Insulated magnetic powder, preparation method and application thereof

Abstract

This invention relates to the field of soft magnetic composite materials, and particularly to an insulating coated magnetic powder, its preparation method, and its application. The method includes the following steps: A. preparing an inner layer solution; B. preparing an outer layer solution; C. preparing a catalytic hydrolysis solution; D. preparing hydroxylated soft magnetic metal powder; E. mixing the inner layer solution, outer layer solution, and catalytic hydrolysis solution and spraying them onto the surface of the fluidized hydroxylated soft magnetic metal powder, thereby depositing an insulating coating layer formed by a gradient composite sol on the surface of the hydroxylated soft magnetic powder; and then sequentially filtering, washing, and drying the hydroxylated soft magnetic powder with the deposited insulating coating layer to obtain the insulating coated magnetic powder. The method for preparing the insulating coated magnetic powder proposed in this invention is simple, easy to operate, and beneficial for improving resistivity and reducing total loss while enhancing coating uniformity, interfacial bonding strength, and crush resistance.

Description

Technical Field

[0001] This invention relates to the field of metal soft magnetic composite materials technology, and in particular to an insulating coated magnetic powder, its preparation method and application. Background Technology

[0002] Soft magnetic composite materials, also known as metal magnetic powder cores, are produced by coating soft magnetic powder with an insulating layer to obtain an insulating-coated magnetic powder. This insulating-coated magnetic powder is then mixed uniformly with a release agent, pressed, and annealed to obtain the final soft magnetic composite material. Due to its advantages such as high permeability, high saturation flux density, and low total loss, soft magnetic composite materials are widely used in transformers, sensors, and choke coils.

[0003] In the preparation of soft magnetic metal composites, the performance of the insulating coated magnetic powder directly determines the final magnetic properties and reliability of the composite material. The performance of the insulating coated magnetic powder, in turn, depends on the insulating coating layer. Therefore, the insulating coating layer is crucial to the performance of soft magnetic metal composites. Currently, the insulating coating systems used in insulating coating layers are mainly divided into two categories: (1) Organic polymer coating system While organic coating materials, such as epoxy resin and polyurethane, possess good adhesion and high insulation resistance, their thermal stability is generally poor. For example, Chinese invention patent CN1224899A discloses a composite magnetic material, its manufacturing method, and Fe-Al-Si soft magnetic alloy powder used therein. It utilizes thermosetting organic resins such as epoxy resin and phenolic resin to coat FeSiAl magnetic powder. Although this can effectively improve resistivity and suppress eddy current losses, it is limited by the upper temperature limit of organic resins, preventing heat treatment above 400°C. This results in insufficient release of internal stress in the magnetic powder, making it difficult to further reduce total losses.

[0004] (2) Inorganic oxide coating system Inorganic insulating materials, such as SiO2, Al2O3, and ZrO2, possess excellent insulation properties and high-temperature stability, meeting the requirements of high-temperature annealing processes. However, their coating method significantly affects the quality of the insulation layer. For example, Chinese invention patent CN100500783A discloses an inorganic insulating adhesive for metal soft magnetic powder cores and its preparation method. It uses an insulating coating layer made of SiO2, Al2O3, ZrO2, and mica powder to coat FeSiAl magnetic powder. Although the process is simple, it is difficult to achieve a uniform and continuous distribution of the coating layer on the surface of the magnetic powder. Furthermore, the bonding between the inorganic oxides and the metal soft magnetic powder matrix is ​​mainly physical adsorption, resulting in weak adhesion. This makes it easy to peel off under pressure or thermal stress, failing to form an effective dense insulating barrier, leading to a decrease in resistivity and an increase in total loss.

[0005] To overcome the aforementioned shortcomings, existing technologies have employed techniques such as organic-inorganic composites. For example, Chinese invention patent CN115762947A discloses an insulating coating method for soft magnetic powder and its application. This method uses water glass and silica sol as binders and composite nano-oxides as insulating fillers to coat the surface of metal powder. However, this process still relies on phosphate for pre-passivation treatment of the magnetic powder, resulting in a brittle phosphate layer. Consequently, during the pressing process, the insulating layer of the coated magnetic powder is still prone to cracking (i.e., poor crush resistance), leading to a decrease in resistivity.

[0006] In summary, existing insulating coated magnetic powders generally suffer from defects such as insufficient coating uniformity, low interfacial bonding strength, and poor crush resistance, which lead to a decrease in resistivity and an increase in total loss. Summary of the Invention

[0007] One of the objectives of this invention is to provide a method for preparing insulating coated magnetic powder. This method is simple, easy to operate, and helps to improve resistivity and reduce total loss while improving coating uniformity, interfacial bonding strength and crush resistance, thereby overcoming the shortcomings of the prior art.

[0008] The second objective of this invention is to provide an insulating coated magnetic powder obtained by the above preparation method, which is beneficial to improve resistivity and reduce total loss while improving coating uniformity, interfacial bonding strength and crush resistance.

[0009] The third objective of this invention is to propose the application of insulating coated magnetic powder in the preparation of soft magnetic composite materials of metals, so that the soft magnetic composite materials prepared using the above-mentioned insulating coated magnetic powder have high resistivity and low total loss.

[0010] To achieve this objective, the present invention adopts the following technical solution: A method for preparing an insulating coated magnetic powder includes the following steps: A. Under an inert atmosphere, 8-10% silicon-aluminum composite precursor, 8-15% silane coupling agent, 0.1-0.2% nano-alumina, 0.5-1% chelating agent and 75-82% anhydrous ethanol are mixed evenly to obtain an inner layer solution. B. Under an inert atmosphere, 10-15% silicon-aluminum composite precursor, 2-4% silane coupling agent, 8-12% nano-alumina, 0.5-1% chelating agent, 1-2% dispersant and 65-75% anhydrous ethanol are mixed evenly to obtain an outer layer solution. C. Mix the acid catalyst, deionized water and anhydrous ethanol evenly to obtain the catalytic hydrolysis solution; D. Hydroxylating the soft magnetic metal powder to obtain hydroxylated soft magnetic metal powder; E. The inner layer solution is delivered to the first infusion pump, the outer layer solution is delivered to the second infusion pump, and the catalytic hydrolysate is delivered to the third infusion pump; The liquids in the first, second and third infusion pumps are mixed and reacted to generate a gradient composite sol online. The gradient composite sol is then atomized and sprayed onto the surface of the fluidized hydroxylated metal soft magnetic powder, so that an insulating coating layer formed by the gradient composite sol is deposited on the surface of the hydroxylated metal soft magnetic powder. Hydroxylated metal soft magnetic powder with an insulating coating deposited on its surface is filtered, washed, and dried sequentially to obtain insulating coated magnetic powder. In steps A and B, the silicon-aluminum composite precursor includes both silicon dioxide precursor and aluminum oxide precursor. In step E, the delivery rate of the inner layer solution decreases linearly from v1 to 0 L / min; the delivery rate of the outer layer solution increases linearly from 0 L / min to v1; the delivery rate of the catalytic hydrolysate is v2, and v2 / v1 is 0.5 to 0.7.

