Iron-based magnetic core with constant low magnetic permeability and preparation method therefor

Abstract

The present invention belongs to the field of magnetic materials, specifically disclosed are an iron-based magnetic core with constant low magnetic permeability and a preparation method therefor and an application thereof. In the present invention, an iron-based amorphous magnetic core is sequentially subjected to a force-field heat treatment at a specific temperature and pressure and a magnetic-field heat treatment, thereby obtaining an iron-based magnetic core with low magnetic permeability. The iron-based magnetic core has a magnetic permeability of less than 1500 and constant at 1-100 kHz.

Description

A constant low permeability iron-based magnetic core and its preparation method Technical Field

[0001] This invention belongs to the field of magnetic materials, specifically relating to a constant low magnetic permeability iron-based magnetic core, its preparation method, and its application. Background Technology

[0002] Iron-based amorphous / nanocrystalline soft magnetic alloys are typically produced by rapidly cooling a master alloy with high-speed copper rollers to create amorphous strips, which are then wound into amorphous magnetic cores. Amorphous magnetic cores generally require appropriate heat treatment processes to finely control the alloy's microstructure. This involves transforming the precipitation of a single magnetic α-Fe phase on the amorphous matrix into a dual-phase structure of amorphous and nanocrystalline components, forming a nanocrystalline magnetic core. This unique dual-phase nanostructure is the main reason why nanocrystalline magnetic cores exhibit excellent overall soft magnetic properties. Therefore, the heat treatment process plays a decisive role in obtaining high-performance iron-based magnetic cores. However, current heat treatment processes generally result in nanocrystalline magnetic cores with high permeability that decreases significantly with increasing frequency. In the 1-100kHz range, the permeability is excessively high and unstable, making it impossible to achieve a constant and low permeability at low frequencies. This limits their application in specific scenarios such as inductors and high-current power devices where a permeability below 1500 ohms is required in the 1-100kHz range, thus restricting their use.

[0003] Therefore, there is an urgent need to develop a magnetic core fabrication process to achieve a magnetic core with a permeability below 1500 in the 1-100KHz range. Summary of the Invention

[0004] In view of the problem of difficulty in obtaining magnetic cores with low and constant permeability in the prior art, the present invention will provide an iron-based magnetic core with constant low permeability and a method for preparing the same.

[0005] To achieve the above objectives, the following technical solutions are specifically included:

[0006] A method for preparing an iron-based magnetic core includes the following steps:

[0007] (1) The iron-based amorphous magnetic core is heated to a preset temperature and simultaneously pressurized to a preset pressure, then cooled to below 200°C and the pressure is released to obtain a pre-burnt magnetic core; the preset temperature is 300-425°C and the preset pressure is 60-150MPa;

[0008] (2) The pre-burnt magnetic core is subjected to magnetic field heat treatment and then cooled to obtain an iron-based magnetic core.

[0009] In the method of the present invention, the iron-based amorphous magnetic core is subjected to force field heat treatment and magnetic field heat treatment at specific temperatures and pressures in sequence to control the grain size, grain orientation and magnetic anisotropy, so that the iron-based magnetic core has the characteristic of effective permeability of 100-1499 at a frequency of 1-100kHz, thus broadening the application scenarios of iron-based magnetic cores.

