FeSi-coated FeNi soft magnetic composite material and preparation method thereof

Abstract

The invention discloses an iron-based soft magnetic composite material and a preparation method thereof, and relates to the technical field of soft magnetic composite materials. The preparation method comprises the following steps: carrying out heat treatment on gas-atomized FeSi powder, and mixing the gas-atomized FeSi powder with FeNi particles to obtain core-shell FeSi-coated FeNi composite powder; then, phosphoric acid and organic matter are adopted for conducting insulation treatment on the core-shell type FeSi-coated FeNi composite powder, and then an insulation FeSi-coated FeNi material is obtained; and finally, mixing the FeSi-coated FeNi soft magnetic powder core with a lubricant, and performing pressing and staged heat treatment to prepare the FeSi-coated FeNi soft magnetic composite material with low magnetic powder core loss and high direct current bias characteristic.

Description

Technical Field

[0001] This invention relates to the field of soft magnetic composite materials technology, and in particular to a FeSi@FeNi soft magnetic composite material and its preparation method. Background Technology

[0002] Soft magnetic composite materials generally refer to a class of soft magnetic materials obtained by insulating Fe or its alloy powder, followed by pressing and heat treatment. Due to their very high resistivity, excellent high-frequency characteristics, three-dimensional magnetic isotropy, high saturation magnetization, and high controllability of size and performance, they play a key role in various motors and inductors as important soft magnetic materials for electromagnetic energy conversion and storage.

[0003] As electronic power technology advances towards higher frequencies, miniaturization, and higher efficiency, higher demands are placed on the comprehensive performance of magnetic powder cores. An ideal magnetic powder core must simultaneously possess high permeability, low loss, good DC bias characteristics, and excellent mechanical formability. Among numerous soft magnetic materials, FeSi alloys have attracted widespread attention due to their high saturation magnetic induction, low cost, and low magnetostriction coefficient. However, their hard and brittle texture leads to poor powder flowability and molding difficulties during insulation coating and pressing, and they also exhibit high eddy current losses at high frequencies. On the other hand, FeNi alloys (such as permalloy) possess extremely high permeability and low loss, but their high cost limits their large-scale application.

[0004] Currently, to improve the performance of single soft magnetic powders, a common approach is to surface-coat the matrix powder. Conventional methods often use a single type of matrix powder (such as pure iron powder or FeSi powder) and apply an organic-inorganic double-layer coating. The organic layer (such as resin or silane) primarily provides interparticle bonding and stress buffering, facilitating molding; the inorganic layer (such as phosphate, SiO2, or Al2O3) is used to achieve electrical insulation between particles, reducing eddy current losses. However, these conventional methods have significant shortcomings: First, for hard and brittle powders such as FeSi, even after coating, their compressibility remains poor, making it difficult to improve the compact density and strength, and prone to cracking during pressing; second, limited by the inherent magnetic properties of the single matrix powder, the resulting magnetic powder core often struggles to achieve an optimal balance between loss and DC bias characteristics, with high-frequency losses remaining relatively high, and the DC bias capability needing further improvement.

[0005] In the prior art, CN118248450A discloses a low-loss, high-DC-bias FeSi soft magnetic composite material. Its preparation method involves mixing FeSi powder, FeSiAl particles, and steel balls to obtain a core-shell structured FeSi@FeSiAl composite powder. After insulating and coating this powder, a lubricant is added and mixed thoroughly. The mixture is then pressed and annealed to obtain the FeSi soft magnetic composite material. However, FeSiAl has high hardness and brittleness, making it prone to breakage during mechanical ball milling and forming a continuous shell by physical embedding / welding onto the FeSi core surface. FeNi alloys (especially those with a Ni content of 40-50%) are softer and have better toughness. Under the same ball milling conditions, they are prone to cold welding, agglomeration, or excessive deformation, making it difficult to control their uniform and complete coating onto the FeSi core surface, easily leading to discontinuous shell layers or core-shell structure damage. Furthermore, FeSiAl's high hardness and brittleness make it prone to breakage during mechanical ball milling and forming a continuous shell by physical embedding / welding onto the FeSi core surface. FeNi alloys (especially those with a Ni content of 40-50%) are relatively soft and tough, making them prone to cold welding, agglomeration, or excessive deformation under the same ball milling conditions. This makes it difficult to control the uniform and complete coating onto the FeSi core surface, easily leading to shell discontinuities or core-shell structure damage. The journal *The Influence of FeNi Nanoparticles on the Microstructures and Soft Magnetic Properties of FeSi Soft Magnetic Composites* discloses the fabrication of FeSi / FeNi soft magnetic powder cores (SMPCs) by coating FeNi nanoparticles onto the surface of FeSi micron-sized powder. In this method, FeNi nanoparticles adhere to the FeSi powder surface, effectively filling the pores between FeSi particles and increasing the density of the SMPC. SMPCs exhibit high permeability (increased by 43.8%) and low iron loss (reduced by 22.1%). However, this simple coating method suffers from discontinuous and incomplete coating layers, resulting in the inability to effectively shield the high anisotropy of the FeSi core. Consequently, the magnetization process remains strongly influenced by the difficulty in reversing the magnetization of the FeSi core.

