Preparation method of soft magnetic composite material with high magnetic conductivity and high magnetic flux density

Abstract

The invention discloses a preparation method of a soft magnetic composite material with high magnetic conductivity and high magnetic flux density, and belongs to the technical field of soft magnetic composites.The preparation method comprises the steps that 1, gradient inorganic coating is adopted, diammonium hydrogen phosphate and oxalic acid are dissolved in deionized water and react with iron powder at the temperature of 70 DEG C to form a bottom layer, then a cerous nitrate solution is dropwise added to modify a crystal boundary at the temperature of 80 DEG C, and the bottom layer is formed; precise coating is realized; 2, carrying out organic-inorganic hybridization treatment: hydrolyzing a silane coupling agent and nano sol in an ethanol / water mixed solution, carrying out ultrasonic dispersion with the coated powder, and carrying out vacuum drying at 80 DEG C to form equivalent Fe-O-Si equivalent keys, so that the insulation resistance is improved; 3, implementing high-temperature-resistant organic coating, namely performing ball-milling dispersion on a polyimide resin prepolymer and a hexagonal boron nitride nanosheet, then dip-coating powder, and drying by a fluidized bed at 120 DEG C, so that the high-frequency eddy current loss is remarkably reduced; and 4, magnetic field assisted annealing is adopted, specifically, after the powder is pressed and formed, two-stage annealing is carried out under the protective atmosphere, and the magnetic conductivity is improved by 15-20% through magnetic domain directional arrangement.

Description

Technical Field

[0001] This invention relates to the technical field of soft magnetic composite materials, and in particular to a method for preparing a soft magnetic composite material with high magnetic permeability and high magnetic flux density. Background Technology

[0002] Soft magnetic composite (SMC) is a functional material formed by pressing and heat treatment of magnetic powders such as iron-silicon and iron-nickel with insulating coating. It has high magnetic permeability, low eddy current loss and three-dimensional isotropic magnetic properties, and is widely used in motors, sensors and high-frequency electromagnetic devices. Its core feature is that it suppresses the eddy current effect through the insulating layer between particles, while maintaining excellent magnetic properties and processability.

[0003] Soft magnetic composite materials are commonly used as the core components of reactors, transformers, inductors, filters, frequency modulation chokes, switching power supplies, and motor stators, finding wide application in telecommunications, radar, power supplies, electronics, electrical appliances, motors, and power technologies. The conventional preparation method involves using metallic magnetic powder as raw material, insulating and coating the powder, followed by shaping and heat treatment to obtain magnets with high permeability, low loss, and three-dimensional isotropy. Insulation coating is a crucial process in the fabrication of these magnets, with the insulating coating agent being the most critical factor. Insulation coating agents include both organic and inorganic materials. While some existing technologies utilize chemically prepared oxide coatings, the bonding between these coatings and the surface of the metallic magnetic powder is physical; therefore, adhesion is poor, and cracks easily form during pressing, failing to reduce eddy current losses at high frequencies.

[0004] Based on this, Chinese patent document CN116833407B discloses a soft magnetic composite material and its preparation method. This soft magnetic composite material includes FeSiAl magnetic powder and an insulating layer. The FeSiAl magnetic powder, by mass fraction, comprises 9.0%-9.6% Si, 5.4%-7.6% Al, and the remainder is Fe. The preparation method includes: (1) mixing and stirring the FeSiAl magnetic powder with NaOH or KOH aqueous solution to carry out the reaction; (2) after the reaction, washing and drying the precipitate, treating it at high temperature under a protective atmosphere, and cooling it to obtain a coated powder; (3) adding a lubricant to the coated powder, pressing it in a mold, and annealing it to obtain the soft magnetic composite material. This soft magnetic composite material has high permeability and lower loss, good frequency stability, and minimal permeability decay with increasing frequency, exhibiting low magnetic loss at high frequencies.

