Composite magnetic core with adjustable magnetic conductivity and preparation method thereof

Abstract

The invention discloses a composite magnetic core with adjustable magnetic conductivity and a preparation method of the composite magnetic core. The composite magnetic core comprises at least one layer of spherical powder magnetic core units and at least one layer of sheet-shaped powder magnetic core units, and the spherical powder magnetic core units and the sheet-shaped powder magnetic core units are alternately arranged in a stacked mode. The effective magnetic conductivity mu of the composite magnetic core ranges from 200 to 500. The spherical powder magnetic core and the sheet-shaped powder magnetic core units are matched to form the composite magnetic core, compared with a traditional spherical powder or sphere-like powder magnetic core, the composite magnetic core has higher magnetic core magnetic conductivity, the magnetic conductivity of the composite magnetic core is controllable between 200 and 500, and the high-frequency loss characteristic is improved to a certain degree; compared with a two-dimensional sheet-shaped magnetic powder core, the composite magnetic core has the advantages that the magnetic conductivity is adjustable, and the anti-saturation characteristic of the magnetic core is improved.

Description

Technical Field

[0001] The invention belongs to the field of magnetic materials, and in particular relates to a composite magnetic core with adjustable magnetic permeability and a preparation method thereof. Background Art

[0002] Compared with ferrite materials, metal powder cores have higher saturation magnetic induction intensity, which is conducive to the miniaturization of devices, and are thus widely used in transformers, inductors and other devices.

[0003] Metal magnetic powder cores are usually composed of spherical or block magnetic powder and insulating materials, which are subsequently sintered at high temperature to form metal magnetic powder cores. Commonly used metal soft magnetic powders mainly include three major systems: Fe-Si, Fe-Si-Al, and Fe-Ni. The morphology of magnetic powder is mostly spherical or quasi-spherical blocks. This morphology with similar three-dimensional dimensions is conducive to improving the fluidity, formability, and product consistency of the powder. However, spherical or quasi-spherical magnetic powders have a large demagnetization factor, and the air gap generated by the insulating coating layer causes the magnetic permeability of the metal magnetic powder core to be generally low (generally less than 200). By adding large-sized metal soft magnetic powder, the magnetic permeability of the core can be improved to a certain extent, but the effect is limited.

[0004] The two-dimensional flaky magnetic powder has a small demagnetization factor in the radial direction, which is beneficial to improve the magnetic permeability and frequency characteristics of the magnetic core, and to a certain extent breaks through the Snoek limit. For example, CN109786096 discloses a two-dimensional layered metal soft magnetic composite material and its preparation method and application. The magnetic permeability of the magnetic core is as high as 600. The reason why the magnetic core has high magnetic permeability is that the flaky magnetic powder has a low demagnetization factor in the diameter direction and the orderly arrangement of the magnetic powder. For another example, ZL109786096 discloses a two-dimensional layered metal soft magnetic composite material and its preparation method and application. The material is a laminated soft magnetic composite material composed of flaky soft magnetic powder and ceramic phase. The preparation method of the magnetic core includes: firstly coating the flaky soft magnetic powder, then pressing the coated magnetic powder into a magnet, and finally annealing to obtain the magnetic core. The composite material has the characteristics of high frequency (reaching 10-100MHz), high saturation magnetization (can reach more than 1 Tesla), high magnetic permeability (megahertz frequency reaches 600), and low loss.

[0005] However, the magnetic permeability of the two-dimensional layered structure magnetic core is too high and not easy to adjust, and its DC superposition characteristic is poor. An air gap needs to be opened during actual use. By reducing the ratio of the size in the diameter direction to the size in the thickness direction of the magnetic powder, the demagnetization factor is increased, and theoretically, the magnetic permeability of the magnetic core can be reduced and the DC superposition characteristic can be improved. However, this will lead to the orderly arrangement effect of the flaky magnetic powder, which will in turn affect the loss characteristics and product consistency of the magnetic core. In addition, increasing the amount of insulating coating material in the magnetic core can reduce the magnetic permeability, but it will cause the saturation magnetic induction intensity to decrease, the DC superposition characteristic will not be significantly improved, and the hysteresis loss will increase significantly.

[0006] Therefore, providing a magnetic core and its preparation method that have a high magnetic permeability and can be controllably adjusted is a technical problem that needs to be solved urgently at present. Summary of the Invention

[0007] In view of the problems that the magnetic permeability of traditional magnetic powder cores in the prior art is generally not high and difficult to improve, and the two-dimensional layered magnetic cores have problems such as too high magnetic permeability and not easy to lower, and poor DC superposition characteristics, the purpose of the present invention is to provide a composite magnetic core with adjustable magnetic permeability and its preparation method. The composite magnetic core of the present invention not only has a high magnetic permeability, but also can be controllably adjusted, which is more conducive to the actual popularization and application of the magnetic core.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] In the first aspect, the present invention provides a composite magnetic core with adjustable magnetic permeability, which includes at least one spherical powder magnetic core unit and at least one flaky powder magnetic core unit, and the spherical powder magnetic core unit and the flaky powder magnetic core unit are alternately stacked;

[0010] The effective magnetic permeability μ of the composite magnetic core is between 200 and 500.

[0011] The present invention uses a spherical powder magnetic core and a flaky powder magnetic core unit to form a composite magnetic core. Compared with the traditional spherical powder or quasi-spherical powder magnetic core, the composite magnetic core of the present invention has a higher magnetic permeability, and moreover, the magnetic permeability of the composite magnetic core of the present invention is controllable between 200 and 500, and the high-frequency loss characteristic is improved to a certain extent; compared with the two-dimensional flaky magnetic powder core, the composite magnetic core of the present invention can reduce the magnetic permeability to 200-500 to improve the anti-saturation characteristic of the magnetic core.

[0012] The structure of the composite magnetic core of the present invention is simple, and its size and performance can be adjusted according to application requirements, with stronger design freedom.

[0013] The following are the preferred technical solutions of the present invention, but they do not limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0014] Preferably, the magnetic permeability of the composite magnetic core is regulated by changing the sizes and structures of the spherical powder magnetic core units and the flaky powder magnetic core units in the composite magnetic core.

[0015] Preferably, the number of layers of the spherical powder magnetic core units is 2 - 10.

[0016] Preferably, the single-layer thickness of the spherical powder magnetic core units is 0.4 mm - 5 mm, preferably 0.4 mm - 2 mm.

[0017] Preferably, the number of layers of the flaky powder magnetic core units is 2 - 9.

[0018] Preferably, the single-layer thickness of the flaky powder magnetic core units is less than or equal to 3 mm, preferably 0.3 mm - 1 mm.

[0019] Preferably, the metal soft magnetic magnetic powder in the spherical powder magnetic core units includes at least one of Fe-Si, Fe-Si-Al, Fe-Ni, Fe-Si-Cr, Fe-Ni, and Fe-Ni-Mo systems.

[0020] Preferably, the morphology of the metal soft magnetic magnetic powder in the spherical powder magnetic core units includes at least one of spherical, ellipsoidal, or quasi-spherical.

[0021] Preferably, the metal soft magnetic magnetic powder in the spherical powder magnetic core units is spherical or ellipsoidal magnetic powder prepared by an air atomization process.

[0022] Preferably, the surface of the metal soft magnetic magnetic powder in the spherical powder magnetic core units has an insulating coating layer.