[0011] Furthermore, according to the molar ratio, the mixing ratio of the aluminum oxide precursor and the silicon dioxide precursor is 1: (5-10).

[0012] Furthermore, in steps A and B, the silane coupling agent includes either γ-aminopropyltriethoxysilane or γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0013] Furthermore, in steps A and B, the particle size of the nano-alumina is 20–50 nm.

[0014] Further, in step C, the catalytic hydrolysis solution comprises, by mass parts, 1-2 parts of acid catalyst, 20-30 parts of deionized water, and 20-30 parts of anhydrous ethanol.

[0015] Further, in step C, the acidic catalyst includes any one of acetic acid, hydrochloric acid, nitric acid, and sulfuric acid; The concentration of the acidic catalyst is 0.01–0.1 mol / L.

[0016] Furthermore, in step D, the method for hydroxylating the soft magnetic metal powder is as follows: The soft magnetic metal powder was immersed in acetone, and then washed with deionized water until neutral. The washed and neutralized soft magnetic metal powder is then dried.

[0017] Further, in step E, the mass of the gradient composite sol is calculated to be 0.5% to 5% of the mass of the soft magnetic metal powder, according to the mass ratio. The v2 is 0.2 to 2 L / min.

[0018] An insulating coated magnetic powder is prepared using the above-described method for preparing insulating coated magnetic powder.

[0019] An application of an insulating coated magnetic powder in the preparation of soft magnetic metal composite materials, wherein the above-mentioned insulating coated magnetic powder is used, and the application method is as follows: The insulating coated magnetic powder and the release agent are mixed evenly to obtain a mixed powder; The mixed powder is pressed into shape to obtain the mixed powder; The mixed powder was annealed under an inert atmosphere to obtain a soft magnetic metal composite material. The annealing curve for the annealing process is as follows: After heating from room temperature to 120°C at a rate of 1–3°C / min, hold at that temperature for 0.5–1 hour. The temperature was increased from 120℃ to 300℃ at a heating rate of 0.5~2℃ / min, and held at that temperature for 1.5~2.5h. The temperature was increased from 300℃ to 500℃ at a heating rate of 0.5~1℃ / min, and held at that temperature for 1.5~2.5h. The temperature was increased from 250℃ to 750℃ at a heating rate of 1-5℃ / min, and held for 1.5-2 hours.

[0020] The technical solution provided by this invention may include the following beneficial effects: 1. The method for depositing the insulating coating layer in this technical solution is essentially a sol-gel method. By controlling the mixing ratio of the inner and outer layer solutions, it ensures that the content of organic phase and inorganic rigid particles in the deposited gel exhibits a continuous gradient distribution from the inner to the outer layer, thus obtaining an insulating coating layer (which is essentially a gradient wet gel coating layer). During the subsequent drying process, the moisture and anhydrous ethanol in this essentially gradient wet gel coating layer evaporate and undergo a certain degree of solidification, resulting in an insulating coating layer with a gradient change in crosslinking density.

[0021] 2. Inside the insulating coating layer, silane coupling agent, silica precursor, and alumina precursor participate in the hydrolysis-condensation reaction under the action of a catalytic hydrolysate. This results in a three-dimensional network structure with gradually changing chemical composition but continuous chemical bonds inside the insulating coating layer. Since the insulating coating layer is gradually deposited from the inside out in the same chemical reaction process, there are no clear physical boundaries between the layers. Instead, they are a single whole seamlessly connected by covalent bonds formed by the hydrolysis-condensation reaction. There are no traditional weak interfaces, which gives the insulating coating layer a high bonding strength.

[0022] 3. Hydroxylated metal soft magnetic powder in a fluidized state refers to the process where hydroxylated metal soft magnetic powder is loaded into a fluidized bed reactor and inert gas such as nitrogen is introduced. This causes the hydroxylated metal soft magnetic powder to be in a "boiling" fluidized state under the action of the gas flow. This ensures that each piece of hydroxylated metal soft magnetic powder has an equal opportunity to be exposed to the atomized sol formed after the gradient composite solution is atomized. This avoids the dead zones caused by the agglomeration and sedimentation of hydroxylated metal soft magnetic powder in traditional stirring coating, ensuring macroscopic and microscopic uniformity. 4. The insulating coating layer with continuously varying porosity and modulus from the inside to the outside, constructed in this technical solution, effectively reduces total loss through the following multiple effects: First, the gradient coating layer avoids stress concentration caused by abrupt changes in modulus between the metal soft magnetic powder matrix and the external insulating coating layer. Furthermore, the nanoporous inorganic structure in the inner layer effectively absorbs and disperses internal stress from the external rigid layer and the processing, significantly reducing the net internal stress acting on the metal soft magnetic powder. This low-stress internal environment means that the energy barrier that needs to be overcome when magnetic domains rotate and domain walls move under the drive of an external magnetic field is significantly reduced, leading to a reduction in irreversible magnetization and thus a significant reduction in total loss on a macroscopic scale. Second, the high-strength interfacial bonding eliminates energy dissipation (such as frictional loss) caused by loosening or microscopic peeling of the coating layer, and provides a stable and undisturbed interface for the reversible and smooth movement of the domain walls, which also helps reduce total loss. Attached Figure Description

[0023] Figure 1 This is a diagram showing the transport rates of the inner layer solution, outer layer solution, and catalytic hydrolysate of the present invention. Detailed Implementation