[0010] Under force field heat treatment, on the one hand, pressure promotes the precipitation of nanocrystals while simultaneously inhibiting their rapid growth. To a certain extent, this controls the grain size, allowing the magnetic core to maintain a relatively low and stable permeability. On the other hand, the presence of the pressure field can induce magnetic anisotropy within the magnetic core, increasing domain wall energy. High domain wall energy prevents domain wall movement, thus, to a certain extent, controlling the domain wall energy results in a relatively low and stable permeability. The inventors of this invention have discovered that the temperature and pressure of force field heat treatment have a significant impact on permeability and its stability. Under force field heat treatment at 300-425℃, the magnetic core can still maintain a relatively low and stable permeability. However, slightly deviating from the above temperature range, higher temperatures lead to excessively high permeability and a sharp decrease in permeability stability, while lower temperatures, although meeting the permeability requirements, still result in a sharp decrease in permeability stability, failing to meet the requirements. Under a force field pressure of 60-150 MPa, the magnetic core can maintain a relatively low and relatively stable permeability. However, slightly deviating from the aforementioned pressure range, although the permeability of the magnetic core meets the requirements, its stability cannot. Therefore, the thermal field of this invention is actually a heat treatment method of rapid heating and rapid cooling. Under the synergistic effect of specific temperature and high pressure, it promotes the continuous precipitation of nanocrystals while inhibiting their growth, controlling the grain state and size in the magnetic core, and simultaneously increasing the domain wall energy to a certain extent, thereby achieving the overall performance effect of low and constant permeability of the magnetic core. The actual function of the magnetic field heat treatment is to induce grain orientation growth, that is, to promote the orientation of nanocrystals along the direction of magnetic field application, thereby inducing magnetic anisotropy and controlling the shape of the hysteresis loop. Force field heat treatment and magnetic field heat treatment work together. Force field heat treatment is needed to control the grain and domain wall energy, and then magnetic field heat treatment is needed to control and induce grain orientation growth. Without the conditions of applying pressure greater than atmospheric pressure or applying a constant magnetic field, the magnetic core cannot maintain the performance of low frequency and low constant permeability, and cannot achieve the performance requirement of 100-1499 effective permeability at a frequency of 1-100kHz of this invention.

[0011] Preferably, in step (1), the iron-based amorphous magnetic core comprises the following elements in atomic percentage: Fe 60-80%, Si 10-20%, B 0-10%, Cu 0-3%, Nb 0-5%, Ni 0-15%, and Co 0-10%.

[0012] More preferably, the iron-based amorphous magnetic core comprises Fe 73.5 Si 15.5 B7Cu1Nb3, Fe 73.5 Si 13.5 B9Cu1Nb3, Fe 63.5 Ni 10 Si 15.5 B7Cu1Nb3, Fe 63.5 Co5Ni5Si 15.5 B7Cu1Nb3, Fe 68.5 Co5Si 15.5 At least one of B7Cu1Nb3.

[0013] The method of this invention is actually a heat treatment method that is effective for a variety of iron-based alloys and adaptable to different types of amorphous magnetic cores. It is particularly suitable for iron-based amorphous magnetic cores within the above-mentioned element content range, so that the magnetic cores made from the above-mentioned iron-based amorphous magnetic cores have an effective permeability of less than 1500 at 1-100KHz.

[0014] Preferably, in step (1), the heating rate of the iron-based amorphous magnetic core to the preset temperature is 5-30℃ / min.

[0015] The heating rate affects the time required to heat an iron-based amorphous magnetic core to a preset temperature. A higher heating rate results in a shorter heating time, allowing the preset heat treatment temperature to be reached more quickly. This prevents excessive grain growth during heating, which could compromise the control of permeability and stability. At the aforementioned heating rate, the magnetic core can achieve an effective permeability of less than 1500 in the 1-100 kHz range.

[0016] Preferably, in step (1), the cooling rate is 50-1000℃ / min.

[0017] After reaching the preset temperature and pressure, the magnetic core begins to cool down. The natural cooling rate of the furnace is generally 6-8℃ / min. If the cooling rate is greater than this range, auxiliary rapid quenching equipment is required. The cooling rate within the above range is considered rapid quenching, which can quickly cool the magnetic core, shorten the time the magnetic core stays at higher temperatures, avoid excessive growth of grains in the magnetic core, effectively control the size of recrystallized grains, and ensure that the final magnetic core maintains low permeability and high stability.

[0018] Preferably, the pressurization method includes at least one of inert gas pressurization and die extrusion pressurization. More preferably, the inert gas includes at least one of argon and nitrogen.

[0019] Preferably, the temperature of the magnetic field heat treatment is 300-380℃, and the magnetic field strength of the magnetic field heat treatment is 800-3000Gs.

[0020] Preferably, the magnetic field heat treatment time is 1-120 min, more preferably 30-60 min.

[0021] Higher magnetic field strength, higher heat treatment temperature, and longer holding time induce greater grain orientation growth, resulting in lower permeability and higher permeability stability. However, higher magnetic field strength, higher heat treatment temperature, and longer holding time not only significantly increase the actual production cycle, cost, and equipment wear, but also reduce the degree of grain orientation growth induced by magnetic field heat treatment. Long-term high-temperature growth can lead to excessive growth of nanocrystals, causing increased permeability and decreased permeability stability. Therefore, under the magnetic field heat treatment conditions within the above range, the objective of maintaining low permeability and high stability of the magnetic core of this invention can be achieved.