[0023] Preferably, the metal soft magnetic magnetic powder in the flaky powder magnetic core units includes at least one of Fe-Si, Fe-Si-Al, Fe-Ni, Fe-Si-Cr, Fe-Ni, and Fe-Ni-Mo systems, preferably at least one of Fe-Si-Al, Fe-Ni, and Fe-Ni-Mo.

[0024] Preferably, the metal soft magnetic magnetic powder in the flaky powder magnetic core units is flaky magnetic powder.

[0025] Preferably, the thickness of the flaky magnetic powder is 0.5 μm - 1.5 μm.

[0026] Preferably, the diameter-to-thickness ratio of the flaky magnetic powder is greater than or equal to 50.

[0027] In the present invention, the diameter-to-thickness ratio refers to the ratio of the average size of the flaky magnetic powder in the diameter direction to the size in the thickness direction.

[0028] In one embodiment, it is required that the surface of the flaky magnetic powder is flat and has no burrs.

[0029] Preferably, the surface of the metal soft magnetic powder in the sheet powder magnetic core unit has an insulating coating layer.

[0030] In a second aspect, the present invention provides a method for preparing a composite magnetic core with adjustable magnetic permeability as described in the first aspect, and the preparation method includes the following steps:

[0031] (1) Provide magnetic powder materials for spherical powder magnetic core units and magnetic powder materials for sheet powder magnetic core units;

[0032] (2) According to the designed structure of the composite magnetic core, add the magnetic powder material corresponding to the outermost magnetic core unit into the mold, perform pre-pressing treatment, and then add the magnetic powder material corresponding to the magnetic core unit adjacent to the outermost magnetic core unit, perform pre-pressing treatment, and optionally repeat the above steps, press and form, and perform heat treatment to obtain the composite magnetic core with the designed structure.

[0033] In the preparation method of the present invention, when the number of layers of both the spherical powder magnetic core unit and the sheet powder magnetic core unit is one layer, there is no need to perform repeated steps. When the number of layers of at least one of the spherical powder magnetic core unit and the sheet powder magnetic core unit is greater than one layer, repeated steps are required, and the specific number of repetitions is determined according to the actual designed structure of the composite magnetic core.

[0034] In one embodiment, the designed structure of the composite magnetic core is spherical powder magnetic core unit - sheet powder magnetic core unit - spherical powder magnetic core unit, and the corresponding preparation method includes:

[0035] (1) Provide magnetic powder materials for spherical powder magnetic core units and magnetic powder materials for sheet powder magnetic core units;

[0036] (2) According to the designed structure of the composite magnetic core, add the magnetic powder material of the spherical powder magnetic core unit into the mold, perform pre-pressing treatment, then add the magnetic powder material of the sheet powder magnetic core unit, perform pre-pressing treatment, and then add the magnetic powder material of the spherical powder magnetic core unit, perform pre-pressing treatment, and then press and form and perform heat treatment to obtain the composite magnetic core with the designed structure.

[0037] In one embodiment, the designed structure of the composite magnetic core is sheet powder magnetic core unit - spherical powder magnetic core unit - sheet powder magnetic core unit - spherical powder magnetic core unit, and the corresponding preparation method includes:

[0038] (1) Provide magnetic powder materials for spherical powder magnetic core units and magnetic powder materials for sheet powder magnetic core units;

[0039] (2) According to the design structure of the composite magnetic core, add the magnetic powder of the sheet-shaped powder magnetic core unit into the mold for pre-pressing treatment, then add the magnetic powder of the spherical powder magnetic core unit for pre-pressing treatment, then add the magnetic powder of the sheet-shaped powder magnetic core unit for pre-pressing treatment, and then add the magnetic powder of the spherical powder magnetic core unit for pre-pressing treatment. After pre-pressing treatment, press and form and perform heat treatment to obtain the composite magnetic core with the designed structure.

[0040] In the preparation method of the present invention, the magnetic powder of the spherical powder magnetic core unit is synthesized into the spherical powder magnetic core unit through high-temperature heat treatment, and the magnetic powder of the sheet-shaped powder magnetic core unit is synthesized into the sheet-shaped powder magnetic core unit through high-temperature heat treatment, and the contact between the units is good.

[0041] In the preparation method of the present invention, the spherical powder magnetic core unit is one layer or multiple layers. When the spherical powder magnetic core unit is multiple layers, the components and size specifications of the metal soft magnetic powder in each layer can be the same or different. The present invention does not make specific limitations, and those skilled in the art can select according to needs.

[0042] In the preparation method of the present invention, the sheet-shaped powder magnetic core unit is one layer or multiple layers. When the sheet-shaped powder magnetic core unit is multiple layers, the components and size specifications of the metal soft magnetic powder in each layer can be the same or different. The present invention does not make specific limitations, and those skilled in the art can select according to needs.

[0043] Preferably, the preparation method of the magnetic powder of the spherical powder magnetic core unit in step (1) includes the following steps:

[0044] (a) Perform acid etching and insulation coating on the spherical, ellipsoidal or quasi-spherical metal soft magnetic powder in sequence to obtain modified spherical magnetic powder;

[0045] (b) Mix the modified spherical magnetic powder with a release agent to obtain the magnetic powder of the spherical powder magnetic core unit.

[0046] The present invention does not limit the particle size of the metal soft magnetic powder in step (a), and those skilled in the art can select according to the performance requirements of the composite magnetic core.

[0047] Preferably, the acid used in the acid etching in step (a) includes at least one of nitric acid, hydrochloric acid, phosphoric acid, hydrofluoric acid, permanganic acid and chromic acid, but is not limited to the above-listed types. Other commonly used corrosive acids in the art are also applicable to the present invention, and preferably at least one of phosphoric acid, chromic acid and permanganic acid.

[0048] The present invention does not make specific limitations on the dosage of the acid used in the acid etching in step (a), and it can be determined according to the performance requirements of the spherical powder magnetic core unit.

[0049] Preferably, the coating agent used in the insulation coating in step (a) is selected from at least one of organic coating agents or inorganic coating agents.

[0050] Preferably, the organic coating agent includes at least one of a coupling agent and a resin. Exemplarily, the coupling agent includes, but is not limited to, a silane coupling agent, a titanate coupling agent, etc.; the resin includes, but is not limited to, an organosilicon resin, an epoxy resin, a phenolic resin, etc.

[0051] Preferably, the inorganic coating agent includes at least one of silica, kaolin, alumina, or titanium dioxide.

[0052] Preferably, the release agent in step (b) includes at least one of zinc stearate, aluminum stearate, and molybdenum disulfide. However, it is not limited to the above-listed types, and other release agents commonly used in the art are also applicable to the present invention.

[0053] The present invention does not specifically limit the amount of the release agent in step (b), and those skilled in the art can determine it according to the performance requirements of the magnetic core.

[0054] As a preferred technical solution of the preparation method of the composite magnetic core of the present invention, the preparation method of the magnetic powder of the sheet powder magnetic core unit in step (1) includes the following steps:

[0055] (A) Acid etching and insulating coating are sequentially performed on the sheet-shaped metal soft magnetic powder to obtain modified spherical magnetic powder;

[0056] (B) The modified spherical magnetic powder is mixed with a release agent to obtain the magnetic powder of the spherical powder magnetic core unit.

[0057] Preferably, the acid used for the acid etching in step (A) includes at least one of nitric acid, hydrochloric acid, phosphoric acid, hydrofluoric acid, permanganic acid, and chromic acid. However, it is not limited to the above-listed types, and other corrosive acids commonly used in the art are also applicable to the present invention. Preferably, it is at least one of phosphoric acid, chromic acid, and permanganic acid.

