| The sintered Nd-Fe-B magnet has been widely used in many emerging fields such as aerospace,wind power generation,and new energy vehicles due to its excellent magnetic properties.During the preparation and application of Nd-Fe-B magnets,a large amount of rare earth elements such as Pr,Nd,Dy,and Tb are required,while high-abundance rare earth elements La,Ce,Y are underutilized,resulting in uneven use of rare earth elements and a continuous increase in production costs of Nd-Fe-B magnets.To fully utilize the resource-rich and lowpriced high-abundance rare earth elements,and to solve the problem of high production cost of Nd-Fe-B magnets,this paper focused on the structural optimization and performance improvement of Y-containing magnets and misch metal magnets by means of grain boundary addition.The main research achievements obtained are as follows:(1)By taking advantage of the characteristics of Ho element 2:14:1 phaseenhanced anisotropy field and excellent phase forming ability,the effect of adding Ho76Al12Ga12 powder on the structural adjustment and performance enhancement of Y-containing magnets was systematically explored.The results showed that after the addition of Ho76Al12Ga12 powder,Ho elements formed a strong anisotropic layer at the grain shell,and the special microstructure of the grain shell structure with Y-rich core,Ho-biased layer,and Ho-rich shell was presented from the inside out.The anisotropy field of the magnet was effectively improved,and due to the addition of Ho elements,a large amount of Nd elements were displaced to the grain boundary,optimizing the intergranular phase in the magnet.As a result,the coercivity of the magnet gradually increased from 0.738 T to 1.374 T,and the temperature coefficient of remanence decreased from-0.1159%/℃ to-0.1000%/℃,while the temperature coefficient of coercivity decreased from-0.6881%/℃ to-0.6267%/℃.This work realized the improvement of microstructure and the enhancement of magnetic properties and thermal stability of Y-containing magnets by Ho element.(2)In terms of modification of misch metal magnets rich in LaCe elements,this experiment used a double primary phase process to prepare(MM0.5,Nd0.5)2Fe14B(MM-50)and(Pr,Nd)2Fe14B sintered magnets with different ratios,and studied the structural optimization and performance enhancement of them.The results showed that with the increase of(Pr,Nd)2Fe14B magnetic powder proportion,the aggregation phenomenon of the rich rare earth phase at the triangular grain boundary was alleviated,and the continuous thin-walled grain boundary phase gradually formed.At the same time,the two types of grains with high and low anisotropy fields inside the magnet worked together to optimize the magnetic properties of the magnet.In this study,the dual-phase magnet was prepared with MM-50 and(Pr,Nd)2Fe14B powders in a ratio of 7:3.The coercivity of the dual-phase magnet was increased to 0.636 T,which was higher than the single-phase misch metal magnet with the similar ratio.(3)As a result of the formation of a low anisotropy layer of partially enriched LaCe grains in the dual primary phase magnet,the function of the high anisotropy layer in enhancing coercivity was not fully utilized.In this experiment,on the basis of the MM-50 magnet,Pr82Co18 powder was introduced by grain phase addition,which promoted the formation of rich-Pr shell layer in the grains and continuous intergranular phase between the grains,resulting in an increase of coercivity from 0.554 T to 1.087 T.Additionally,under the joint action of uniformly distributed Co elements and rich-Pr shell layers,the RE2(Fe,Co)14B phase was formed inside the grains with higher saturation magnetization,resulting in an increase of the remanence from 1.227 T to 1.292 T.The above work realized the dual improvement of remanence and coercivity of misch metal magnets through the rational design of grain phase additives. |
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