[0024] This technical solution provides a method for preparing insulating coated magnetic powder, including the following steps: A. Under an inert atmosphere, 8-10% silicon-aluminum composite precursor, 8-15% silane coupling agent, 0.1-0.2% nano-alumina, 0.5-1% chelating agent and 75-82% anhydrous ethanol are mixed evenly to obtain an inner layer solution. B. Under an inert atmosphere, 10-15% silicon-aluminum composite precursor, 2-4% silane coupling agent, 8-12% nano-alumina, 0.5-1% chelating agent, 1-2% dispersant and 65-75% anhydrous ethanol are mixed evenly to obtain an outer layer solution. C. Mix the acid catalyst, deionized water and anhydrous ethanol evenly to obtain the catalytic hydrolysis solution; D. Hydroxylating the soft magnetic metal powder to obtain hydroxylated soft magnetic metal powder; E. The inner layer solution is delivered to the first infusion pump, the outer layer solution is delivered to the second infusion pump, and the catalytic hydrolysate is delivered to the third infusion pump; The liquids in the first, second and third infusion pumps are mixed and reacted to generate a gradient composite sol online. The gradient composite sol is then atomized and sprayed onto the surface of the fluidized hydroxylated metal soft magnetic powder, so that an insulating coating layer formed by the gradient composite sol is deposited on the surface of the hydroxylated metal soft magnetic powder. Hydroxylated metal soft magnetic powder with an insulating coating deposited on its surface is filtered, washed, and dried sequentially to obtain insulating coated magnetic powder. In steps A and B, the silicon-aluminum composite precursor includes both silicon dioxide precursor and aluminum oxide precursor. In step E, the delivery rate of the inner layer solution decreases linearly from v1 to 0 L / min; the delivery rate of the outer layer solution increases linearly from 0 L / min to v1; the delivery rate of the catalytic hydrolysate is v2, and v2 / v1 is 0.5 to 0.7.

[0025] To address the common technical problems of insufficient coating uniformity, low interfacial bonding strength, and poor crush resistance in existing insulating coated magnetic powders, this technical solution proposes a method for preparing insulating coated magnetic powders, including A (preparing an inner layer solution), B (preparing an outer layer solution), C (preparing a catalytic hydrolysis solution), D (hydroxylating the soft magnetic metal powder), and E (depositing an insulating coating layer). By optimizing the preparation method and raw materials, it is beneficial to improve resistivity and reduce total loss while enhancing coating uniformity, interfacial bonding strength, and crush resistance, thereby meeting practical application requirements.

[0026] Specifically, in this technical solution, the delivery rate of the inner layer solution decreases linearly from v1 to 0 L / min; the delivery rate of the outer layer solution increases linearly from the initial 0 L / min to v1; and the delivery rate v2 of the catalytic hydrolysate remains unchanged (specifically as follows). Figure 1 As shown in the figure, the mixing ratio of the inner and outer solutions was controlled in an orderly manner, and the formation mechanism of the insulating coating layer with continuously changing chemical composition on the surface of hydroxylated metal soft magnetic powder was realized as follows: In the initial stage of coating, the gradient composite sol in contact with the hydroxylated metal soft magnetic powder is mainly the sol obtained after the reaction of the inner layer solution and the catalytic hydrolysis solution. This sol is rich in a high proportion of silane coupling agent and a basic amount of silicon-aluminum composite precursor. Its hydrolysis and condensation form a hybrid gel layer with a Si-O-Si network structure as the backbone and interspersed with a large number of relatively flexible organic chains (introduced by the silane coupling agent). Due to the high proportion of flexible organic chains introduced by the silane coupling agent, the tight cross-linking of the network is effectively suppressed, so that the cross-linking density of the hybrid gel layer is maintained at a low level, and it exhibits excellent flexibility in the green state before annealing.

[0027] During the transition phase of coating, the proportion of the outer layer solution in the gradient composite sol increases while the proportion of the inner layer solution decreases. As the mixing ratio of the outer layer solutions dynamically changes, the proportion of rigid alumina nanoparticles in the newly deposited gel continuously increases, while the concentration of the silane coupling agent decreases accordingly. This achieves a smooth transition from a "high organic, low filler" structure to a "high inorganic, high filler" structure.

[0028] In the final stage of coating, the gradient composite sol is mainly the sol obtained after the reaction of the outer layer solution and the catalytic hydrolysis solution, that is, forming a high-hardness outer layer gel with silane coupling agent as the interface connecting phase, nano-alumina as the reinforcing phase, and dense silica-alumina oxide as the matrix.

[0029] In summary, the method for depositing the insulating coating layer in this technical solution is essentially a sol-gel method. By controlling the mixing ratio of the inner and outer layer solutions, it ensures that the content of organic phase and inorganic rigid particles in the deposited gel exhibits a continuous gradient distribution from the inner to the outer layer, resulting in an insulating coating layer (which is essentially a gradient wet gel coating layer). During the subsequent drying process, the moisture and anhydrous ethanol in this essentially gradient wet gel coating layer evaporate and undergo a certain degree of solidification, resulting in an insulating coating layer with a gradient change in crosslinking density.

[0030] Furthermore, in the subsequent annealing process for preparing the metal soft magnetic composite material, the organic phases such as the silane coupling agent in the insulating coating layer are decomposed and released by heat. The removal of the organic phase causes the inner layer of the insulating coating layer to transform into a porous, low-modulus SiO2-Al2O3 structure, while the outer layer, rich in nano-Al2O3 particles, forms a dense, high-modulus insulating coating layer after sintering.

[0031] It should be noted that although the decomposition of organic phases such as silane coupling agents poses a risk of forming pores, the organic phase can be decomposed and released gradually by using the conventional slow step heating method in existing technologies. This allows the pores to be controlled at the nanoscale and forms a coherent porous-dense gradient structure. Ultimately, an insulating coating layer with a continuous gradient change in porosity and modulus from the inside to the outside is obtained on the surface of the metal soft magnetic powder.

[0032] Secondly, as described above, the final result of this technical solution is an insulating coating layer with continuously varying composition and structure. This insulating coating layer is a complete whole, without discrete interlayer interfaces. For ease of analysis and explanation, based on its gradient change trend from the metal powder substrate to the outer surface, it can be conceptually defined as three functional regions: the inner layer region, the transition region, and the outer layer region. This definition method serves only for descriptive convenience; its essence is a functionally graded material with a stepless transition in performance. The inner layer (i.e., the inner region) of the insulating coating layer, in its green state (i.e., after drying and before annealing), exhibits excellent flexibility due to its rich flexible organic phase, effectively absorbing and releasing interfacial stress and preventing interfacial cracking. After annealing, this organic phase decomposes, and the inner layer evolves into a nanoporous inorganic structure. Its stress buffering function is achieved by the compressibility of the porous body, thereby maintaining the integrity of the interface between the hydroxylated metal soft magnetic powder and the insulating coating layer throughout the entire process.