[0006] Therefore, it is necessary to develop a FeSi-based soft magnetic composite material that can effectively balance excellent formability, low core loss, and high DC bias characteristics. Summary of the Invention

[0007] To address the aforementioned limitations of the prior art, the present invention aims to provide a FeSi@FeNi soft magnetic composite material and its preparation method. The present invention involves heat-treating atomized FeSi powder and then mixing it with FeNi particles to obtain a core-shell FeSi@FeNi composite powder. Next, the core-shell FeSi@FeNi composite powder is insulated with phosphoric acid and organic matter to obtain an insulating FeSi@FeNi material. Finally, this material is mixed with a lubricant and then pressed and subjected to staged heat treatment to obtain a FeSi@FeNi soft magnetic composite material with low magnetic core loss and high DC bias characteristics.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing FeSi@FeNi soft magnetic composite material, comprising the following steps: (1) After heat treatment of the gas-atomized FeSi powder, it is mixed with FeNi particles and stirred under the action of steel balls to obtain core-shell FeSi@FeNi composite powder; (2) The core-shell FeSi@FeNi composite powder is subjected to insulation treatment and granulated to obtain insulating FeSi@FeNi material; the insulating FeSi@FeNi material is mixed with a lubricant, pressed, and then placed in an inert atmosphere for heat treatment and cooled to obtain FeSi@FeNi soft magnetic composite material.

[0009] Preferably, in step (1), the atomized FeSi powder is prepared by particle size distribution of atomized FeSi powder with a particle size of -200 mesh and atomized FeSi powder with a particle size of -400 mesh, and its laser particle size is D10: 8-12μm, D50: 27-32μm, D90: 65-70μm.

[0010] As a preferred option, in step (1), the specific operation of heat treatment is as follows: place the gas-atomized FeSi powder in an inert atmosphere and treat it at 700-750℃ for 1.5-2.5h.

[0011] Furthermore, the inert atmosphere is a nitrogen atmosphere.

[0012] Preferably, in step (1), the content of Si in the atomized FeSi powder is 0.4wt%-0.6wt%, and the balance is Fe.

[0013] Preferably, in step (1), the Ni content in the FeNi powder is 40wt%-50wt%, and the balance is Fe.

[0014] Preferably, in step (1), the mass ratio of atomized FeSi powder to FeNi powder is (7.5-8.5):(1.5-2.5).

[0015] Preferably, in step (1), the stirring speed is 100-1000 r / min and the stirring time is 20-30 min.

[0016] Preferably, in step (2), the specific operation for insulating the core-shell FeSi@FeNi composite powder is as follows: Phosphoric acid is added to acetone to obtain a phosphating solution; the core-shell FeSi@FeNi composite powder is mixed with the phosphating solution and then subjected to phosphating treatment; organic matter is added to the phosphating system and mixed to obtain insulating FeSi@FeNi powder.

[0017] Furthermore, the organic material is an organosilicon resin and / or an epoxy resin.

[0018] Furthermore, the insulating FeSi@FeNi powder contains 0.4wt%-1.0wt% phosphoric acid and 0.5wt%-1.0wt% organic matter.

[0019] Preferably, in step (2), the lubricant is zinc stearate.

[0020] Preferably, in step (2), the amount of lubricant added is 0.4wt%-0.8wt% of the mass of the insulating FeSi@FeNi material.

[0021] Preferably, in step (2), the inert atmosphere is a nitrogen atmosphere.

[0022] Preferably, the specific steps of heat treatment in step (2) are as follows: Stage 1: Heat to 300-350℃ at a heating rate of 5-8℃ / min, and hold for 15-25 minutes; Stage 2: Heat to 650-680℃ at a heating rate of 10-15℃ / min, and hold for 8-12 minutes; Stage 3: Increase the temperature to 710-750℃ at a heating rate of 2-4℃ / min, and hold for 25-35 minutes.

