The Microstructure And Magnetic Properties Of Mn-Al-C Magnets Prepared By Melt-sppinning And High Pressure Thermal Compression

In recent years,the bottleneck of the development of rare earth permanent magnet material and the international rare earth crisis make the research of rare earth free permanent magnet material hot.Mn-Al based rare earth free permanent magnet material has good mechanical properties,corrosion resistance,and so on.The advantages of high anisotropy constant,low density and low cost of raw materials have been active in the research of permanent magnet materials.In Mn-Al-based permanent magnets,the hard magnetic phase is metastable phaseτphase,and the preparation of high contentτphase and the regulation of microstructure have always been two major problems in the study of the system.In this paper,Mn-Al-C permanent magnetic materials with highτphase content were prepared by melt spinning and high pressure thermal compression.The effect of small-size atomic radius C atom on the microstructure and magnetic properties of Mn-Al-based ribbons was studied systemly.The anisotropic bulk was prepared by high pressure thermal compression deformation process,and the microstructure of the sample was controlled by changing the parameters of high pressure thermal compression deformation process,so that the magnetic properties of the sample could be improved.The effect of C on the microstructure and magnetic properties of Mn₅₄Al_（46-x）C_x quenched permanent magnet was studied.By changing the content of C in Mn₅₄Al_（46-x）C_x alloy,the precursor with high temperature phaseεas the main phase was prepared by means of melt spinning successfully.Then the precursor was annealed at a series temperature,so that the high temperature phase transformed into hard magnetic phase,and the ribbons with the hard magnetic phaseτphase as the main phase were obtained.It was found that the grain size of the alloy was refined by adding appropriate amount of C,and the coercivity of the alloy was improved by increasing the pinning point in the crystal structure.In addition,the decomposition temperature of the hard magnetic phase is increased and the stability of the hard magnetic phaseτphase is improved with the addition of C atom.The magnetic properties of the alloy can be improved by adding appropriate amount of C element.When the alloy composition is Mn₅₄Al₄₄C₂,the composite magnetic properties of the ribbons annealed at 550℃are the highest,（BH）_max=1.6 MGOe,H_ci=1.8 kOe,B_r=3.8 kG,M_s=7.2 kG.The effects of deformation temperature and holding time on the microstructure and magnetic properties of Mn₅₄Al₄₄C₂ anisotropic nanocrystalline bulk were investigated.The ribbons withεphase as the main phase were used as precursors.The high pressure thermal compression experiments were carried out under different deformation temperature and holding time,and the high temperature phase was completely transformed into the hard magnetic phaseτphase,and the dense anisotropic Mn-Al-C nanocrystalline bulk material was prepared.It was found that the maximum magnetic properties of the magnets were obtained when the deformation temperature was 550℃and the holding time was 30s:M_s=4.8 kG,B_r=3.1 kG,H_ci=3.0 kOe,（BH）_max=1.8 MGOe;The grain size of the magnet prepared by high pressure thermal compression is less than 200 nm,the hard magnetic phase has a certain degree of orientation arrangement,orientation degree of the magnet can be improved up to 0.4.