Preparation method and application of iron-based nanocrystalline magnetic core

Abstract

This invention discloses a method for preparing and applying an iron-based nanocrystalline magnetic core, belonging to the field of soft magnetic materials technology. The preparation method includes the following steps: preparing a Fe-Si-B-Cu-Nb-(M) system (M=Mo, V) amorphous thin strips of a specific composition; winding the thin strips and then subjecting them to multi-stage isothermal annealing, which includes at least five sequentially increasing isothermal plateaus set near the crystallization initiation temperature. This invention precisely controls the microstructure of the nanocrystals through a multi-stage annealing process. The resulting magnetic core possesses both excellent stress resistance (permeability attenuation rate ≤15% after 10% radial deformation) and extremely high high-frequency permeability (≥20000 at 100 kHz), making it particularly suitable for high-frequency power electronic devices in complex stress environments such as new energy vehicles and 5G communications.

Description

Technical Field

[0001] This invention relates to the field of soft magnetic materials and device manufacturing technology, and in particular to a method for preparing and applying an iron-based nanocrystalline magnetic core. Background Technology

[0002] With the rapid development of 5G / 6G communications, new energy vehicles, aerospace, and other fields, the demand for high-frequency, high-efficiency, and high-reliability power electronic devices is becoming increasingly urgent. Soft magnetic materials, as core materials for devices such as transformers, inductors, and inverters, directly determine the overall performance of these devices. Fe-based nanocrystalline alloys, due to their high saturation magnetic induction intensity (B... s ≥1.2 T), high-frequency permeability (μ), low coercivity (H c With its excellent temperature stability, it has become an ideal soft magnetic material for high-frequency power electronic devices.

[0003] Currently, commercially available Fe-based nanocrystalline alloys (such as Finemet® and Vitroperm®) typically employ annealing processes to control the magnetic properties of their cores. However, in actual production and applications, external stresses are transmitted to the core. For example, during the manufacturing process, the core undergoes curing, coating, and assembly, introducing new stresses that degrade core performance. In applications, under complex mechanical stress environments (such as vehicle vibration, impact, and assembly stress), the magnetic properties of traditional nanocrystalline cores exhibit significant degradation, primarily manifested as decreased permeability and increased iron loss, severely impacting the long-term stability and reliability of devices. This is mainly due to the introduction of external stresses, which cause energy fluctuations and changes in the microstructure within the core material, leading to alterations in core performance and consequently affecting the magnetization process. Therefore, developing a nanocrystalline core fabrication process that possesses both excellent soft magnetic properties and superior resistance to stress effects has become a critical technical challenge urgently needing to be addressed in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing iron-based nanocrystalline magnetic cores and their applications. This invention uses multi-stage annealing to alleviate the phenomenon that the actual temperature of the magnetic core increases significantly due to the concentrated burst of thermal energy during the nucleation process of the nanocrystalline phase. It can effectively control the grain size, crystallization volume fraction and internal stress distribution of the nanocrystals, reduce the magnetostriction coefficient, and enhance the magnetic anisotropy induced by the magnetic field, thereby significantly improving the magnetic performance stability of the magnetic core under mechanical stress.

[0005] This invention is achieved through the following technical solutions:

[0006] This invention protects a method for preparing an iron-based nanocrystalline magnetic core, comprising the following steps: isothermal annealing of an iron-based amorphous magnetic core under a protective atmosphere at no less than five isothermal platforms between 300 ℃ and 580 ℃; after the annealing is completed, the magnetic core is cooled to room temperature to obtain the iron-based nanocrystalline magnetic core.

[0007] This invention precisely controls the microstructure of nanocrystals through a multi-stage annealing process. The resulting magnetic core possesses both excellent stress resistance (permeability attenuation rate ≤15% after 10% radial deformation) and extremely high high-frequency permeability (≥20000 at 100 kHz), making it particularly suitable for high-frequency power electronic devices in complex stress environments such as new energy vehicles and 5G communications.