[0058] The present invention does not specifically limit the amount of the acid used for the acid etching in step (A), and it can be determined according to the performance requirements of the sheet powder magnetic core unit.

[0059] Preferably, the coating agent used for the insulating coating in step (A) is selected from at least one of an organic coating agent or an inorganic coating agent.

[0060] Preferably, the organic coating agent includes at least one of a coupling agent and a resin. Exemplarily, the coupling agent includes, but is not limited to, a silane coupling agent, a titanate coupling agent, etc.; the resin includes, but is not limited to, an organosilicon resin, an epoxy resin, a phenolic resin, etc.

[0061] Preferably, the inorganic coating agent includes at least one of silica, kaolin, alumina, or titanium dioxide.

[0062] Preferably, the mold release agent in step (B) includes at least one of zinc stearate, aluminum stearate, and molybdenum disulfide. However, it is not limited to the above-listed types, and other commonly used mold release agents in this field are also applicable to the present invention.

[0063] The present invention does not specifically limit the dosage of the mold release agent in step (B), and those skilled in the art can determine it according to the performance requirements of the magnetic core.

[0064] It should be noted that steps such as the above-mentioned acid etching and coating do not significantly damage the flaky morphology and structure of the magnetic powder.

[0065] In the present invention, the alloy systems in the magnetic powder materials of the spherical powder magnetic core unit and the flaky powder magnetic core unit (that is, the systems of the magnetic powders used respectively) are not limited, and preferably have similar optimal heat treatment temperatures.

[0066] As a preferred technical solution of the preparation method of the composite magnetic core of the present invention, the pressure of each pre-pressing is independently 800 MPa - 1300 MPa.

[0067] Preferably, the pressure of the compression molding is 1800 MPa - 2000 MPa.

[0068] Preferably, the gas in the atmosphere of the heat treatment includes at least one of a protective gas and a reducing gas.

[0069] Preferably, the protective gas includes at least one of nitrogen, argon, or helium.

[0070] Preferably, the reducing gas includes hydrogen.

[0071] Preferably, the temperature of the heat treatment is 600 °C - 800 °C.

[0072] Preferably, the heat preservation time of the heat treatment is 2 h - 5 h.

[0073] The numerical ranges described in the present invention not only include the above-listed point values, but also include any point values between the above numerical ranges not listed. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the ranges.

[0074] Compared with the prior art, the present invention has the following beneficial effects:

[0075] The present invention uses spherical powder magnetic cores and sheet powder magnetic core units to form a composite magnetic core. Compared with traditional spherical powder or quasi-spherical powder magnetic cores, the composite magnetic core of the present invention has a higher magnetic core permeability. Moreover, the magnetic permeability of the composite magnetic core of the present invention is controllable between 200 and 500, and the high-frequency loss characteristics are improved to a certain extent. Compared with two-dimensional sheet magnetic powder cores, the composite magnetic core of the present invention can adjust the magnetic permeability down to 200-500 to improve the anti-saturation characteristics of the magnetic core.

[0076] The structure of the composite magnetic core of the present invention is simple, and its size and performance can be adjusted according to application requirements, with stronger design freedom. Description of the Drawings

[0077] Figure 1 It is a schematic structural diagram of the composite magnetic core of an embodiment of the present invention. Detailed Embodiments

[0078] The technical solution of the present invention will be further described below with reference to the drawings and through specific embodiments.

[0079] The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0080] In one embodiment, the present invention provides a composite magnetic core with adjustable magnetic permeability. The composite magnetic core includes at least one layer of spherical powder magnetic core units and at least one layer of sheet powder magnetic core units, and the spherical powder magnetic core units and the sheet powder magnetic core units are alternately stacked.

[0081] The effective magnetic permeability μ of the composite magnetic core is between 200 and 500. The effective magnetic permeability can be, for example, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 315, 330, 325, 330, 350, 370, 380, 400, 410, 420, 430, 450, 470, 480 or 500, etc.

[0082] In one embodiment of the present invention, a composite magnetic core is formed by combining spherical powder magnetic cores and sheet powder magnetic core units. Compared with traditional spherical powder or quasi-spherical powder magnetic cores, the composite magnetic core of the present invention has a higher magnetic core permeability. Moreover, the magnetic permeability of the composite magnetic core of the present invention is controllable between 200 and 500, and the high-frequency loss characteristics are improved to a certain extent. Compared with two-dimensional sheet magnetic powder cores, the composite magnetic core of the present invention can adjust the magnetic permeability down to 200-500 to improve the anti-saturation characteristics of the magnetic core.

[0083] The composite magnetic core provided in one embodiment of the present invention has a simple structure, and its size and performance can be adjusted according to application requirements, with stronger design freedom.

[0084] In one embodiment, the magnetic permeability of the composite magnetic core is regulated by changing the sizes and structures of the spherical powder magnetic core units and the flake powder magnetic core units in the composite magnetic core.

[0085] In one embodiment, the number of layers of the spherical powder magnetic core units is 2 - 10, such as 2, 3, 4, 5, 6, 7, 8 or 10.

[0086] In one embodiment, the single-layer thickness of the spherical powder magnetic core units is 0.4 mm - 5 mm, such as 0.4 mm, 0.5 mm, 0.6 mm, 0.8 mm, 1 mm, 1.2 mm, 1.5 mm, 1.7 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm or 5 mm, etc.

[0087] In one embodiment, the number of layers of the flake powder magnetic core units is 2 - 9, such as 2, 3, 4, 5, 6, 8 or 9.

[0088] In one embodiment, the single-layer thickness of the flake powder magnetic core units is less than or equal to 3 mm, such as 3 mm, 2.8 mm, 2.7 mm, 2.6 mm, 2.5 mm, 2.4 mm, 2.2 mm, 2 mm, 1.8 mm, 1.7 mm, 1.6 mm, 1.5 mm, 1.4 mm, 1.2 mm, 1 mm, 0.5 mm, 0.4 mm or 0.3 mm, etc. If the single-layer thickness of the flake powder magnetic core units is too large, it is not conducive to the orderly arrangement of the flake magnetic powder. Further preferably, it is 0.3 mm - 1 mm.

[0089] In one embodiment, the metal soft magnetic magnetic powder in the spherical powder magnetic core units includes at least one of Fe - Si, Fe - Si - Al, Fe - Ni, Fe - Si - Cr, Fe - Ni and Fe - Ni - Mo systems.

[0090] In one embodiment, the morphology of the metal soft magnetic magnetic powder in the spherical powder magnetic core units includes at least one of spherical, ellipsoidal or quasi-spherical.

[0091] In one embodiment, the metal soft magnetic magnetic powder in the spherical powder magnetic core units is spherical or ellipsoidal magnetic powder prepared by an air atomization process.

[0092] In one embodiment, the surface of the metal soft magnetic magnetic powder in the spherical powder magnetic core units has an insulating coating layer.

[0093] In one embodiment, the metal soft magnetic magnetic powder in the flake powder magnetic core units includes at least one of Fe - Si, Fe - Si - Al, Fe - Ni, Fe - Si - Cr, Fe - Ni and Fe - Ni - Mo systems, preferably at least one of Fe - Si - Al, Fe - Ni and Fe - Ni - Mo.

[0094] In one embodiment, the metal soft magnetic powder in the sheet-shaped powder magnetic core unit is sheet-shaped magnetic powder.