[0033] Furthermore, this technical solution involves hydroxylating the metal soft magnetic powder to remove impurities and oil stains from its surface, exposing the hydroxyl groups on the powder surface, thereby obtaining hydroxylated metal soft magnetic powder with a surface rich in hydroxyl groups. Silane coupling agents, silica precursors, and alumina precursors can react under the action of a catalytic hydrolysis solution to generate substances containing active hydroxyl groups, such as silanols (-Si-OH), silanols (Si-OH), and aluminum hydroxyl groups (Al-OH). The active hydroxyl groups in these substances can undergo condensation reactions with the hydroxyl groups on the surface of the hydroxylated metal soft magnetic powder to form covalent bonds, thereby transforming the physical adsorption between the insulating coating layer and the metal soft magnetic powder into a strong chemical bond, greatly improving the bonding strength between the insulating coating layer and the metal soft magnetic powder.

[0034] Furthermore, within the insulating coating layer, silane coupling agents, silica precursors, and alumina precursors participate in a hydrolysis-condensation reaction under the action of a catalytic hydrolysate. This results in a three-dimensional network structure with gradually changing chemical composition but continuous chemical bonds within the insulating coating layer. Since the insulating coating layer is gradually deposited from the inside out in the same chemical reaction process, there are no clear physical boundaries between the layers. Instead, they are a single, seamless whole connected by covalent bonds formed through the hydrolysis-condensation reaction. There are no traditional weak interfaces, resulting in high bonding strength within the insulating coating layer.

[0035] In summary, this technical solution achieves high interfacial bonding strength through the high bonding strength within the insulating coating layer, the bonding strength between the insulating coating layer and the soft magnetic metal powder, and the absorption and release of thermal and deformation stress by the insulating coating layer.

[0036] Furthermore, the fluidized state of hydroxylated metal soft magnetic powder refers to loading hydroxylated metal soft magnetic powder into a fluidized bed reactor and introducing inert gas such as nitrogen, so that the hydroxylated metal soft magnetic powder is in a "boiling" fluidized state under the action of the gas flow. This ensures that each hydroxylated metal soft magnetic powder has an equal opportunity to be exposed to the atomized sol formed after the gradient composite solution is atomized, avoiding the dead zones caused by the agglomeration and sedimentation of hydroxylated metal soft magnetic powder in traditional stirring coating, and ensuring macroscopic and microscopic uniformity.

[0037] Furthermore, this technical solution achieves instantaneous and uniform mixing of the inner layer solution, outer layer solution, and catalytic hydrolysate by instantaneously mixing the gradient composite sol and atomizing and spraying it. This avoids component fluctuations and unevenness caused by batch stirring and ensures that the sol components sprayed at each moment are as precise and controllable as possible on a time scale, thereby forming a consistent gradient structure on the surface of the hydroxylated metal soft magnetic powder.

[0038] In summary, this technical solution improves the uniformity of coating the surface of hydroxylated metal soft magnetic powder through the aforementioned multiple effects.

[0039] Furthermore, in this technical solution, the outer layer (i.e., the outer region) of the insulating coating layer with a high cross-linking density can act as a "rigid skeleton" to withstand the main stress during compression molding, effectively preventing direct contact and extrusion deformation of metal particles. The inner region, in contact with the hydroxylated metal soft magnetic powder, can undergo elastic or plastic deformation during subsequent compression molding when the powder particles undergo plastic deformation and displacement, giving the insulating coated magnetic powder good toughness to buffer local stress. Simultaneously, the nano-alumina uniformly dispersed in the insulating coating layer acts as a rigid reinforcing phase, enhancing the compressive strength and hardness of the insulating coating layer through its high modulus characteristics. Furthermore, its surface hydroxyl groups are chemically bonded into the three-dimensional network structure, forming a strong interfacial bond, effectively hindering the propagation of microcracks. This results in the insulating coating layer possessing high compressive strength, fracture resistance, and overall structural integrity, ensuring that the insulating coated magnetic powder is not easily damaged during high-pressure molding, thus guaranteeing high crush resistance.

[0040] Finally, as described above, this technical solution achieves uniform coating, high interfacial bonding strength, and high crush resistance. Furthermore, the insulating coating layer prepared using this solution has relatively high density. The synergistic effect of these multiple aspects ensures that the final insulating-coated magnetic powder possesses extremely high resistivity: First, uniform coating ensures no exposed hydroxylated metal soft magnetic powder, completely cutting off potential conductive paths. Second, the combined effect of extremely high interfacial bonding strength and high crush resistance effectively maintains the structural integrity and continuity of the insulating coating layer during high-pressure molding and subsequent processing, preventing defects caused by mechanical stress. Finally, the high density in the outer layer of the insulating coating layer allows it to provide extremely high intrinsic resistance even when the thickness is relatively thin. These multiple effects work together to achieve high insulation performance, endowing the insulating-coated magnetic powder with high resistivity.

[0041] Furthermore, the insulating coating layer with continuously varying porosity and modulus from the inside to the outside, constructed in this technical solution, effectively reduces total loss through the following multiple effects: First, the gradient coating layer avoids stress concentration caused by abrupt changes in modulus between the metal soft magnetic powder matrix and the external insulating coating layer. The nanoporous inorganic structure in the inner layer effectively absorbs and disperses internal stress from the external rigid layer and during processing, significantly reducing the net internal stress acting on the metal soft magnetic powder. This low-stress internal environment means that the energy barrier that needs to be overcome when magnetic domains rotate and domain walls move under the drive of an external magnetic field is significantly reduced, leading to a reduction in irreversible magnetization and thus a significant reduction in total loss on a macroscopic scale. Second, the high-strength interfacial bonding eliminates energy dissipation (such as frictional loss) caused by loosening or microscopic peeling of the coating layer, and provides a stable and undisturbed interface for the reversible and smooth movement of the domain walls, which also helps reduce total loss.