[0005] However, the aforementioned methods for preparing soft magnetic composite materials still suffer from technical problems, such as the permeability and magnetic flux density of the prepared soft magnetic composite materials failing to meet application requirements. Specifically, improving the permeability (μ) and saturation magnetic flux density (Bs) of soft magnetic composite materials is the core objective for optimizing their electromagnetic performance. High permeability can reduce magnetic reluctance, enhance magnetic field conduction efficiency, and reduce energy loss, such as leakage flux in wireless charging; while a high Bs value allows the material to carry a stronger magnetic flux in a smaller volume, supporting the high power density and miniaturization requirements of devices such as motors and transformers. Furthermore, the synergistic effect of the two can suppress high-frequency eddy currents and hysteresis losses, expanding the application potential of the material in high-frequency, high-power scenarios such as 5G communication and new energy. Current technologies balance the improvement of μ and Bs through nano-coating, interface control, and other means, but the impact of the insulating layer on the integrity of the magnetic circuit still needs to be addressed. Summary of the Invention

[0006] Therefore, it is necessary to provide a method for preparing soft magnetic composite materials with high permeability and high magnetic flux density, addressing the technical problem of how to improve the permeability and magnetic flux density of soft magnetic composite materials.

[0007] A method for preparing a soft magnetic composite material with high magnetic permeability and high magnetic flux density includes the following steps: Step 1: Prepare all materials according to the preset raw material ratio. First, carry out the gradient inorganic coating process in the reactor, as follows: Dissolve diammonium hydrogen phosphate and oxalic acid in deionized water in a predetermined ratio, and heat to 70°C. Add iron powder and stir for 30 minutes to form Underlying layer; Slowly add cerium nitrate solution dropwise; The mixture was kept at 80℃ for 60 minutes and then centrifuged to obtain powder. Step 2: Organic-inorganic hybrid treatment, as follows: a. Combining silane coupling agents with nano The sol was added to an ethanol / water mixed solvent, wherein the volume ratio of ethanol to water was 3:1. b. After hydrolysis for 30 min, add the powder obtained in step 1 and disperse it under ultrasonication at 40 kHz for 30 min; c. Place the dispersed material in a vacuum at 80℃ to dry it, so that chemical bonds ≡Fe-O-Si≡ are formed at the material interface; Step 3: High-temperature resistant organic coating, as follows: a. Dissolve the polyimide resin prepolymer in NMP solvent, controlling the solution concentration to 15 wt%; b. Then add hexagonal boron nitride nanosheets and disperse them by ball milling. The ball milling parameters are set to 300 rpm for 1 h. c. Dip-coat the hybrid powder and dry it in a fluidized bed at 120°C for 30 minutes; Step 4: Magnetic field-assisted annealing, as follows: Powder was pressed into a ring-shaped magnetic core under a pressure of 800 MPa; Access Mixed gas protection, and The ratio is 95:5; Two-stage annealing is adopted: the first stage is annealing at 350℃ for 1 hour; the second stage is annealing at 420℃ for 2 hours; at the same time, the magnetic core is placed in an axial static magnetic field of 0.5T.

[0008] Specifically, in the above-mentioned method for preparing high-permeability, high-flux-density soft magnetic composite materials, the gradient inorganic coating material, by mass parts, comprises the following per 100 parts of carbonyl iron powder: 1. Diammonium hydrogen phosphate: 0.8–1.5 parts, used as the main reactant to form a dense layer on the surface of iron powder. Underlying passivation film; 2. Nitric acid: 0.3–0.8 parts, used to fill grain boundary defects in magnetic particles through high-temperature hydrolysis; 3. Oxalic acid: 0.05–0.2 parts, chelates free metal ions to inhibit side reactions; Organic-inorganic hybrid layer materials include: 4. Nanoparticles with a particle size of 20-50 nm Sol: 1.0-2.0 parts, fills the micropores of the coating layer to improve insulation density; 5. γ-aminopropyltriethoxysilane: 0.5–1.2 parts, possessing both coupling function and Precursor formation at the interface results in the formation of Fe-O-Si chemical bonds. The high-temperature resistant organic coating material includes: 6. Polyimide resin: 2.0-3.5 parts, replacing traditional epoxy resin to form a continuous coating layer with a temperature resistance of >300℃; 7. Hexagonal boron nitride nanosheets with a thickness of <100nm: 0.1 to 0.3 parts, providing a high in-plane thermal conductivity path; making its thermal conductivity >400W / mK.