[0023] In a second aspect, the present invention provides a FeSi@FeNi soft magnetic composite material prepared by the above-described preparation method.

[0024] The beneficial effects of this invention are: 1. This invention involves heat-treating atomized FeSi powder and then mixing it with FeNi particles to obtain a core-shell FeSi@FeNi composite powder. Next, the core-shell FeSi@FeNi composite powder is insulated with phosphoric acid and organic matter to obtain an insulating FeSi@FeNi material. Finally, this material is mixed with a lubricant and then pressed and subjected to staged heat treatment to obtain a FeSi@FeNi soft magnetic composite material with low magnetic core loss and high DC bias characteristics. In the core-shell FeSi@FeNi composite powder, gas-atomized FeSi alloy powder serves as the core, and FeNi alloy particles form the shell, with the two tightly bonded together through mechanical fusion. This core-shell structure offers the following advantages: (1) The FeSi core provides the basis for high saturation magnetization, while the FeNi shell provides extremely high permeability and low coercivity. By utilizing the close combination of the two, the magnetic moment can be efficiently coupled and transmitted at the interface, so that the material has both high saturation magnetization and high permeability.

[0025] (2) The FeSi core has a high resistivity and the FeNi shell has a low resistivity. Under the action of a high-frequency electromagnetic field, the eddy current is confined in the high-resistivity FeSi core, while the low-resistivity FeNi shell forms a good magnetic permeability path, ensuring high permeability. This structure suppresses eddy current loss and maintains high-frequency permeability.

[0026] (3) Heat treatment of atomized FeSi powder can reduce its hardness and brittleness, and the outer plastic FeNi shell plays a role in stress buffering and transfer during the pressing process. The combined effect of the two completely solves the industry bottleneck of poor formability and easy cracking of pure FeSi powder, making it possible to obtain high-density and high-strength pressed blanks.

[0027] 2. This invention utilizes a segmented heat treatment method to prepare FeSi@FeNi soft magnetic composite materials. First, the pressed powder is treated at 300-350℃. At this temperature, organic matter (lubricant and resin) decomposes, volatilizes, and is discharged in a controlled manner, preventing the preform from cracking due to instantaneous large-scale gas generation. Then, it is treated at 650-680℃. At this temperature, residual complex organic matter is further decomposed, and carbon residues have sufficient time to be carried away by the protective atmosphere through diffusion, preventing the formation of conductive carbon slag and ensuring the purity and resistivity of the insulating layer. After the insulating layer has been fully cured and stabilized, it is treated at 710-750℃, which completely eliminates the plastic deformation internal stress generated by the powder particles during pressing, promotes the migration of magnetic domain walls and the rearrangement of magnetic moments, significantly reduces coercivity (Hc), thereby greatly reducing hysteresis loss. It also releases the interfacial stress between the FeSi core and the FeNi shell, enhancing magnetic coupling. Attached Figure Description

[0028] Figure 1 Electron micrograph of the core-shell FeSi@FeNi composite powder prepared in Example 1; Figure 2 Electron micrograph of the core-shell FeSi@FeNi composite powder prepared in Example 2; Figure 3 Electron micrograph of the core-shell FeSi@FeNi composite powder prepared in Example 3; Figure 4 Electron micrograph of the core-shell FeSi@FeNi composite powder prepared in Comparative Example 4. Detailed Implementation

[0029] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0030] In existing technologies, while single FeSi exhibits high saturation magnetization and low coercivity, its permeability is often not optimal, and its magnetic properties have a limited adjustable range. More importantly, its relatively low resistivity leads to a significant increase in eddy current losses in high-frequency applications, making it difficult to directly apply to the VHF band. Single FeNi is known for its extremely high initial permeability and extremely low coercivity, but its relatively low saturation magnetization and high raw material cost limit its widespread application in high-power, low-cost fields. Simply mixing FeSi and FeNi physically fails to achieve a fundamental synergy in magnetic properties. The magnetism of the two is merely an independent linear superposition, and may even lead to magnetic decoupling due to poor interface contact, failing to achieve a "1+1>2" performance gain. Furthermore, the mixing process is difficult to ensure uniformity, resulting in product performance fluctuations. In terms of electrical performance, the low resistivity of FeNi particles induces significant eddy current losses and may accidentally form conductive paths with FeSi particles, further exacerbating overall losses.