[0022] Preferably, the iron-based amorphous magnetic core in step (1) is formed by winding iron-based amorphous strip.

[0023] Preferably, the magnetic field direction of the magnetic field heat treatment in step (2) is parallel to the width direction of the iron-based amorphous ribbon.

[0024] Preferably, in step (2), the cooling is natural cooling.

[0025] Preferably, the permeability of the iron-based magnetic core is constant at a frequency of 1-100kHz, and the permeability of the iron-based magnetic core is 1500-14999; the iron-based magnetic core contains an amorphous phase and nano-sized grains.

[0026] More preferably, when the permeability of the iron-based magnetic core is constant, the rate of change of the effective permeability of the iron-based magnetic core at a frequency of 1-100kHz is ≤5%.

[0027] The present invention also provides an application of the aforementioned iron-based magnetic core in the fabrication of inductors and high-current power devices.

[0028] Compared with the prior art, the present invention has the following beneficial effects: by subjecting the iron-based amorphous magnetic core to force field heat treatment and magnetic field heat treatment at specific temperatures and pressures, the present invention can obtain an iron-based magnetic core with low permeability, and the iron-based magnetic core has a constant permeability of less than 1500 at 1-100kHz. Attached Figure Description

[0029] Figure 1 shows the X-ray diffraction (XRD) pattern of the self-made amorphous ribbon.

[0030] Figure 2 is a physical image of the magnetic core prepared in Example 1.

[0031] Figure 3 is a comparison diagram of the magnetic domain structure between Example 1 (left) and Comparative Example 3 (right).

[0032] Figure 4 shows the relationship between the effective permeability and frequency of the iron-based nanocrystalline soft magnetic alloy cores in Examples 1-16.

[0033] Figure 5 shows the relationship between the effective permeability and frequency of the iron-based nanocrystalline soft magnetic alloy cores in Comparative Examples 1–7. Detailed Implementation

[0034] To better illustrate the purpose, technical solution, and advantages of this invention, specific embodiments will be used to further explain the invention below. Unless otherwise specified, the test methods used in the embodiments and / or comparative examples are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available.

[0035] The amorphous ribbons used in the following examples and comparative examples can be purchased from the market or obtained by conventional methods. The methods for obtaining the ribbons can include the following processes: (1) component proportioning; (2) master alloy melting; (3) ribbon spinning and ribbon winding to obtain the corresponding amorphous ribbons.

[0036] Example 1

[0037] A method for preparing an iron-based magnetic core includes the following steps:

[0038] (1) The alloy Fe, in atomic percentage terms 73.5 Si 15.5 B7Cu1Nb3 amorphous ribbon (self-made, its XRD results are shown in Figure 1) was wound into an amorphous magnetic core. The amorphous magnetic core was then placed in a furnace, evacuated, and filled with inert argon gas to create a certain pressure in the system. The system was heated to the force field heat treatment temperature of 350°C at a heating rate of 15°C / min. At the same time, argon gas was continuously added to pressurize the system to a preset pressure of 130MPa. Subsequently, the system was cooled at a cooling rate of 100°C / min. After cooling to below 200°C, the pressure was released until room temperature and atmospheric pressure were reached, resulting in a pre-burnt magnetic core.

[0039] (2) The pre-burnt magnetic core is placed in the magnetic field heat treatment furnace and heated to the magnetic field heat treatment temperature of 350°C at a heating rate of 10°C / min. At this time, a magnetic field parallel to the width direction of the magnetic core is applied and held for 60 minutes under the action of a magnetic field strength of 1000Gs. The core is then cooled to room temperature with the furnace to obtain the iron-based magnetic core.

[0040] Examples 2-15 and Comparative Examples 1-7

[0041] The only difference between Examples 2-15 and Comparative Examples 1-7 and Example 1 is that in steps (1)-(2), the heating and cooling rates, force field heat treatment temperature, preset pressure, magnetic field strength, magnetic field heat treatment temperature or holding time are different. See Table 1 for details.