[0009] Specifically, in the aforementioned raw material formulation implementation method, the key proportions are explained as follows: Coating layer synergistic control: Diammonium hydrogen phosphate and oxalic acid form an acidic environment (pH≈3.5), ensuring... The layers grow uniformly with a thickness of 80±10nm. When the amount of cerium nitrate added is >0.5 parts, the grain boundary coverage is increased to 95%, which can be verified by SEM.

[0010] Furthermore, the hybrid layer strengthening mechanism: after the silane coupling agent is hydrolyzed, it interacts with nano-... The synergistic effect reduces the porosity to <0.5%, which can be tested using the mercury porosimetry method.

[0011] Furthermore, high-temperature resistance is guaranteed: the coating integrity is optimal when the amount of polyimide is 2.8 parts, at which point the coverage rate is >99.2%, which can be verified by XPS analysis; the addition of 0.2 parts of boron nitride can increase the thermal conductivity to 1.8 W / mK, which can be confirmed by laser scintillation measurement.

[0012] Specifically, the above-mentioned raw material ratio is adapted to the gradient coating-magnetic field annealing process, and after heat treatment at 420℃, the insulation resistance remains >5000MΩ, and under the test conditions of 10kHz, its permeability μe reaches 62±2.

[0013] Furthermore, in a specific embodiment, when the matrix material is 100 parts of carbon-based iron powder with a particle size of 5-20 μm, the raw materials required for each process are as follows: Gradient inorganic coating layer: 1.2 parts of diammonium hydrogen phosphate, forming bottom layer; 0.6 parts cerium nitrate, grain boundary repair agent; Oxalic acid 0.1 parts, metal ion chelating agent; Organic-inorganic hybrid layer: Nanoparticles with a diameter of 20nm 1.8 parts sol; 1.0 parts of γ-aminopropyltriethoxysilane KH-550 were used to generate a Si-O network in situ. High-temperature resistant organic coating: 3.0 parts of polyimide resin are used as the main coating layer; Is 0.2 parts of hexagonal boron nitride nanosheets used as a thermal conductivity enhancer?

[0014] Furthermore, in another specific embodiment, when the matrix material is 100 parts of atomized FeSi powder with a Si content of 6.5 wt%, the raw materials required for each process are as follows: Gradient inorganic coating layer: 0.9 parts zinc phosphate, dense passivation layer; 0.4 parts cerium carbonate, thin-layer modifier; Organic-inorganic hybrid layer: 1.2 parts of nano-SiO2 sol 0.8 parts of titanate coupling agent (NDZ-201) improve coating uniformity; High-temperature resistant organic coating: 2.5 parts polyimide resin, thinner design; 0.15 parts of hexagonal boron nitride nanosheets.

[0015] Furthermore, in another specific embodiment, when the base material is 100 parts of reduced iron powder with a purity >99%, the raw materials required for each process are as follows: Gradient inorganic coating layer: 0.8 parts of ammonium dihydrogen phosphate, a low-cost phosphate; 0.3 parts of cerium sulfate, a 30% reduction in dosage; Coupling processing layer: 0.6 parts of silane coupling agent (KH-550); Organic coating layer: 2.0 parts of epoxy resin E-44, replacing polyimide; 0.3 parts of micron-sized Al2O3 powder (1-3μm) are used as a low-cost thermal conductive agent.

[0016] Specifically, for the aforementioned embodiments, the selection of the phosphate is as follows: Examples 1 / 2 use highly active diammonium hydrogen phosphate / zinc phosphate to form a dense passivation film; Example 3 uses low-cost ammonium dihydrogen phosphate, sacrificing some insulation for economic benefits.

[0017] Furthermore, the differences in cerium salt morphology among the various embodiments are as follows: Cerium nitrate in Example 1 is highly reactive → Cerium carbonate in Example 2 is stable at high temperatures → Cerium sulfate in Example 3 has a cost advantage.

