Study On Magnetic Properties And Low Loss Properties Of FeSiAl Powder Core

With the power electronic devices’developing trend of high frequency,miniaturization and lightweight in recent years,higher requirements are put forward for the physical properties of soft magnetic composites（saturation magnetization,resistivity,magnetic loss and high-frequency stability）,and the existing soft magnetic composites are gradually hard to satisfy the increasing technical needs.Taking the FeSiAl alloy with high resistivity,magnetocrystalline anisotropy constant and magnetostrictive coefficient close to zero as the research object,this paper studied the effects of carbonyl iron powder filling,additional transverse bias field（external and internal）and insulating coating on the magnetic properties of FeSiAl based soft magnetic composites.The microstructure,saturation magnetization,permeability,magnetic loss,magnetic spectrum DC bias characteristics and loss separation mechanism were analyzed.The main results are as follows:1.The preparation of FeSiAl/carbonyl iron powder soft magnetic composites was studied.FeSiAl/carbonyl iron powder soft magnetic composites were prepared by filling an appropriate amount of carbonyl iron powder between FeSiAl micron particles passivated by phosphoric acid in situ.The microstructure and magnetic properties of the soft magnetic composite were tested and the results show that filling an appropriate amount of carbonyl iron powder can improve the permeability and saturation magnetization of FeSiAl magnetic particle core and reduce the magnetic loss.Under the optimal sample preparation conditions,the magnetic loss value is about 490 kW/m³（100 mT,100 kHz）.2.The magnetic properties of FeSiAl/SiO₂ soft magnetic composite under transverse bias field were studied.It is found that under the action of 140kA/m transverse bias field,the permeability of the soft magnetic composite decreases by about 8%.Compared with the soft magnetic material without magnetic field,the magnetic loss decreases by about 32%when the magnetic flux density is 50 mT and the frequency is 10 kHz.By fitting the loss separation formula,it is found that the reduction of magnetic loss under transverse bias field mainly comes from the reduction of hysteresis loss.3.The coating structure of FeSiAl alloy particles/SrFe₁₂O₁₉（SrM）ferrite was designed.M-type permanent magnet hexagonal SRM ferrite was used to coat FeSiAl alloy powder.The SrM ferrite shell in the sample was magnetized by external magnetic field to form an internal bias field.The magnetic properties of FeSiAl alloy particles/SrM ferrite coated structure samples were analyzed.When the content of SrM ferrite is 8.1 wt.%,the magnetic permeability decreases by about 14%and the magnetic loss decreases by about 50%.It is found that the built-in bias field can effectively reduce the hysteresis loss,while the eddy current loss is basically not affected,and its effect is the same as that of the external transverse bias field.4.FeSiAl/hexagonal boron nitride（hBN）soft magnetic composites were designed.Layered hBN was coated on the surface of aerosolized FeSiAl particles to prepare FeSiAl/hBN soft magnetic composites.The magnetic properties of the structural sample are analyzed.The experiment shows that when the hBN content is 1 wt.%,the magnetic loss value of the sample is about 392 kW/m³（100 mT,100 kHz）,and the imaginary part cut-off frequency of the complex permeability is higher than 30 MHz,indicating that the material has potential application value in high-frequency working environment.The results of loss separation show that the sample has a very small eddy current loss coefficient,which may be due to the fact that hBN coating effectively blocks the eddy current between FeSiAl alloy particles.Under the action of 140kA/m transverse bias field,the magnetic loss of the sample is further reduced to about 256 kW/m³（100 mT,100 kHz）,which is far lower than that of similar products of Meici company.