New progress in the development and industrialization of high-abundance é’‡ mixed rare earth permanent magnet materials by Ningbo Materials of the Chinese Academy of Sciences

Recently, the Institute of Rare Earth Magnetic Functional Materials of the Institute of Materials Technology and Engineering of the Chinese Academy of Sciences has made a series of progress in the development and industrialization of high-abundance é’‡ mixed rare earth permanent magnet materials. The structural design of the hard magnetic main phase and the optimal control of the interface distribution have developed high-coercivity magnets with excellent temperature resistance, which has broken the application bottleneck of high-abundance rare earth elements in the field of permanent magnets.
The magnetic properties of sintered Nd-Fe-B permanent magnets depend on the phase composition and microstructure of the magnets. The phase composition and microstructure of the magnets are mainly controlled by the metallurgical behavior of alloying elements during the preparation process. The researchers first systematically studied the high-abundance rare earth elements. La/Ce/Y distribution and migration characteristics during magnet preparation, clarifying the influence of La/Ce/Y on the phase and microstructure of the alloy. It is found that in the process of rapid setting, La and Ce are enriched in the grain boundary phase of the alloy, and Y is mainly enriched in the 2:14:1 main phase of the alloy. The analysis shows that the introduction of Y can stabilize the tetragonal phase and avoid La. , Ce damage to the hard magnetic phase structure. In the subsequent process, Y further segregates from the grain boundary to the interior of the main phase grains. Figure 1 reflects the differences in the distribution of different high-abundance rare earth elements in the alloy caused by this rare earth metallurgical behavior.
Based on the understanding of the metallurgical behavior characteristics and the magnetization reversal mechanism, the researchers further proposed the structural design idea of ​​Y segregation in the main phase, and obtained the core-shell structure in which Y is segregated in the main phase grain core. As shown in Fig. 2, the lower Y content of the grain surface layer makes the main phase grain have a shell region with a higher anisotropy field, which can effectively suppress the demagnetization nucleation process of the grain surface and enhance the coercive force of the magnet. Further, by rationally designing the grain boundary components and utilizing the dissolution and precipitation of the grain boundary phase region, the problems of grain adhesion, grain boundary phase loss and segregation due to grain growth and strong migration and segregation behavior of rare earth lanthanum elements are solved. The continuous uniform grain boundary is coated with the hard magnetic phase of the core-shell structure, which effectively enhances the magnetic isolation effect between the grains, so that the high-abundance 钇 mixed rare earth magnet exhibits high room temperature coercive force and excellent Temperature resistance, the maximum magnetic energy product can obtain magnetic properties greater than 40MGOe within 40% of Y instead of Nd. Y replaces 15% Nd to obtain magnetic properties with coercive force greater than 17kOe, and the overall performance is better than that of Ce substituted magnet. This study combines the main phase structure control and grain boundary enhancement technology to solve the problem of difficult phase and structural heterogeneity of high abundance rare earth magnets.

Related research results have been published in IEEE Trans. Magn. (2015, 51(8): 1-4), Appl. Phys. Lett. (2017, 110(17): 172405), Acta Mater. (154 (2018) 343 -354) In academic journals, it is supported by projects such as the National Key R&D Program and the National Natural Science Foundation. The team is cooperating with Chinalco, one of China's six major Rare Earth Groups, to develop high-abundance é’‡ mixed rare earth magnet industrialization technology, and initially realized technology transfer and batch production at the production base of Chinalco Group (pictured 3), and at the Jiangsu Rare Earth New Materials Industry Development Forum held in Changzhou in June 2018, the relevant results were promoted and received extensive attention from the relevant units of the rare earth industry chain.

Fig.1 TEM microstructure and interface element distribution of different high-abundance rare earth elements (La, Ce, Y) substituted alloys

Fig. 2 Microstructure of Y-substituted magnets and distribution of internal elements in grains

Figure 3 Product introduction of Chinalco's pilot production site (left) and Y-mixed rare earth magnets (right)