High operating frequency soft magnetic composite material and method of making same

Abstract

This invention relates to a high-frequency soft magnetic composite material and its preparation method, comprising: (1) master alloy smelting: melting metal raw materials according to A 1‑x B x The master alloy is prepared by proportioning and vacuum induction melting; A is a magnetic metal or its alloy, B is an active metal, 0.5% < x < 20%; (2) Atomization powder preparation: the master alloy is prepared into powder by atomization method, and powder with a size of less than 50 μm is screened out; (3) Powder treatment: the powder obtained in step (2) is heat-treated in a protective atmosphere containing a preset oxygen content, and then mixed with binder for granulation; (4) Molding: the treated powder is shaped under a preset pressure. The present invention utilizes the internal oxidation effect to generate a dense high-resistivity non-magnetic oxide layer and a loose iron oxide layer on the surface to achieve insulation between metal magnetic powders and effectively alleviate the insulation layer damage caused by stress concentration during high pressure molding. The soft magnetic composite material has a high working frequency.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of magnetic materials, and particularly relates to a high working frequency soft magnetic composite material and a preparation method thereof. BACKGROUND

[0002] Soft magnetic material can produce a magnetic response under the excitation of an external magnetic field, and is a basic material for the electronic information industry. By winding one or more groups of metal coils on a magnetic material and passing an electric current, magnetic devices such as transformers, inductors, mutual inductors, and filters can be made. Increasing the working frequency of soft magnetic material can significantly reduce the size of various soft magnetic devices under the same power density. In particular, with the rapid development of the third generation of power semiconductors, there is an urgent need for high-frequency soft magnetic materials with a working frequency of megahertz. When soft magnetic material works at high frequency, it mainly faces two problems: the eddy current loss increases significantly, and the magnetic permeability rapidly decays, leading to the failure of related devices.

[0003] Soft magnetic material includes metal soft magnetic material, soft magnetic composite material, and soft magnetic ferrite material. The soft magnetic ferrite is made of oxides such as iron oxide, zinc oxide, manganese oxide, and nickel oxide, and is essentially a kind of magnetic ceramic. It has a very high resistivity, which can significantly reduce the high-frequency eddy current loss. At the same time, by refining the grain and eliminating the domain wall, the high-frequency domain wall resonance is suppressed, and the working frequency of the soft magnetic ferrite can be increased to more than megahertz, which has initially realized the application in high-frequency power devices. The most important problem of soft magnetic ferrite is that its saturation magnetic flux density is too low, usually less than 500 mT, which is not conducive to further reducing the size of the device and improving the direct current bias characteristics of the device.

[0004] Soft magnetic composite material is a composite material made of metal soft magnetic powder after insulation coating and molding. It can fully utilize the high saturation magnetic flux density of the metal soft magnetic material matrix, and after the surface of the metal powder is insulated, the resistivity of the composite material can be significantly improved, reducing the high-frequency eddy current loss. At the same time, in order to further reduce the magnetic dilution effect introduced in the insulation coating process, high-resistance ferrite material is generally used to insulate the metal soft magnetic powder. However, during the molding of the soft magnetic composite material, the pressure often reaches more than 1 GPa, stress concentration occurs between the metal magnetic powders, the insulation coating layer is damaged, and the eddy current increases dramatically at high frequency. The working frequency of the soft magnetic composite material is generally lower than 500 kHz, and at more than megahertz, the magnetic permeability still rapidly decays and the loss still significantly increases.

[0005] In the previous research, it was found that the fundamental reason for the rapid decay of the magnetic permeability and the rapid increase of the loss of the soft magnetic composite material at a frequency of more than megahertz is that the insulation coating layer is damaged during high-pressure pressing, the insulation fails, the resistivity decreases, the eddy current increases, the eddy current generates a reverse magnetic field, which suppresses the magnetization process, causing the magnetic permeability to rapidly decay and the loss to increase. SUMMARY

[0006] Based on the above-mentioned shortcomings and deficiencies existing in the prior art, one of the purposes of the present application is to at least solve one or more of the above-mentioned problems existing in the prior art, in other words, one of the purposes of the present application is to provide a high working frequency soft magnetic composite material and a preparation method thereof, while realizing insulation in the soft magnetic composite material and relieving the destruction of the insulation counter layer under high pressure, so as to improve the working frequency of the soft magnetic composite material.

