Soft Magnetic Composite Powder Core For Motor

Soft magnetic composite is widely used in the manufacture of motor soft magnetic cores and other electronic devices due to their excellent soft magnetic properties such as high saturation magnetization,high resistivity and low loss at medium and high frequencies.With the development of high-speed motors and the increase in motor speed,power electronic equipment is gradually developing in the direction of high frequency,miniaturization and high conversion efficiency.In order to meet the development needs,higher requirements are put forward for the soft magnetic properties of soft magnetic composite materials.Soft magnetic composite materials need to further reduce the magnetic loss generated at medium and high frequencies.Selecting a cladding material with high insulation and a suitable cladding process is a key step to ensure the integrity and cladding effect of the cladding layer.It is also an effective method to reduce the magnetic loss of the material.In this paper,water atomized iron powder is used as the matrix material.The Mg O,phosphate and Si O₂ are used as insulating coating materials respectively.Iron-based soft magnetic composite materials are prepared through four different insulating coating methods,which can reduce the composite material’s resistance to medium and high frequencies.Magnetic loss,and characterize and analyze the morphology of the coated magnetic powder and the soft magnetic properties of the material after molding and annealing.（1）Fe/MgO soft magnetic composites were successfully prepared by mechanical mixing method with basic magnesium carbonate as Mg O source.By studying the influence of various parameters on the soft magnetic properties of the material during the mixing process.It was found that when the Mg O content was 0.2 wt%,the mechanical mixing time was 30 min,and 0.8 wt%glass powder binder was added 10min before the end of the mixing to produce Fe/Mg O soft magnetic composite material with relatively excellent performance was obtained,and the magnetic loss of the material was 362 W/kg（500 m T,1000 Hz）.However,this preparation process is prone to incomplete coating,and the H₂O and CO₂ produced by the decomposition of basic magnesium carbonate at high temperature will also damage the coating.Therefore,the heat treatment temperature of this composite material should not exceed 500°C.（2）In order to ensure the integrity of the coating layer,the water atomized iron powder was passivated by the phosphoric acid passivation method to realize the insulation coating of the atomized iron powder by iron phosphate salt,and the iron/phosphate soft magnetic composite material.In order to find the best experimental parameters in the passivation coating process,the effects of solvent type,phosphating solution concentration,iron powder ratio,annealing temperature,iron powder particle size distribution and solid lubricant addition on iron/phosphoric acid were systematically studied.Effect of salt on soft magnetic properties of soft magnetic composites.The results show that the passivation effect of acetone phosphate solution is better than that of phosphoric acid aqueous solution,and when the concentration of phosphating solution is 0.10 g/m L,the proportion of iron powder is 0.62 g/m L,and the magnetic properties of composite materials are annealed at 500℃.The loss is the smallest,which is 44 W/kg（500 m T,1000 Hz）,which is 87.8%lower than the magnetic loss of Fe/Mg O soft magnetic composite prepared by mechanical mixing.Increasing the content of large particle size magnetic powder and the distribution range of magnetic powder particle size and adding solid lubricant to the magnetic powder can effectively improve the comprehensive magnetic properties of the composite material.However,the phosphate coating is easy to decompose and fail at high temperature.Therefore,the heat treatment temperature of the iron/phosphate soft magnetic composite should not exceed 500°C.（3）The passivation treatment of the powder particles of the Fe/Mg O soft magnetic composite material prepared by mechanical mixing can improve the cladding effect of the composite material.The magnetic loss of the material is 147W/kg（500 m T,1000 Hz）.The magnetic loss is 59.4%lower than that before passivation.In order to further improve the soft magnetic properties of Fe/Mg O soft magnetic composite materials,the characteristics of easy evaporation of Mg are used,and the high-temperature evaporation method is used to first passivate the iron powder with phosphoric acid,and then passivate the iron powder and magnesium.The scraps were mixed,and Mg vapor reacted with phosphate to form Mg O in a vacuum and high temperature environment,which was coated on the surface of iron powder,and a new type of Fe/Mg O soft magnetic composite material was prepared.The maximum annealing temperature of the Fe/Mg O soft magnetic composite prepared by this method is 650℃,and increasing the molding temperature during the pressing process can effectively increase the sample density and reduce the magnetic loss of the material.When the Mg content is 0.4 wt%,the hot-pressing temperature is80℃,and the annealing temperature is 600℃.The magnetic loss of the composite is the smallest,which is 51 W/kg（500 m T,1000 Hz）,which is softer than Fe/Mg O prepared by mechanical mixing.The magnetic loss of the magnetic composite material is reduced by 85.9%.（4）Fe/SiO₂ soft magnetic composites were prepared by using the sol-gel method and using Tetraethyl orthosilicate（TEOS）and Na₂Si O₃ as silicon sources to insulate iron powder.Under the optimal experimental parameters,the soft magnetic properties of Fe/Si O₂ soft magnetic composites prepared from different silicon sources are not much different.When using TEOS as the silicon source to prepare Fe/Si O₂ soft magnetic composites,using ethanol as the hydrolysis solvent of TEOS can effectively reduce the magnetic loss of the composites,the amount of TEOS added is 0.05 m L/g,and the volume ratio of ammonia water to TEOS is 2:1,the magnetic loss of the composite material is the smallest,which is 45 W/kg（500 m T,1000 Hz）,and the magnetic permeability is 253.When using Na₂Si O₃ as the silicon source to prepare Fe/Si O₂ soft magnetic composites,the amount of solvent in the gel corresponding to the iron powder added is 0.2 m L/g,and the magnetic loss of the composite material is the smallest when the amount of Si O₂ is 0.4 wt%（0.0005 mol）,is 46 W/kg（500 m T,1000 Hz）,and the magnetic permeability is 258.In this paper,different soft magnetic composite materials were successfully prepared by four coating processes.The iron/phosphate soft magnetic composite material prepared by phosphoric acid passivation method had the smallest magnetic loss of 44 W/kg（500 m T,1000 Hz）,which significantly reduces the magnetic loss of the material at medium and high frequencies,and improves the comprehensive magnetic properties of the composite material.It is a soft magnetic material that may be used in high-speed motors.