[0042] It should be noted that in this technical solution, the hydrolysis rate of aluminum oxide precursors (such as aluminum isopropoxide) is typically extremely fast, while the hydrolysis rate of silica precursors (such as tetraethyl orthosilicate) is relatively slow. Due to the significant difference in their hydrolysis rates, simply mixing the raw materials directly can easily lead to uneven composition. Therefore, this technical solution uses a chelating agent (such as acetylacetone) to inhibit the excessively rapid hydrolysis of the aluminum oxide precursor, ensuring that the hydrolysis rates of each component are matched as closely as possible, thereby facilitating the formation of a uniform gradient composite sol.

[0043] Meanwhile, since raw materials such as silane coupling agents are easily hydrolyzed in an aqueous environment, if the inner layer solution and the catalytic hydrolysate, as well as the outer layer solution and the catalytic hydrolysate, are mixed beforehand, the hydrolysis and condensation reactions between the inner layer solution and the catalytic hydrolysate, and between the outer layer solution and the catalytic hydrolysate, may have already progressed to a significant extent, resulting in the formation of large clusters or particles within the sol. Therefore, this technical solution involves transporting the inner layer solution, the outer layer solution, and the catalytic hydrolysate separately.

[0044] It should be noted that the reason for using a silicon-aluminum composite precursor instead of a silicon precursor or an aluminum precursor in this technical solution is as follows: (1) Coordinating thermal expansion mismatch and improving thermal stability: The thermal expansion coefficient of pure SiO2 differs greatly from that of soft magnetic metal powder, which will generate high stress at the interface during heat treatment and service, leading to cracking of the insulating coating. Introducing the Al2O3 phase with a thermal expansion coefficient between the two can construct a composite structure with a gradient transition in thermal expansion coefficient, effectively alleviating interfacial thermal stress and significantly improving the integrity of the insulating coating in thermal cycling.

[0045] (2) Achieving a balance between rigidity and toughness and optimizing mechanical properties: A single Al2O3 insulating coating layer is hard and brittle, and is prone to breakage during pressing; while a single SiO2 insulating coating layer is too soft and is prone to excessive deformation under high pressure. By constructing a silicon-aluminum composite system, the synergistic effect of rigidity and toughness is achieved: the Al2O3 component provides high hardness and strength, while the SiO2 component imparts toughness and stress buffering ability, so that the insulating coating layer has both high resistance to breakage and shape retention under pressing and complex stress.

[0046] It should be noted that this technical solution cannot achieve stepwise adjustment of the reaction system's pH value and control of water addition because macroscopic adjustment of the reactor's pH value and control of water volume represent an indirect, global control of the reaction environment. The so-called "gradient" formed by the aforementioned method heavily relies on the statistical differences in the deposition rates of each component under different pH and hydrolysis degrees. Essentially, it is a stack of discontinuous, multi-layered structures with abrupt changes in composition. These structural abrupt interfaces become stress concentration points and weak points in performance.

[0047] It should be noted that the soft magnetic powder in this technical solution can be pure ferromagnetic powder, iron-silicon based magnetic powder, or iron-nickel based magnetic powder, etc., and the specific type is not limited here. The chelating agent in this technical solution can be acetylacetone, and the specific type is not limited here. The dispersant can be polyvinylpyrrolidone, and the specific type is not limited here.

[0048] Preferably, the silica precursor includes any one of tetraethyl orthosilicate and methyl orthosilicate; the aluminum oxide precursor includes any one of aluminum isopropoxide, aluminum sec-butoxide, and aluminum ethoxide.

[0049] Preferably, in step E, the drying temperature is 60–80°C and the drying time is 4–10 hours.

[0050] This technical solution optimizes the drying parameters to ensure effective drying by removing moisture and anhydrous ethanol from the gradient wet gel coating layer.

[0051] To further explain, the mixing ratio of the aluminum oxide precursor and the silicon dioxide precursor, calculated according to the molar ratio, is 1:(5-10).

[0052] This technical solution optimizes the mixing ratio of aluminum oxide and silicon dioxide precursors to ensure sufficient and uniform incorporation of aluminum atoms into the Si-O-Si network structure. This effectively forms a Si-O-Al hybrid phase with a thermal expansion coefficient between that of pure SiO2 and metal magnetic powder, thereby alleviating interfacial thermal stress and preventing cracking of the insulating coating. Simultaneously, the aluminum content at this ratio serves to strengthen the inorganic framework as a network formant, improving the hardness and thermal stability of the insulating coating. It also avoids the network structure distortion and increased brittleness caused by excessively high aluminum content (>1:5) or the insignificant adjustment effect caused by excessively low aluminum content (<1:10), thus optimizing the toughness, rigidity, and thermal compatibility of the insulating coating.

[0053] To further clarify, in steps A and B, the silane coupling agent includes either γ-aminopropyltriethoxysilane or γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0054] The nonpolar organic groups contained in γ-aminopropyltriethoxysilane and γ-(2,3-epoxypropoxy)propyltrimethoxysilane can effectively improve the flexibility of the three-dimensional network structure, making the inner layer region more flexible in the green state before annealing. Therefore, by using either methyltrimethoxysilane or phenyltrimethoxysilane as the silane coupling agent, this technical solution helps to ensure the performance of the obtained insulating coated magnetic powder.

[0055] To further clarify, in steps A and B, the particle size of the nano-alumina is 20–50 nm.

[0056] This technical solution utilizes the limited particle size of nano-alumina, which not only effectively weakens the tendency of particle aggregation, promoting stable and uniform dispersion, but also possesses a high specific surface area. This allows it to effectively hinder the propagation of microcracks through mechanisms such as crack deflection, bridging, and pinning, thereby improving the performance of the insulating coating. Furthermore, its size matches the sol-gel network, effectively filling pores and promoting densification, which helps form a denser insulating coating during annealing.

[0057] To further explain, in step C, the catalytic hydrolysis solution comprises 1-2 parts of acid catalyst, 20-30 parts of deionized water, and 20-30 parts of anhydrous ethanol, calculated by mass fraction.

[0058] This technical solution optimizes the formulation of the catalytic hydrolysis solution to create a stable and moderately acidic environment. This environment effectively promotes the hydrolysis of the alumina and silica precursors while inhibiting their premature and excessively rapid condensation reactions. This avoids localized agglomeration or the formation of gel particles, ensuring the formation of a uniform, stable, and sprayable gradient composite sol, laying the foundation for obtaining a dense and defect-free insulating coating layer.

[0059] To further clarify, in step C, the acidic catalyst includes any one of acetic acid, hydrochloric acid, nitric acid, and sulfuric acid; The concentration of the acidic catalyst is 0.01–0.1 mol / L.

