Study On Preparation And Magnetic Behavior Of MnBi Permanent Magnetic Alloy

In recent years,the huge demand for rare earth permanent magnet materials lead to the excessive consumption of rare earth resources,new low-rare earth or non-rare earth permanent magnet materials become a hot spot.MnBi alloy is a new type of non-rare earth permanent magnet material,which has a high coercivity,moderate saturation magnetization and?BH?max,a positive coercivity temperature coefficient.It can be used in medium and high temperature environments.In this paper,the effects of different compositions,ingot pre-annealing parameters and milling parameters on the microstructure and magnetic properties of the alloy were studied in order to obtain high performance MnBi permanent magnet alloy materials.The magnetization behavior of MnBi/NdFeB composite magnets was investigated.?1?The effect of milling process parameters on magnetic properties of MnBi alloyIn order to improve the low temperature phase?LTP?content and magnetic properties of MnBi alloy,MnBi permanent magnetic alloy was prepared by arc melting and high-energy ball milling.It is found that the composition and milling time are important parameters for the magnetic properties.Therefore,the preparation process of MnBi permanent magnet alloy has optimized based on orthogonal experiment.It is found that the most significant factor main for the intrinsic coercivity of MnBi alloy is the Mn content.The optimized preparation conditions is alloy composition Mn₅₀Bi₅₀ and milling time 2 h.The intrinsic coercivity of the sample is as high as 1680 kA/m when temperature is 450 K,indicating excellent high temperature characteristics.The LTP content was the highest for Mn₅₀Bi₅₀0 alloy when the milling time is 2 h.The coercivity mechanism of MnBi alloy at room temperature and high temperature is nucleation mechanism.?2?The effect of non-rare earth element doping on magnetic properties of MnBi alloy.At present,it is difficult to prepare pure LTP MnBi alloy,and elemental doping is an important method to improve the permanent magnetic properties of MnBi alloy.Based on the optimization of the preparation conditions of MnBi permanent magnet alloy,the effects of Ga and Nb doping on microstructure and magnetic properties of MnBi alloy were investigated.The saturation magnetization of MnBi alloy decreases,the intrinsic coercivity increases,and the degree of orientation increases from 0.74 to0.79 with the increase of Ga content,indicating that the magnetic anisotropy of the alloy increases with Ga doping.The LTP content of MnBi alloy increases,and the saturation magnetization increases accordingly with the Nb doping.?3?The effect of pre-annealing of ingot on microstructure and magnetic properties of MnBi alloyThe LTP phase content of MnBi alloy increases,the saturation magnetization of the alloy increases greatly,while the intrinsic coercivity remains almost unchanged after the MnBi alloy ingot is pre-annealed.XRD result show that the value of I_MnBi?101?/I_Bi?012?reaches the maximum when pre-annealing time is 12 h,which is consistent with the trend of saturation magnetization.?4?Synthesis,Structure and Magnetization Behaviors of MnBi/Fe₃B/Nd₂Fe₁₄B nanocomposite alloyMnBi and Fe₃B/Nd₂Fe₁₄B alloy were synthesized by nano-scale with high-energy ball milling method.The microstructure and magnetic properties of MnBi/Fe₃B/Nd₂Fe₁₄B nanocomposites can be studied.As shown in the XRD results,LTP MnBi and Bi phases accompanied by Nd₂Fe₁₄B,Fe₃B and?-Fe phases were observed with the addition of Mn₅₅Bi₄₅ alloy.It was found that the coercivity from 192.8 kA/m to 311.2 kA/m with the Mn₅₅Bi₄₅content is 40 wt%.The?M and D?H?-H plots suggested the occurrence of a stronger exchange-coupling occurring between the hard and soft magnetic phase for the sample with the addition of 40 wt%Mn₅₅Bi₄₅.From 298K to 350K,a positive temperature coefficient is founded in 40 wt%Mn₅₅Bi₄₅/60 wt%Nd_4.5Fe_76.5Nb_0.5B_18.5alloy powder,which caused by the addition of Mn₅₅Bi₄₅ in the magnet.