The diffusion of Tb in sintered Nd-Fe-B magnets by the grain boundary diffusion process can significantly enhance coercivity. However, due to the influence of microstructures at different depths, the coercivity increment and temperature stability gradually decreases with the increase of diffusion depth, and exhibit good corrosion resistance at a sub-surface layer (300–1000 μm). According to the Electron Probe Micro-analyzer (EPMA) test results and the diffusion mechanism, the grain boundary and intragranular diffusion behavior under different Tb concentration gradients were analyzed, and the diffusion was divided into three stages. The first stage is located on the surface of the magnet, which formed a thick core-shell structure and a large number of RE-rich phases. The second stage is located in the sub-surface layer, forming a uniform and continuous RE-rich phase and thin core-shell structure. The third stage is located deeper in the magnet, and the Tb enrichment only existed at the triangular grain boundary.

This study investigates the effect of Ce on the diffusion behavior of Dy-Cu alloys. The addition of Ce reduces the diffusion source melting point and promotes the formation of low-melting alloy phases, benefiting the diffusion behavior. The diffusion source with 10 wt.% of Ce shows the best magnetic performance, the coercivity of the magnet increases from 18.47 kOe to 23.60 kOe, and the incremental coercivity reaches 5.13 kOe. Ce diffusion improves the utilization of Dy, enhances diffusion uniformity, and promotes coercivity improvement. Ce also optimizes and regulates grain boundary phase structure distribution, consistent with magnetic property changes. Dy₇₀Cu₃₀ with an excessive thick shell layer wastes Dy and reduces utilization, while Dy₆₀Ce₁₀Cu₃₀ has a relatively thin and uniform shell layer. Ce mainly distributes in the intergranular phase region, promoting Dy diffusion from the intergranular phase to form a shell layer. Excessive Ce can distort the magnet’s crystal structure, hindering magnetic property improvement. This study provides insights into optimizing the diffusion process and improving the Dy-Cu alloy.

This article investigates the relationship between the magnetic properties of magnets and the percentage and distribution of the CeFe₂ phase at different sintering temperatures. At the lower sintering temperature, the grain boundary phase flow of the magnet is poor, more hole defects are generated in the magnet, and the comprehensive magnetic properties of the magnet are poor. An increase in sintering temperature increases the ratio of CeFe₂ phase, improves the fluidity of grain boundary liquid phase, fills the hole defects and causes an increase in remanence. However, an increase in grain size also inhibits the coercivity of the magnet at this temperature. When the sintering temperature reaches 1080 °C, the CeFe₂ phase ratio continues to increase, providing more liquid phase. The phase Ce₂Fe₁₇ was also decomposed into liquid phase, the continuity and wettability of grain boundary phase were optimized, and the coercivity reached a maximum of 13.18 kOe. However, the orientation of the magnet changed and the proportion of the main phase decreased, resulting in a slight decrease in the remanence (B_r = 13.17 kGs).

Rare earth resource recycling is an important endeavor for environmental protection and resource utilization. This study explores the method of preparing regenerated magnets using waste magnets as raw materials based on existing processes. By utilizing existing Nd-Fe-B production equipment, various waste magnets are transformed into recycled powder. Next, nascent Nd-Fe-B powders with slightly higher rare earth content are selected as the repairing agent. The regenerated magnets are prepared by incorporating the nascent powder into the recycled powder. The focus lies in investigating the repairing effect of the nascent powder repairing agent on the microstructure of regenerated magnets and exploring the influence of sintering temperature and powder addition on the magnetic properties and microstructure of the regenerated magnets. The results showed that the nascent powder increased the proportion of grain boundary phases and effectively repaired the grain boundary structure of the regenerated magnets. In addition, the Pr element in the nascent powder replaces the Ce element in the recycled powder, which ultimately improves the magnetic properties of the regenerated magnet in a comprehensive manner. This study provides valuable insights and guidance for rare earth resource recycling and the preparation of regenerated magnets.