Study On The Properties Of Nd-Fe-B Magnets Prepared By Grain Boundary Diffusion Sintering Of Low Melting Point Heavy Rare Earth Allo

Sintered Nd-Fe-B magnets have excellent magnetic properties,but their temperature stability and corrosion resistance are poor.In order to improve these problems,people usually add heavy rare earth elements.The traditional single alloy method of adding heavy rare earth elements can improve the coercivity and thermal stability of magnets,but it consumes a large amount of heavy rare earth elements.Therefore,in this study,three low melting point alloys,Dy-Cu,Dy-Cu-Ga,and（Pr-Dy）-Cu-Ga,were designed as diffusion sources to diffuse on the surface of sintered Nd-Fe-B magnets using grain boundary diffusion technology to reduce the consumption of heavy rare earths.By searching for the best heat treatment process,the reasons for improving the magnetic properties,temperature stability,and corrosion resistance of magnets due to grain boundary diffusion were studied.This research has important application value for developing high-performance and low-cost magnets.In this paper,we first discussed how to improve the performance of sintered Nd-Fe-B magnets by adding Dy-Cu and Dy-Cu-Ga low melting point alloys,while optimizing the grain boundary diffusion process.By studying the diffusion effects of diffusion sources with different composition ratios on magnets,it is concluded that the low melting point heavy rare earth alloy Dy₇₀Cu₁₅Ga₁₅ has the best magnetic properties and microstructure after diffusion.After coating a Dy₇₀Cu₁₅Ga₁₅ low melting point alloy source on the surface of N40M sintered Nd-Fe-B magnets through a patch process and a sputtering process,and obtaining the optimal heat treatment diffusion process through orthogonal experiments,the residual magnetism and maximum magnetic energy product are slightly reduced while significantly improving the intrinsic coercive force,especially when the sputtering time of the sputtering process is 180minutes.Grain boundary diffusion optimizes the distribution of grain boundary phases,forming（Nd,Dy）₂Fe₁₄B phases,enhancing the anisotropic field of the defect layer,inhibiting the nucleation of demagnetized domains,and making the Nd rich phase transition in the thin layer straight and continuous,effectively isolating adjacent main phases,weakening the magnetic coupling effect.At high temperatures,the grain boundary diffusion magnet has a relatively low reduction in magnetic flux and a relatively small irreversible magnetic flux loss rate,so it has good high-temperature stability.In addition,electrochemical experiments have found that the diffused Dy₇₀Cu₁₅Ga₁₅ alloy magnet has better corrosion resistance than the original magnet.The study also found that after diffusion,the main phase peak of the magnet shifted towards a large angle,which is due to the result of Dy entering the main phase replacement part Nd.Secondly,based on the diffusion of Dy₇₀Cu₁₅Ga₁₅ low melting point alloy,a（Pr Dy）-Cu Ga alloy diffusion source was prepared by using partial light rare earth element Pr instead of heavy rare earth element Dy,reducing costs.By comparing the magnetic properties of diffusion samples with different ratios of Pr and Dy content,it is concluded that the sample with(Pr₇₅Dy₂₅)₇₀Cu₁₅Ga₁₅ alloy source diffusion has the best comprehensive performance.Pr element increases the amount of rare earth in the main phase grains,resulting in a larger main phase volume fraction of the magnet,resulting in a significant increase in remanence and maximum magnetic energy product.In addition,due to more low melting point elements that modify the microstructure and distribute more uniformly,the squareness of the magnet is better.The(Pr₇₅Dy₂₅)₇₀Cu₁₅Ga₁₅ alloy diffusion magnet has higher grain orientation,wide and straight grain boundary phase transitions,smaller and more numerous main phase grains,and forms a（Nd,Pr,Dy）₂Fe₁₄B core shell layer.The remanence temperature coefficient and coercive force temperature coefficient of the diffusion sample have been improved compared to the original sample,indicating that the temperature stability of the diffusion sample has been improved.