[0008] Preferably, the isothermal annealing treatment specifically refers to: Level 1: heating to the first isothermal plateau of 330℃~380℃ and holding for 20-60 min; Level 2: then heating to the second isothermal plateau of 410℃~430℃ and holding for 20-60 min; Level 3: heating to the third isothermal plateau of 440℃~460℃ and holding for 20-60 min; Level 4: heating to the fourth isothermal plateau of 470℃~490℃ and holding for 20-60 min; Level 5: heating to the fifth isothermal plateau of 500℃~520℃ and holding for 20-60 min; Level 6: heating to the sixth isothermal plateau of 530℃~550℃ and holding for 20-60 min; Level 7: heating to the seventh isothermal plateau of 560℃~580℃ and holding for 120-160 min. The heating rate of the first or second isothermal platform is 1-10 ℃ / min, and the heating rate of other isothermal platforms is 0.5-1.5 ℃ / min.

[0009] Further preferred, the isothermal annealing treatment specifically refers to: Level 1: heating to the first isothermal plateau of 350 ℃ and holding for 30 min; Level 2: then continuing to heat to the second isothermal plateau of 420 ℃ and holding for 60 min; Level 3: then heating to the third isothermal plateau of 450 ℃ and holding for 30 min; Level 4: then heating to the fourth isothermal plateau of 480 ℃ and holding for 30 min; Level 5: then heating to the fifth isothermal plateau of 510 ℃ and holding for 30 min; Level 6: then heating to the sixth isothermal plateau of 540 ℃ and holding for 30 min; Level 7: then heating to the seventh isothermal plateau of 570 ℃ and holding for 140 min.

[0010] Preferably, the iron-based amorphous magnetic core is Fe. a Si b B c Cu d Nb e M fThe amorphous magnetic core is formed by M being either Mo or V, and a, b, c, d, e, and f being atomic percentages that satisfy the following conditions: 70≤a≤86, 1≤b≤17, 7≤c≤15, 0.5≤d≤1.5, 0≤e≤3, 0≤f≤2, and a+b+c+d+e+f=100.

[0011] Further optimization yields a, b, c, d, e, and f that satisfy: a = 73.5, b = 15.5, c = 7, d = 1, 1.5 ≤ e ≤ 3.0, 0 ≤ f ≤ 1.5, and a + b + c + d + e + f = 100.

[0012] Preferably, the iron-based amorphous magnetic core is prepared by the following steps: weighing the raw materials according to the specified ratio, melting and casting them into alloy ingots in a vacuum induction melting furnace, remelting the alloy ingots under vacuum conditions to prepare amorphous thin strips, and then fabricating the amorphous thin strips into the iron-based amorphous magnetic core. The raw materials used are pure metals or intermediate alloys.

[0013] Further optimization yields amorphous ribbons with a thickness of 10-33 μm. The amorphous ribbons are prepared using a single-roll rapid quenching method at a roll speed of 25-35 m / s (preferably 30 m / s).

[0014] The present invention also protects the iron-based nanocrystalline magnetic core obtained by the preparation method described above, wherein the iron-based nanocrystalline magnetic core has a two-phase structure of amorphous matrix inlaid with α-Fe(Si) nanocrystals.

[0015] Preferably, under no mechanical stress, the effective permeability μ of the iron-based nanocrystalline magnetic core at a frequency of 100 kHz is... e ≥ 20000.

[0016] This invention also protects a power electronic device comprising the aforementioned iron-based nanocrystalline magnetic core. The power electronic device is suitable for high-frequency, high-stress operating environments, including but not limited to new energy vehicle motor drivers, 5G communication power modules, and aerospace power systems.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] 1. The iron-based nanocrystalline magnetic core prepared by this invention exhibits minimal magnetic performance attenuation (≤15%) after being subjected to 10% radial compressive strain, demonstrating excellent stress resistance.

[0019] 2. This invention optimizes the microstructure through multi-stage annealing using a new process. The high-frequency soft magnetic properties (f≥80kHz) of the magnetic core are superior to those obtained by the traditional three-step annealing process, meeting the needs of modern power electronic devices for higher frequency and higher efficiency.