[0095] In one embodiment, the thickness of the sheet-shaped magnetic powder is 0.5 μm - 1.5 μm, such as 0.5 μm, 0.7 μm, 0.8 μm, 1 μm, 1.2 μm, 1.3 μm, 1.4 μm, or 1.5 μm, etc. If the size (i.e., thickness) of the sheet-shaped magnetic powder in the thickness direction is too large, it will lead to a relatively high eddy current loss during the operation of the magnetic core; if the size of the sheet-shaped magnetic powder in the thickness direction is too small, the magnetic powder is likely to crack or deform during the subsequent pressing process, which is not conducive to obtaining a sheet-shaped powder magnetic core unit with good orientation and high magnetic permeability.

[0096] In one embodiment, the diameter-to-thickness ratio of the sheet-shaped magnetic powder is greater than or equal to 50, such as 50, 52, 53, 55, 56, 58, 60, 62, 64, 65, 66, 68, 70, 73, 75, 80, 85, 90, or 95, etc. If the diameter-to-thickness ratio is too small, the magnetic permeability of the magnetic core cannot be significantly improved. More importantly, a small diameter-to-thickness ratio will prevent the sheet-shaped magnetic powder from achieving good ordered orientation, thereby affecting the loss and magnetic permeability of the magnetic core.

[0097] In the present invention, the diameter-to-thickness ratio refers to the ratio of the average size of the sheet-shaped magnetic powder in the diameter direction to the size in the thickness direction.

[0098] In one embodiment, it is required that the surface of the sheet-shaped magnetic powder is flat and free of burrs.

[0099] In one embodiment, the surface of the metal soft magnetic powder in the sheet-shaped powder magnetic core unit has an insulating coating layer.

[0100] In yet another embodiment of the present invention, a method for preparing a composite magnetic core with adjustable magnetic permeability as described above is provided. The preparation method includes the following steps:

[0101] (1) Provide the magnetic powder materials for the spherical powder magnetic core unit and the sheet-shaped powder magnetic core unit;

[0102] (2) According to the designed structure of the composite magnetic core, add the magnetic powder material corresponding to the outermost magnetic core unit into the mold, perform pre-pressing treatment, and then add the magnetic powder material corresponding to the magnetic core unit adjacent to the outermost magnetic core unit, perform pre-pressing treatment, and optionally repeat the above steps, press and form, and perform heat treatment to obtain a composite magnetic core with the designed structure.

[0103] In the preparation method of the present invention, when the number of layers of both the spherical powder magnetic core unit and the flake powder magnetic core unit is one layer, there is no need to perform repeated steps. When the number of layers of at least one of the spherical powder magnetic core unit and the flake powder magnetic core unit is greater than one layer, repeated steps are required, and the specific number of repetitions is determined according to the actual design structure of the composite magnetic core.

[0104] In one embodiment, the design structure of the composite magnetic core is spherical powder magnetic core unit - flake powder magnetic core unit - spherical powder magnetic core unit, and the corresponding preparation method includes:

[0105] (1) Provide the magnetic powder of the spherical powder magnetic core unit and the magnetic powder of the flake powder magnetic core unit;

[0106] (2) According to the design structure of the composite magnetic core, add the magnetic powder of the spherical powder magnetic core unit into the mold, perform pre-pressing treatment, then add the magnetic powder of the flake powder magnetic core unit, perform pre-pressing treatment, and then add the magnetic powder of the spherical powder magnetic core unit. After performing pre-pressing treatment, press and form and perform heat treatment to obtain the composite magnetic core with the design structure.

[0107] In one embodiment, the design structure of the composite magnetic core is flake powder magnetic core unit - spherical powder magnetic core unit - flake powder magnetic core unit - spherical powder magnetic core unit, and the corresponding preparation method includes:

[0108] (1) Provide the magnetic powder of the spherical powder magnetic core unit and the magnetic powder of the flake powder magnetic core unit;

[0109] (2) According to the design structure of the composite magnetic core, add the magnetic powder of the flake powder magnetic core unit into the mold, perform pre-pressing treatment, then add the magnetic powder of the spherical powder magnetic core unit, perform pre-pressing treatment, then add the magnetic powder of the flake powder magnetic core unit, perform pre-pressing treatment, and then add the magnetic powder of the spherical powder magnetic core unit. After performing pre-pressing treatment, press and form and perform heat treatment to obtain the composite magnetic core with the design structure.

[0110] In the preparation method of the present invention, the magnetic powder of the spherical powder magnetic core unit is synthesized into the spherical powder magnetic core unit through high-temperature heat treatment, and the magnetic powder of the flake powder magnetic core unit is synthesized into the flake powder magnetic core unit through high-temperature heat treatment, and the contact between each unit is good.

[0111] In the preparation method of the present invention, the spherical powder magnetic core unit is one layer or multiple layers. When the spherical powder magnetic core unit is multiple layers, the components and size specifications of the metal soft magnetic powder in each layer can be the same or different, and the present invention does not make specific limitations. Those skilled in the art can select according to needs.

[0112] In the preparation method of the present invention, the flaky powder magnetic core unit is one layer or multiple layers. When the flaky powder magnetic core unit is multiple layers, the components and size specifications of the metal soft magnetic powder in each layer can be the same or different, which is not specifically limited in the present invention, and those skilled in the art can select according to needs.

[0113] In one embodiment, the preparation method of the magnetic powder material of the spherical powder magnetic core unit in step (1) includes the following steps:

[0114] (a) Etching and insulating coating are sequentially performed on spherical, ellipsoidal or quasi-spherical metal soft magnetic powder to obtain modified spherical magnetic powder;

[0115] (b) Mix the modified spherical magnetic powder with a mold release agent to obtain the magnetic powder material of the spherical powder magnetic core unit.

[0116] The present invention does not limit the particle size of the metal soft magnetic powder in step (a), and those skilled in the art can select according to the performance requirements of the composite magnetic core.

[0117] In one embodiment, the acid used for etching in step (a) includes at least one of nitric acid, hydrochloric acid, phosphoric acid, hydrofluoric acid, permanganic acid and chromic acid, but is not limited to the above-listed types. Other commonly used corrosive acids in the art are also applicable to the present invention, and preferably at least one of phosphoric acid, chromic acid and permanganic acid.

[0118] In step (a) of the present invention, the purpose of etching is to passivate the surface of the magnetic powder and form salts on the surface of the magnetic powder to improve the surface insulation of the magnetic powder and the binding property with the coating agent.

[0119] The present invention does not specifically limit the amount of the acid used for etching in step (a), which can be determined according to the performance requirements of the spherical powder magnetic core unit.

[0120] In one embodiment, the coating agent used for insulating coating in step (a) is selected from at least one of an organic coating agent and an inorganic coating agent.

[0121] In step (a) of the present invention, the purpose of insulating coating is to improve the surface insulation of the magnetic powder and the insulation between magnetic powders, increase the resistivity of the entire magnetic core unit, and at the same time, the surface of the coated magnetic powder has a certain adhesiveness and has a certain mechanical strength after subsequent molding treatment.

[0122] In one embodiment, the organic coating agent includes at least one of a coupling agent and a resin. Exemplarily, the coupling agent includes but is not limited to silane coupling agent, titanate coupling agent, etc.; the resin includes but is not limited to silicone resin, epoxy resin, phenolic resin, etc.

[0123] In one embodiment, the inorganic coating agent includes at least one of silica, kaolin, alumina or titanium dioxide.

[0124] In one embodiment, the release agent in step (b) includes at least one of zinc stearate, aluminum stearate and molybdenum disulfide. However, it is not limited to the above-listed types, and other commonly used release agents in the art are also applicable to the present invention.

