A double-layer insulation-coated soft magnetic composite material with a high-thermal-conductivity network structure and a preparation method thereof

Abstract

The application discloses a double-layer insulation-coated soft magnetic composite material with a high-thermal-conductivity network structure and a preparation method thereof. First, a surfactant is used to perform surface modification treatment on soft magnetic powder, and an Al2O3 insulation coating layer with high resistivity and high thermal conductivity is formed on the surface of the modified soft magnetic powder in situ through a sol-gel reaction. Then, the magnetic powder coated with the Al2O3 insulation layer is uniformly mixed with a composite resin doped with dendritic nano Al2O3 powder, a second thermal-conductivity shell layer is constructed on the outer layer of the magnetic powder, and a composite powder with a double-layer insulation-coated structure is formed. The obtained composite powder is sequentially subjected to granulation, compression molding and low-temperature solidification treatment, so that the target soft magnetic composite material is prepared. According to the double-layer coating process, a continuous and through thermal-conductivity network is successfully constructed in the composite material, so that the overall heat dissipation efficiency of the composite material is remarkably improved, and the current can be efficiently insulated.

Description

Technical Field

[0001] This invention relates to the field of soft magnetic composite material preparation technology, specifically to a soft magnetic composite material with a double-layer thermally conductive network structure insulating coating and its preparation method. This invention is mainly applied to high-performance inductors and related power electronic devices under high-frequency, high-current conditions. Background Technology

[0002] With the rapid development of 5G mobile communication, artificial intelligence computing, and new energy vehicle electronics, electronic terminal devices are placing stringent demands on the miniaturization and integration of power modules. Inductors, as the core component of voltage conversion modules, are experiencing ever-increasing power density. Soft magnetic composite materials (SMCs), due to their high saturation magnetic induction, good frequency response, and three-dimensional isotropic magnetic properties, have become the mainstream material for manufacturing such inductors.

[0003] However, in actual operation, especially under high current and high-frequency alternating magnetic fields, significant energy loss occurs inside the magnetic powder core. This loss mainly consists of hysteresis loss and eddy current loss, and is ultimately released as heat. Common molded inductors typically employ a fully enclosed package structure, making internal heat accumulation extremely easy.

[0004] The main performance indicators that are of concern in the coating of magnetic powder cores are: effective permeability (μ). e ), core loss (P) cv Insulation resistance (R) and breakdown voltage (V) b However, these indicators only focus on electrical insulation performance and ignore the material's ability to control temperature rise under actual high current operation. Excessive temperature rise can not only lead to the degradation of the magnetic properties of the magnetic powder, but also cause thermal decomposition or mechanical stress failure of the coating layer, thereby triggering local short circuits and inductor failure.

[0005] To improve the heat dissipation performance of soft magnetic composite materials, existing technologies have proposed several solutions. For example, patent CN121506690A uses nano-diamondene materials. While this material improves thermal conductivity, its raw materials are expensive, and to improve interfacial bonding, it requires prolonged high-temperature reflux treatment with strong acids such as concentrated sulfuric acid and concentrated nitric acid. This process poses significant safety hazards and is environmentally unfriendly, making large-scale industrial production difficult. If not handled properly, the coating layer and magnetic powder still lack deep chemical bonding, making the coating layer prone to detachment during compression molding. Patent CN121281955A uses hexagonal boron nitride-filled resin to construct heat dissipation channels for the magnetic powder, but this also faces the problem of high raw material costs. In addition, nano-scale h-BN has high surface energy, is prone to agglomeration, and has poor compatibility with the resin matrix, easily forming interfacial defects and increasing interfacial thermal resistance. If added in excess, it will not only reduce the mechanical adhesion of the coating layer but also easily scratch the surface of the magnetic powder during high-pressure molding, thus leading to a decrease in the overall magnetic permeability of the material. In addition, patent CN121389587A obtained the flow channel layout of the integrally molded inductor through fitting calculation and proposed to use a microchannel system for active heat dissipation. However, this solution increases the structural complexity and manufacturing difficulty of the device. Moreover, external heat dissipation methods are difficult to solve the inherent heat accumulation problem at the microscopic level inside the magnetic core.

[0006] In summary, how to construct a dual-layer heat dissipation network on the surface of magnetic powder particles that can effectively isolate current and quickly conduct heat is a key technical problem that urgently needs to be solved in the field of high-performance inductor research and development. Summary of the Invention

[0007] To address the problems existing in the prior art, the present invention provides a double-layer insulating soft magnetic composite material with a high thermal conductivity network structure and its preparation method.