[0031] Furthermore, while CN118248450A discloses a method of mixing FeSi powder, FeSiAl particles, and steel balls to obtain a core-shell structured FeSi@FeSiAl composite powder, followed by insulating coating, adding lubricant, mixing, pressing, and annealing to obtain a FeSi soft magnetic composite material, the significant differences in hardness, toughness, and other physical properties between FeNi and FeSiAl particles mean that directly replacing FeSiAl with FeNi in this patent often results in an uneven and incomplete shell coating in the resulting core-shell composite material.

[0032] Based on this, the present invention provides a FeSi@FeNi soft magnetic composite material, the preparation method of which is as follows: after heat treatment of gas-atomized FeSi powder, it is mixed with FeNi particles to obtain core-shell FeSi@FeNi composite powder; then, the core-shell FeSi@FeNi composite powder is insulated with phosphoric acid and organic matter to obtain insulating FeSi@FeNi material; finally, it is mixed with a lubricant, and then pressed and subjected to staged heat treatment to obtain FeSi@FeNi soft magnetic composite material with low magnetic core loss and high DC bias characteristics.

[0033] The high permeability of the FeNi shell and its densification effect during pressing significantly improve the magnetic path, resulting in a substantial increase in effective permeability. Simultaneously, this structure achieves a significant reduction in core loss through multiple mechanisms, including FeNi particles filling the air gap, a composite insulating layer suppressing eddy currents, and releasing internal stress to reduce hysteresis losses. Furthermore, the FeSi@FeNi soft magnetic composite material retains the high saturation magnetic induction (Bs) of the FeSi core, and minimizes the proportion of non-magnetic materials through optimized insulating coating, thus achieving good DC bias characteristics while maintaining high Bs. In addition, the uniform and continuous insulating shell effectively blocks eddy current paths, giving the material high resistivity and ensuring its low-loss advantage at high frequencies.

[0034] Furthermore, this invention, through heat treatment and particle size distribution of the gas-atomized FeSi powder, while simultaneously controlling the ball milling speed, ensures a tight bond between the FeNi plastic deformation and the FeSi core, forming a continuous and complete shell, thereby achieving a significant increase in magnetic permeability and a reduction in losses. This synergistic optimization of "structure-process-performance" cannot be achieved through simple reasoning involving material replacement.

[0035] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0036] The experimental materials used in the embodiments of this invention are all conventional experimental materials in the art and can be purchased through commercial channels.

[0037] In this invention, the content of Si in the atomized FeSi powder is 0.5 wt%, with the balance being Fe; the content of Ni in the FeNi powder is 45 wt%, with the balance being Fe; both the atomized FeSi powder and FeNi particles were purchased from Shandong Luyin New Material Technology Co., Ltd.

[0038] Example 1: Preparation method of FeSi@FeNi soft magnetic composite material (1) The atomized FeSi powder with a particle size of -200 mesh and the atomized FeSi powder with a particle size of -400 mesh were subjected to particle size distribution to obtain atomized FeSi powder with laser particle size of D10:10μm, D50:30μm, and D90:68μm; the atomized FeSi powder was placed in a nitrogen atmosphere and treated at 720℃ for 2h, and then mixed with FeNi particles. Under the action of steel balls, it was stirred at 500r / min for 25min to obtain core-shell FeSi@FeNi composite powder; the mass ratio of atomized FeSi powder to FeNi particles was 8:2. (2) Phosphoric acid is added to acetone to obtain a phosphating solution; the core-shell FeSi@FeNi composite powder and the phosphating solution are mixed and then subjected to phosphating treatment; organosilicon resin is added to the phosphating system and mixed to obtain insulating FeSi@FeNi powder, wherein the content of phosphoric acid in the insulating FeSi@FeNi powder is 0.7wt% and the content of organic matter is 0.8wt%. The insulating FeSi@FeNi powder is granulated to obtain insulating FeSi@FeNi material. After mixing insulating FeSi@FeNi material and zinc stearate, the amount of lubricant added was 0.6 wt% of the mass of the insulating FeSi@FeNi material; then, heat treatment was carried out under a nitrogen atmosphere to obtain FeSi@FeNi soft magnetic composite material; the specific operation of the heat treatment was as follows: Stage 1: Heat to 320℃ at a heating rate of 6℃ / min and hold for 20min; Stage 2: Heat to 670℃ at a heating rate of 12℃ / min and hold for 10 min; Phase 3: Heat to 730℃ at a heating rate of 3℃ / min and hold for 30 minutes.

