Abstract：Dy diffusion process is a novel method to increase coercivity of sintered NdFeB magnets and optimize thermal performance. In this work, a facile Dy-diffusion process was carried out. DyF3 powder as Dy precusor was dispersed in a solvent, and then the NdFeB magnet was immersed into the solvent. A uniform DyF3 coating was obtained on the magent surface after dying. The magnet with Dy coating was heated to diffuse Dy under a high vacuum condition. The influence of Dy-diffusion process on the properties of magnets and mechanism of the diffusion were investigated. An optimal Dy-diffusion process was obtained when the heating treatment was conducted at 920 ° C for 5 hours. Coercivity of the magnet obtained by the optimal process reachs to 19.53 kOe with a negligible decrease of remanence. Analysis of microstructure and elements distribution indicate that the diffusion was driven by the concentration difference, and the grain boundary provides a highway for the diffusion of Dy element from the surface to the inside. A magnet of 3 mm thickness could be penetrated by using this Dy diffusion process. Within the range of about 689 um from the magnet surface, the diffusion of Dy element is sufficient and uniform. Beyond this range, the Dy element begins to display in a gradient distribution.
2019, Vol. 26 