Study On Preparation Of Cheap Ce,Gd Gd Rare Earth Permanent Magnets And Performance Improvement Of Grain Boundary Diffusion

Sintered Nd-Fe-B,as the third generation rare earth permanent magnet material,is currently the most widely used permanent magnet material with the strongest magnetic properties,which is widely used in national defense,machinery,computers and new energy and other important fields.With the rapid development of modern science and technology and information industry,the demand for Nd-Fe-B permanent magnet is increasing day by day,and the increasing consumption of rare earth resources has become a more and more serious problem,which makes the price of various rare earth elements higher and higher.And rare earth elements are often mined in the form of synbiosis.With the preparation of sintered Nd-Fe-B,Pr,Nd,Dy,Td and other elements are largely consumed,and cheap and rich Ce element is piled up in a large number,so in order to reduce production costs and promote efficient and balanced utilization of rare earth resources in our country.The research on high performance and cheap Ce containing magnets has become one of the hot spots in the field of rare earth permanent magnet.At the same time,the price of Gd element is very low compared with Pr and Nd.The addition of proper amount of Gd is also conducive to improving the performance of magnets under the condition of low cost.Therefore,this paper prepared two kinds of cheap rare earth permanent magnets with different Ce and Gd contents,and selected different diffusion sources to improve the performance of the magnets through grain boundary diffusion,studied the best process of grain boundary diffusion,and analyzed the relationship between the performance of the magnets and the microstructure.The main research results are as follows:（1）The magnets with Ce and Gd content of 30 wt.%of the total rare earth[（Pr,Nd）_22.4Gd₁Ce_8.6Fe_balM_0.5B_0.95]and Ce and Gd content of 70 wt.%of the total rare earth[（Pr,Nd）_9.6Gd_7.8Ce_14.6Fe_balM_0.5B_0.95]were prepared by traditional powder metallurgy process.where M is Al,Co,Zr,etc.The performance of 30wt.%Ce-Gd magnet is B_r=12.58 k Gs,H_cj=13.78 k Oe,（BH）_max=35.56 MGOe,,70 wt.%Ce-Gd magnet is B_r=9.739 k Gs,H_cj=8.305 k Oe,（BH）_max=21.90 MGOe.By analyzing the microstructure and composition distribution of the two magnets,it is found that the content of Ce and Gd in the 70wt.%Ce-Gd magnet is higher both in the main phase and in the grain boundary.More Ce and Gd enter the main phase,leading to the degradation of magnet performance.However,a large number of REFe₂ phase and Gd elements in the grain boundary phase play a role in optimizing the microstructure of the magnet,which makes up for the loss of magnetic properties caused by the addition of Ce and Gd to a certain extent,making it possible to prepare magnets with certain magnetic properties at low cost.（2）DyF₃ and DyH₂ were diffused at the grain boundaries of the two magnets,and the heat treatment process was adjusted according to the diffusion effect.The optimal heat treatment process of diffused DyF₃ is 920℃/5h+500℃/2h.The coercivity of 30wt.%Ce-Gd magnet is increased from the original13.78 k Oe to 15.90 k Oe,with an increase of 15.38%.The coercivity of 70wt.%Ce-Gd magnet is also greatly improved.It increased from 8.035 k Oe to 9.912k Oe by 23.36%.Grain boundary diffusion DyH₂ under the optimal diffusion process of 900℃/5h+500℃/2h,the coercivity of 30wt.%Ce-Gd magnet is significantly increased to 20.02 k Oe,with an increase of 45.28%.For 70wt.%Ce-Gd magnet,the coercivity increases to 12.65 k Oe,an increase of 57.44%,and the temperature stability of both magnets is improved.The microstructure observation shows that continuous grain boundaries are formed inside the two diffused magnets,but the grain boundary phase distribution near the surface of DyH₂ diffused magnets is more continuous and uniform than that of DyF₃diffused magnets,and the core shell structure of the main phase is more obvious.The composition analysis showed that the main grain edge formed a Dy rich shell,and the REFe₂ phase existed in the grain boundary of both magnets,which improved the wettability of grain boundary and formed a non-ferromagnetic grain boundary phase.The generation of a large number of continuous grain boundaries and the formation of Dy-rich hard magnetized shells are the main reasons for the coercivity enhancement of diffused magnets.（3）The co-diffusion of PrH₃ and Nd H₃（PN for short）was studied,and the mixed diffusion effect of Pr H₃,Nd H₃ and DyH₂（PND for short）was also explored.Under the optimum diffusion process condition,the coercivity of30wt.%Ce-Gd was increased from 13.78 k Oe to 16.95 k Oe by diffusion PN.The coercivity of 70wt.%Ce-Gd magnet is increased by 23.00%,from8.035k Oe to 10.96 k Oe by 36.40%,and the remanence is also increased from9.739 k Gs to 10.12 k Gs.Mixed diffusion PND can also greatly increase the coercivity of 30wt.%Ce-Gd magnet to 20.36 k Oe,with an increase of 47.75%.For 70wt.%Ce-Gd magnet,the coercivity increases from 8.035 k Oe to 13.47k Oe,with an increase of 67.64%.In addition,the residual magnetic loss of both magnets is small,and the temperature stability is improved.By observing the microstructure and analyzing the composition of magnets,it is found that the microstructure of the above diffusion magnets has been optimized to varying degrees.Moreover,the introduction of Pr H₃ and Nd H₃ into the diffusion source changes the composition of the grain boundary phase,and a large amount of Pr,Nd and Al elements are enriched in the grain boundary phase with grayish white contrast RE:Fe=1:2.Moreover,the content of Dy element in this phase is very small,which reduces the consumption of Dy element to a certain extent,Dy element is enriched more on the surface of the main phase,forming a thicker hard magnetized Dy-rich shell,which greatly improves the coercivity of the magnet.