[0039] The electron micrograph of the core-shell FeSi@FeNi composite powder prepared in this embodiment is shown below. Figure 1 As shown, by Figure 1 It can be seen that a uniform and continuous FeNi shell is formed on the surface of the FeSi core, with no obvious pores.

[0040] Example 2: Preparation method of FeSi@FeNi soft magnetic composite material (1) The atomized FeSi powder with a particle size of -200 mesh and the atomized FeSi powder with a particle size of -400 mesh were subjected to particle size distribution to obtain atomized FeSi powder with laser particle size of D10: 8μm, D50: 27μm, and D90: 65μm; the atomized FeSi powder was placed in a nitrogen atmosphere and treated at 700℃ for 1.5h, and then mixed with FeNi particles. Under the action of steel balls, it was stirred at 100r / min for 20min to obtain core-shell FeSi@FeNi composite powder; the mass ratio of atomized FeSi powder to FeNi particles was 7.5:2.5. (2) Phosphoric acid is added to acetone to obtain a phosphating solution; the core-shell FeSi@FeNi composite powder and the phosphating solution are mixed and then subjected to phosphating treatment; organosilicon resin is added to the phosphating system and mixed to obtain insulating FeSi@FeNi powder, wherein the content of phosphoric acid in the insulating FeSi@FeNi powder is 0.4wt% and the content of organic matter is 0.5wt%. The insulating FeSi@FeNi powder is granulated to obtain insulating FeSi@FeNi material. After mixing insulating FeSi@FeNi material and zinc stearate, the amount of lubricant added was 0.4 wt% of the mass of the insulating FeSi@FeNi material; then, heat treatment was carried out under a nitrogen atmosphere to obtain FeSi@FeNi soft magnetic composite material; the specific operation of the heat treatment was as follows: Stage 1: Heat to 300℃ at a heating rate of 5℃ / min and hold for 15min; Stage 2: Heat to 650℃ at a heating rate of 10℃ / min and hold for 8 minutes; Stage 3: Heat to 710℃ at a heating rate of 2℃ / min and hold for 25min.

[0041] The electron micrograph of the core-shell FeSi@FeNi composite powder prepared in this embodiment is shown below. Figure 2 As shown. By Figure 2 It can be seen that a uniform and continuous FeNi shell is formed on the surface of the FeSi core, with no obvious pores.

[0042] Example 3: Preparation method of FeSi@FeNi soft magnetic composite material (1) The atomized FeSi powder with a particle size of -200 mesh and the atomized FeSi powder with a particle size of -400 mesh were subjected to particle size distribution to obtain atomized FeSi powder with laser particle size of D10:12μm, D50:32μm, and D90:70μm; the atomized FeSi powder was placed in a nitrogen atmosphere and treated at 750℃ for 2.5h, and then mixed with FeNi particles. Under the action of steel balls, it was stirred at 1000r / min for 30min to obtain core-shell FeSi@FeNi composite powder; the mass ratio of atomized FeSi powder to FeNi particles was 8.5:1.5. (2) Phosphoric acid is added to acetone to obtain a phosphating solution; the core-shell FeSi@FeNi composite powder and the phosphating solution are mixed and then subjected to phosphating treatment; organosilicon resin is added to the phosphating system and mixed to obtain insulating FeSi@FeNi powder, wherein the content of phosphoric acid in the insulating FeSi@FeNi powder is 1.0 wt% and the content of organic matter is 1.0 wt%. The insulating FeSi@FeNi powder is granulated to obtain insulating FeSi@FeNi material. After mixing insulating FeSi@FeNi material and zinc stearate, the amount of lubricant added was 0.8 wt% of the mass of the insulating FeSi@FeNi material; then, heat treatment was carried out under a nitrogen atmosphere to obtain FeSi@FeNi soft magnetic composite material; the specific operation of the heat treatment was as follows: Stage 1: Heat to 350℃ at a heating rate of 8℃ / min and hold for 25min; Stage 2: Heat to 680℃ at a heating rate of 15℃ / min and hold for 12 minutes; Phase 3: Heat to 750℃ at a heating rate of 4℃ / min and hold for 35min.

