Research On The Correlation Between The Properties Of Raw Powders And The Properties And Microstructure Of Hot-Deformed Magnets

After the sintered magnets and the bonded magnets,hot-deformed magnets become a new type of magnet.Because it has smaller grains,needs fewer heavy rare earth and don't need to be oriented in magnetic field.However,compared with the sintered magnets that are applied widely,the magnetic properties of hot-deformed magnets are still relatively low,especially the coercivity.The magnetic properties of hot-deformed magnets are closely related to its microstructure,so it is very important to study the microstructure.In order to improve the macroscopic magnetic properties of hot-deformed magnets,many researchers optimized the microstructure of magnets from two aspects:adjustment of process parameters and introduction of elements.The research results show that the main reasons for the enhancement of magnetic properties of hot-deformed magnets are refinement of grains and uniform distribution of RE-rich phase at the grain boundary.So based on our team's research on the process,we designed experiments to study the microstructure and macroscopic properties of hot-deformed magnets in this thesis,with the aim of obtaining high-performance hot-deformed magnets.In this thesis,the particles size of magnetic powders was firstly studied,and its influence on the microstructure and macroscopic properties of hot-pressed and hot-deformed magnets was analyzed.By analyzing the experimental results,it is found that the hot-pressed magnets prepared by 80?120 mesh magnetic powders have relatively high magnetic properties,and the best magnetic properties of hot-pressed magnets are Hcj=18.67 kOe,Br=7.78 kGs,(BH)max=13.32 MGOe.In addition,the microstructure analysis shows that the particles size of magnetic powders can seriously affect the density of hot-pressed magnets,when the particles size is large,the pore defects in the direction of particle height are easy to appear;when the particles size is small,there are not only defects of height direction,length direction,but also defects of small particles aggregation.On the other hand,the magnetic properties of the hot-deformed magnets were higher when the particles size is in 80-120 mesh and 120-170 mesh,and in 80-120 mesh the properties of are Hcj=14.76 kOe,Br=13.16 kGs,(BH)max=40.07 MGOe,in 120?170 mesh the properties are Hcj=14.42 kOe?Br=13.32 kGs?(BH)max=40.77 MGOe.However,the influence of particles size on the microstructure of hot-deformed magnets is mainly in the distribution of RE-rich phase,and it has little influence on the grains size of hot-deformed magnets.When the particles size is small,it is easy to cause the enrichment of rare earth elements at the particles interface and affect the macroscopic magnetic properties of hot-deformed magnets.The grains size of the hot deformed magnets does not change with the change of particles size,and the length is stable at about 237 nm,the height is stable at about 55 nm.In this thesis,the influence of the presence of noncrystalline phase in magnetic powders on the structure and properties of hot-deformed magnets was studied.The research results show that hot-deformed magnets prepared by magnetic powders with relatively high amorphous content have higher magnetic properties and orientation.And when the magnetic powders were prepared at the wheel speed of 35 m/s,its amorphous content was relatively high,and the magnetic properties of hot-deformed magnets prepared by them are Hcj?14.50 kOe,Br=13.26 kGs,(BH)max=40.28 MGOe,and its performance was 4.2 kOe,0.76 kGs and 7.53 MGOe higher than that of hot-deformed magnets prepared by 25 m/s wheel speed magnetic powders,respectively.As for the influence of the amorphous content of magnetic powders on the microstructure of hot-deformed magnets,the distribution of rare earth rich phases in hot-deformed magnets is the main one.When the amorphous content of the magnetic powders is relatively high,the rare earth phase of hot-deformed magnets is mainly uniform distributed around the grains,the overall microstructure uniformity of the hot-deformed magnets is relatively good,and the magnetic properties of hot-deformed magnets are higher.When the amorphous content of the magnetic powders is relatively low,the rare earth phase of hot-deformed magnets is mainly distributed uniformly around the particles.The overall microstructure uniformity of hot-deformed magnets is relatively poor,so the overall magnetic properties of hot-deformed magnets are relatively low.In addition,the simulation results of OOMMF show that the anti-magnetization domain is formed in RE-rich grain boundary phase in the process of demagnetization.And the hot-deformed magnets with small grains size and RE-rich phase mainly distributed among the grains have lower demagnetization energy and relatively later change of exchange energy in the process of demagnetization,so they have higher magnetic properties.