[0007] In order to achieve the above-mentioned purposes of the application, the following technical solutions are adopted in the present application:

[0008] A preparation method of a high working frequency soft magnetic composite material, comprising the following steps:

[0009] (1) Master alloy smelting: proportioning metal raw materials according to A 1-x B x to vacuum induction smelting into a master alloy; wherein A is a magnetic metal or an alloy thereof, B is an active metal, 0.5% < x < 20%;

[0010] (2) Atomization powdering: the master alloy is prepared into powder by atomization method, and the powder with a size less than 50 μm is screened out;

[0011] (3) Powder treatment: the powder obtained in step (2) is heat treated in a protective atmosphere containing a preset oxygen content, and then mixed with an adhesive for granulation;

[0012] (4) Forming: the treated powder is formed under a preset pressure.

[0013] As a preferred scheme, in the step (1),

[0014] The magnetic metal is iron;

[0015] The alloy is a ferrous alloy, and the ferrous alloy is one or more of ferrosilicon, iron-nickel, ferrosilicon-nickel, iron-nickel-molybdenum, iron-cobalt, iron-cobalt-silicon, iron-based amorphous, and iron-based nanocrystalline.

[0016] As a preferred scheme, in the step (1), the active metal is one or more of aluminum, magnesium, titanium, and chromium.

[0017] As a preferred scheme, in the step (2), the atomization powdering adopts gas atomization powdering, and the oxygen partial pressure is 0.01-10%; or the atomization powdering adopts water atomization powdering.

[0018] As a preferred scheme, in the step (3), the protective atmosphere is argon or nitrogen, and the preset oxygen content is 0.01-21%.

[0019] As a preferred solution, in the step (3), the temperature of the heat treatment is 400-1000℃, and the time of the heat treatment is 0.5-3 hours.

[0020] As a preferred solution, in the step (4), the preset pressure is 300MPa-2GPa.

[0021] As a preferred solution, in the step (4), the forming method is cold pressing forming, hot pressing forming, cold sintering forming or discharge plasma sintering forming.

[0022] The application provides a high working frequency soft magnetic composite material prepared by the preparation method according to any one of the above solutions, wherein the metal magnetic powder has a core-shell structure of metal matrix / inner oxidation layer / outer oxidation layer from inside to outside, and the size of the metal magnetic powder is less than 50μm.

[0023] The metal matrix is a magnetic metal or an alloy thereof, the inner oxidation layer is an active metal oxide, and the outer oxidation layer is a magnetic metal oxide.

[0024] As a preferred solution, the saturation magnetic flux density is greater than 700mT, the resistivity is higher than 10 3 μΩ·cm, the cutoff frequency is higher than 10MHz, and the magnetic permeability is greater than 10.

[0025] Compared with the prior art, the application has the following beneficial effects:

[0026] The application introduces a certain proportion of active metals (aluminum, magnesium, titanium and chromium) into a magnetic metal master alloy formula, generates an oxidation layer on the surface of the atomized powder by controlling the oxygen content in the atomization atmosphere during atomization powder production, and further controls the temperature, time and atmosphere of the subsequent heat treatment of the powder, so that the metal particles form a core-shell structure of metal matrix / inner oxidation layer / outer oxidation layer, the size of the magnetic powder is less than 50μm, and the metal magnetic powders are completely insulated; the inner oxidation layer is generated in situ on the surface of the particles and has good bonding with the metal matrix, the outer oxidation layer is a porous loose structure, can effectively link stress concentration during pressing forming, reduce the damage to the insulation layer, and finally can significantly inhibit the conduction effect between the metal magnetic powders, and the selection of the magnetic powder with a size of less than 50μm can also maximize the reduction of the domain wall structure inside the magnetic powder, thereby simultaneously significantly reducing the eddy current effect and the magnetic resonance effect, and increasing the working frequency of the soft magnetic composite material to more than 10MHz. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 It is an electron microscope image of the core-shell structure of the metal matrix / inner oxidation layer / outer oxidation layer of the metal magnetic powder after heat treatment in the application. DETAILED DESCRIPTION

[0028] The technical solutions of the application are further explained and described below through specific embodiments.