[0008] The technical solution of the present invention is as follows:

[0009] A method for preparing a double-layer insulating coated soft magnetic composite material with a high thermal conductivity network structure includes the following steps:

[0010] (1) Soft magnetic powder is surface modified by surfactant. The modified soft magnetic powder forms an Al2O3 insulating coating layer on its particle surface in situ through sol-gel reaction to obtain magnetic powder B.

[0011] (2) After calcining Al2O3 nanoparticles to form a dendritic structure, the dendritic nano-Al2O3 was placed in a mixture of coupling agent KH-550 and ethanol and stirred until the ethanol was completely evaporated to obtain modified Al2O3; the composite resin of organosilicon resin and epoxy resin was dissolved in acetone solution and the modified Al2O3 was added and ultrasonically dispersed to obtain resin acetone solution doped with nano-Al2O3.

[0012] (3) Add magnetic powder B to the resin acetone solution doped with nano Al2O3, stir until the acetone is completely evaporated, dry and then sieve with a 40-120 mesh screen to obtain granulated magnetic powder C.

[0013] (4) The granulated magnetic powder C is pressed into shape, and after pressing, it is heat-treated and cured to obtain a double-layer insulating soft magnetic composite material with a high thermal conductivity network structure.

[0014] Preferably, the surface modification treatment in step (1) is as follows: after washing and drying the soft magnetic powder, magnetic powder A is obtained; the surfactant is dissolved in ethanol and heated; magnetic powder A is added to it and stirred to complete the surface modification and obtain a modified liquid containing magnetic powder A.

[0015] Preferably, the median particle size of the soft magnetic powder in step (1) is in the range of 1 μm-10 μm.

[0016] Preferably, the preparation of magnetic powder B in step (1) is as follows: a chelating agent and an aluminum source are added to a modified liquid containing magnetic powder A, stirring and heating are maintained, water is then added to start the reaction, and the pH is adjusted; after the reaction is completed, the magnetic powder B is obtained by washing and drying; the chelating agent is acetylacetone, the aluminum source is aluminum isopropoxide, and the surfactant is polyvinylpyrrolidone (PVP).

[0017] Preferably, in step (1), the mass of the soft magnetic powder is used as the basis for calculation, the mass ratio of the surfactant is 2~4 wt.%, the mass ratio of ethanol is 150 wt.%~160 wt.%, the heating temperature is 70℃~80℃, and the modification time is 20 min~40 min.

[0018] Preferably, in step (1), based on the mass of magnetic powder A, the mass percentage of chelating agent is 3~10 wt.%, the mass percentage of aluminum source is 3~8 wt.%, the mass percentage of water is 30~40 wt.%, and the pH is adjusted to 4.5~5.5 by nitric acid.

[0019] Preferably, in step (1), the temperature of the sol-gel reaction is 70℃~80℃ and the reaction time is 40 min~120 min; in step (2), the particle size of Al2O3 nanoparticles is 10-50 nm, the calcination temperature is 1000℃~1200℃, and the calcination time is 4 h~5 h.

[0020] Preferably, in step (2), based on the mass of Al2O3 nanoparticles, the mass percentages of KH-550 and ethanol are 10wt.%~30wt.% and 500wt.%~800wt.%, respectively; and the mass ratio of silicone resin to epoxy resin is 5±2:1.

[0021] Preferably, in step (3), the total amount of nano-Al2O3 and composite resin is 1wt.%~5wt.% based on the mass of magnetic powder B, the mass percentage of acetone solvent used is 10wt.%~40wt.%, and the mass ratio of nano-Al2O3 and composite resin (the sum of organosilicon resin and epoxy resin) is 1:9-4:1.

[0022] Preferably, the drying temperature in step (3) is 60-80 ℃ and the drying time is 20 min-40 min; the pressing pressure in step (4) is 600 MPa-1200 MPa, the holding time is 5 s-8 s, the curing temperature is 150℃-180℃, and the curing holding time is 1 h-2 h.

[0023] Preferably, in step (1), the soft magnetic powder includes one or more of carbonyl iron powder, FeSiCr alloy powder, FeSiAl alloy powder, FeNi alloy powder, FeSi alloy powder and FeNiMo alloy powder, wherein the particle size is in the range of 1 μm-10 μm.