[0060] This technical solution limits the type and concentration of acidic catalysts, which allows for the selection of appropriate acidic catalysts and concentrations based on actual conditions, thus improving the flexibility of the solution.

[0061] It should be noted that the concentration of acidic catalyst in this technical solution, which is 0.01–0.1 mol / L, refers to the concentration of hydrogen chloride in the hydrochloric acid stock solution when the acidic catalyst is hydrochloric acid, not the concentration of hydrogen ions (H+) in the final mixed reaction system. + The calculated concentration of ) is 0.01–0.1 mol / L, and the same applies to other types of acidic catalysts.

[0062] To further explain, the method for hydroxylating the soft magnetic metal powder in step D is as follows: The soft magnetic metal powder was immersed in acetone, and then washed with deionized water until neutral. The washed and neutralized soft magnetic metal powder is then dried.

[0063] This technical solution optimizes the hydroxylation treatment method for soft magnetic metal powder, which helps to eliminate organic pollutants, impurities, or oxide layers adsorbed on the surface of the soft magnetic metal powder, exposes and creates more surface hydroxyl groups, thereby improving the interfacial bonding strength.

[0064] To further explain, in step E, the mass of the gradient composite sol, calculated according to the mass ratio, is 0.5% to 5% of the mass of the soft magnetic metal powder; The v2 is 0.2 to 2 L / min.

[0065] This technical solution limits the mass of the gradient composite sol to 0.5-5% of the mass of the soft magnetic metal powder, enabling the gradient composite sol to more completely encapsulate the soft magnetic metal powder, thereby improving the encapsulation quality and uniformity.

[0066] Furthermore, by limiting v2, this technical solution allows for the selection of an appropriate conveying speed based on actual production needs, thereby improving the flexibility of the solution.

[0067] An insulating coated magnetic powder is prepared using the above-described method for preparing insulating coated magnetic powder.

[0068] This solution also proposes an insulating coated magnetic powder prepared by an insulating coated magnetic powder preparation method, which is beneficial to improve resistivity and reduce total loss while improving coating uniformity, interfacial bonding strength and crush resistance.

[0069] An application of an insulating coated magnetic powder in the preparation of soft magnetic metal composite materials, wherein the above-mentioned insulating coated magnetic powder is used, and the application method is as follows: The insulating coated magnetic powder and the release agent are mixed evenly to obtain a mixed powder; The mixed powder is pressed into shape to obtain the mixed powder; The mixed powder was annealed under an inert atmosphere to obtain a soft magnetic metal composite material. The annealing curve for the annealing process is as follows: After heating from room temperature to 120°C at a rate of 1–3°C / min, hold at that temperature for 0.5–1 hour. The temperature was increased from 120℃ to 300℃ at a heating rate of 0.5~2℃ / min, and held at that temperature for 1.5~2.5h. The temperature was increased from 300℃ to 500℃ at a heating rate of 0.5~1℃ / min, and held at that temperature for 1.5~2.5h. The temperature was increased from 250℃ to 750℃ at a heating rate of 1-5℃ / min, and held for 1.5-2 hours.

[0070] This invention also proposes the application of insulating coated magnetic powder in the preparation of soft magnetic composite materials of metals, so that the soft magnetic composite materials prepared by using insulating coated magnetic powder have high resistivity and low total loss.

[0071] Furthermore, this technical solution optimizes the annealing curve by setting a slow heating rate and sufficient holding time, allowing organic materials such as silane coupling agents to decompose and escape gradually and orderly, thereby forming small, closed nanoscale pores rather than destructive macroscopic pores, which helps to ensure product performance.

[0072] It should be noted that the pressure and pressing time used in the pressing and molding process are those commonly used in the existing methods for preparing soft magnetic metal composite materials, and are not limited here. Furthermore, the pressure and pressing time are not the focus of this technical solution.

[0073] Preferably, the release agent comprises any one of zinc stearate, magnesium stearate, stearic acid, barium stearate, calcium stearate, molybdenum disulfide, and polyethylene glycol; the amount of the release agent added, calculated by mass percentage, is 0.1% to 0.5% of the amount of the insulating coated magnetic powder added.

[0074] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0075] Performance testing: Surface morphology: The uniformity and integrity of the coating thickness of the insulating coated magnetic powder were observed by scanning electron microscopy.

[0076] Interface strength: High-frequency ultrasonic scanning is used to generate internal images, allowing direct observation of interface defects such as delamination and debonding.

[0077] Compression resistance: The insulating coated magnetic powder and zinc stearate are mixed evenly to obtain a mixed powder; the mixed powder is pre-pressed at 850MPa for 35s and then pressed at 2100MPa for 35s to test whether the insulating coated magnetic powder will break during the pressing process.

[0078] Resistivity measurement: A four-probe resistor was used for measurement.

[0079] Total loss: The insulating coated magnetic powder obtained in the comparative example and the examples were mixed evenly with zinc stearate to obtain a mixed powder; wherein, the amount of zinc stearate added was 0.2% of the amount of insulating coated magnetic powder added by mass percentage; the mixed powder was pre-pressed at 850 MPa for 35 s and then pressed at 2100 MPa for 35 s to obtain a mixed powder; under a nitrogen atmosphere, the mixed powder was heated from room temperature to 120°C at a heating rate of 2°C / min and held for 1 h; then heated from 120°C to 300°C at a heating rate of 1°C / min and held for 1.5 h; then heated from 300°C to 500°C at a heating rate of 0.5°C / min and held for 2 h; finally, heated from 250°C to 750°C at a heating rate of 3°C / min and held for 1.5 h to obtain a soft magnetic metal composite material; the obtained soft magnetic metal composite material was processed according to the standard GB / T The test was conducted according to 3658-2022, "Method for Measurement of Magnetic Properties of Soft Magnetic Metallic Materials and Powder Metallurgical Materials in the Frequency Range of 20Hz to 100kHz". The test condition was 100kHz.

[0080] Magnetic permeability: The same method as for total loss was used to prepare the soft magnetic composite material of metal; the obtained soft magnetic composite material of metal was tested according to the standard "GB / T 28869.3-2023 Measurement method of magnetic core made of soft magnetic material Part 3: Magnetic properties under high excitation level"; the test conditions were 50KHz and 100mT.

