| The rapid development of Nd-Fe-B rare earth?RE?permanent magnetic materials results in the excessive consumption of medium and heavy rare earth elements,such as Pr,Nd,Dy,Tb.The results in the price hike of these elements and increase production cost ultimately.However,the application of La and Ce elements in RE permanent magnetic materials has not been paid proper attention,which has resulted market backlog and waste of RE resources.Secondly,the RE purification process is complicated,expensive,manpower consuming and causes environmental pollution.Therefore,from the perspective of raw material cost and national strategies,it is imperative to use Misch-metal in research and development of RE permanent magnetic materials.In this thesis,the nanocrystalline MM-Fe-B based alloys and magnets were prepared by using the Misch-metal from Longnan ore,and the relationship of the magnetic properties,microstructure,thermal stability and composition were explored in depth.Firstly,the nanocrystalline MM-Fe-B based alloy was prepared by melt quenching technique.The alloy composition was optimized by changing the ratio between La/Ce and Pr/Nd.The results show that with the increase of La/Ce content the coercivity and remanence decrease gradually.The results of Henkel curve show that the change of La/Ce and Pr/Nd ratio has no obvious effects on the exchange coupling among the main phase grains,the grain size and the relative orientation of the magnetic moment.When the La/Ce and Pr/Nd are in natural ratio,the average recovery permeability of the alloy is the smallest,i.e.,1.33×10-4H/m.This indicates that the alloy in the natural ratio state has a stronger resistance to external magnetic field interference in the periodic reverse magnetic field,the properties of the alloy is Hcj=598 kA/m,Jr=0.83 T and?BH?max=102 kJ/m3.Sencondly,after determining the ratio of La/Ce and Pr/Nd of the alloy,the alloy composition was further optimized by changing the total amount of RE,and the influences of RE content on the magnetic properties,thermal stability and microstructure of the alloy were studied by transmission electron microscopy and comprehensive physical property measurement system.The results show that as the MM content increases,the coercivity of all the ribbons shows an increasing trend,while the remanence shows a decreasing trend.With the content of the MM increases,the thermal stability has deteriorated.By the EDS analysis,we have clarified that the temperature stability is mainly related to the distribution of RE content in the main phase.The comprehensive properties of the alloy obtained under the optimum processing conditions are:Hcj=899 kA/m,Jr=0.87 T and?BH?max=116 kJ/m3.This study has certain advantages for the production of cost-effective MM-Fe-B magnets.Finally,based on the above-mentioned optimal alloy,an isotropic nanocrystalline MM-Fe-B based magnet was prepared by spark plasma sintering.The relationship between sintering temperature and phase composition,microstructure,magnetic properties of nanocrystalline magnets was investigated.The results show that as the sintering temperature increases,the porosity in the magnet decreases,and the density of the magnet is significantly increases.The 700?/50 MPa/5 min was determined to be the optimum sintering conditions whereby the magnet has a higher density and a relatively small grain size and have the best comprehensive magnetic properties of Hcj=525 kA/m,Jr=0.76 T,?BH?max=82 kJ/m3.This paper mainly studies the properties,structure and magnetic properties of nanocrystalline MM-Fe-B based alloys and magnets prepared by southern ionic mixed rare earth.This work is of certain academic value and practical significance in the research and development of RE permanent magnets using the southern ionic mixed rare earth elements. |
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