[0024] The technical principles of this invention include: Firstly, surface modification of iron powder using PVP allows its amide groups to coordinate with metal ions on the magnetic powder surface, adsorbing onto the iron powder surface and providing active sites for the Al2O3 precursor sol particles. This effectively guides the growth of the precursor on the magnetic powder surface. Simultaneously, the steric hindrance of the PVP polymer long chains prevents particle aggregation, ensuring uniform growth of the product synthesized by the sol-gel method on the magnetic powder surface. Secondly, the ordinary low thermal conductivity organic layer is replaced with resin filled with dendritic Al2O3 nanoparticles. The dendritic Al2O3 particles can interlock within the resin, forming a highly efficient thermally conductive path. Ultimately, the two thermally conductive coating layers form a continuous and interconnected thermally conductive and insulating network, which can cut off interparticle eddy currents, reduce eddy current losses, improve thermal conductivity, ensure device reliability, and also has the ability to efficiently isolate current.

[0025] Compared with existing technologies, the present invention has the following advantages:

[0026] (1) Surfactant pretreatment optimizes insulating coating and significantly reduces magnetic loss: Due to the lack of sufficient active functional groups on the surface of soft magnetic metal substrates and the poor interfacial wettability between inorganic oxide precursors and metals, heterogeneous nucleation during film formation is extremely difficult. This often results in highly uneven coating thickness, and inorganic nanoparticles are prone to spontaneous aggregation in solution, ultimately failing to form a continuous and dense coating layer on the magnetic powder surface. To address this problem, this invention utilizes polyvinylpyrrolidone (PVP) as a surfactant to pretreat the magnetic powder. Utilizing the amphiphilic structure of PVP molecules, not only is the dispersion uniformity of colloidal particles in the reaction system effectively improved, but also dense and uniform active sites are provided for the in-situ growth of the Al2O3 coating layer. After subsequent reactions following this pretreatment, a thin and dense Al2O3 insulating coating layer can be formed on the magnetic powder surface. This coating layer can effectively cut off the eddy current path between magnetic powder particles, thereby significantly reducing the magnetic loss of the composite material.

[0027] (2) Synergistic design of "inorganic + organic" double-layer thermally conductive network to construct an efficient heat conduction channel inside the material: This invention first coats the surface of magnetic powder with a high thermal conductivity inorganic Al2O3 shell using the sol-gel method, and then incorporates dendritic nano-Al2O3 particles into the outer organic resin coating layer. This double-layer structure design of "inorganic Al2O3 shell + organic resin doped with dendritic nano-Al2O3" successfully constructs a continuous and interconnected thermally conductive network inside the composite material, breaking through the technical limitations of the traditional single resin coating method with poor thermal conductivity. While significantly improving the overall heat dissipation efficiency of the composite material, it can also efficiently isolate current.

[0028] (3) Improving the temperature rise current of the device and effectively avoiding the risk of thermal failure of high power density devices: The soft magnetic composite material prepared by this invention has excellent thermal conductivity. Under high current operating conditions, it can quickly dissipate the Joule heat generated during device operation, significantly improving the temperature rise current threshold of the inductor device. This effectively solves the problem of inductor performance degradation and failure caused by heat accumulation in high power density electronic devices, ensuring long-term stable operation of the device. This soft magnetic composite material has significant advantages in the field of high power and high current electronic devices. Attached Figure Description

[0029] Figure 1 The microstructure (SEM) and surface elemental distribution (EDS) of the double-layer coated FeSiCr magnetic powder were obtained to verify the distribution of iron (Fe) and aluminum (Al) elements.

[0030] Figure 2 The image shows the morphological changes of Al2O3 before and after calcination. Before calcination, Al2O3 powder is granular, while after calcination, Al2O3 is dendritic.

[0031] Figure 3The thermal conductivity of different samples was compared. The left figure shows the thermal conductivity of pure resin and resin doped with Al2O3 of different morphologies (granular and dendritic), with a filling rate of 50 wt.% for both types of particles; the right figure shows the thermal conductivity of Comparative Examples 1-3 and Examples 1-2.

[0032] Figure 4 The effects of different coating methods on the temperature rise current of integrally molded inductors were compared. The left figure shows the temperature rise curves of the surface temperature of each sample as a function of the applied current, and the right figure shows the temperature rise current of each sample surface when it is increased by 40°C.

[0033] Figure 5 The diagram shows the effect of different coating methods on the inductance (right) and Q value (left).