[0020] 3. The preparation process proposed in this invention is controllable and has good compatibility. The multi-stage isothermal annealing process parameters are clear, which makes it easy to implement on industrial continuous production lines. It can also be seamlessly connected with existing integrated transverse magnetic field annealing furnaces, which is convenient for large-scale production and promotion.

[0021] The mechanism of the iron-based nanocrystalline magnetic core proposed in this invention is clear, and the root cause of its performance improvement is well-defined. Its effectiveness stems from the optimization of the microstructure through multi-stage annealing, thereby maintaining the stability of the magnetic domain structure and magnetization process under stress. Attached Figure Description

[0022] Figure 1 The XRD patterns of the quenched thin strips obtained in Examples 1-3 are shown.

[0023] Figure 2 The results show the microstructure and grain statistics of the magnetic core after annealing; among them, Figure 2 'a' represents a multi-stage annealing process. Figure 2 b represents the traditional annealing process.

[0024] Figure 3 This is the actual temperature change curve of the magnetic core during the annealing process; among which, Figure 3 a represents the multi-stage annealing process of Comparative Example 1. Figure 3 b represents the traditional annealing process of Example 1. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are considered to be commercially available materials and reagents that can be obtained through conventional markets and other commercial channels.

[0026] Example 1

[0027] A method for preparing and applying an iron-based nanocrystalline magnetic core includes the following steps:

[0028] (1) Raw materials and smelting: Industrial pure iron, copper, industrial silicon, ferroniobium, and ferroboron are used as raw materials, according to Fe 73.5 Si 15.5 The atomic ratio of B7Cu1Nb3 was smelted in a vacuum induction furnace and cast into ingots at a smelting temperature of 1500 °C~1600 °C and a casting temperature of 1380 °C~1450 °C.

[0029] (2) Strip preparation: After remelting the alloy ingot, an amorphous strip with a thickness of 18 μm was prepared by single-roll rapid quenching at a roll speed of 30 m / s. XRD (e.g.) Figure 1 As shown in the figure, it is confirmed to be completely amorphous.

[0030] (3) Core winding: The amorphous thin strip is wound into a toroidal core with an outer diameter of 40 mm, an inner diameter of 32 mm, and a height of 15 mm.

[0031] (4) Multi-stage isothermal annealing: The toroidal core was placed in a nitrogen atmosphere annealing furnace and heated to the first isothermal platform T1 (350 ℃) at 10 ℃ / min and held for 30 min; then heated to the second isothermal platform T2 (420 ℃) ​​at 3 ℃ / min and held for 60 min; then heated to the third isothermal platform T3 (450 ℃) at 1 ℃ / min and held for 30 min; then heated to the fourth isothermal platform T4 (480 ℃) at 0.5 ℃ / min and held for 30 min; then heated to the fifth isothermal platform T5 (510 ℃) at 0.5 ℃ / min and held for 30 min; then heated to the sixth isothermal platform T6 (540 ℃) at 0.5 ℃ / min and held for 30 min; then heated to the seventh isothermal platform T7 (570 ℃) at 0.5 ℃ / min and held for 140 min. min; Cooling: After the holding time at the seventh isothermal platform T7 is completed, the core was cooled to room temperature with the furnace to obtain an iron-based nanocrystalline magnetic core. The obtained magnetic core was then subjected to performance testing.

[0032] Example 2

[0033] A method for preparing an iron-based nanocrystalline magnetic core includes the following steps:

[0034] (1) Raw materials and smelting: Industrial pure iron, copper, industrial silicon, ferroniobium, and ferroboron are used as raw materials, according to Fe 73.5 Si 15.5 B7Cu1Nb 1.5 Mo 1.5 The atomic ratio of the ingredients is used to melt the raw materials into ingots in a vacuum induction furnace.

