Preparation And Loss Reduction Mechanism Of Iron-based Soft Magnetic Composites With High Permeability And Low Loss

The soft magnetic composite material can be regarded as an overall multi-phase system containing at least one dielectric phase,and the purpose of reducing loss was achieved by insulating coating of a dielectric relative to a single particle.The insulating coated soft magnetic powder was made into devices by different molding methods,and then heat treated to relieve residual internal stress.As a new type of magnetic functional material,soft magnetic composite material has the characteristics of high magnetic permeability and low loss,and has the complex formability of powder metallurgy,so that it has new applications in the fields of energy,communication,medical treatment,machinery manufacturing and other fields in modern society.The application of soft magnetic composite materials at medium and high frequencies requires further suppression of eddy current loss.Insulating coating was used as an important means to block the induced current between particles in an alternating magnetic field,which can be divided into organic coating and inorganic coating.Inorganic coating has poor adhesion,but good thermal stability.The film formed by the organic coating was uniform,but the annealing temperature that can withstand was low,and the residual internal stress cannot be fully released.The materials used in these two coating methods are mostly non-magnetic materials,and the induced magnetic dilution effect will reduce the magnetic permeability.In this paper,three different insulation coating methods are used to reduce the magnetic loss at medium and high frequency,and to improve the permeability through the transition of insulating materials from non-magnetic to magnetic.Characterize the morphology and microstructure of the coated particles.During the surface treatment of phytic acid,PA-and iron ions are combined in the aqueous solution,and part of the crystallization occurs during annealing to form a composite film containing metal chelate,phosphate,iron oxide and hydroxide.Through the electrodynamic polarization curve test,it was found that the corrosion resistance of the sample has been optimized,and the environmental adaptability has been improved.The in-situ coating formed on the surface of the reduced iron powder can block the conduction path of the induced current in the alternating magnetic field and reduce the eddy current loss between particles.However,since the insulating coating layer was a non-magnetic material,the magnetic dilution effect reduces the magnetic permeability.To alleviate the magnetic dilution effect,an iron-based soft magnetic composite material coated with nanometer Mg0.2Cu0.3Zn0.5Fe2O4 ferrite was prepared by ball milling.Mg0.2Cu0.3Zn0.5Fe2O4 ferrite has soft magnetic properties and high resistivity.During the ball milling process,the impact of the ball milling beads flattened the ellipsoid-shaped reduced iron powder,and the agglomerated nano ferrite was dispersed on the surface of the reduced iron powder to form an insulating layer.The increase of the flat reduced iron powder also changed the internal microstructure of the molded sample from granular to lamellar,and the magnetic interaction between the powders changed the magnetic flux density.However,the layered structure also causes stress concentration,hinders the movement of magnetic domains,and increases the coercive force.The change of the microstructure increases the magnetic anisotropy and shape anisotropy,resulting in an increase in magnetic loss.In order to further alleviate the influence caused by the magnetic dilution effect,a magnetic insulating material was constructed through phosphoric acid surface treatment of carbonyl iron powder.The mixing ratio of the small particle size carbonyl iron powder and the large particle size reduced iron powder can be changed to achieve the coating effect in the three-dimensional space after molding.Phosphoric acid surface treatment can improve the resistivity of small particle size carbonyl iron powder.Observation of the microstructure after forming shows that the multiple insulating interfaces inside the carbonyl iron powder aggregation area can better block the current path and effectively reduce the eddy current loss.However,the non-uniformity of the distribution will increase the coercive force and affect the hysteresis loss.By comparing the initial permeability and maximum permeability of the iron-based soft magnetic composites prepared by the three coating methods,it was found that the addition of magnetic insulating materials improves the magnetic interaction inside the sample and increases the permeability.The transition of insulating materials from non-magnetic to magnetic improves the potential of the sample in the application of medium and high frequency,which is conducive to the miniaturization of the device.