Study On Key Technologies Of Ferrite Coated FeSiAl Magnetic Powder Core

With the rapid development of the electronics industry,people’s demand for electronic devices is also increasing,and correspondingly,miniaturization,high power,low loss characteristics are also required from magnetic electronic devices.In order to meet the performance requirements of magnetic powder cores for electronic devices,FeSiAl alloy powder was selected for preparation of metal composite magnetic powder cores.However,FeSiAl alloy has a large eddy current loss in high frequency applications,and ferrite coating agent with good performances was prepared by solid-state reaction method.The effects of NiZn ferrite,MnZn ferrite and SiO₂ single coating on the properties of FeSiAl composite magnetic powder cores were studied.Moreover,the effects of joint coating,molding pressure,annealing temperature and holding time on composite magnetic powder cores were also studied.Firstly,the FeSiAl alloy powder prepared using gas atomization method was selected,and the oxidation products on the surface of FeSiAl alloy powder were reduced by preheating treatment,which improved the comprehensive performance of magnetic powder core.At the same time,vacuum argon annealing was applied to avoid the reaction between the protective atmosphere and FeSiAl alloy.The binder is composed of 0.5 wt.%PVB,which can provide bonding and fluidity for granulation powder,and 0.5 wt.%silicone resin,which can retain silicon oxide in annealed magnetic powder core and enhance the density of magnetic powder core.Secondly,the effects of three coating agents on the properties of FeSiAl composite magnetic powder cores were studied.High-performance ferrite coating agent can be obtained by solid-state reaction method and high-energy ball milling method.SiO₂ powder with a particle size of 500 nm is used.NiZn ferrite can stabilize the initial permeability and specific saturation magnetization of the composite magnetic powder core,but its effect of increasing resistivity and reducing power loss is limited.MnZn ferrite has a high initial permeability,and the effect of improving the initial permeability,specific saturation magnetization and hysteresis loss of composite magnetic powder cores is better than that of NiZn ferrite.However,its resistivity is low,and cannot improve the high frequency loss characteristics of magnetic powder cores.The high resistivity of SiO₂ can significantly improve the resistivity of the composite magnetic powder core and reduce the eddy current loss,which is better than that of NiZn ferrite.However,SiO₂ is a non-magnetic material,and deteriorates the the initial permeability and specific saturation magnetization of the composite magnetic powder core even at a small amount.Then,based on the research results of a single coating scheme,a joint coating study was carried out for the above three coating agents.Using the joint coating of NiZn ferrite and MnZn ferrite,the effect on improving the resistivity of magnetic powder core is not obvious.As a result,the effect of improving the power consumption characteristics of magnetic powder core in high frequency band is not significant.The joint coating of SiO₂ and NiZn ferrite was also adopted,but the SiO₂ addition deteriorates the magnetic properties such as the initial permeability of the magnetic powder core.The joint coating of SiO₂ and MnZn ferrite can take into account both the initial permeability and power loss.Finally,the research on the preparation process of the composite magnetic powder core shows that the appropriate molding pressure can increase the density of the magnetic powder core,and improve the magnetic properties such as permeability and power consumption.Moreover,appropriate annealing temperature and annealing time can promote FeSiAl alloy to form D0₃ superlattice ordered structure,eliminate the internal stress of magnetic powder core and improve its comprehensive magnetic properties.