[0125] In step (b) of the present invention, the purpose of adding the release agent is to improve the fluidity of the magnetic powder after insulation coating, and to improve the formability and demolding effect of the magnetic powder.

[0126] The present invention does not specifically limit the dosage of the release agent in step (b), and those skilled in the art can determine it according to the performance requirements of the magnetic core.

[0127] As a preferred technical solution of the preparation method of the composite magnetic core of the present invention, the preparation method of the magnetic powder material of the sheet powder magnetic core unit in step (1) includes the following steps:

[0128] (A) Acid etching and insulation coating are sequentially performed on the sheet-shaped metal soft magnetic powder to obtain modified spherical magnetic powder;

[0129] (B) Mix the modified spherical magnetic powder with a release agent to obtain the magnetic powder material of the spherical powder magnetic core unit.

[0130] Preferably, the acid used in the acid etching in step (A) includes at least one of nitric acid, hydrochloric acid, phosphoric acid, hydrofluoric acid, permanganic acid and chromic acid. However, it is not limited to the above-listed types, and other commonly used corrosive acids in the art are also applicable to the present invention, and preferably at least one of phosphoric acid, chromic acid and permanganic acid.

[0131] In step (A) of the present invention, the purpose of acid etching is to passivate the surface of the magnetic powder and form salts on the surface of the magnetic powder to improve the surface insulation of the magnetic powder and the binding property with the coating agent.

[0132] The present invention does not specifically limit the dosage of the acid used in the acid etching in step (A), and it can be determined according to the performance requirements of the sheet powder magnetic core unit.

[0133] In one embodiment, the coating agent used in the insulation coating in step (A) is selected from at least one of an organic coating agent or an inorganic coating agent.

[0134] In step (A) of the present invention, the purpose of insulation coating is to improve the insulation of the magnetic powder surface and between the magnetic powders, increase the resistivity of the entire magnetic core unit, and at the same time, the surface of the coated magnetic powder has a certain adhesiveness and has a certain mechanical strength after subsequent pressing treatment.

[0135] In one embodiment, the organic coating agent includes at least one of a coupling agent and a resin. Exemplarily, the coupling agent includes, but is not limited to, silane coupling agents, titanate coupling agents, etc.; the resin includes, but is not limited to, silicone resins, epoxy resins, phenolic resins, etc.

[0136] In one embodiment, the inorganic coating agent includes at least one of silica, kaolin, alumina, or titanium dioxide.

[0137] In one embodiment, the mold release agent in step (B) includes at least one of zinc stearate, aluminum stearate, and molybdenum disulfide. However, it is not limited to the above-listed types, and other commonly used mold release agents in the art are also applicable to the present invention.

[0138] In step (B) of the present invention, the purpose of adding the mold release agent is to improve the fluidity of the magnetic powder after insulation coating, and to improve the formability and demolding effect of the magnetic powder.

[0139] The present invention does not specifically limit the dosage of the mold release agent in step (B), and those skilled in the art can determine it according to the performance requirements of the magnetic core.

[0140] It should be noted that the above steps such as acid etching and coating do not significantly damage the flaky morphology and structure of the magnetic powder.

[0141] In the present invention, the alloy system in the magnetic powder material of the spherical powder magnetic core unit and the magnetic powder material of the flaky powder magnetic core unit (that is, the system of the magnetic powder used respectively) is not limited, and preferably has similar optimal heat treatment temperatures.

[0142] As a preferred technical solution of the method for preparing the composite magnetic core of the present invention, the pressure for each pre-pressing is independently 800 MPa - 1300 MPa, such as 800 MPa, 820 MPa, 830 MPa, 840 MPa, 850 MPa, 860 MPa, 880 MPa, 900 MPa, 925 MPa, 950 MPa, 970 MPa, 980 MPa, 990 MPa, 1000 MPa, 1010 MPa, 1020 MPa, 1050 MPa, 1080 MPa, 1100 MPa, 1115 MPa, 1130 MPa, 1140 MPa, 1150 MPa, 1160 MPa, 1180 MPa, 1200 MPa, 1220 MPa, 1250 MPa, 1275 MPa or 1300 MPa, etc.

[0143] In the preparation method of the present invention, pre-pressing treatment is carried out after each addition of magnetic powder. The purpose is to form a relatively firm plane during the subsequent one-layer pressing (pre-pressing treatment or pressing into shape), which is beneficial to the orderly arrangement of flaky magnetic powder. If the pre-pressing pressure is too small, the lower plane will be unstable, affecting the orderly arrangement of magnetic powder in the flaky magnetic core; if the pre-pressing pressure is too large, a small part of the magnetic powder will undergo multiple deformations, easily damaging the morphology of the flaky magnetic powder, introducing more stress at the same time, and the high pressure will cause greater damage to the mold.

[0144] In one embodiment, the pressure for pressing into shape is 1800 MPa - 2000 MPa, such as 1800 MPa, 1820 MPa, 1830 MPa, 1850 MPa, 1875 MPa, 1900 MPa, 1915 MPa, 1925 MPa, 1950 MPa, 1960 MPa, 1980 MPa or 2000 MPa, etc.

[0145] In one embodiment, the gas in the atmosphere for heat treatment includes at least one of a protective gas and a reducing gas.

[0146] In one embodiment, the protective gas includes at least one of nitrogen, argon or helium.

[0147] In one embodiment, the reducing gas includes hydrogen.

[0148] In one embodiment, the temperature of the heat treatment is 600 °C - 800 °C, such as 600 °C, 625 °C, 650 °C, 660 °C, 670 °C, 680 °C, 700 °C, 725 °C, 750 °C, 770 °C or 800 °C, etc.

[0149] In one embodiment, the heat preservation time of the heat treatment is 2 h - 5 h, such as 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h or 5 h, etc.

[0150] Based on the above embodiments, the following typical but non-limiting examples are provided:

[0151] Example 1

[0152] This example provides a composite magnetic core, which is composed of two layers of spherical powder magnetic core units and one layer of flaky powder magnetic core unit. The structure from the bottom layer to the top layer is as follows: the first spherical powder magnetic core unit - the flaky powder magnetic core unit - the second spherical powder magnetic core unit. The metal soft magnetic powder in the first spherical powder magnetic core unit and the second spherical powder magnetic core unit is spherical FeSiAl, and the metal soft magnetic powder in the flaky powder magnetic core unit is flaky FeSiAl. The thickness of the flaky FeSiAl is 1.1 μm, and the diameter-thickness ratio is 73.

[0153] The thicknesses of the first spherical powder magnetic core unit, the sheet powder magnetic core unit, and the second spherical powder magnetic core unit are all 1.2 mm.

[0154] The preparation method of the composite magnetic core provided by this embodiment includes the following steps:

[0155] (1) Prepare the magnetic powder materials for the spherical powder magnetic core unit and the sheet powder magnetic core unit. Specifically:

[0156] The preparation method of the magnetic powder material for the spherical powder magnetic core unit includes the following steps:

[0157] (a) Use nitric acid to etch spherical FeSiAl to passivate the surface of the magnetic powder. Then, use silicon dioxide to conduct insulating coating on the etched spherical magnetic powder to obtain modified spherical magnetic powder;

[0158] (b) Mix the modified spherical magnetic powder with zinc stearate to obtain the magnetic powder material for the spherical powder magnetic core unit.

[0159] The preparation method of the magnetic powder material for the sheet powder magnetic core unit includes the following steps:

[0160] (A) Use hydrochloric acid to etch sheet FeSiAl to passivate the surface of the magnetic powder. Then, use alumina to conduct insulating coating on the etched spherical magnetic powder to obtain modified sheet magnetic powder;

[0161] (B) Mix the modified sheet magnetic powder with aluminum stearate to obtain the magnetic powder material for the sheet powder magnetic core unit.