[0029] Example 1

[0030] The preparation method of the soft magnetic composite material of this example comprises the following steps:

[0031] 90% pure iron and 10% pure aluminum (atomic ratio) are vacuum induction melted into a master alloy; then the master alloy is atomized by gas atomization with an oxygen partial pressure of 1%, and the powder smaller than 37 μm is screened out after airflow classification, and is annealed at 700°C for 1 hour in an argon atmosphere with an oxygen partial pressure of 10%. The obtained powder is mixed with an epoxy resin adhesive, and is cold-pressed into a soft magnetic composite material at 800 MPa.

[0032] In the soft magnetic composite material, the metal magnetic powder has a core-shell structure with a base of iron, an inner oxidation layer (i.e. inner shell layer) of aluminum oxide, and an outer oxidation layer (i.e. outer shell layer) of iron oxide, as shown in Figure 1 .

[0033] The soft magnetic composite material has a saturation magnetic flux density of 1800 mT, a resistivity of 4 x 10 5 μΩ·cm, a cutoff frequency of 40 MHz, and a permeability of 30.

[0034] Example 2

[0035] The preparation method of the soft magnetic composite material of this example comprises the following steps:

[0036] 95% iron-nickel alloy and 5% pure magnesium (atomic ratio) are vacuum induction melted into a master alloy; then the master alloy is atomized by gas atomization with an oxygen partial pressure of 0.5%, and the powder smaller than 20 μm is screened out after airflow classification, and is annealed at 800°C for 0.5 hour in an argon atmosphere with an oxygen partial pressure of 5%. The obtained powder is mixed with a phenolic resin adhesive, and is cold-pressed into a soft magnetic composite material at 600 MPa.

[0037] In the soft magnetic composite material, the metal magnetic powder has a core-shell structure with a base of iron-nickel alloy, an inner oxidation layer of magnesium oxide, and an outer oxidation layer of iron oxide.

[0038] The soft magnetic composite material has a saturation magnetic flux density of 1200 mT, a resistivity of 9 x 10 4 μΩ·cm, a cutoff frequency of 100 MHz, and a permeability of 35.

[0039] Example 3

[0040] The preparation method of the soft magnetic composite material of this example comprises the following steps:

[0041] A master alloy was prepared by vacuum induction melting of 97% iron-silicon alloy and 3% pure chromium (atomic ratio). Then, the master alloy was atomized by gas atomization powder preparation with an oxygen partial pressure of 0.01%. After air classification, powder smaller than 10 μm was sieved and annealed at 600°C for 1.5 hours in an argon atmosphere with an oxygen partial pressure of 10%. The resulting powder was mixed with a silicone resin binder and then cold-pressed at 900 MPa to form a soft magnetic composite material.

[0042] In soft magnetic composite materials, the metal magnetic powder has a core-shell structure with an iron-silicon alloy matrix, an inner oxide layer of chromium oxide, and an outer oxide layer of iron oxide.

[0043] The soft magnetic composite material has a saturation magnetic flux density of 1500 mT and a resistivity of 1.5 × 10⁻⁶ mT. 5 μΩ·cm, cutoff frequency 400MHz, permeability 15.

[0044] Example 4:

[0045] The preparation method of the soft magnetic composite material in this embodiment includes the following steps:

[0046] A master alloy was prepared by vacuum induction melting of 85% iron-nickel-molybdenum alloy and 15% pure titanium (atomic ratio). Then, the master alloy was atomized by gas atomization powder preparation with an oxygen partial pressure of 0.05%. After air classification, the powder smaller than 5μm was sieved and annealed at 650℃ for 1.5 hours in an argon atmosphere with an oxygen partial pressure of 15%. The resulting powder was mixed with epoxy resin adhesive and then cold-pressed at 800MPa to form a soft magnetic composite material.

[0047] In soft magnetic composite materials, the metal magnetic powder has a core-shell structure with an iron-nickel-molybdenum alloy matrix, an inner oxide layer of titanium oxide, and an outer oxide layer of iron oxide.