[0081] Example 1 A. Under a nitrogen atmosphere, 10% silicon-aluminum composite precursor, 8% γ-aminopropyltriethoxysilane, 0.1% nano-alumina with a particle size of 50 nm, 0.5% acetylacetone and 81.4% anhydrous ethanol were mixed evenly to obtain an inner layer solution. B. Under a nitrogen atmosphere, 12% silicon-aluminum composite precursor, 2% γ-aminopropyltriethoxysilane, 10% nano-alumina with a particle size of 50 nm, 0.8% acetylacetone, 1% polyvinylpyrrolidone and 74.2% anhydrous ethanol were mixed evenly to obtain an outer layer solution. C. Mix 1 part hydrochloric acid, 20 parts deionized water, and 30 parts anhydrous ethanol by mass to obtain a catalytic hydrolysis solution; the concentration of hydrochloric acid is 0.05 mol / L. D. Prepare soft magnetic metal powder, immerse the soft magnetic metal powder in acetone, remove it and wash it with deionized water until neutral; dry the washed soft magnetic metal powder to obtain hydroxylated soft magnetic metal powder; the soft magnetic metal powder is iron-silicon based magnetic powder. E. The inner layer solution is delivered to the first infusion pump, the outer layer solution is delivered to the second infusion pump, and the catalytic hydrolysate is delivered to the third infusion pump; The liquids in the first, second and third infusion pumps are mixed and reacted to generate a gradient composite sol online. The gradient composite sol is then atomized and sprayed onto the surface of the fluidized hydroxylated metal soft magnetic powder, so that an insulating coating layer formed by the gradient composite sol is deposited on the surface of the hydroxylated metal soft magnetic powder. Hydroxylated metal soft magnetic powder with an insulating coating deposited on its surface was filtered, washed, and dried at 60°C for 8 hours to obtain insulating coated magnetic powder. In both steps A and B, the silicon-aluminum composite precursor includes tetraethyl orthosilicate and aluminum isopropoxide; the mixing ratio of aluminum isopropoxide and tetraethyl orthosilicate is 1:8 according to the molar ratio. In step E, the delivery rate of the inner layer solution decreases linearly from v1 to 0 L / min; the delivery rate of the outer layer solution increases linearly from 0 L / min to v1; the delivery rate of the catalytic hydrolysate is v2, v2 is 1 L / min, and v2 / v1 is 0.6. Based on the mass ratio, the mass of the gradient composite sol is 2% of the mass of the soft magnetic metal powder.

[0082] Example 2 A. Under a nitrogen atmosphere, 8% silicon-aluminum composite precursor, 12% γ-aminopropyltriethoxysilane, 0.2% nano-alumina with a particle size of 30 nm, 1% acetylacetone and 78.8% anhydrous ethanol were mixed evenly to obtain an inner layer solution. B. Under a nitrogen atmosphere, 10% silicon-aluminum composite precursor, 4% γ-aminopropyltriethoxysilane, 12% nano-alumina with a particle size of 30 nm, 0.5% acetylacetone, 1.5% polyvinylpyrrolidone and 72% anhydrous ethanol were mixed evenly to obtain an outer layer solution. C. Mix 2 parts acetic acid, 30 parts deionized water, and 30 parts anhydrous ethanol by mass to obtain a catalytic hydrolysis solution; the concentration of acetic acid is 0.02 mol / L. D. Prepare soft magnetic metal powder, immerse the soft magnetic metal powder in acetone, remove it and wash it with deionized water until neutral; dry the washed soft magnetic metal powder to obtain hydroxylated soft magnetic metal powder; the soft magnetic metal powder is iron-nickel based magnetic powder. E. The inner layer solution is delivered to the first infusion pump, the outer layer solution is delivered to the second infusion pump, and the catalytic hydrolysate is delivered to the third infusion pump; The liquids in the first, second and third infusion pumps are mixed and reacted to generate a gradient composite sol online. The gradient composite sol is then atomized and sprayed onto the surface of the fluidized hydroxylated metal soft magnetic powder, so that an insulating coating layer formed by the gradient composite sol is deposited on the surface of the hydroxylated metal soft magnetic powder. Hydroxylated metal soft magnetic powder with an insulating coating deposited on its surface was filtered, washed, and dried at 60°C for 10 hours to obtain insulating coated magnetic powder. In both steps A and B, the silicon-aluminum composite precursor includes tetraethyl orthosilicate and aluminum sec-butoxide; the mixing ratio of aluminum sec-butoxide and tetraethyl orthosilicate is 1:5 according to the molar ratio. In step E, the delivery rate of the inner layer solution decreases linearly from v1 to 0 L / min; the delivery rate of the outer layer solution increases linearly from 0 L / min to v1; the delivery rate of the catalytic hydrolysate is v2, v2 is 0.2 L / min, and v2 / v1 is 0.7. Based on the mass ratio, the mass of the gradient composite sol is 3% of the mass of the soft magnetic metal powder.

[0083] Example 3 A. Under a nitrogen atmosphere, 9% silicon-aluminum composite precursor, 15% γ-(2,3-epoxypropoxy)propyltrimethoxysilane, 0.1% nano-alumina with a particle size of 20 nm, 0.8% acetylacetone and 75.1% anhydrous ethanol were mixed evenly to obtain an inner layer solution. B. Under a nitrogen atmosphere, 15% silicon-aluminum composite precursor, 3% γ-(2,3-epoxypropoxy)propyltrimethoxysilane, 8% nano-alumina with a particle size of 20 nm, 1% acetylacetone, 2% polyvinylpyrrolidone and 71% anhydrous ethanol were mixed evenly to obtain an outer layer solution. C. Mix 2 parts nitric acid, 30 parts deionized water, and 20 parts anhydrous ethanol by mass to obtain a catalytic hydrolysis solution; the concentration of nitric acid is 0.03 mol / L. D. Prepare soft magnetic metal powder, immerse the soft magnetic metal powder in acetone, remove it and wash it with deionized water until neutral; dry the washed soft magnetic metal powder to obtain hydroxylated soft magnetic metal powder; the soft magnetic metal powder is iron-nickel based magnetic powder. E. The inner layer solution is delivered to the first infusion pump, the outer layer solution is delivered to the second infusion pump, and the catalytic hydrolysate is delivered to the third infusion pump; The liquids in the first, second and third infusion pumps are mixed and reacted to generate a gradient composite sol online. The gradient composite sol is then atomized and sprayed onto the surface of the fluidized hydroxylated metal soft magnetic powder, so that an insulating coating layer formed by the gradient composite sol is deposited on the surface of the hydroxylated metal soft magnetic powder. Hydroxylated metal soft magnetic powder with an insulating coating deposited on its surface was filtered, washed, and dried at 80°C for 6 hours to obtain insulating coated magnetic powder. In both steps A and B, the silicon-aluminum composite precursor includes methyl orthosilicate and aluminum ethoxide; the mixing ratio of aluminum ethoxide and methyl orthosilicate is 1:10 according to the molar ratio. In step E, the delivery rate of the inner layer solution decreases linearly from v1 to 0 L / min; the delivery rate of the outer layer solution increases linearly from 0 L / min to v1; the delivery rate of the catalytic hydrolysate is v2, v2 is 0.3 L / min, and v2 / v1 is 0.5. Based on the mass ratio, the mass of the gradient composite sol is 1% of the mass of the soft magnetic metal powder.