[0162] (2) According to the designed structure of the composite magnetic core, add the magnetic powder material for the spherical powder magnetic core unit into the mold, perform pre-pressing treatment (pressure is 1000 MPa), then add the magnetic powder material for the sheet powder magnetic core unit, perform pre-pressing treatment (pressure is 900 MPa), then add the magnetic powder material for the spherical powder magnetic core unit again, perform pre-pressing treatment (pressure is 1000 MPa), and then press and form (pressure is 1900 MPa) and perform heat treatment (atmosphere is nitrogen atmosphere, temperature is 700 °C, time is 3 h) to obtain the composite magnetic core with the designed structure.

[0163] Manufacture an annular magnetic core with an inner diameter of 12.7 mm and an outer diameter of 7.6 mm according to the above process, wind wire on it, and test the core losses Pcv(50 kHz, 100 mT), Pcv(500 kHz, 50 mT). Use the inductance method to test the effective magnetic permeability μ of the magnetic core, and the results are shown in Table 1.

[0164] Example 2

[0165] This embodiment provides a composite magnetic core, which consists of two layers of spherical powder magnetic core units and two layers of flake powder magnetic core units. The structure from the bottommost layer to the topmost layer is as follows: the first spherical powder magnetic core unit - the first flake powder magnetic core unit - the second spherical powder magnetic core unit - the second flake powder magnetic core unit.

[0166] The metal soft magnetic powder in the first spherical powder magnetic core unit and the second spherical powder magnetic core unit is spherical FeSiAl, and the metal soft magnetic powder in the first flake powder magnetic core unit and the second flake powder magnetic core unit is flake FeSiAl. The thickness of the flake FeSiAl is 1.1 μm, and the diameter-to-thickness ratio is 73.

[0167] The thickness of both the first spherical powder magnetic core unit and the second spherical powder magnetic core unit is 1.2 mm, and the thickness of both the first flake powder magnetic core unit and the second flake powder magnetic core unit is 0.6 mm.

[0168] The preparation method of the composite magnetic core provided by this embodiment includes the following steps:

[0169] (1) Prepare the magnetic powder materials for the spherical powder magnetic core unit and the flake powder magnetic core unit. Specifically:

[0170] The preparation method of the magnetic powder material for the spherical powder magnetic core unit includes the following steps:

[0171] (a) Use hydrofluoric acid to etch the spherical FeSiAl to passivate the surface of the magnetic powder. Then, use titanium dioxide to perform insulation coating on the etched spherical magnetic powder to obtain modified spherical magnetic powder.

[0172] (b) Mix the modified spherical magnetic powder with molybdenum disulfide to obtain the magnetic powder material for the spherical powder magnetic core unit.

[0173] The preparation method of the magnetic powder material for the flake powder magnetic core unit includes the following steps:

[0174] (A) Use permanganic acid to etch the flake FeSiAl to passivate the surface of the magnetic powder. Then, use alumina to perform insulation coating on the etched spherical magnetic powder to obtain modified flake magnetic powder.

[0175] (B) Mix the modified flake magnetic powder with aluminum stearate to obtain the magnetic powder material for the flake powder magnetic core unit.

[0176] (2) According to the design structure of the composite magnetic core, add the magnetic powder of the spherical powder magnetic core unit into the mold, perform pre-pressing treatment (pressure: 1200 MPa), then add the magnetic powder of the flake powder magnetic core unit, perform pre-pressing treatment (pressure: 800 MPa), and then add the magnetic powder of the spherical powder magnetic core unit again, perform pre-pressing treatment (pressure: 900 MPa), and then press and form (pressure: 2000 MPa) and perform heat treatment (atmosphere: nitrogen atmosphere, temperature: 800 °C, time: 2 h) to obtain the composite magnetic core with the designed structure.

[0177] Prepare the toroidal magnetic core by the same method as in Example 1, and perform tests by the same test method as in Example 1. The results are shown in Table 1.

[0178] Example 3

[0179] This example provides a composite magnetic core, which is composed of two layers of spherical powder magnetic core units and one layer of flake powder magnetic core unit. The structure from the bottom layer to the top layer is as follows: the first spherical powder magnetic core unit - the flake powder magnetic core unit - the second spherical powder magnetic core unit. The metal soft magnetic powder in the first spherical powder magnetic core unit and the second spherical powder magnetic core unit is spherical FeSiAl, the metal soft magnetic powder in the flake powder magnetic core unit is flake FeSiAl, the thickness of the flake FeSiAl is 1.1 μm, and the diameter-thickness ratio is 73.

[0180] The thickness of both the first spherical powder magnetic core unit and the second spherical powder magnetic core unit is 1.4 mm, and the thickness of the flake powder magnetic core unit is 0.8 mm.

[0181] The preparation method of the composite magnetic core provided in this example includes the following steps:

[0182] (1) Prepare the magnetic powder of the spherical powder magnetic core unit and the magnetic powder of the flake powder magnetic core unit. Specifically:

[0183] The preparation method of the magnetic powder of the spherical powder magnetic core unit includes the following steps:

[0184] (a) Use hydrochloric acid to etch the spherical FeSiAl to passivate the surface of the magnetic powder. Then, use kaolin to perform insulation coating on the etched spherical magnetic powder to obtain modified spherical magnetic powder.

[0185] (b) Mix the modified spherical magnetic powder with molybdenum disulfide to obtain the magnetic powder of the spherical powder magnetic core unit.

[0186] The preparation method of the magnetic powder of the flake powder magnetic core unit includes the following steps:

[0187] (A) Use hydrochloric acid to etch the flake FeSiAl to passivate the surface of the magnetic powder. Then, use alumina to perform insulation coating on the etched spherical magnetic powder to obtain modified flake magnetic powder.

[0188] (B) Mix the modified flaky magnetic powder with zinc stearate to obtain the magnetic powder material for the flaky powder magnetic core unit.

[0189] (2) According to the designed structure of the composite magnetic core, add the magnetic powder material for the spherical powder magnetic core unit into the mold, perform pre-pressing treatment (pressure: 1100 MPa), then add the magnetic powder material for the flaky powder magnetic core unit, perform pre-pressing treatment (pressure: 1000 MPa), then add the magnetic powder material for the spherical powder magnetic core unit again, perform pre-pressing treatment (pressure: 1100 MPa), and then press and form (pressure: 1800 MPa) and perform heat treatment (atmosphere: a mixed atmosphere of argon and hydrogen, the volume ratio of hydrogen in the mixed atmosphere is 5%, temperature: 600 °C, time: 5 h) to obtain the composite magnetic core with the designed structure.

[0190] Prepare a toroidal magnetic core according to the same method as in Example 1, and perform tests according to the same test method as in Example 1. The results are shown in Table 1.

[0191] Comparative Example 1

[0192] As a comparative example of Example 1, the difference from Example 1 is that a magnetic body with a thickness of 3.6 mm is made of the magnetic powder material for the spherical powder magnetic core unit, and this magnetic core does not contain flaky magnetic powder.

[0193] Prepare a toroidal magnetic core according to the same method as in Example 1, and perform tests according to the same test method as in Example 1. The results are shown in Table 1.

