Iron-based nanocrystalline magnetic core with low frequency and constant permeability, and preparation method therefor and use thereof

Abstract

The present invention belongs to the field of magnetic materials. Particularly disclosed are an iron-based nanocrystalline magnetic core with low frequency and constant permeability, and a preparation method therefor and the use thereof. In the present invention, the iron-based nanocrystalline magnetic core with low permeability can be obtained by sequentially subjecting an iron-based amorphous magnetic core to force field heat treatment and magnetic field heat treatment, and the iron-based nanocrystalline magnetic core has the characteristic of constant permeability under a low frequency of 1-100 kHz.

Description

A low-frequency constant permeability iron-based nanocrystalline magnetic core, its preparation method and application Technical Field

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

[0002] Iron-based amorphous / nanocrystalline soft magnetic alloys, as a new generation of "dual green" energy-saving materials, are widely used in new energy vehicles, photovoltaic energy storage, consumer electronics, mobile communications and other fields due to their excellent comprehensive soft magnetic properties, such as high saturation magnetic induction intensity, low coercivity, high permeability and low loss.

[0003] Iron-based amorphous / nanocrystalline soft magnetic alloys are typically produced by rapidly cooling a master alloy with high-speed copper rollers to create amorphous ribbons, 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 nanocrystalline magnetic cores. However, existing heat treatment processes, such as conventional annealing in atmosphere furnaces (vacuum or N2) and magnetic field annealing, often result in nanocrystalline magnetic cores with high permeability that decreases significantly with increasing frequency. This makes them unsuitable for applications requiring low to medium permeability and good frequency characteristics, thus limiting their application.

[0004] To obtain low to medium permeability, industrial processes typically involve tension annealing of amorphous ribbons before winding them into magnetic cores. This aims to reduce the permeability of nanocrystalline magnetic cores by inducing anisotropy under applied tension. However, tension annealing of amorphous ribbons presents several challenges. Firstly, excessive tension can lead to brittle fracture during heat treatment, while insufficient tension limits the permeability reduction. Secondly, existing equipment is limited by factors such as the heat treatment tensioning equipment fixtures, ribbon width, and surface morphology. It can only perform tension annealing on narrow, flat ribbons, and the wider the ribbon, the more uneven the tension distribution. Furthermore, the more surface defects a ribbon has, the more likely these defects will become fracture concentration points during tension annealing. Additionally, the brittleness of crystalline ribbons after tension annealing results in significant brittleness, leading to low efficiency, easy fracture, and low plasticity during core winding. Therefore, the existing technology of tension annealing amorphous ribbon to reduce the permeability of nanocrystalline magnetic cores has great limitations. It is difficult to obtain nanocrystalline magnetic cores with good medium-low permeability that maintain constant or relatively stable permeability, and it cannot be widely used in inductors in various high-frequency, AC and DC superposition applications.

[0005] Therefore, there is an urgent need to develop a fabrication process for nanocrystalline magnetic cores that skips the annealing process of the strip and directly processes the wound magnetic core, in order to reduce the permeability while maintaining the constant permeability of the nanocrystalline magnetic core. Summary of the Invention

[0006] In view of the problem of difficulty in obtaining nanocrystalline magnetic cores with medium to low and constant magnetic permeability in the prior art, the present invention will provide a low-frequency constant magnetic permeability iron-based nanocrystalline magnetic core, its preparation method and application.

[0007] To achieve the above objectives, the following technical solutions are specifically included:

[0008] A method for preparing an iron-based nanocrystalline magnetic core includes the following steps:

[0009] (1) Heat the iron-based amorphous magnetic core to a preset temperature and simultaneously pressurize it to a preset pressure, then cool it to below 200°C and start releasing the pressure to obtain a pre-burnt magnetic core; the preset pressure is greater than atmospheric pressure;

[0010] (2) The pre-burnt magnetic core is subjected to magnetic field heat treatment and cooled to obtain an iron-based nanocrystalline magnetic core.

[0011] In the method of this invention, the iron-based amorphous magnetic core is subjected to force field heat treatment and magnetic field heat treatment sequentially, resulting in an iron-based nanocrystalline magnetic core with constant permeability. Under force field heat treatment, on the one hand, pressure induces the precipitation of nanocrystals while simultaneously inhibiting their rapid growth. This, to a certain extent, controls the grain size, maintaining a relatively low and stable permeability. On the other hand, the presence of the pressure field induces magnetic anisotropy within the core, increasing domain wall energy. High domain wall energy prevents domain wall movement, thus, to a certain extent, controlling the domain wall energy to maintain a relatively low and stable permeability. The actual function of magnetic field heat treatment is to induce grain orientation growth, that is, to cause the nanocrystals to align along the direction of the applied magnetic field, 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 controls the grain and domain wall energy, while magnetic field heat treatment further controls and induces grain orientation growth. Preferably, the preset temperature is 430-525℃.