[0035] (2) Strip preparation: After remelting the alloy ingot, an amorphous strip with a thickness of 18 μm was prepared by single-roll rapid quenching at a roll speed of 30 m / s. XRD (e.g.) Figure 1 As shown in the figure, it is confirmed to be completely amorphous.

[0036] (3) Core winding: The amorphous thin strip is wound into a toroidal core with an outer diameter of 40 mm, an inner diameter of 32 mm, and a height of 15 mm.

[0037] (4) Multi-stage isothermal annealing: The toroidal core was placed in a nitrogen atmosphere annealing furnace and heated to the first isothermal platform T1 (350 ℃) at 10 ℃ / min and held for 30 min; then heated to the second isothermal platform T2 (420 ℃) ​​at 3 ℃ / min and held for 60 min; then heated to the third isothermal platform T3 (450 ℃) at 1 ℃ / min and held for 30 min; then heated to the fourth isothermal platform T4 (480 ℃) at 0.5 ℃ / min and held for 30 min; then heated to the fifth isothermal platform T5 (510 ℃) at 0.5 ℃ / min and held for 30 min; then heated to the sixth isothermal platform T6 (540 ℃) at 0.5 ℃ / min and held for 30 min; then heated to the seventh isothermal platform T7 (570 ℃) at 0.5 ℃ / min and held for 140 min. min; Cooling: After the T7 platform heat preservation was completed, the furnace was cooled to room temperature to obtain an iron-based nanocrystalline magnetic core. The obtained magnetic core was then subjected to performance testing.

[0038] Example 3

[0039] A method for preparing and applying an iron-based nanocrystalline magnetic core includes the following steps:

[0040] (1) Raw materials and smelting: Industrial pure iron, copper, industrial silicon, ferroniobium, and ferroboron are used as raw materials, according to Fe 73.5 Si 15.5 B7Cu1Nb 1.5 V 1.5 The atomic ratio of the ingredients is used to melt the raw materials into ingots in a vacuum induction furnace.

[0041] (2) Strip preparation: After remelting the alloy ingot, an amorphous strip with a thickness of 18 μm was prepared by single-roll rapid quenching at a roll speed of 30 m / s. XRD (e.g.) Figure 1 As shown in the figure, it is confirmed to be completely amorphous.

[0042] (3) Core winding: The amorphous thin strip is wound into a toroidal core with an outer diameter of 40 mm, an inner diameter of 32 mm, and a height of 15 mm.

[0043] (4) Multi-stage isothermal annealing: The toroidal core was placed in a nitrogen atmosphere annealing furnace and heated to the first isothermal platform T1 (350 ℃) at 10 ℃ / min and held for 30 min; then heated to the second isothermal platform T2 (420 ℃) ​​at 3 ℃ / min and held for 60 min; then heated to the third isothermal platform T3 (450 ℃) at 1 ℃ / min and held for 30 min; then heated to the fourth isothermal platform T4 (480 ℃) at 0.5 ℃ / min and held for 30 min; then heated to the fifth isothermal platform T5 (510 ℃) at 0.5 ℃ / min and held for 30 min; then heated to the sixth isothermal platform T6 (540 ℃) at 0.5 ℃ / min and held for 30 min; then heated to the seventh isothermal platform T7 (570 ℃) at 0.5 ℃ / min and held for 140 min. min; Cooling: After the T7 platform heat preservation was completed, the furnace was cooled to room temperature to obtain an iron-based nanocrystalline magnetic core. The obtained magnetic core was then subjected to performance testing.

[0044] Comparative Example 1

[0045] Similar to Example 1, except that step (4) adopts a three-step annealing process: the toroidal magnetic core is placed in a nitrogen atmosphere annealing furnace, heated to the first-level isothermal platform T1 (420 ℃) ​​at 10 ℃ / min and held for 60 min; then the temperature is increased to 480 ℃ at 1 ℃ / min and held for 60 min; then the temperature is increased to 570 ℃ at 0.5 ℃ / min and held for 140 min. After the holding period, the core is cooled to obtain a conventional magnetic core.