[0048] The soft magnetic composite material has a saturation magnetic flux density of 1000 mT and a resistivity of 8.5 × 10⁻⁶ mT. 5 μΩ·cm, cutoff frequency 800MHz, permeability 12.

[0049] Comparative Examples 1-4:

[0050] The metal powders in the above four embodiments were directly mixed with the corresponding resins and granulated, and then molded under the corresponding pressure. The saturation magnetic flux, permeability and cutoff frequency were measured, as shown in Table 1.

[0051] Table 1 Material properties of Comparative Examples 1-4

[0052]

[0053] It can be seen that the soft magnetic composite material prepared by the application can significantly improve the cutoff frequency under the same magnetic powder matrix and the same pressure compared with the traditional preparation method.

[0054] Comparative Example 5:

[0055] The difference between the present comparative example and Example 1 is that the argon atmosphere is an anaerobic condition, and the other processes are the same as those of Example 1.

[0056] In the soft magnetic composite material, the metal magnetic powder has an iron-aluminum alloy as the matrix, and an oxidation layer is not formed on the surface of the particles due to the anaerobic treatment, so the insulation of the magnetic powder cannot be realized.

[0057] The soft magnetic composite material has a saturation magnetic flux density of 1600mT, a resistivity of 2x10 3 μΩ·cm, a cutoff frequency of 0.1MHz, and a permeability of 52.

[0058] Since there are numerous embodiments of the application, all components, component contents and process parameters can be determined according to application requirements within the corresponding ranges, and the experimental data of each embodiment are numerous and not suitable for being listed and explained one by one here, but the contents to be verified and the final conclusions obtained by each embodiment are close.

[0059] The above only describes the preferred embodiments and principles of the application in detail, and for ordinary skilled persons in the art, the specific implementation manner can be changed according to the idea provided by the application, and these changes should also be considered as the protection scope of the application.

Claims

1. A method for preparing a high-operating-frequency soft magnetic composite material, characterized in that, Includes the following steps: (1) Master alloy smelting: The metal raw materials are smelted according to A 1-x B x The alloy is prepared by proportioning and vacuum induction melting; wherein A is a magnetic metal or its alloy, B is an active metal, and 0.5% < x < 20%; (2) Atomization powder preparation: The master alloy is prepared into powder by atomization and the powder with a size of less than 50 μm is sieved out; (3) Powder treatment: The powder obtained in step (2) is heat-treated in a protective atmosphere containing a preset oxygen content, and then mixed with the binder and granulated. (4) Molding: The processed powder is shaped under a preset pressure; In step (1), the magnetic metal is iron; The alloy is an iron alloy, which is one or more of the following: iron-silicon, iron-nickel, iron-silicon-nickel, iron-nickel-molybdenum, iron-cobalt, and iron-cobalt-silicon. In step (1), the active metal is one or more of aluminum, magnesium, titanium, and chromium; In step (2), the atomization powdering adopts gas atomization powdering with an oxygen partial pressure of 0.01-10%; In step (3), the protective atmosphere is argon or nitrogen, and the preset oxygen content is 0.01-21%. In soft magnetic composite materials, the metal magnetic powder has a core-shell structure consisting of an inner metal matrix, an inner oxide layer, and an outer oxide layer, from the inside out. The metal substrate is a magnetic metal or its alloy, the inner oxide layer is an active metal oxide, and the outer oxide layer is a magnetic metal oxide.

2. The preparation method according to claim 1, characterized in that, In step (3), the heat treatment temperature is 400-1000℃ and the heat treatment time is 0.5-3 hours.

3. The preparation method according to claim 1, characterized in that, In step (4), the preset pressure is 300MPa to 2GPa.

4. The preparation method according to claim 1, characterized in that, In step (4), the forming method is cold pressing, hot pressing, cold sintering or spark plasma sintering.

5. The high-operating-frequency soft magnetic composite material prepared by the method according to claim 1, characterized in that, Saturation magnetic flux density greater than 700 mT, resistivity greater than 10 3 μΩ·cm, cutoff frequency higher than 10MHz, permeability greater than 10.

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