[0042] Example 16

[0043] The difference between this embodiment 1 and the previous embodiment is that the alloy in this embodiment contains Fe by atomic percentage. 73.5 Si 13.5 B9Cu1Nb3 amorphous ribbon, the amorphous ribbon is obtained in the same way as the amorphous ribbon in Example 1. It can be obtained by commercially available methods or by self-made methods using conventional methods. The self-made methods in this example and Example 1 may include the following processes: (1) component ratio; (2) master alloy melting; (3) then through strip spinning and strip winding to obtain the corresponding amorphous ribbon.

[0044] Table 1

[0045] The iron-based magnetic cores prepared in the above embodiments and comparative examples were subjected to performance tests: the inductance L of the magnetic core was measured using a Keysight Agilent 4294A precision impedance analyzer with an applied magnetic field of 1 A / m and a frequency range of 1 kHz to 100 kHz; the effective permeability μ was measured. e The value is obtained through the inductance L conversion formula: μ e = (L×L) e ) / (N 2 ×A e ),

[0046] Where L is the core inductance, μ e L is the effective permeability of the magnetic core. e A is the magnetic circuit length of the magnetic core. e Where N is the effective cross-sectional area of ​​the magnetic core, and N is the number of coil turns (test condition: 1 turn).

[0047] μ e Calculation method for rate of change %: μ e Rate of change % = (μ e(1kHz) -μ e(100kHz) ) / μ e(1kHz) ×100%, in this invention μ e A change rate of less than 5% is considered constant permeability.

[0048] Table 2

[0049] Based on the analysis of Table 2 and Figures 2 and 4-5, and as can be seen from Examples 1-16 and Comparative Examples 1-7, the present invention combines force field and magnetic field heat treatment, and requires heat treatment under specific temperature and pressure conditions, which enables the iron-based magnetic core to have a low, stable or constant effective permeability in the range of 100-1499 at 1-100KHz.

[0050] In the method of this invention, under force field heat treatment, the heating / cooling rate, heat treatment temperature, holding time, and pressure all have a certain influence on the permeability and stability of the iron-based nanocrystalline magnetic core. This is because: on the one hand, pressure promotes the precipitation of nanocrystals but simultaneously inhibits their rapid growth, thus controlling the grain size to maintain a relatively low and stable permeability of the magnetic core; on the other hand, the presence of the pressure field can induce magnetic anisotropy within the magnetic core, increasing the domain wall energy. High domain wall energy prevents domain wall movement, thus controlling the domain wall energy to maintain a relatively low and stable permeability of the magnetic core. The goal of this invention is to achieve a constant effective permeability of 100-1499 within the 1-100 kHz range for applications in specific fields. As can be observed from Examples 1-3, 8-9, and 16 above, under a thermal field, the heating rate can be selected from 5-30℃ / min, the cooling rate from 50-1000℃ / min, and different types of amorphous magnetic cores can be selected, all of which can achieve the magnetic properties required by this invention within a relatively wide range. The aforementioned heating and cooling rates are considered rapid heating and cooling in industrial production, shortening the time of the magnetic core during heat treatment and preventing excessive grain growth in the magnetic core, which could lead to substandard permeability and stability. Especially during the cooling process, the natural furnace cooling rate is generally 6-8℃ / min; cooling rates exceeding this range require auxiliary rapid quenching equipment. As can be seen from Examples 1, 4-7 and Comparative Examples 1, 4-7, the temperature and pressure of the force field heat treatment have a very significant impact on the permeability and stability. Under a force field heat treatment at 300-425℃, the magnetic core can still maintain a relatively low and relatively stable permeability. However, slightly deviating from the above temperature range, the temperature is too high, leading to excessively high permeability and a sharp decrease in permeability stability. While the permeability meets the requirements at slightly lower temperatures, its stability still decreases sharply, failing to meet the requirements. Under a force field pressure of 60-150MPa, the magnetic core can maintain a relatively low and relatively stable permeability. However, slightly deviating from the above pressure range, although the permeability meets the requirements, its stability fails to meet the requirements. Therefore, the thermal field of this invention is actually a heat treatment method of rapid heating and rapid cooling. Under the synergistic effect of specific temperature and high pressure, it promotes the continuous precipitation of nanocrystals while inhibiting nanocrystal growth, controlling the grain state and size in the magnetic core, and to a certain extent increasing the domain wall energy, thus achieving the overall performance effect of low and constant permeability of the magnetic core.

