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• The effects of annealing on the microstructures and magnetic properties of Ga and Cu co-added Nd-Fe-B magnet were investigated. • The intrinsic coercivity increases from 9.17 kOe to 18.67 kOe after annealing, which shows an increment of 103.5%. • The main reasons for the substantial increase of intrinsic coercivity are discussed. Post-sinter annealing is essential to improve the microstructures and magnetic properties in NdFeB-based sintered permanent magnetic materials. In this paper, investigated systemically are the effects of post-sinter annealing on the microstructures and magnetic performance of Ga and Cu co-doping Nd 2 Fe 14 B based sintered magnets. It is found out that the intrinsic coercive force of the magnets increased from 9.17 kOe to 18.67 kOe after two stage post-sinter annealing (PSA), which shows an extraordinary increment of 103.5%. The remanence, with a decreasing percentage of 1.95%, slightly decreases from 13.87 kGs to 13.60 kGs. The substantial increase of intrinsic coercivity is mainly attributed to the improvement of clean and thin continuous grain boundary layers, the smoothness of hard magnetic matrix phase and the appearance of the RE 6 (Fe, M) 14 antiferromagnetic phase during annealing. The reduction of the remanence is caused by the deteriorated orientation degree and reduced volume fraction of hard magnetic main phases after post-sinter annealing. [ABSTRACT FROM AUTHOR]

• This study provides a method using of Tb hydride in suspension to improve coercivity in sintered NdFeB magnets. • This work investigated Tb diffusion behavior from coating layer to the magnet. • Tb rich core-shell structure and continuous grain boundary in the magnet, which effective increase in coercivity. Grain boundary diffusion of Tb can improve the microstructural and magnetic properties of NdFeB magnets. In this paper, we investigated diffusion behavior and coercivity enhancement by dip-coating TbH 3 powders in sintered NdFeB magnets. The results show that the coercivity increased rapidly from 14.02 kOe to 23.72 kOe after diffusion. Tb atoms diffused to the surface of the magnet and then into the interior, forming a network Tb-rich shell around (PrNd) 2 Fe 14 B grains. The higher magnetocrystalline anisotropy (PrNd,Tb) 2 Fe 14 B phases determine the coercivity enhancement. The Tb diffusion model was build up from coating layer to the magnet. This work may shed light on developing sintered NdFeB magnets with coercivity enhancement by diffusion technology. [ABSTRACT FROM AUTHOR]