Enhancement of Coercivity in Sintered NdFeB Magnets by Weak Alternating Magnetic Field-Assisted Grain Boundary Diffusion
The influence of weak alternating magnetic field-assisted grain boundary diffusion on the coercivity of commercial N35 grade sintered Nd-Fe-B magnets was studied by depositing 0.3 wt％Dy metal on the magnet surface using physical vapor deposition and applying a weak magnetic field with a frequency of 50 Hz during the heat treatment process at 910℃.Magnetic property tests show that compared to the original magnet,both conventional diffusion and 0.3 T weak alternating magnetic field-assisted diffusion increase the coercivity by 3.28 kOe and 5.02 kOe,respectively.Based on BSE-SEM images,the grain size distribution in the diffused magnets is analyzed using ImageJ software.It is found that the grain size does not further increase during the magnetic field-assisted diffusion process,while the average grain size of the magnet diffuses by conventional diffu-sion increases by approximately 0.5 μm.EDS line scan results show that within the range of 400 μm to 1500μm from the Dy-coated surface of the magnet,the Dy content of the magnet diffused with magnetic field assistance is significantly higher than that of the conventionally diffused magnet.These results indicate that weak alternating magnetic field-assisted grain boundary diffusion can effectively suppress grain growth and increase the diffusion depth of Dy along the grain boundaries.The improvement in coercivity is attributed to the combined effects of these mechanisms.The experimental results provide a new approach for further optimizing the grain boundary diffusion process of sintered Nd-Fe-B magnets.
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