[0046] Comparative Example 2

[0047] The composition is the same as in Example 2, except that step (4) adopts a three-step annealing process: the toroidal magnetic core is placed in a nitrogen atmosphere annealing furnace, heated to the first-level isothermal platform T1 (420 ℃) ​​at 10 ℃ / min and held for 60 min; then the temperature is increased to 480 ℃ at 1 ℃ / min and held for 60 min; then the temperature is increased to 570 ℃ at 0.5 ℃ / min and held for 140 min. After the holding period, the core is cooled to obtain a conventional magnetic core.

[0048] Comparative Example 3

[0049] The composition is the same as in Example 3, except that step (4) adopts a three-step annealing process: the magnetic core is placed in a nitrogen atmosphere annealing furnace, heated to the first-level isothermal platform T1 (420 ℃) ​​at 10 ℃ / min and held for 60 min; then the temperature is increased to 480 ℃ at 1 ℃ / min and held for 60 min; then the temperature is increased to 570 ℃ at 0.5 ℃ / min and held for 140 min. After the holding period, the core is cooled to obtain a conventional magnetic core.

[0050] Figure 1 It can be seen that the three alloy strips prepared are all amorphous structures, and the XRD results show that the peaks are diffuse between 40° and 50°. Figure 2 These are the TEM results and grain statistics for Example 1 and Comparative Example 1. (By...) Figure 2 The results showed that the grain size after multi-stage annealing was slightly smaller than that after traditional three-step annealing. Furthermore, the actual temperature rise curves of the magnetic cores showed... Figure 3 It can be clearly seen that Figure 3 The second platform in Figure a clearly shows a temperature surge in the actual core temperature. This surge occurs because a large amount of heat is released during the core nucleation and growth stage, causing the actual core temperature to exceed the set temperature. This provides additional energy for grain growth, leading to larger grains and increased magnetocrystalline anisotropy, which affects the core's stress sensitivity. In contrast, the actual temperature rise curve of the core after multi-stage annealing is shown in Figure a. Figure 3 As shown in b, no temperature surge was observed between the T4 and T6 platforms, and the actual temperature basically matched the set temperature. The multi-stage annealing process allows the magnetic core to release heat slowly during the grain nucleation and growth stage, effectively avoiding temperature differences caused by temperature surge.

[0051] Tables 1 and 2 list the experimental test results of Comparative Examples 1-3 and Examples 1-3. The comparison reveals that the magnetic core prepared by the multi-stage isothermal annealing process provided by this invention exhibits optimal high-frequency permeability under stress-free conditions. More importantly, after undergoing significant mechanical stress, its magnetic performance attenuation is far lower than that of traditional processes, demonstrating superior stress resistance.

[0052] Table 1 shows the permeability test results of the magnetic core before and after deformation after traditional three-step annealing process:

[0053] Table 2 shows the magnetic permeability test results of the magnetic core before and after radial deformation following the multi-stage isothermal annealing process:

[0054] The proposed method for preparing Fe-based nanocrystalline magnetic cores optimizes performance primarily by leveraging the multi-stage annealing process designed in this invention. This multi-stage annealing allows for the gradual release of rapid quenching stress in the core. At temperatures exceeding 420°C, each isothermal plateau, in addition to stress release, also moderates energy release during grain nucleation and growth, resulting in a significant improvement in stress resistance. This optimized core retains its stress resistance even after subsequent magnetic field annealing and other post-processing steps. The preparation process is clearly defined and compatible with existing nanocrystalline magnetic core production lines, requiring only the addition of multi-stage isothermal annealing sections before the existing transverse magnetic field annealing furnace. The prepared magnetic cores can be widely applied in fields demanding extremely high high-frequency efficiency and mechanical reliability, such as new energy vehicle drive motors, on-board chargers (OBCs), 5G communication base station power supplies, photovoltaic inverters, and aerospace power systems.