[0194] Table 1

[0195]

[0196] As can be seen from the above table, by compounding the spherical powder magnetic core unit and the flaky powder magnetic core, the magnetic permeability of the magnetic core is greatly improved. At the same time, the magnetic permeability of the magnetic core can be regulated by changing the sizes and structures of the spherical powder magnetic core unit and the flaky powder magnetic core unit. At the same time, compared with the pure spherical powder magnetic core (Comparative Example 1), the loss of the composite magnetic core at high frequencies is slightly lower.

[0197] Example 4

[0198] This example provides a composite magnetic core. For the structural schematic diagram, see Figure 1 , which consists of three layers of spherical powder magnetic core units and two layers of flaky powder magnetic core units. The structure from the bottom layer to the top layer is as follows: the first spherical powder magnetic core unit - the first flaky powder magnetic core unit - the second spherical powder magnetic core unit - the second flaky powder magnetic core unit - the third spherical powder magnetic core unit.

[0199] The metallic soft magnetic powder in the first spherical powder magnetic core unit and the third spherical powder magnetic core unit is spherical FeNi, and the metallic soft magnetic powder in the second spherical powder magnetic core unit is spherical FeSiAl. The metallic soft magnetic powder in the first flake powder magnetic core unit and the second flake powder magnetic core unit is flake FeSiAl. The thickness of the flake FeSiAl is 1.1 μm, and the diameter-to-thickness ratio is 73.

[0200] The thickness of both the first spherical powder magnetic core unit and the third spherical powder magnetic core unit is 1.2 mm, the thickness of the second spherical powder magnetic core unit is 0.4 mm, and the thickness of both the first flake powder magnetic core unit and the second flake powder magnetic core unit is 0.6 mm.

[0201] The preparation method of the composite magnetic core provided in this embodiment includes the following steps:

[0202] (1) Prepare the magnetic powder materials for the spherical powder magnetic core unit and the flake powder magnetic core unit. Specifically:

[0203] The preparation method of the magnetic powder material for the spherical powder magnetic core unit includes the following steps:

[0204] (a) Use hydrofluoric acid to etch the spherical magnetic powder (FeNi or FeSiAl) to passivate the surface of the magnetic powder. Then, use alumina to conduct insulation coating on the etched spherical magnetic powder to obtain modified spherical magnetic powder.

[0205] (b) Mix the modified spherical magnetic powder with aluminum stearate to obtain the magnetic powder material for the spherical powder magnetic core unit.

[0206] The preparation method of the magnetic powder material for the flake powder magnetic core unit includes the following steps:

[0207] (A) Use chromic acid to etch the flake FeSiAl to passivate the surface of the magnetic powder. Then, use alumina to conduct insulation coating on the etched spherical magnetic powder to obtain modified flake magnetic powder.

[0208] (B) Mix the modified flake magnetic powder with aluminum stearate to obtain the magnetic powder material for the flake powder magnetic core unit.

[0209] (2) According to the designed structure of the composite magnetic core, add the magnetic powder material for the spherical powder magnetic core unit into the mold, conduct pre-pressing treatment (pressure is 1050 MPa), then add the magnetic powder material for the flake powder magnetic core unit, conduct pre-pressing treatment (pressure is 950 MPa), and then add the magnetic powder material for the spherical powder magnetic core unit again. After conducting pre-pressing treatment (pressure is 900 MPa), press and mold (pressure is 1850 MPa) and conduct heat treatment (atmosphere is helium atmosphere, temperature is 850 °C, time is 3 h) to obtain the composite magnetic core with the designed structure.

[0210] The toroidal core was prepared in the same manner as in Example 1 and tested using the same test method as in Example 1. The results are shown in Table 2.

[0211] Comparative Example 2

[0212] As a comparative example of Example 4, the difference from Example 4 is that the thickness of the flaky FeSiAl is 0.4 μm and the aspect ratio is 69.

[0213] The toroidal core was prepared in the same manner as in Example 1 and tested using the same test method as in Example 1. The results are shown in Table 2.

[0214] Comparative Example 3

[0215] As a comparative example of Example 4, the difference from Example 4 is that the thickness of the flaky FeSiAl is 1.9 μm and the aspect ratio is 78.

[0216] The toroidal core was prepared in the same manner as in Example 1 and tested using the same test method as in Example 1. The results are shown in Table 2.

[0217] Comparative Example 4

[0218] As a comparative example of Example 4, the difference from Example 4 is that the thickness of the flaky FeSiAl is 1.1 μm and the aspect ratio is 43.

[0219] The toroidal core was prepared in the same manner as in Example 1 and tested using the same test method as in Example 1. The results are shown in Table 2.

[0220] Table 2

[0221]

[0222] As can be seen from the above table, the thickness and aspect ratio of the flaky magnetic powder in the flaky powder core unit need to be controlled within a certain range. Beyond this range, it will affect the orderly arrangement of the magnetic powder, and thus affect the loss characteristics of the core, especially the loss at high frequencies.

[0223] Example 5

[0224] This example provides a composite core, which consists of two layers of spherical powder core units and one layer of flaky powder core unit. The structure from the bottom layer to the top layer is: the first spherical powder core unit - the flaky powder core unit - the second spherical powder core unit.

[0225] The metal soft magnetic powder in the first spherical powder core unit and the second spherical powder core unit is spherical FeSiAl, and the metal soft magnetic powder in the flaky powder core unit is flaky FeNiMo. The thickness of the flaky FeNiMo is 0.9 μm and the aspect ratio is 98.

[0226] The thickness of each first spherical powder magnetic core unit is 0.8 mm, the thickness of the second spherical powder magnetic core unit is 1.2 mm, and the thickness of the sheet powder magnetic core unit is 0.4 mm.

[0227] The preparation method of the composite magnetic core provided by this embodiment includes the following steps:

[0228] (1) Prepare the magnetic powder materials for the spherical powder magnetic core unit and the sheet powder magnetic core unit. Specifically:

[0229] The preparation method of the magnetic powder material for the spherical powder magnetic core unit includes the following steps:

[0230] (a) Use nitric acid to etch spherical FeSiAl to passivate the surface of the magnetic powder. Then, use titanium dioxide to perform insulation coating on the etched spherical magnetic powder to obtain modified spherical magnetic powder;

[0231] (b) Mix the modified spherical magnetic powder with zinc stearate to obtain the magnetic powder material for the spherical powder magnetic core unit.

[0232] The preparation method of the magnetic powder material for the sheet powder magnetic core unit includes the following steps:

[0233] (A) Use phosphoric acid to etch sheet FeNiMo to passivate the surface of the magnetic powder. Then, use alumina to perform insulation coating on the etched spherical magnetic powder to obtain modified sheet magnetic powder;

[0234] (B) Mix the modified sheet magnetic powder with aluminum stearate to obtain the magnetic powder material for the sheet powder magnetic core unit.

[0235] (2) According to the designed structure of the composite magnetic core, add the magnetic powder material for the spherical powder magnetic core unit into the mold and perform pre-pressing treatment (pressure: 800 MPa). Then, add the magnetic powder material for the sheet powder magnetic core unit and perform pre-pressing treatment (pressure: 1000 MPa). Then, add the magnetic powder material for the spherical powder magnetic core unit again and perform pre-pressing treatment (pressure: 1200 MPa). After that, press and form (pressure: 1950 MPa) and perform heat treatment (atmosphere: nitrogen atmosphere, temperature: 750 °C, time: 3 h) to obtain the composite magnetic core with the designed structure.

[0236] Prepare a toroidal magnetic core according to the same method as in Example 1 and perform tests according to the same test method as in Example 1. The results are shown in Table 3.