[0043] The electron micrograph of the core-shell FeSi@FeNi composite powder prepared in this embodiment is shown below. Figure 3 As shown. By Figure 3 It can be seen that a uniform and continuous FeNi shell is formed on the surface of the FeSi core, with no obvious pores. As the FeNi content decreases, the FeNi content attached to the FeSi surface is less than that of the powder with a mass ratio of 8:2 between atomized FeSi powder and FeNi particles.

[0044] Comparative Example 1: The difference between this comparative example and Example 1 is that only FeSi soft magnetic materials were prepared using gas-atomized FeSi powder. The specific preparation method is as follows: (1) The atomized FeSi powder with a particle size of -200 mesh and the atomized FeSi powder with a particle size of -400 mesh were subjected to particle size distribution to obtain atomized FeSi powder with laser particle size of D10:10μm, D50:30μm, and D90:68μm; the atomized FeSi powder was placed in a nitrogen atmosphere and treated at 720℃ for 2h to obtain FeSi powder. (2) Phosphoric acid is added to acetone to obtain a phosphating solution; FeSi powder and phosphating solution are mixed and then subjected to phosphating treatment; organosilicon resin is added to the phosphating system and mixed to obtain insulating FeSi powder, wherein the content of phosphoric acid in the insulating FeSi powder is 0.7wt% and the content of organic matter is 0.8wt%. The insulating FeSi powder is granulated to obtain insulating FeSi material; the insulating FeSi material and zinc stearate are mixed, and the amount of lubricant added is 0.6wt% of the mass of the insulating FeSi material; then, heat treatment is carried out under a nitrogen atmosphere to obtain FeSi soft magnetic material; the specific operation of heat treatment is as follows: Stage 1: Heat to 320℃ at a heating rate of 6℃ / min and hold for 20min; Stage 2: Heat to 670℃ at a heating rate of 12℃ / min and hold for 10 min; Phase 3: Heat to 730℃ at a heating rate of 3℃ / min and hold for 30 minutes.

[0045] Comparative Example 2: The difference between this comparative example and Example 1 is that only FeNi particles are used to prepare FeNi soft magnetic materials. The specific preparation method is as follows: Phosphoric acid is added to acetone to obtain a phosphating solution; FeNi particles and the phosphating solution are mixed and then subjected to phosphating treatment; organosilicon resin is added to the phosphating system and mixed to obtain insulating FeNi powder, wherein the insulating FeNi powder contains 0.7wt% phosphoric acid and 0.8wt% organic matter; the insulating FeNi powder is granulated to obtain insulating FeNi material. After mixing insulating FeNi material and zinc stearate, the amount of lubricant added is 0.6 wt% of the mass of the insulating FeNi material; then, heat treatment is carried out under a nitrogen atmosphere to obtain FeNi soft magnetic material; the specific operation of heat treatment is as follows: Stage 1: Heat to 320℃ at a heating rate of 6℃ / min and hold for 20min; Stage 2: Heat to 670℃ at a heating rate of 12℃ / min and hold for 10 min; Phase 3: Heat to 730℃ at a heating rate of 3℃ / min and hold for 30 minutes.

[0046] Comparative Example 3: The difference between this comparative example and Example 1 is that the gas-atomized FeSi powder and FeNi particles are only physically mixed. The specific preparation method is as follows: (1) The atomized FeSi powder with a particle size of -200 mesh and the atomized FeSi powder with a particle size of -400 mesh were subjected to particle size distribution to obtain atomized FeSi powder with laser particle size of D10:10μm, D50:30μm, and D90:68μm; the atomized FeSi powder was placed in a nitrogen atmosphere and treated at 720℃ for 2h, and then mixed with FeNi particles to obtain FeSi / FeNi composite powder; wherein the mass ratio of atomized FeSi powder to FeNi particles was 8:2. (2) Add phosphoric acid to acetone to obtain phosphating solution; mix FeSi / FeNi composite powder and phosphating solution and then perform phosphating treatment; add organosilicon resin to the phosphating system and mix to obtain insulating FeSi / FeNi powder, wherein the content of phosphoric acid in the insulating FeSi / FeNi powder is 0.7wt% and the content of organic matter is 0.8wt%. Granulate the insulating FeSi / FeNi powder to obtain insulating FeSi / FeNi material. After mixing insulating FeSi / FeNi material and zinc stearate, the amount of lubricant added is 0.6 wt% of the mass of the insulating FeSi / FeNi material; then, heat treatment is carried out under a nitrogen atmosphere to obtain FeSi / FeNi composite soft magnetic material. The specific operation of heat treatment is as follows: Stage 1: Heat to 320℃ at a heating rate of 6℃ / min and hold for 20min; Stage 2: Heat to 670℃ at a heating rate of 12℃ / min and hold for 10 min; Phase 3: Heat to 730℃ at a heating rate of 3℃ / min and hold for 30 minutes.