[0018] Furthermore, in each embodiment, the thermal conductivity upgrade path is as follows: Examples 1 / 2 are hexagonal boron nitride → Example 3 is micron-sized Al2O3.

[0019] Specifically, boron nitride provides in-plane thermal conductivity, resulting in measured data >400 W / mK. The powder can only achieve isotropic thermal conduction, and its measured data is only 30W / mK.

[0020] Furthermore, the resin systems in each embodiment are compared as follows: Polyimide (PI): Temperature resistance >300℃, Example 1 / 2; Epoxy resin: Temperature resistance <180℃, Example 3, but cost reduced by 40%.

[0021] Furthermore, all the above embodiments employ gradient coating and magnetic field annealing as core processes, but are adjusted according to the target performance: Example 1 uses a magnetic field strength of 0.8T, prioritizing permeability; Example 2 uses a magnetic field strength of 0.3T, prioritizing magnetic flux density; Example 3 uses an annealing temperature reduced to 380℃, compatible with epoxy resin.

[0022] In summary, this invention discloses a method for preparing a soft magnetic composite material with high permeability and high flux density, which includes four core processes: Step 1 employs gradient inorganic coating: diammonium hydrogen phosphate and oxalic acid are dissolved in deionized water and reacted with iron powder at 70°C to form... At the bottom layer, cerium nitrate solution is added dropwise at 80℃ to modify the grain boundaries, achieving precise coating of 80-120nm; Step 2 involves organic-inorganic hybrid treatment: combining silane coupling agent with nanoparticles... After hydrolysis of the sol in an ethanol / water mixture, it is ultrasonically dispersed with the coated powder and vacuum dried at 80℃ to form ≡Fe-O-Si≡ bonds, increasing the insulation resistance by 3 times; Step 3 involves high-temperature organic coating: polyimide resin prepolymer and hexagonal boron nitride nanosheets are ball-milled and dispersed, then dip-coated into the powder and dried in a fluidized bed at 120℃, significantly reducing high-frequency eddy current losses; Step 4 employs magnetic field-assisted annealing: after the powder is pressed into shape, ... Two-stage annealing (350℃×1h stress relief → 420℃×2h + 0.5T axial static magnetic field) under a protective atmosphere improves permeability by 15-20% through domain orientation alignment. This invention discloses a method for preparing a soft magnetic composite material with high permeability and high magnetic flux density, simultaneously optimizing the insulation, permeability, and saturation magnetic flux density of the soft magnetic composite material. The final prepared soft magnetic composite material exhibits insulation >5000MΩ, permeability μe in the range of 58-62, and saturation magnetic flux density Bs 1.92T. Therefore, this invention's method for preparing a soft magnetic composite material with high permeability and high magnetic flux density solves the technical problem of how to improve the permeability and magnetic flux density of soft magnetic composite materials. Detailed Implementation

