Dy, Pr/Nd)2Fe14B core-shell structures which contribute to improving the coercivity. Moreover, the Dy concentration on the surface of the (Pr75Dy25)70Al10Ga20 diffused magnets decreased with the Pr substitution for the Dy element. The openness of the recoil loops for the (Pr75Dy25)70Al10Ga20 diffused magnets is smaller than that of the original magnets and Dy70Al10Ga20 diffused magnets. The results show that the (Pr75Dy25)70Al10Ga20 alloys can effectively optimize the microstructure and improve the magnetic properties and thermal stability of the sintered Nd-Fe-B magnets.