Preparation And Properties Of FeSi Magnetic Powder Cores With High Performance

Soft magnetic composite（SMCs）is a magnetic material composed of ferromagnetic particles and insulating coating materials.Due to its three-dimensional isotropic structure,low loss in high frequency and other excellent magnetic properties,the soft magnetic composite is widely used in transformers,inductors and other electrical equipment.With the development of high frequency,miniaturization and high power of modern electronic devices,higher requirements are put forward for the performance of magnetic core materials.In this paper,FeSi magnetic powder core,FeSi/carbonyl iron magnetic powder core and FeSi/hexagonal boron nitride magnetic powder core were prepared by using FeSi powder as the main magnetic powder.The influence of material composition and preparation process on the performance of magnetic powder core was systematically studied.FeSi-based magnetic powder core was prepared by powder metallurgy.The effects of particle size ratio,resin content,molding pressure and sintering temperature on the microstructure and magnetic properties of magnetic powder core were studied.The magnetic powder core prepared by single coarse particle（200 mesh）has large internal pores.The addition of fine particle（400 mesh FeSi powder）can fill the gap between coarse particle to improve the density,and then optimize the performance of magnetic powder core.Pressing pressure and sintering temperature will also affect the performance of magnetic powder core.When the pressure is small,the density of the magnetic powder core will be low,but if the pressing pressure is too high,the insulating layer on the surface of the magnetic powder will be damaged.The selection of sintering temperature is required to release the internal stress to the maximum extent while ensuring a small amount of resin decomposition.When the amount of fine powder is 20 wt%,the amount of resin is 2 wt%,the molding pressure is 1300MPa and the heat treatment temperature is 500℃,the FeSi magnetic powder core achieves the excellent comprehensive performance:permeability of 64,Saturation magnetization of 190.1emu/g,DC-bias performance of 66%（100Oe）,quality factor of48.8 and core loss of 7.38 W/kg（20 m T,100 k Hz）.FeSi/carbonyl iron magnetic powder core was prepared by powder metallurgy.The effects of carbonyl iron powder content,resin content,molding pressure and heat treatment temperature on the microstructure and magnetic properties of FeSi/carbonyl iron magnetic powder core were studied.Compared with FeSi powder,carbonyl iron powder has good molding performance,but its magnetic loss is large.Therefore,it is necessary to adjust the composition ratio and process parameters to ensure high permeability under the condition of low loss.In addition,the preparation process also has a significant impact on the performance of magnetic powder core.If the molding pressure is too low,the magnetic powder is not compacted.There will be many voids in the magnetic powder core,resulting in low permeability.But if the pressure is too high,the particles are broken,which is adverse to obtaining excellent magnetic properties.Otherwise,if the sintering temperature is too low.The internal stress is not completely released,but if the sintering temperature is too high,the resin will decompose,so it needs a suitable molding pressure and sintering temperature.When the content of carbonyl iron powder is 25 wt%,the content of resin is 2 wt%,molding pressure is 1200 MPa and sintering temperature is 500℃,FeSi/carbonyl iron magnetic powder core has the best comprehensive properties:permeability of 69,saturation magnetization of 202 emu/g and core loss of 11.1 W/kg（20 m T,100 k Hz）.The microscopic loss of the magnetic core is inevitable,which leads to local heating of the device.FeSi/h-BN magnetic powder core with high thermal conductivity was prepared by introducing hexagonal boron nitrite（h-BN）,and the influence of h-BN content on the magnetic and thermal properties of FeSi/h-BN magnetic powder core was studied.When the content of h-BN is 2 wt%,FeSi/h-BN magnetic powder core has good comprehensive magnetic properties and the best thermal conductivity:permeability of 50.1,saturation magnetization of 177.6 emu/g,core loss of 7.59 W/kg（100 k Hz,20 m T）and thermal conductivity of 8.124 W^-1K^-1.