Abstract：In this study, the thermal diffusion process of high-abundance permanent magnets ((La,Ce)0.2(Pr,Nd)0.8)FebalB was investigated. Meanwhile, the thermal diffusion behavior of heavy rare earth was analyzed. The high-abundant magnets present a poor thermal diffusion effect because of the magnets with more Ce and La content. In order to solve this problem, a direct thermal diffusion process was proposed. The sintered magnets were directly performed thermal diffusion treatment. The optimal thermal diffusion process parameter is 880℃×8 h+500℃×2 h, and the coercivity is directly increased from 8.11 kOe to 18.38 kOe. Compared to the coercivity and grain size of magnet diffused after aging, the coercivity increases by 10.4%, and the average grain size is reduced about 14%, respectively. According to Fick's second law, the diffusion coefficients of Dy were calculated. The coefficients into the main phase grain and the grain boundary are D1=4.8×10?6 μm2·s?1 and D2=1.1 μm2·s?1, respectively. The thermal diffusion of Dy in the high-abundance rare earth magnet is slower than that of the ordinary magnet. It should take longer time to form (Nd/Ce/La/Dy)2Fe14B shell. The long-term thermal diffusion results in an increase of the grain size and oxygen content, this is the reason why the high-abundance magnets present a poor thermal diffusion effect. By using the direct thermal diffusion process, the aging and thermal diffusion processes can be combined. This process would shorten the time for the magnets during high-temperature treatment. Therefore, the grain size of the magnets could be reduced and the microstructure of the magnets would be improved, which result into enhancement of the magnet coercivity. Direct thermal diffusion process avoids grain coarsing and shortens the working process, so it is of great significance to improve the coercivity of high-abundance rare earth permanent magnets.
2024, Vol. 31 