[0051] Under magnetic field heat treatment, the magnetic field strength, holding time, and heat treatment temperature can all have a certain impact on the permeability and stability of iron-based nanocrystalline magnetic cores. This is because the actual effect of magnetic field heat treatment is to induce grain orientation growth, that is, to promote the orientation of nanocrystals along the direction of magnetic field application, thereby inducing magnetic anisotropy and controlling the shape of the hysteresis loop. As can be seen from Examples 1 and 10-15 above, the magnetic field heat treatment temperature is 300-380℃, the magnetic field strength is 800-3000Gs, and the holding time is 30-120min. The higher the magnetic field strength, the higher the heat treatment temperature, and the longer the holding time, the greater the degree of induced grain orientation growth, the lower the magnetic permeability, and the higher the magnetic permeability stability. However, the higher the magnetic field strength, the higher the heat treatment temperature, and the longer the holding time, the more significantly the actual production cycle, cost, and equipment wear and tear are increased. Moreover, the degree of induced grain orientation growth by magnetic field heat treatment will decrease, and long-term high-temperature growth will lead to excessive growth of nanocrystals, resulting in increased magnetic permeability and decreased magnetic permeability stability. Therefore, the preferred magnetic field heat treatment conditions of the present invention are as follows: magnetic field heat treatment temperature is 300-380℃, magnetic field strength is 800-3000Gs, and holding time is 30-120min.

[0052] As can be seen from Example 1 and Comparative Examples 1-3, force field heat treatment and magnetic field heat treatment are complementary. It is necessary to control the grain and domain wall energy by force field heat treatment, and then control the grain orientation growth by magnetic field heat treatment. Without the conditions of applying pressure greater than atmospheric pressure or applying a constant magnetic field, the magnetic core cannot maintain the performance of low frequency and low constant magnetic permeability.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing an iron-based magnetic core, characterized in that, Includes the following steps: (1) The iron-based amorphous magnetic core is heated to a preset temperature and simultaneously pressurized to a preset pressure, then cooled to below 200°C and the pressure is released to obtain a pre-burnt magnetic core; the preset temperature is 300-425°C and the preset pressure is 60-150MPa; (2) The pre-burnt magnetic core is subjected to magnetic field heat treatment and then cooled to obtain an iron-based magnetic core.

2. The method for preparing the iron-based magnetic core as described in claim 1, characterized in that, In step (1), the heating rate of the iron-based amorphous magnetic core to the preset temperature is 5-30℃ / min.

3. The method for preparing the iron-based magnetic core as described in claim 1, characterized in that, In step (1), the cooling rate is 50-1000℃ / min; the pressurization method includes at least one of gas pressure pressurization and mold extrusion pressurization.

4. The method for preparing the iron-based magnetic core as described in claim 1, characterized in that, In step (2), the temperature of the magnetic field heat treatment is 300-380℃, and the magnetic field strength of the magnetic field heat treatment is 800-3000Gs.

5. The method for preparing the iron-based magnetic core as described in claim 1, characterized in that, In step (2), the magnetic field heat treatment time is 1-120 min, and the cooling is natural cooling.

6. The method for preparing the iron-based magnetic core as described in claim 1, characterized in that, The iron-based amorphous magnetic core mentioned in step (1) is formed by winding iron-based amorphous strip, and the magnetic field direction of the magnetic field heat treatment mentioned in step (2) is parallel to the width direction of the iron-based amorphous strip.

7. The method for preparing the iron-based magnetic core as described in claim 1, characterized in that, In step (1), the iron-based amorphous magnetic core comprises the following elements in atomic percentage: Fe 60-80%, Si 10-20%, B 0-10%, Cu 0-3%, Nb 0-5%, Ni 0-15%, and Co 0-10%.

8. An iron-based magnetic core prepared by the method of any one of claims 1-7.

9. The iron-based magnetic core as described in claim 8, characterized in that, The iron-based magnetic core has a constant permeability at frequencies of 1-100kHz, and the permeability of the iron-based magnetic core is 100-1499; the iron-based magnetic core contains an amorphous phase and nano-sized grains.

10. The application of the iron-based magnetic core according to claim 8 or 9 in the manufacture of inductors and high-current power devices.

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