[0084] Comparative Example 1 The preparation method and raw materials of this comparative example are the same as those of Example 1. The difference is that the outer layer solution was not used in step E of this comparative example.

[0085] Comparative Example 2 The preparation method and raw materials of this comparative example are the same as those of Example 1. The difference is that the inner layer solution was not used in step E of this comparative example.

[0086] The insulating coated magnetic powders prepared in the examples and comparative examples were subjected to performance tests, and the results are shown in Table 1 below: Table 1. Test results of relevant performance of insulating coated magnetic powder

[0087] As can be seen from the test data in Table 1, the insulating coated magnetic powder obtained by this technical solution is beneficial to improve resistivity and reduce total loss while improving coating uniformity, interfacial bonding strength and crush resistance, so as to meet the actual application requirements.

[0088] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these embodiments will all fall within the scope of protection of the present invention.

Claims

1. A method for preparing an insulating coated magnetic powder, characterized in that, Includes the following steps: A. Under an inert atmosphere, 8-10% silicon-aluminum composite precursor, 8-15% silane coupling agent, 0.1-0.2% nano-alumina, 0.5-1% chelating agent and 75-82% anhydrous ethanol are mixed evenly to obtain an inner layer solution. B. Under an inert atmosphere, 10-15% silicon-aluminum composite precursor, 2-4% silane coupling agent, 8-12% nano-alumina, 0.5-1% chelating agent, 1-2% dispersant and 65-75% anhydrous ethanol are mixed evenly to obtain an outer layer solution. C. Mix the acid catalyst, deionized water and anhydrous ethanol evenly to obtain the catalytic hydrolysis solution; D. Hydroxylating the soft magnetic metal powder to obtain hydroxylated soft magnetic metal powder; E. The inner layer solution is delivered to the first infusion pump, the outer layer solution is delivered to the second infusion pump, and the catalytic hydrolysate is delivered to the third infusion pump; The liquids in the first, second and third infusion pumps are mixed and reacted to generate a gradient composite sol online. The gradient composite sol is then atomized and sprayed onto the surface of the fluidized hydroxylated metal soft magnetic powder, so that an insulating coating layer formed by the gradient composite sol is deposited on the surface of the hydroxylated metal soft magnetic powder. Hydroxylated metal soft magnetic powder with an insulating coating deposited on its surface is filtered, washed, and dried sequentially to obtain insulating coated magnetic powder. In steps A and B, the silicon-aluminum composite precursor includes both silicon dioxide precursor and aluminum oxide precursor. In step E, the delivery rate of the inner layer solution decreases linearly from v1 to 0 L / min; the delivery rate of the outer layer solution increases linearly from 0 L / min to v1; the delivery rate of the catalytic hydrolysate is v2, and v2 / v1 is 0.5 to 0.

7.

2. The method for preparing an insulating coated magnetic powder according to claim 1, characterized in that, The mixing ratio of the aluminum oxide precursor and the silicon dioxide precursor is 1: (5-10) according to the molar ratio.

3. The method for preparing an insulating coated magnetic powder according to claim 1, characterized in that, In steps A and B, the silane coupling agent includes either γ-aminopropyltriethoxysilane or γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

4. The method for preparing an insulating coated magnetic powder according to claim 1, characterized in that, In both steps A and B, the particle size of the nano-alumina is 20–50 nm.

5. The method for preparing an insulating coated magnetic powder according to claim 1, characterized in that, In step C, the catalytic hydrolysis solution comprises 1-2 parts of acid catalyst, 20-30 parts of deionized water, and 20-30 parts of anhydrous ethanol, calculated by mass fraction.

6. The method for preparing an insulating coated magnetic powder according to claim 1, characterized in that, In step C, the acidic catalyst includes any one of acetic acid, hydrochloric acid, nitric acid, and sulfuric acid; The concentration of the acidic catalyst is 0.01–0.1 mol / L.

7. The method for preparing an insulating coated magnetic powder according to claim 1, characterized in that, In step D, the method for hydroxylating the soft magnetic metal powder is as follows: The soft magnetic metal powder was immersed in acetone, and then washed with deionized water until neutral. The washed and neutralized soft magnetic metal powder is then dried.

8. The method for preparing an insulating coated magnetic powder according to claim 1, characterized in that, In step E, the mass of the gradient composite sol is calculated to be 0.5% to 5% of the mass of the soft magnetic metal powder, according to the mass ratio. The v2 is 0.2 to 2 L / min.

9. An insulating coated magnetic powder, characterized in that... It is prepared using the method for preparing insulating coated magnetic powder according to any one of claims 1 to 8.

10. The application of an insulating coated magnetic powder in the preparation of soft magnetic metal composite materials, characterized in that, The application method using the insulating coated magnetic powder as described in claim 9 is as follows: The insulating coated magnetic powder and the release agent are mixed evenly to obtain a mixed powder; The mixed powder is pressed into shape to obtain the mixed powder; The mixed powder was annealed under an inert atmosphere to obtain a soft magnetic metal composite material. The annealing curve for the annealing process is as follows: After heating from room temperature to 120°C at a rate of 1–3°C / min, hold at that temperature for 0.5–1 hour. The temperature was increased from 120℃ to 300℃ at a heating rate of 0.5~2℃ / min, and held at that temperature for 1.5~2.5h. The temperature was increased from 300℃ to 500℃ at a heating rate of 0.5~1℃ / min, and held at that temperature for 1.5~2.5h. The temperature was increased from 250℃ to 750℃ at a heating rate of 1-5℃ / min, and held for 1.5-2 hours.

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