[0012] The stability of the magnetic core's permeability is related to the temperature of the force field heat treatment. When the preset temperature is within the range of 430-525℃, the effective permeability of the magnetic core gradually increases with increasing temperature, and the rate of change of permeability does not show a clear pattern. However, slightly deviating from the above temperature range, the rate of change of the effective permeability of the magnetic core in the 1-100KHz range is greater than 10%, and the stability of the permeability deteriorates significantly. Therefore, at the above-mentioned force field heat treatment temperature, the iron-based nanocrystalline magnetic core of the present invention exhibits a more stable effective permeability.

[0013] Preferably, in step (1), the preset pressure is 30-120 MPa.

[0014] The stability of the magnetic core's permeability is related to the pressure of the force field heat treatment. Within a preset pressure range of 30-120 MPa, as the pressure gradually increases, the magnetic core's permeability and its rate of change decrease accordingly. Within this pressure range, the magnetic core can exhibit excellent permeability stability in the 1-100 kHz range. However, higher pressures lead to higher energy consumption and greater pressure requirements on the equipment, increasing costs. Excessively high pressures are also detrimental to large-scale production. Therefore, while meeting actual performance requirements, a relatively lower pressure should be rationally selected to better suit the production conditions.

[0015] Preferably, in step (1), the heating rate of the iron-based amorphous magnetic core to the preset temperature is 5-30℃ / min.

[0016] Preferably, in step (1), the cooling rate is 50-1000℃ / min; the pressurization method includes at least one of inert gas pressurization and die extrusion pressurization.

[0017] The frequency used in a magnetic core is related to the stability of its permeability. The inventors of this invention discovered that during force field heat treatment, with a heating rate of 5-30℃ / min and a cooling rate of 50-1000℃ / min, the effective permeability of the magnetic core and its rate of change decrease with increasing heating or cooling rates. To maintain stable permeability, the heating and cooling rates can be increased to a certain extent, and the force field heat treatment time can be shortened, thereby reducing the permeability of the magnetic core while maintaining stable permeability.

[0018] Preferably, the inert gas includes at least one of argon and nitrogen.

[0019] Preferably, in step (2), the temperature of the magnetic field heat treatment is 350-430℃, the magnetic field strength of the magnetic field heat treatment is 800-3000Gs, and the time of the magnetic field heat treatment is 10-300min, more preferably 60-120min.

[0020] The magnetic field strength, temperature, and time of magnetic field heat treatment have a certain impact on the permeability and stability of the magnetic core. After force field heat treatment, increasing the magnetic field can reduce the permeability and its rate of change of the magnetic core. However, as the magnetic field strength increases, the decrease in permeability is not significant. But if the magnetic field heat treatment time is too long or the temperature is too high, the grain size in the magnetic core will increase significantly, which will increase the permeability and its rate of change to a certain extent. Moreover, from the perspective of production conditions, the higher the temperature and the longer the time of magnetic field heat treatment, the longer the production cycle and the energy consumption will increase. Therefore, the inventors of this invention have discovered that when the magnetic field strength is 800-3000 Gs, the magnetic field heat treatment temperature is 350-430℃, and the magnetic field heat treatment time is 10-300 min, the magnetic core can maintain high permeability stability at 1-100 kHz.

[0021] Preferably, the iron-based amorphous magnetic core in step (1) is formed by winding iron-based amorphous strip, and the magnetic field direction of the magnetic field heat treatment in step (2) is parallel to the width direction of the iron-based amorphous strip.

[0022] Preferably, in step (2), the cooling is natural cooling, and the cooling is from 100°C to room temperature.

[0023] 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%.

[0024] 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.

[0025] The method of this invention is actually a heat treatment method that is effective for a variety of iron-based alloys and is suitable for different types of amorphous magnetic cores.

[0026] Preferably, the permeability of the iron-based nanocrystalline magnetic core is constant at frequencies of 1-100kHz.

[0027] More preferably, the permeability variation rate of the iron-based nanocrystalline magnetic core at a frequency of 1-100kHz is ≤10%, more preferably ≤5%.

[0028] Generally, the permeability of iron-based nanocrystalline magnetic cores varies significantly at different frequencies. However, in inductors used in high-frequency, AC / DC superimposed applications, the smaller the permeability variation, the more stable the performance of the iron-based nanocrystalline magnetic core. This results in a longer service life and more stable performance when used in the fabrication of inductors for high-frequency, AC / DC superimposed applications. The iron-based nanocrystalline magnetic core of this invention maintains high permeability stability within the 1-100kHz range, better meeting the requirements for applications in high-frequency, AC / DC superimposed inductors.