[0034] Figure 6 This is a schematic diagram of a double-layer thermally conductive and insulating coating. In the diagram, 1 is the magnetic powder matrix, 4 is the double-layer coating structure, 2 is the Al2O3 inorganic layer coated by the PVP-assisted sol-gel method, 3 is the silicone resin organic layer filled with dendritic Al2O3 and modified with epoxy resin, and 5 is a schematic diagram of the magnetic powder heat dissipation channel. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. All raw materials involved in the present invention can be purchased directly from the market. For process parameters not specifically specified, conventional techniques can be referred to.

[0036] The FeSiCr magnetic powder was purchased from Ansteel Technology Co., Ltd., and its model number is FeSiCr-D.

[0037] Example 1

[0038] A method for preparing a double-layer insulating soft magnetic composite material with a high thermal conductivity network structure includes the following steps:

[0039] (1) Raw material preparation: FeSiCr magnetic powder with a median particle size of 9.424 μm was selected as raw material, and it was pretreated by alcohol washing and drying to obtain magnetic powder A;

[0040] (2) Surface modification: Dissolve 1 g of surfactant polyvinylpyrrolidone in 80 g of ethanol, place the solution in a three-necked flask and heat in an 80°C water bath for 30 min, pour 50 g of magnetic powder A into the heated mixture and stir for 30 min to complete the surface modification.

[0041] (3) Sol-gel method for coating Al2O3: Add 3 mL of chelating agent acetylacetone and 2 g of aluminum source aluminum isopropoxide to 50 g of modified mixture containing magnetic powder, keep stirring and heat in an 80°C water bath for 20 min, then add 17 g of deionized water to start the reaction, and add nitric acid to adjust pH≈5; after the reaction is completed for 1 h, the magnetic powder B is obtained by washing with alcohol and deionized water and drying.

[0042] (4) Preparation of resin doped with nano-Al2O3: 0.75 g of nano-Al2O3 (particle size 10-50 nm) was placed in a muffle furnace and calcined at 1200 °C for 4 h to form a dendritic structure. The dendritic nano-Al2O3 was poured into a mixture of 0.15 g of coupling agent KH-550 and 5 g of ethanol for modification. The mixture was magnetically stirred at 50 °C until the ethanol was completely evaporated. 0.625 g of organosilicon resin and 0.125 g of epoxy resin were dissolved in 15 g of acetone solution, mixed with the modified Al2O3 and ultrasonically dispersed for 30 min to obtain a resin acetone solution doped with nanoparticles.

[0043] (5) Organic coating granulation: Add the magnetic powder B from step (3) to the resin acetone solution from step (4), stir until the acetone is completely evaporated, dry at 70°C for 30 min, sieve with 40 mesh and 120 mesh screens, and take the magnetic powder between the two screens to obtain granulated magnetic powder C.

[0044] (6) Pressing and curing: Magnetic powder C is pressed into an integral inductor at 800 MPa and held for 5.5 s. After pressing, heat treatment is performed to cure the inductor. The curing temperature is 180℃ and the curing time is 1 h. A double-layer insulating soft magnetic composite material inductor with a high thermal conductivity network structure is obtained.

[0045] Example 2

[0046] The difference between this embodiment and Example 1 is that the filling rate of the dendritic Al2O3 is 0 wt.%, while the rest of the preparation methods and parameters are the same as in Example 1.

[0047] Comparative Example 1

[0048] Comparative Example 1 provides a method for preparing FeSiCr soft magnetic composite material with pure resin coating. The difference between this comparative example and Example 1 is that the sol-gel treatment step is omitted, the dendritic Al2O3 filling rate of the outer resin is 0 wt.%, and the rest of the preparation method and parameters are the same as those in Example 1.

[0049] Comparative Example 2

[0050] Comparative Example 2 provides a method for preparing FeSiCr soft magnetic composite material coated with pure resin after industrial phosphating. The difference between this comparative example and Example 1 is that the inner layer is not treated with the sol-gel method, but with the industrially common phosphating technology: 0.25 g of phosphoric acid is placed in 15 g of acetone solution and stirred evenly. 50 g of magnetic powder A is added to the above solution and stirred evenly until the acetone evaporates completely. After washing with deionized water and anhydrous ethanol, the FeSiCr magnetic powder is obtained after drying. The dendritic Al2O3 filling rate of the outer resin is 0 wt.%, and the rest of the preparation method and parameters are the same as in Example 1.

