The Effect Of PrFe Alloy Grain Boundary Diffusion On Microstructure And Magnetic Properties Of Sintered NdFeB Magnets

As an excellent permanent magnet material,sintered Nd Fe B permanent magnetic material is widely used in electrical appliances,motors and other modern equipment.With the development of the application field of magnetic materials,the demand for coercivity of sintered Nd-Fe-B permanent magnetic materials is increasing.In recent years,grain boundary diffusion,as an effective method to improve coercivity,has become the focus of research.In the conventional diffusion process with heavy rare earth elements（Tb,Dy,etc.）alloys as diffusion sources,the strengthening of coercivity comes from the formation of high anisotropic field shell structure,but the optimization of grain boundary continuity is not obvious,and the demagnetization exchange coupling effect needs to be improved.The continuity of grain boundaries can be improved by using trace elements and non-heavy rare earths to form low melting point alloy diffusion sources.At the same time,based on the dependence of grain boundary structure and coercivity,RE₆Fe₁₃Ga grain boundary phase formation process will optimize the microstructure of sintered Nd-Fe-B magnets,so that the coordination of diffusion source and original magnet is of great significance to the improvement of coercivity.In this paper,by means of grain boundary diffusion,according to the phase formation characteristics and composition range of RE₆Fe₁₃Ga phase,the formation of continuous grain boundary structure and the optimization of RE₆Fe₁₃Ga relative magnet surface were promoted,and the sintered Nd-Fe-B magnets with high coercivity were obtained.The grain boundary phase formation mechanism and the effect of grain boundary diffusion on grain boundary phase and structure of sintered Nd Fe B magnets were clarified.The main research results are as follows:（1）The effect of grain boundary diffusion of PrFe alloy on the grain boundary structure and magnetic properties of magnets with low B content of Ga has been studied systematically.With the increase of the PrFe alloy diffusion source content,the coercivity of the magnet increases rapidly from 15.77k Oe,and the 22.2 k Oe coercivity magnet is obtained when the ratio of the diffusion source content to the magnet mass is 8 wt.%,while the coercivity decreases with the further increase of the PrFe alloy diffusion source content.Phase analysis and structure show that under proper grain boundary diffusion of PrFe alloy,RE₆Fe₁₃Ga phase is formed in the magnet during tempering and is accompanied by the formation of continuous grain boundary phase.In addition,by adjusting the proportion of PrFe alloy elements in the diffusion source,the effect of the diffusion behavior of Pr elements on the grain boundary structure and Ga element distribution was found.Therefore,the optimization of the microstructure and element distribution of grain boundary phases in PrFe alloy grain boundary diffusion magnets finally leads to a great increase in the coercivity of sintered Nd Fe B permanent magnets during tempering.（2）Furthermore,the phase composition and magnetic properties of low B magnets without Ga were studied by introducing Ga element into magnets by grain boundary diffusion PrFeGa alloy.The magnetic properties of the magnets show that the magnets with the highest comprehensive magnetic properties can be obtained by grain boundary diffusion of the Pr₇₀Fe₃₀Ga₁₀diffusion source,and the coercivity of the magnets is increased from 12.09 k Oe to 22.51 k Oe compared with the unadded original magnets.However,with the increase of Ga content in the diffusion source,the improvement of magnetic properties decreases.Elemental analysis shows that the introduction of Ga element into the magnet surface optimizes its distribution through grain boundary diffusion,regulates the local grain boundary structure,and promotes the phase formation and continuous grain boundary phase formation of non-ferromagnetic RE₆Fe₁₃Ga phase during tempering.Therefore,the coercivity of the magnet is significantly improved.On the other hand,the excessive diffusion of Ga elements will lead to the enrichment of Ga elements in the triangular crystal region,and the diffusion of Pr elements will be inhibited,resulting in the weakening of grain boundary continuity.