[0047] Comparative Example 4: The difference between this comparative example and Example 1 is that the atomized FeSi powder was not heat-treated during the preparation of the FeSi / FeNi composite soft magnetic material. The specific steps are as follows: (1) The atomized FeSi powder with a particle size of -200 mesh and the atomized FeSi powder with a particle size of -400 mesh were subjected to particle size distribution to obtain atomized FeSi powder with laser particle size of D10:10μm, D50:30μm, and D90:68μm; the atomized FeSi powder was mixed with FeNi particles and stirred at 500r / min for 25min under the action of steel balls to obtain core-shell FeSi@FeNi composite powder; wherein the mass ratio of atomized FeSi powder to FeNi particles was 8:2. (2) Phosphoric acid is added to acetone to obtain a phosphating solution; the core-shell FeSi@FeNi composite powder and the phosphating solution are mixed and then subjected to phosphating treatment; organosilicon resin is added to the phosphating system and mixed to obtain insulating FeSi@FeNi powder, wherein the content of phosphoric acid in the insulating FeSi@FeNi powder is 0.7wt% and the content of organic matter is 0.8wt%. The insulating FeSi@FeNi powder is granulated to obtain insulating FeSi@FeNi material. After mixing the insulating FeSi@FeNi material and zinc stearate, the amount of lubricant added was 0.6 wt% of the mass of the insulating FeSi@FeNi material; then, heat treatment was carried out under a nitrogen atmosphere. The specific operation of the heat treatment was as follows: Stage 1: Heat to 320℃ at a heating rate of 6℃ / min and hold for 20min; Stage 2: Heat to 670℃ at a heating rate of 12℃ / min and hold for 10 min; Phase 3: Heat to 730℃ at a heating rate of 3℃ / min and hold for 30 minutes.

[0048] The electron microscope image of the core-shell FeSi@FeNi composite powder prepared in this comparative example is shown below. Figure 4 As shown. By Figure 4 It can be seen that the FeNi shell coating on the FeSi core surface is uneven and discontinuous, with obvious pores and FeNi peeling in some areas. This shows that the untreated FeSi powder has high hardness and brittleness, making it difficult to form a good core-shell bonding structure with FeNi particles.

[0049] Experimental example: The performance of the soft magnetic materials prepared in Example 1 and Comparative Examples 1-4 was tested, and the results are shown in Table 1.

[0050] The specific testing method is as follows: 1. Effective permeability: The method in GB / T 3658-2008 "Test Method for AC Magnetic Properties of Soft Magnetic Materials" is used to measure the permeability on the toroidal core using an impedance analyzer.

[0051] 2. Core loss: The total loss of the toroidal core under specific conditions is directly measured using a power analyzer in conjunction with an excitation circuit, according to the method in GB / T 3658-2022 "Method for Measurement of AC Magnetic Properties of Soft Magnetic Materials - Toroidal Specimens".

[0052] 3. Saturation magnetic induction intensity: The magnetic induction intensity value when the magnetization intensity no longer increases significantly is measured using a DC BH hysteresis loop apparatus under a sufficiently high external magnetic field, according to the method in GB / T 13012-2008 "Test Method for DC Magnetic Properties of Soft Magnetic Materials".

[0053] 4. DC Bias Characteristics: Using the superimposed DC bias method, an impedance analyzer and a DC power supply are used to simultaneously apply an AC test signal and an adjustable DC bias magnetic field to the toroidal core. The decrease in effective permeability as the DC bias magnetic field increases is measured.

[0054] The retention rate of permeability under a DC bias field of 100 Oe (approximately 7.96 kA / m) is used for quantification. A higher retention rate indicates stronger resistance to DC magnetization and better performance of the material.

[0055] 5. Resistivity: Measured using a four-probe resistivity tester according to the method in GB / T 351-2019 "Methods for Measurement of Resistivity of Metallic Materials". Table 1 Electromagnetic properties of the materials obtained in Example 1 and Comparative Examples 1-4 As shown in Table 1, the present invention, after heat treatment of FeNi, uses it as a raw material to prepare core-shell FeSi@FeNi composite powder, followed by insulation and annealing treatments, to obtain FeSi@FeNi soft magnetic composite material. The effective permeability, core loss, DC bias characteristics, and resistivity of this material are all superior to those of Comparative Examples 1 and 3. While Comparative Example 2 has good permeability and low core loss, its saturation magnetic induction is low and its cost is high. This demonstrates that the core-shell structure effectively integrates the high saturation magnetic induction of FeSi and the high permeability of FeNi, achieving a synergistic improvement in functionality.