[0055] The above description of the embodiments is only for the purpose of helping to understand the technical solution and core idea of ​​the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing an iron-based nanocrystalline magnetic core, characterized in that, The process includes the following steps: placing the iron-based amorphous magnetic core in a vacuum atmosphere annealing furnace under a protective atmosphere, and performing isothermal annealing treatment with no less than five isothermal platforms between 300 ℃ and 580 ℃. After the annealing treatment is completed, the magnetic core is cooled to room temperature to obtain the iron-based nanocrystalline magnetic core.

2. The preparation method according to claim 1, characterized in that, The isothermal annealing process specifically refers to: Level 1: heating to the first isothermal plateau of 330 ℃~380 ℃ and holding for 20-60 min; Level 2: Then continue to raise the temperature to the second isothermal plateau of 410 ℃~430 ℃ and hold for 20-60 min; Level 3: Raise the temperature to the third isothermal plateau of 440 ℃~460 ℃ and hold for 20-60 min; Level 4: Raise the temperature to the fourth isothermal plateau of 470 ℃~490 ℃ and hold for 20-60 min; Level 5: Raise the temperature to the fifth isothermal plateau of 500℃~520℃ and hold for 20-60 minutes; Level 6: Reheat to the sixth isothermal plateau of 530 ℃~550 ℃ and hold for 20-60 min; Level 7: Reheat to the seventh isothermal plateau of 560 ℃~580 ℃ and hold for 120-160 min. The heating rate of the first or second isothermal plateau is 1-10 ℃ / min, and the heating rate of other isothermal plateaus is 0.5-1.5 ℃ / min.

3. The preparation method according to claim 2, characterized in that, The isothermal annealing process specifically refers to: Level 1: heating to the first isothermal plateau of 350 ℃ and holding for 30 min; Level 2: then continuing to heat to the second isothermal plateau of 420 ℃ and holding for 60 min; Level 3: Reheat to the third isothermal plateau of 450 ℃ and hold for 30 min; Level 4: Raise the temperature to the fourth isothermal plateau of 480 ℃ and hold for 30 min; Level 5: Reheat to the fifth isothermal plateau of 510 ℃ and hold for 30 min; Level 6: Reheat to the sixth isothermal plateau of 540 ℃ and hold for 30 min; Level 7: Reheat to the seventh isothermal plateau of 570 ℃ and hold for 140 min.

4. The preparation method according to any one of claims 1-3, characterized in that, The iron-based amorphous magnetic core is Fe a Si b B c Cu d Nb e M f The amorphous magnetic core is formed by M being either Mo or V, and a, b, c, d, e, and f being atomic percentages that satisfy the following conditions: 70≤a≤86, 1≤b≤17, 7≤c≤15, 0.5≤d≤1.5, 0≤e≤3, 0≤f≤2, and a+b+c+d+e+f=100.

5. The preparation method according to claim 4, characterized in that, a, b, c, d, e, f satisfy: a=73.5, b=15.5, c=7, d=1, 1.5≤e≤3.0, 0≤f≤1.5, a+b+c+d+e+f=100.

6. The preparation method according to claim 4, characterized in that, The iron-based amorphous magnetic core is prepared by the following steps: weighing the raw materials according to the proportion, melting and casting them into alloy ingots in a vacuum induction melting furnace, remelting the alloy ingots under vacuum conditions to prepare amorphous thin strips, and then making the amorphous thin strips into the iron-based amorphous magnetic core.

7. The preparation method according to claim 6, characterized in that, The thickness of the amorphous ribbon is 10-33 μm.

8. The iron-based nanocrystalline magnetic core obtained by the preparation method according to any one of claims 1-7, characterized in that, The iron-based nanocrystalline magnetic core has a two-phase structure with an amorphous matrix inlaid with α-Fe(Si) nanocrystals.

9. A power electronic device, characterized in that, The invention comprises an iron-based nanocrystalline magnetic core obtained by any one of the preparation methods of claims 1-7 or an iron-based nanocrystalline magnetic core as described in claim 8. The power electronic device is suitable for high-frequency and high-stress working environments, including but not limited to new energy vehicle motor drivers, 5G communication power modules, and aerospace power systems.

Images