[0237] Comparative Example 5

[0238] As a comparative example of Example 5, the difference from Example 5 is that no pre-pressing treatment is performed after adding magnetic powder each time.

[0239] The toroidal core was prepared in the same manner as in Example 1 and tested in the same testing method as in Example 1. The results are shown in Table 3.

[0240] Comparative Example 6

[0241] As a comparative example of Example 5, the difference from Example 5 is that the pressure without pre-pressing treatment after each addition of magnetic powder is 700 MPa.

[0242] The toroidal core was prepared in the same manner as in Example 1 and tested in the same testing method as in Example 1. The results are shown in Table 3.

[0243] Comparative Example 7

[0244] As a comparative example of Example 5, the difference from Example 5 is that the pressure without pre-pressing treatment after each addition of magnetic powder is 1500 MPa.

[0245] The toroidal core was prepared in the same manner as in Example 1 and tested in the same testing method as in Example 1. The results are shown in Table 3.

[0246] Table 3

[0247]

[0248]

[0249] As can be seen from the above table, the magnetic permeability of the core without pre-pressing treatment is low and the loss is very high, mainly because the flaky magnetic powder does not form an ordered arrangement, thus causing high eddy current loss. At the same time, in order to obtain excellent magnetic permeability and loss characteristics, the pre-pressure should be controlled within a certain range.

[0250] The applicant declares that the present invention uses the above embodiments to illustrate the detailed method of the present invention, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent replacement of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A composite magnetic core with adjustable permeability, characterized in that, the composite magnetic core includes at least one layer of spherical powder magnetic core units and at least one layer of flake powder magnetic core units, and the spherical powder magnetic core units and the flake powder magnetic core units are alternately stacked; the effective permeability μ of the composite magnetic core is between 200 and 500.

2. The composite magnetic core with adjustable permeability according to claim 1, characterized in that, by changing the sizes and structures of the spherical powder magnetic core units and the flake powder magnetic core units in the composite magnetic core, the permeability of the composite magnetic core is adjusted.

3. The composite magnetic core with adjustable permeability according to claim 1 or 2, characterized in that, the number of layers of the spherical powder magnetic core units is 2 - 10; preferably, the single-layer thickness of the spherical powder magnetic core units is 0.4 mm - 5 mm, preferably 0.4 mm - 2 mm; preferably, the number of layers of the flake powder magnetic core units is 2 - 9; preferably, the single-layer thickness of the flake powder magnetic core units is less than or equal to 3 mm, preferably 0.3 mm - 1 mm.

4. The composite magnetic core with adjustable permeability according to any one of claims 1 - 3, characterized in that, the metal soft magnetic powder in the spherical powder magnetic core units includes at least one of Fe - Si, Fe - Si - Al, Fe - Ni, Fe - Si - Cr, Fe - Ni, and Fe - Ni - Mo systems; preferably, the morphology of the metal soft magnetic powder in the spherical powder magnetic core units includes at least one of spherical, ellipsoidal, or quasi-spherical; preferably, the metal soft magnetic powder in the spherical powder magnetic core units is spherical or ellipsoidal magnetic powder prepared by an air atomization process; preferably, the surface of the metal soft magnetic powder in the spherical powder magnetic core units has an insulating coating layer.

5. The composite magnetic core with adjustable permeability according to any one of claims 1 - 4, characterized in that, the metal soft magnetic powder in the flake powder magnetic core units includes at least one of Fe - Si, Fe - Si - Al, Fe - Ni, Fe - Si - Cr, Fe - Ni, and Fe - Ni - Mo systems, preferably at least one of Fe - Si - Al, Fe - Ni, and Fe - Ni - Mo; preferably, the metal soft magnetic powder in the flake powder magnetic core units is flake magnetic powder; preferably, the thickness of the flake magnetic powder is 0.5 μm - 1.5 μm; preferably, the aspect ratio of the flake magnetic powder is greater than or equal to 50; preferably, the surface of the metal soft magnetic powder in the flake powder magnetic core units has an insulating coating layer.

6. A preparation method of the composite magnetic core with adjustable permeability according to any one of claims 1 - 5, characterized in that, the preparation method includes the following steps: (1) Provide the magnetic powder materials for the spherical powder magnetic core units and the magnetic powder materials for the flake powder magnetic core units; (2) According to the designed structure of the composite magnetic core, add the magnetic powder material corresponding to the outermost magnetic core unit into the mold, perform pre-pressing treatment, then add the magnetic powder material corresponding to the magnetic core unit adjacent to the outermost magnetic core unit, perform pre-pressing treatment, and optionally repeat the above steps, press and form and perform heat treatment to obtain the composite magnetic core with the designed structure.

7. The preparation method of the composite magnetic core with adjustable permeability according to claim 6, characterized in that, the preparation method of the magnetic powder material of the spherical powder magnetic core unit in step (1) comprises the following steps: (a) Acid etching and insulation coating are sequentially carried out on spherical, ellipsoidal or quasi-spherical metal soft magnetic powders to obtain modified spherical magnetic powders; (b) The modified spherical magnetic powders are mixed with a release agent to obtain the magnetic powder material of the spherical powder magnetic core unit; Preferably, the acid used in the acid etching in step (a) includes at least one of nitric acid, hydrochloric acid, phosphoric acid, hydrofluoric acid, permanganic acid and chromic acid, preferably at least one of phosphoric acid, chromic acid and permanganic acid; Preferably, the coating agent used in the insulation coating in step (a) is selected from at least one of organic coating agents or inorganic coating agents; Preferably, the organic coating agent includes at least one of coupling agents and resins; Preferably, the inorganic coating agent includes at least one of silica, kaolin, alumina or titanium dioxide; Preferably, the release agent in step (b) includes at least one of zinc stearate, aluminum stearate and molybdenum disulfide.

8. The preparation method of the composite magnetic core with adjustable permeability according to claim 6 or 7, characterized in that, the preparation method of the magnetic powder material of the sheet powder magnetic core unit in step (1) comprises the following steps: (A) Acid etching and insulation coating are sequentially carried out on sheet-shaped metal soft magnetic powders to obtain modified spherical magnetic powders; (B) The modified spherical magnetic powders are mixed with a release agent to obtain the magnetic powder material of the sheet powder magnetic core unit; Preferably, the acid used in the acid etching in step (A) includes at least one of nitric acid, hydrochloric acid, phosphoric acid, hydrofluoric acid, permanganic acid and chromic acid, preferably at least one of phosphoric acid, chromic acid and permanganic acid; Preferably, the coating agent used in the insulation coating in step (A) is selected from at least one of organic coating agents or inorganic coating agents; Preferably, the organic coating agent includes at least one of coupling agents and resins; Preferably, the inorganic coating agent includes at least one of silica, kaolin, alumina or titanium dioxide; Preferably, the release agent in step (B) includes at least one of zinc stearate, aluminum stearate and molybdenum disulfide.

9. The preparation method of the composite magnetic core with adjustable permeability according to any one of claims 6-8, characterized in that, the pressure of each pre-pressing is independently 800 MPa - 1300 MPa; Preferably, the pressure of the compression molding is 1800 MPa - 2000 MPa.

10. The preparation method of the composite magnetic core with adjustable permeability according to any one of claims 6-9, characterized in that, the gas in the atmosphere of the heat treatment includes at least one of protective gas and reducing gas; Preferably, the protective gas includes at least one of nitrogen, argon or helium; Preferably, the reducing gas includes hydrogen; Preferably, the temperature of the heat treatment is 600 °C - 800 °C; Preferably, the heat preservation time of the heat treatment is 2 h - 5 h.

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