[0029] Preferably, the permeability of the iron-based nanocrystalline magnetic core is 1300-35000.

[0030] More preferably, the permeability of the iron-based nanocrystalline magnetic core is 1500-14999.

[0031] The present invention also provides an application of the aforementioned iron-based nanocrystalline magnetic core in the fabrication of inductors for high-frequency, AC and DC superposition applications.

[0032] 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 in sequence, the present invention can obtain an iron-based nanocrystalline magnetic core with low magnetic permeability, and the iron-based nanocrystalline magnetic core has the characteristic of constant magnetic permeability at low frequencies of 1-100kHz. Attached Figure Description

[0033] Figure 1 shows the X-ray diffraction (XRD) pattern of the self-made amorphous ribbon.

[0034] Figure 2 is a comparison diagram of the magnetic domain structure between Example 1 (left) and Comparative Example 5 (right).

[0035] Figure 3 is a physical image of the iron-based nanocrystalline magnetic core of Example 1.

[0036] Figure 4 shows the relationship between the effective permeability and frequency of the iron-based nanocrystalline soft magnetic alloy cores in Examples 1-17.

[0037] Figure 5 shows the relationship between the effective permeability and frequency of the iron-based nanocrystalline soft magnetic alloy cores in Comparative Examples 1–5. Detailed Implementation

[0038] 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.

[0039] 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.

[0040] Example 1

[0041] A method for preparing an iron-based nanocrystalline magnetic core includes the following steps:

[0042] (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 480°C at a heating rate of 10°C / min. At the same time, argon gas was continuously added to pressurize the system to a preset pressure of 80MPa. 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-sintered magnetic core.

[0043] (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 380°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 1500Gs. The core is then cooled to room temperature with the furnace to obtain an iron-based nanocrystalline magnetic core.

[0044] Examples 2-17 and Comparative Examples 1-5

[0045] The only difference between Examples 2-17 and Comparative Examples 1-5 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.

[0046] Table 1

[0047] The iron-based nanocrystalline magnetic cores prepared above were subjected to performance tests: the inductance L of the nanocrystalline magnetic cores was measured using a Keysight Agilent 4294A precision impedance analyzer under 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 ),

[0048] 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).

[0049] 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.

[0050] Table 2

[0051] Based on the analysis of Table 2 and Figures 2 and 4-5, and as can be seen from Examples 1-17 and Comparative Examples 1-5, in the method of the present invention, the temperature is first increased to a preset temperature and pressure under force field heat treatment, then rapidly quenched and cooled to below 200°C, and then subjected to magnetic field heat treatment. The present invention combines force field and magnetic field heat treatment, enabling the iron-based nanocrystalline magnetic core to have a low, stable, or constant effective permeability at 1-100 kHz. In the above embodiments, the effective permeability is in the range of 1500-14999.

[0052] 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 induces magnetic anisotropy within the magnetic core, increasing domain wall energy. This high domain wall energy prevents domain wall movement, thus, to a certain extent, controlling the domain wall energy to maintain a relatively low and stable permeability. Magnetic field heat treatment, in effect, induces grain orientation growth, causing nanocrystals to align along the direction of the applied magnetic field, thereby inducing magnetic anisotropy and controlling the shape of the hysteresis loop. Force field heat treatment and magnetic field heat treatment work in tandem; force field heat treatment controls the grain size and domain wall energy, while magnetic field heat treatment further controls and induces grain orientation growth. This invention, by altering the heat treatment process, controls the grain size, state, magnetic anisotropy, and hysteresis loop shape to obtain a magnetic core with stable permeability in the 1-100 kHz range. Furthermore, as can be seen from Examples 1-17 and Comparative Examples 3-5, without the conditions of applying pressure greater than atmospheric pressure or applying a constant magnetic field, the magnetic core produced cannot maintain the performance of low frequency and low constant permeability, and cannot achieve the performance requirement of the present invention of an effective permeability of 1500-14999 at a frequency of 1-100kHz.

[0053] In Examples 2, 3, 1, and 4, the heating rate gradually increases, and the effective permeability of the magnetic core and its rate of change decrease accordingly. In Examples 9, 1, and 10, the cooling rate gradually increases, and the effective permeability of the magnetic core and its rate of change decrease accordingly. Furthermore, the cooling rate is significantly higher than the natural cooling rate of 6-8°C / min. This is because the present invention is equipped with a quenching device during cooling, thereby achieving a higher cooling rate and reducing the time required for both heating and cooling processes. It can be observed that the frequency used by the magnetic core is related to the stability of its permeability. At different frequencies, maintaining a stable permeability of the magnetic core can be achieved by increasing the heating and cooling rates to a certain extent and shortening the force field heat treatment time, thus reducing the permeability of the magnetic core while maintaining a stable permeability.