[0056] Furthermore, the magnetic properties of the material prepared in Comparative Example 4 were significantly lower than those in Comparative Example 1, especially with a marked increase in core loss. This is related to the uneven and discontinuous coating of the FeNi shell. Therefore, heat treatment of FeSi can effectively promote uniform coating of the FeNi shell, thereby improving the magnetic properties of the composite material.

[0057] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing FeSi@FeNi soft magnetic composite material, characterized in that, Includes the following steps: (1) After heat treatment of the gas-atomized FeSi powder, it is mixed with FeNi particles and stirred under the action of steel balls to obtain core-shell FeSi@FeNi composite powder; (2) The core-shell FeSi@FeNi composite powder is subjected to insulation treatment and granulated to obtain insulating FeSi@FeNi material; the insulating FeSi@FeNi material is mixed with a lubricant, pressed, and then placed in an inert atmosphere for heat treatment and cooled to obtain FeSi@FeNi soft magnetic composite material.

2. The preparation method of FeSi@FeNi soft magnetic composite material as described in claim 1, characterized in that, In step (1), the gas-atomized FeSi powder is prepared by particle size distribution of gas-atomized FeSi powder with a particle size of -200 mesh and gas-atomized FeSi powder with a particle size of -400 mesh. Its laser particle size is D10: 8-12μm, D50: 27-32μm, D90: 65-70μm.

3. The preparation method of FeSi@FeNi soft magnetic composite material as described in claim 1, characterized in that, In step (1), the specific operation of heat treatment is as follows: place the gas-atomized FeSi powder in an inert atmosphere and treat it at 700-750℃ for 1.5-2.5h; the inert atmosphere is a nitrogen atmosphere.

4. The preparation method of FeSi@FeNi soft magnetic composite material as described in claim 1, characterized in that, In step (1), the content of Si in the atomized FeSi powder is 0.4wt%-0.6wt%, and the balance is Fe; the content of Ni in the FeNi powder is 40wt%-50wt%, and the balance is Fe. The mass ratio of atomized FeSi powder to FeNi powder is (7.5-8.5):(1.5-2.5).

5. The preparation method of FeSi@FeNi soft magnetic composite material as described in claim 1, characterized in that, In step (1), the stirring speed is 100-1000 r / min and the stirring time is 20-30 min.

6. The preparation method of FeSi@FeNi soft magnetic composite material as described in claim 1, characterized in that, In step (2), the specific operation for insulating the core-shell FeSi@FeNi composite powder is as follows: Phosphoric acid is added to acetone to obtain a phosphating solution; the core-shell FeSi@FeNi composite powder is mixed with the phosphating solution and then subjected to phosphating treatment; organic matter is added to the phosphating system and mixed to obtain insulating FeSi@FeNi powder.

7. The preparation method of FeSi@FeNi soft magnetic composite material as described in claim 6, characterized in that, The organic matter is organosilicon resin and / or epoxy resin; in the insulating FeSi@FeNi powder, the content of phosphoric acid is 0.4wt%-1.0wt% and the content of organic matter is 0.5wt%-1.0wt%.

8. The method for preparing the FeSi@FeNi soft magnetic composite material as described in claim 1, characterized in that, In step (2), the lubricant is zinc stearate; the amount of lubricant added is 0.4wt%-0.8wt% of the mass of the insulating FeSi@FeNi material.

9. The method for preparing the FeSi@FeNi soft magnetic composite material as described in claim 1, characterized in that, In step (2), the inert atmosphere is a nitrogen atmosphere; the specific steps of the heat treatment are as follows: Stage 1: Heat to 300-350℃ at a heating rate of 5-8℃ / min, and hold for 15-25 minutes; Stage 2: Heat to 650-680℃ at a heating rate of 10-15℃ / min, and hold for 8-12 minutes; Stage 3: Increase the temperature to 710-750℃ at a heating rate of 2-4℃ / min, and hold for 25-35 minutes.

10. The FeSi@FeNi soft magnetic composite material prepared by the preparation method according to any one of claims 1-9.

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