Study On The Magnetic Property Control And Domain Structure Of Sintered Magnet With Misch-metal

The rare-earth permanent magnet industry has been booming since Nd-Fe-B magnets were discovered in the 1980s.As the necessary elements for the Nd-Fe-B sintered magnets preparation,Pr and Nd have been widely used for decades,resulting in the large number of piles of symbiotic element,such as La and Ce,which caused the cost increment and unbalanced use of rare earth resources.Therefore,the application of La,Ce and MM with high abundance has been one of the research directions.The magnetic properties of RE-Fe-B sintered magnet are closely related to the microstructure and element distribution of the magnet,so the sintered MM-Fe-B magnet is more valuable because of its complex microstructure and element distribution.In this paper,high performance(Nd_1-xMM_x)-Fe-B sintered magnets were prepared by mixing and sintering Nd-Fe-B powder and MM-Fe-B powder in different proportions using the preparation process of double principal phase.The magnetic properties,especially the coercivity,were improved by adding Nd-Al-Cu alloy powder to improve the performance and microstructure of the magnet.The sintered magnet with nominal composition(Nd_1-xMM_x)-Fe-B?x=0?0.3?0.5?0.7?1?was prepared by mixed rare earth?MM?combined with dual principal phase process.Its magnetic properties decreased and the remanence of the sample reduced by 26.25%?14.21kGs-10.48kGs?with the MM/RE increased from 0%-100%,while the coercivity and magnetic energy product were significantly reduced by 89.25%?13.40kOe-1.44kOe?and78.86%?48.54MGOe-10.26MGOe?,respectively.The magnetic residual magnetism,coercivity and magnetic energy product of the magnet were maintained at 13.17kGs,6.23kOe and39.88MGOe with 30wt.%MM-Fe-B powder introduction,and the magnetic ability was maintained well.XRD results showed that the phase composition of(Nd_1-xMM_x)-Fe-B sintered magnet possessed 2:14:1 structure with the increase of MM content.When the MM content exceeded 30wt.%,the diffraction peak of REFe₂ phase appears,and the intensity of the diffraction peak increases with the increase of MM content,which indicates that the content ofREFe₂ phase in magnet increases.The SEM-EDS and domain structure of(Nd_0.5MM_0.5)-Fe-B sintered magnet were analyzed,revealing that La and Ce elements in the MM magnet were diffused into the main phase grains of Nd-Fe-B.Observation of magnetic domains that parallel to orientation by magneto-optical Kerr microscope,when x=0,the domain structure of the magnet are bar domain,The domain structure of some grains of the magnet with MM tends to maze domain,and in the grains of La-Ce-rich tends to be maze domain,indicating that the orientation degree of the magnet is poor.In order to further optimize the microstructure and coercivity of the magnet,1wt.%Nd-Al-Cu alloy powder was added to the sintered magnet(Nd_1-xMM_x)-Fe-B?x=0.3?0.5?0.7?.Without reducing the remanence,when x=0.3,coercivity increased by 51%?6.23kOe-9.38kOe?;when x=0.5,coercivity increased by 21%?5.90kOe-7.14kOe?;when x=0.7,coercivity increased by 43%?3.18kOe-4.55kOe?.It is found that the reason for the increase of coercivity is that the agglomeration of rare earth rich is improved,a uniform thin-layer grain boundary phase formation and the main phase grains are surrounded,which weakens the coupling effect between main phase grains.At the same time,due to the diffusion of Nd element,it forces the core-shell structure of the magnet changed from that of La?Ce elements outside and Nd elements inside to La?Ce elements outside and Nd elements inside,which improves the anisotropy of grain edge.