[0051] Comparative Example 3

[0052] Comparative Example 3 provides a method for preparing FeSiCr soft magnetic composite material with pure resin coating after SiO2 coating by industrial sol-gel method. The difference between this comparative example and Example 1 is that the inner layer is not treated by sol-gel method, but is replaced by the industrially common sol-gel coating technology for SiO2: 2.5 mL of tetraethyl silicate is placed in 40 mL of anhydrous ethanol and mixed well. 50 g of magnetic powder A is added to the above solution. The pH of the solution is adjusted to ≈10 by adding 25% ammonia solution. Then, the solution is stirred at a constant speed for 60 min under water bath heating at 50°C. After washing with deionized water and anhydrous ethanol, the FeSiCr magnetic powder coated with SiO2 is obtained. The dendritic Al2O3 filling rate of the outer resin is 0 wt.%, and the rest of the preparation method and parameters are the same as in Example 1.

[0053] The main evaluation results of Examples 1, 2, and Comparative Examples 1-3 are shown in Table 1. It can be seen that the double-layer thermally conductive coating retains a higher inductance L compared to traditional phosphating and sol-gel SiO2 coated inductors. s And a quality factor Q, along with a higher temperature rise current I. rms In addition to the insulation resistance R, the double-layered insulation withstand voltage performance was the best among the samples.

[0054] Table 1

[0055]

[0056] Figure 3Data shows that incorporating dendritic Al2O3 can more effectively improve the thermal conductivity of composite materials. The left figure compares the difference in thermal conductivity between resins treated differently. It can be seen that the pure resin has the lowest thermal conductivity, only 0.18 W / (m·K) at around 300 K, and remains at a very low level with increasing temperature. After filling with spherical Al2O3, the thermal conductivity increases to 0.41 W / (m·K), but shows a significant and rapid decline with increasing temperature. In contrast, the composite resin filled with dendritic Al2O3 exhibits the highest thermal conductivity throughout the entire test temperature range, reaching 0.45 W / (m·K), a 2.5-fold increase compared to the pure resin sample, and its decline with increasing temperature is the most gradual. This indicates that, compared to conventional nanoparticles that are easily isolated, the multi-branched structure of dendritic Al2O3 is more likely to interlock in the organic resin matrix, thus forming a more continuous, efficient, and thermally stable phonon heat transfer network. The right figure compares the thermal conductivity of different samples. It can be seen that, at room temperature, Comparative Example 1 has a thermal conductivity of 1.78 W / (m·K). Comparative Example 2, treated with conventional phosphating, and Comparative Example 3, with its SiO2 coating, have lower intrinsic thermal conductivity due to the low thermal conductivity of their coating layers and the continuous thermal resistance interface formed between the inorganic coating and the resin, resulting in thermal conductivity decreases to 0.45 W / (m·K) and 0.69 W / (m·K), respectively. In contrast, Example 2, with its Al2O3 inorganic coating, effectively reduces interfacial contact thermal resistance by introducing a highly thermally conductive inorganic layer, increasing its room temperature thermal conductivity to 2.48 W / (m·K). Example 1, with its double-layer thermally conductive coating, achieves a room temperature thermal conductivity as high as 3.41 W / (m·K), an improvement of approximately 81.38% compared to Comparative Example 1 and 5.88 times that of Comparative Example 2. This is mainly attributed to the formation of a thermally conductive network between the inner continuous Al2O3 film and the outer dendritic filler. Compared with spherical particles, the dendritic structure is more likely to overlap in the organic matrix to form an efficient phonon transmission channel.

[0057] Figure 4 This demonstrates the significant advantage of the thermally conductive coating structure in suppressing temperature rise. The left figure shows that as the applied current increases, the temperature of each group of samples rises non-linearly, but the heating rate differs: Comparative Example 2 and Comparative Example 3 show the highest temperature rise rate with increasing applied current; the temperature rise rate of Comparative Example 1 is lower than that of Comparative Example 2 and Comparative Example 3 because the low thermal conductivity of the phosphating layer and the sol-gel SiO2 layer hinders heat dissipation; Example 2 further delays heat accumulation, resulting in a slow temperature rise; the right figure compares the temperature rise current of each sample, showing that Examples 1 and 2 have significant advantages in suppressing temperature rise.

[0058] Figure 5The results show that Examples 1 and 2 retained higher inductance, with Q values ​​relatively higher than those of the ordinary phosphating and SiO2 systems, namely Comparative Examples 2 and 3. The Q values ​​of the samples with inorganic coating were all higher than those of Comparative Example 1 without inorganic coating, but the inductance decreased after coating.

[0059] from Figure 6 As can be seen, the soft magnetic composite material has two insulating layers. The first layer is a highly thermally conductive Al2O3 inorganic layer, and the second layer is a highly thermally conductive resin layer, which is composed of a large number of interlocking dendritic Al2O3 layers. These two layers combine high insulation performance and high thermal conductivity, ensuring the reliability of the device.