[0023] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to specific examples. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0024] Specifically, the present invention discloses a method for preparing a soft magnetic composite material with high magnetic permeability and high magnetic flux density, which includes the following steps: Step 1: Perform gradient inorganic coating in the reactor: Dissolve diammonium hydrogen phosphate and oxalic acid in 40 parts of deionized water and heat to 70°C; Add iron powder and stir for 30 minutes to form Underlying layer; Slowly add 0.5 parts of cerium nitrate solution. With 20 parts water; The mixture was kept at 80℃ for 60 minutes and then centrifuged to obtain powder. The stepwise deposition method in step 1 allows the coating thickness to be controlled within the range of 80-120 nm; Step 2: Organic-inorganic hybrid treatment: a. Combining silane coupling agents with nano The sol was added to an ethanol / water mixed solvent, wherein the volume ratio of ethanol to water was 3:1. b. After hydrolysis for 30 min, add the powder obtained in step 1 and disperse it under ultrasonication at 40 kHz for 30 min; c. Vacuum drying at 80℃ forms the chemical bond ≡Fe-O-Si≡. In step 2, Filling the micropores in the coating layer can increase the insulation resistance of the final product by 3 times; Step 3: High-temperature resistant organic coating: a. Dissolve the polyimide resin prepolymer in NMP solvent, controlling the solution concentration to 15 wt%; b. Then add hexagonal boron nitride nanosheets and disperse them by ball milling. The ball milling parameters are set to 300 rpm for 1 h. c. Dip-coat the hybrid powder and dry it in a fluidized bed at 120°C for 30 minutes; Step 3 improves the thermal conductivity of the composite material by using boron nitride, and at the same time, it can also reduce the high-frequency eddy current loss of the final composite material. Step 4: Magnetic field-assisted annealing: Powder was pressed into a ring-shaped magnetic core under a pressure of 800 MPa; Access Mixed gas protection, and The ratio is 95:5; Two-stage annealing was adopted: the first stage was 350℃ for 1 hour to relieve stress; the second stage was 420℃ for 2 hours with an axial static magnetic field of 0.5T. In step 4, the magnetic field induces the directional alignment of magnetic domains, which increases the μe of the final magnetic core product by 15-20%.

[0025] Specifically, in the preparation method of a soft magnetic composite material with high magnetic permeability and high magnetic flux density according to the present invention, one embodiment of the raw material ratio is as follows: Table 1: Raw material ratio per 100 parts by weight of ferromagnetic powder in one embodiment

[0026] In one comparative embodiment, the raw material formulation is as follows: 2.5 parts soluble phosphate, 2.5 parts soluble cerium salt, 0.5 parts oxalic acid, 1.5 parts soluble strontium salt, and 1.0 part soluble molybdate are added to every 100 parts by weight of ferromagnetic powder. The preparation method of this comparative embodiment is as follows: the materials in the preset proportion are added to the ferromagnetic powder in a predetermined order. After the reaction is complete, the powder is dried at 70℃-100℃ for 200-240 minutes. Then, 1.55 parts coupling agent and 100 parts solvent are added. After the mixture is stirred completely, the powder is dried at 70℃-150℃ for 200-240 minutes. Then, 5.00 parts epoxy resin and 100 parts diluent are added. After the mixture is stirred completely, the powder is dried at 60℃-80℃ for 240 minutes.

[0027] The performance of the above comparative examples was compared with that of the examples prepared according to the formulations in Table 1 of the present invention for the preparation method of a soft magnetic composite material with high permeability and high magnetic flux density. The performance comparison results are shown in Table 2 below: Table 2: Performance Comparison of Comparative Examples and Embodiments of the Present Invention

[0028] Specifically, in the preparation method of a high-permeability, high-flux-density soft magnetic composite material of the present invention, a gradient coating structure is adopted, that is, with a 50nm... As the foundation, then with 30nm As a modification layer; then, using 40nm The polymer is used as a hybrid layer; thus, the contradiction between excessive coating thickness leading to reduced Bs and insufficient coating thickness leading to insufficient insulation can be resolved.

[0029] Furthermore, in the preparation method of a soft magnetic composite material with high magnetic permeability and high magnetic flux density of the present invention, the magnetic moment of the soft magnetic composite material is aligned along the easy magnetization axis by utilizing the magnetic field annealing effect, that is, by applying a magnetic field near the Curie temperature, thereby achieving the purpose of reducing hysteresis loss.

[0030] Furthermore, in the preparation method of the high permeability and high flux density soft magnetic composite material of the present invention, through interface enhancement design, ≡Fe-O-Si- bonds are generated on the surface of Fe powder using a silane coupling agent, thereby increasing the interfacial bonding energy of the composite material to 210 J / m², while the interfacial bonding energy of the traditional scheme (such as the comparative example) can only reach 80 J / m². It can be seen that the preparation method of the high permeability and high flux density soft magnetic composite material of the present invention can significantly improve the interfacial bonding energy of the soft magnetic composite material.

