Synergistic effect of non-rare earth elements in Ce-La-Tb-Cu-Al diffusion source for Nd-Fe-B magnets with high coercivity and high electrical resistivity

Simultaneously enhancing the coercivity and resistivity of Nd-Fe-B magnets for motor rotors with cost-effective additives and less deterioration of energy product is facing severe challenges. Grain boundary diffusion is an effective solution. In this work, Ce-La-Tb-Cu-Al alloys with distinct advantage in material cost are proposed to effectively improve the coercivity and resistivity of sintered Nd-Fe-B magnets, which exhibits similar optimization with the Pr-Tb-based diffused sources. The results show that after diffusion by Ce_8.5La₃₄Tb_27.5Cu_30-xAl_x (x = 0, 10, 20, 30), the coercivity of the magnet has increased by up to 9.79 kOe and the resistivity has increased by up to 0.58 Ω·μm. The underlying physical mechanism and synergistic effect of non-rare earth elements are clarified. The improvement of coercivity is mainly attributed to the lower melting point of the diffusion source by proper ratio of Al/Cu, which effectively optimizes the wettability and distribution of grain boundary (GB) phase and promotes the diffusion efficiency of Tb. Meanwhile, compared with Cu, Al is more conducive to increasing the O content of the continuous GB phase, forming more rare earth-rich oxides for isolating the main phase grains, and thereby enhancing the resistivity of the magnet. This study provides a reasonable approach for selecting non-rare earth elements to improve the comprehensive electromagnetic performance of Nd-Fe-B magnets.