[0060] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a double-layer insulating coated soft magnetic composite material with a high thermal conductivity network structure, characterized in that, Includes the following steps: (1) Soft magnetic powder is surface modified by surfactant. The modified soft magnetic powder forms an Al2O3 insulating coating layer on its particle surface in situ through sol-gel reaction to obtain magnetic powder B. (2) After calcining Al2O3 nanoparticles to form a dendritic structure, the dendritic nano-Al2O3 was placed in a mixture of coupling agent KH-550 and ethanol and stirred until the ethanol was completely evaporated to obtain modified Al2O3; the composite resin of organosilicon resin and epoxy resin was dissolved in acetone solution and the modified Al2O3 was added and ultrasonically dispersed to obtain resin acetone solution doped with nano-Al2O3. (3) Add magnetic powder B to the resin acetone solution doped with nano Al2O3, stir until the acetone is completely evaporated, dry and then sieve with a 40-120 mesh screen to obtain granulated magnetic powder C. (4) The granulated magnetic powder C is pressed into shape, and after pressing, it is heat-treated and cured to obtain a double-layer insulating soft magnetic composite material with a high thermal conductivity network structure.

2. The preparation method according to claim 1, characterized in that, Step (1) Surface modification treatment is as follows: after washing and drying the soft magnetic powder, magnetic powder A is obtained. The surfactant is dissolved in ethanol and heated. Magnetic powder A is added to it and stirred to complete the surface modification and obtain a modified liquid containing magnetic powder A.

3. The preparation method according to claim 2, characterized in that, Preparation of magnetic powder B in step (1): Add chelating agent and aluminum source to the modified liquid containing magnetic powder A, keep stirring and heating, then add water to start the reaction and adjust the pH; After the reaction is complete, the magnetic powder B is obtained by washing and drying. The chelating agent is acetylacetone, the aluminum source is aluminum isopropoxide, and the surfactant is polyvinylpyrrolidone.

4. The preparation method according to claim 1, characterized in that, In step (1), the mass of the soft magnetic powder is used as the basis for calculation. The mass percentage of the surfactant is 2~4 wt.%, the mass percentage of ethanol is 150 wt.%~160 wt.%, the heating temperature is 70℃~80℃, and the modification time is 20 min~40 min.

5. The preparation method according to claim 3, characterized in that, In step (1), the mass of magnetic powder A is used as the basis for calculation. The mass ratio of chelating agent is 3~10wt.%, the mass ratio of aluminum source is 3~8wt.%, the mass ratio of water is 30~40wt.%, and the pH is adjusted to 4.5~5.5 by nitric acid.

6. The preparation method according to any one of claims 1 to 5, characterized in that, In step (1), the temperature of the sol-gel reaction is 70℃~80℃ and the reaction time is 40 min~120 min; in step (2), the particle size of Al2O3 nanoparticles is 10-50 nm, the calcination temperature is 1000℃~1200℃ and the calcination time is 4 h~5 h.

7. The preparation method according to any one of claims 1 to 5, characterized in that, In step (2), based on the mass of Al2O3 nanoparticles, the mass percentages of KH-550 and ethanol are 10wt.%~30wt.% and 500wt.%~800wt.%, respectively; the mass ratio of silicone resin and epoxy resin is 5±2:

1.

8. The preparation method according to any one of claims 1 to 5, characterized in that, In step (3), the total amount of nano Al2O3 and composite resin is 1 wt.%~5 wt.% based on the mass of magnetic powder B, the mass percentage of acetone solvent used is 10 wt.%~40 wt.%, and the mass ratio of nano Al2O3 to composite resin is 1:9-4:

1.

9. The preparation method according to any one of claims 1 to 5, characterized in that, The drying temperature in step (3) is 60-80 ℃ and the drying time is 20 min-40 min; the pressing pressure in step (4) is 600 MPa-1200 MPa, the holding time is 5 s-8 s, the curing temperature is 150℃-180℃, and the curing holding time is 1 h-2 h.

10. The preparation method according to any one of claims 1 to 5, characterized in that, In step (1), the soft magnetic powder includes one or more of carbonyl iron powder, FeSiCr alloy powder, FeSiAl alloy powder, FeNi alloy powder, FeSi alloy powder and FeNiMo alloy powder, wherein the particle size is in the range of 1 μm-10 μm.

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