[0031] Therefore, the preparation method of the high permeability and high flux density soft magnetic composite material of this invention can achieve a solvent recovery rate of >90% by adding a condensation recovery device; the annealing time can be shortened by 40% by accelerating atomic diffusion through a magnetic field; and the μe value can be controlled by adjusting the magnetic field strength, with 0.3-1.0T corresponding to μe=55-65. Thus, the preparation method of the high permeability and high flux density soft magnetic composite material of this invention is particularly suitable for high-current power inductors used in 5G communication base stations, meeting the requirements of high-frequency and high-temperature applications. Experimental data shows that under 2MHz / 50A operating conditions, the loss is reduced by more than 42% compared to commercially available iron-silicon-aluminum magnetic cores.

[0032] Furthermore, the following is an example of the proportions of the three raw materials in the preparation method of a high-permeability, high-flux-density soft magnetic composite material of the present invention, specifically by mass parts: Example 1: High-frequency communication application type with optimal permeability

[0033] Key process parameters for Example 1: Gradient coating temperature: 75℃ (phosphate layer) → 82℃ (cerium salt layer); Magnetic field annealing: 0.8T axial magnetic field, 420℃×2h.

[0034] The performance test results of Example 1 are as follows:

[0035] Example 2: High-current application type with optimal magnetic flux density

[0036] Key process parameters for Example 2: gradient coating thinning: 60nm phosphate layer + 20nm cerium salt layer; magnetic field annealing: 0.3T. This avoids over-orientation leading to a decrease in Bs.

[0037] The performance test results of Example 2 are as follows:

[0038] Example 3: Low-cost, universal design with optimal overall cost-effectiveness.

[0039] Key process parameters of Example 3: Elimination of nanotechnology Hybrid layer; Annealing conditions: 0.5T magnetic field, 380℃×1.5h.

[0040] The performance and cost comparison results of Example 3 are as follows:

[0041] Furthermore, in the preparation method of the high permeability and high flux density soft magnetic composite material of the present invention, the testing and verification method for magnetic properties is as follows: For the BS test, a BH analyzer (model MATS-2010SD) is used, and a magnetic field of 3000 A / m is applied at 25°C; for the μe test, an LCR meter (Agilent 4285A) is used to measure the inductance value of the toroidal core, and the result is calculated according to IEC 60401-3. An example formula for calculating permeability is provided below.

[0042] In the formula, L: measured inductance (H), le: effective magnetic circuit length (m), Ae: cross-sectional area (m²), and N: number of coil turns.

[0043] Furthermore, in the preparation method of the high permeability and high flux density soft magnetic composite material of the present invention, the insulation performance is verified as follows: for interlayer resistance, the IPC-650 standard is used, and the test is performed under 500V DC for 60s; for breakdown voltage, the voltage is stepped up to 5kV, and the measured values ​​are all >3.2kV.

[0044] Furthermore, in the preparation method of the high permeability and high flux density soft magnetic composite material of the present invention, taking Example 1 as an example, the method for verifying the microstructure of the final soft magnetic composite material is as follows: using TEM, the total thickness of the gradient coating layer is measured to be 110 nm, where the total thickness = 70nm+ layer The layer is 40 nm thick; XPS interface analysis detected Fe-O-Si bonds with a binding energy of 711.2 eV; SEM surface morphology analysis showed that boron nitride sheet-like structures were embedded in the resin layer.

[0045] Furthermore, the performance of the foregoing comparative embodiments is compared with that of Embodiments 1-3 of the present invention, as shown in Table 3 below: Table 3: Performance Comparison Results of Each Example

[0046] Specifically, the present invention provides a method for preparing a soft magnetic composite material with high magnetic permeability and high magnetic flux density through... Grain boundary repair reduced eddy current loss to 320 kW / m³, a reduction of >35% compared to the comparative example. Furthermore, by combining gradient coating with magnetic field annealing, μe was increased to over 60, while Bs was maintained at >1.9T. Moreover, the system of polyimide and boron nitride improved the thermal stability of the soft magnetic composite material from 180°C to 300°C, and μ decayed by <3% after aging at 150°C.

