Effect of grain boundary diffusion in TbF3-Al mixed electrophoresis on properties of sintered Nd-Fe-B magnets

•Preparation of TbF3-Al mixed diffusion source of GBDP with adjustable part by EPD.•The coercivity of TbF3-Al diffusion magnet increases obviously (40.9 %) after GBDP.•Al promotes formation of Tb-rich thin GB phase and increases diffusion depth of Tb. The grain boundary diffusion process of heavy rare-earth elements and low-melting metal can improve the coercivity (Hcj) of sintered Nd-Fe-B magnet significantly. In this work, the effect of TbF3-Al diffusion source on the magnetic properties and microstructure of magnets were investigated. Ratio of TbF3 and Al adjusted by parameters of electrophoretic deposition. The Hcj of the TbF3-Al diffusion magnet increased by 40.9% compared to original magnet. The temperature stability of TbF3-Al diffusion magnet was also improved. Microstructural investigations indicate that Al can promote the formation of Tb-rich thin grain boundary phase and increase the isolation between the main phases. In addition, Al can promote the diffusion of TbF3 into the magnet.