[0054] In Comparative Examples 1, 5, 1, 6, and 2, as the temperature of the force field heat treatment gradually increased, the effective permeability of the magnetic core gradually increased, and the rate of change of permeability did not show a clear pattern. However, in Examples 1 and 5-6, the force field heat treatment temperature was 430-525℃, and the effective permeability at a frequency of 1-100kHz was 1500-14999, with a permeability change rate of <5%. Comparative Examples 1 and 2 were 400℃ and 560℃, respectively. However, the effective permeability of Comparative Example 1 (which provides a valid comparison with Example 7) was 1211-1381, with a permeability change rate of 12.31%, while the effective permeability of Comparative Example 2 was 27116-32216, with a permeability change rate of 15.83%. It is evident that when the force field heat treatment temperature deviates slightly from the 430-525℃ range, the permeability of the magnetic core changes significantly. Controlling the permeability and its stability requires specific force field heat treatment temperatures. Furthermore, the pressure of the force field heat treatment also has a certain impact on the permeability and stability of the magnetic core. In Examples 7, 1, and 8, as the pressure of the force field heat treatment gradually increases, the permeability of the magnetic core and its rate of change decrease accordingly. The present invention can select a force field heat treatment pressure of 30-120 MPa. Within this pressure range, considering the influence of temperature on permeability during force field heat treatment, the trends of temperature and pressure on permeability are opposite. Force field heat treatment requires simultaneous control of both pressure and temperature within a relatively suitable range to better control the permeability of the magnetic core and achieve higher permeability stability of the magnetic core in the 1-100 kHz range.

[0055] In Examples 11, 12, and 13, the magnetic field strength gradually increased during magnetic field heat treatment, resulting in a slight decrease in the permeability of the magnetic core and a gradual decrease in the rate of change of permeability. In Examples 14, 1, and 15, the temperature gradually increased during magnetic field heat treatment, leading to an initial decrease followed by an increase in permeability and its change. In Examples 16, 1, and 17, the time gradually increased during magnetic field heat treatment, resulting in an initial decrease followed by an increase in permeability and its change. It is evident that the magnetic field strength, temperature, and time of magnetic field heat treatment have a certain impact on the permeability and stability of the magnetic core. Based on Examples 1, 11-17, and Comparative Example 4 (magnetic field strength of 0), it can be seen that after force field heat treatment, increasing the magnetic field can reduce the permeability and its rate of change of the magnetic core. However, as the magnetic field strength increases, the decrease in permeability is not significant. However, if the magnetic field heat treatment time is too long or the temperature is too high, the grain size in the magnetic core will increase significantly, which will, to some extent, increase the permeability and its rate of change. Furthermore, from a production perspective, higher temperatures and longer treatment times increase the production cycle and energy consumption.

[0056] 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 nanocrystalline magnetic core, characterized in that, Includes the following steps: (1) Heat the iron-based amorphous magnetic core to a preset temperature and simultaneously pressurize it to a preset pressure, then cool it to below 200°C and start releasing the pressure to obtain a pre-burnt magnetic core; the preset pressure is greater than atmospheric pressure; (2) The pre-burnt magnetic core is subjected to magnetic field heat treatment and cooled to obtain an iron-based nanocrystalline magnetic core.

2. The method for preparing the iron-based nanocrystalline magnetic core as described in claim 1, characterized in that, In step (1), the preset temperature is 430-525℃ and the preset pressure is 30-120MPa.

3. The method for preparing the iron-based nanocrystalline 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.

4. The method for preparing the iron-based nanocrystalline 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.

5. The method for preparing the iron-based nanocrystalline magnetic core as described in claim 1, characterized in that, In step (2), the temperature of the magnetic field heat treatment is 350-430℃, the magnetic field strength of the magnetic field heat treatment is 800-3000Gs, and the time of the magnetic field heat treatment is 1-300min.

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

7. The method for preparing the iron-based nanocrystalline 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 nanocrystalline magnetic core prepared by the method of any one of claims 1-7.

9. The iron-based nanocrystalline magnetic core as described in claim 8, characterized in that, The iron-based nanocrystalline magnetic core has a constant permeability at frequencies ranging from 1 to 100 kHz.

10. The application of the iron-based nanocrystalline magnetic core according to claim 8 or 9 in the fabrication of inductors for high-frequency, AC / DC superposition applications.

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