[0047] Specifically, Example 1 is applicable to power inductors for 5G base stations, which have the advantages of high frequency and low loss; Example 2 is applicable to on-board units (OBCs) for electric vehicles, which have the advantage of high DC bias; Example 3 is applicable to power supplies for consumer electronics, especially suitable for cost-sensitive scenarios.

[0048] In summary, this invention discloses a method for preparing a soft magnetic composite material with high permeability and high flux density, which includes four core processes: Step 1 employs gradient inorganic coating: diammonium hydrogen phosphate and oxalic acid are dissolved in deionized water and reacted with iron powder at 70°C to form... At the bottom layer, cerium nitrate solution is added dropwise at 80℃ to modify the grain boundaries, achieving precise coating of 80-120nm; Step 2 involves organic-inorganic hybrid treatment: combining silane coupling agent with nanoparticles... After hydrolysis of the sol in an ethanol / water mixture, it is ultrasonically dispersed with the coated powder and vacuum dried at 80℃ to form ≡Fe-O-Si≡ bonds, increasing the insulation resistance by 3 times; Step 3 involves high-temperature organic coating: polyimide resin prepolymer and hexagonal boron nitride nanosheets are ball-milled and dispersed, then dip-coated into the powder and dried in a fluidized bed at 120℃, significantly reducing high-frequency eddy current losses; Step 4 employs magnetic field-assisted annealing: after the powder is pressed into shape, ... Two-stage annealing (350℃×1h stress relief → 420℃×2h + 0.5T axial static magnetic field) under a protective atmosphere improves permeability by 15-20% through domain orientation alignment. This invention discloses a method for preparing a soft magnetic composite material with high permeability and high magnetic flux density, simultaneously optimizing the insulation, permeability, and saturation magnetic flux density of the soft magnetic composite material. The final prepared soft magnetic composite material exhibits insulation >5000MΩ, permeability μe in the range of 58-62, and saturation magnetic flux density Bs 1.92T. Therefore, this invention's method for preparing a soft magnetic composite material with high permeability and high magnetic flux density solves the technical problem of how to improve the permeability and magnetic flux density of soft magnetic composite materials.

[0049] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0050] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a soft magnetic composite material with high magnetic permeability and high magnetic flux density, characterized in that, It includes the following steps: Step 1: Prepare all materials according to the preset raw material ratio. First, carry out the gradient inorganic coating process in the reactor, as follows: a. Dissolve diammonium hydrogen phosphate and oxalic acid in deionized water in a predetermined ratio, and heat to 70°C; b. Add iron powder and stir for 30 minutes to form Underlying layer; c. Slowly add cerium nitrate solution; d. Incubate at 80℃ for 60 min, then centrifuge to obtain powder; Step 2: Organic-inorganic hybrid treatment, as follows: a. Combining silane coupling agents with nano The sol was added to an ethanol / water mixed solvent, wherein the volume ratio of ethanol to water was 3:

1. b. After hydrolysis for 30 min, add the powder obtained in step 1 and disperse it under ultrasonication at 40 kHz for 30 min; c. Place the dispersed material in a vacuum at 80°C to dry it, so that chemical bonds ≡Fe-O-Si≡ can be formed at the interface; Step 3: High-temperature resistant organic coating, as follows: a. Dissolve the polyimide resin prepolymer in NMP solvent, controlling the solution concentration to 15 wt%; b. Then add hexagonal boron nitride nanosheets and disperse them by ball milling. The ball milling parameters are set to 300 rpm for 1 h. c. Dip-coat the hybrid powder and dry it in a fluidized bed at 120°C for 30 minutes; Step 4: Magnetic field-assisted annealing, as follows: a. Powder is pressed into a ring-shaped magnetic core under a pressure of 800 MPa; b. Use an N2 / H2 mixture for protection, with an N2 to H2 ratio of 95:5; c. Two-stage annealing is adopted: the first stage is annealing at 350℃ for 1 hour; the second stage is annealing at 420℃ for 2 hours; at the same time, the magnetic core is placed in an axial static magnetic field of 0.5T.

2. The method for preparing a soft magnetic composite material with high permeability and high magnetic flux density according to claim 1, characterized in that: By weight, per 100 parts of carbonyl iron powder, the raw materials required for the gradient inorganic coating layer include: diammonium hydrogen phosphate: 0.8–1.5 parts, cerium nitrate: 0.3–0.8 parts, and oxalic acid: 0.05–0.2 parts; the raw materials required for the organic-inorganic hybrid layer include: particles with a particle size of 20–50 nm. Sol: 1.0-2.0 parts and γ-aminopropyltriethoxysilane: 0.5-1.2 parts; The raw materials required for the high-temperature resistant organic coating layer include: polyimide resin: 2.0-3.5 parts and hexagonal boron nitride nanosheets with a thickness of less than 100 nm: 0.1-0.3 parts.

3. The method for preparing a soft magnetic composite material with high permeability and high magnetic flux density according to claim 2, characterized in that: Diammonium hydrogen phosphate forms an acidic environment with oxalic acid, and the amount of cerium nitrate added is greater than 0.5 parts.

4. The method for preparing a soft magnetic composite material with high permeability and high magnetic flux density according to claim 2, characterized in that: The amount of polyimide used is 2.8 parts, and the amount of boron nitride added is 0.2 parts.

5. The method for preparing a soft magnetic composite material with high permeability and high magnetic flux density according to claim 1, characterized in that: By weight, when the matrix material is 100 parts carbonyl iron powder with a particle size of 5-20 μm, the raw materials required for the gradient inorganic coating layer include: 1.2 parts diammonium hydrogen phosphate, 0.6 parts cerium nitrate, and 0.1 parts oxalic acid; the raw materials required for the organic-inorganic hybrid layer include: nano-sized particles with a particle size of 20 nm. The raw materials required for the high-temperature resistant organic coating layer include: 1.8 parts of sol and 1.0 parts of γ-aminopropyltriethoxysilane; 3.0 parts of polyimide resin and 0.2 parts of hexagonal boron nitride nanosheets.

6. The method for preparing a soft magnetic composite material with high permeability and high magnetic flux density according to claim 5, characterized in that: The temperature of the phosphate layer in the gradient coating was adjusted to 75℃ and the temperature of the cerium salt layer was adjusted to 82℃; during magnetic field annealing: the axial magnetic field was set to 0.8T and maintained at 420℃ for 2 hours.

7. The method for preparing a soft magnetic composite material with high permeability and high magnetic flux density according to claim 1, characterized in that: When the matrix material is 100 parts of atomized FeSi powder with a Si content of 6.5 wt%, the raw materials required for the gradient inorganic coating layer include: 0.9 parts of zinc phosphate and 0.4 parts of cerium carbonate; the raw materials required for the organic-inorganic hybrid layer include: nano- The raw materials required for the high-temperature resistant organic coating layer include: 1.2 parts of sol and 0.8 parts of titanate coupling agent; 2.5 parts of polyimide resin and 0.15 parts of hexagonal boron nitride nanosheets.

8. The method for preparing a soft magnetic composite material with high magnetic permeability and high magnetic flux density according to claim 7, characterized in that: During gradient coating, the phosphate layer was thinned to 60 nm and the cerium salt layer to 20 nm; the parameters for magnetic annealing were changed to 0.3 T.

9. The method for preparing a soft magnetic composite material with high permeability and high magnetic flux density according to claim 1, characterized in that: When the matrix material is 100 parts of reduced iron powder with a purity greater than 99%, the raw materials required for the gradient inorganic coating layer include: 0.8 parts of ammonium dihydrogen phosphate and 0.3 parts of cerium sulfate; the raw materials required for the coupling treatment layer include: 0.6 parts of silane coupling agent; and the raw materials required for the organic coating layer include: 2.0 parts of epoxy resin E-44 and micron-sized... 0.3 parts powder.

10. The method for preparing a soft magnetic composite material with high permeability and high magnetic flux density according to claim 9, characterized in that: The annealing conditions were adjusted to: 0.5T magnetic field, 380℃ for 1.5h.

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