Current pre-annealing method of iron-based soft magnetic alloy and iron-based soft magnetic alloy strip

Abstract

This application relates to a current-based pre-annealing method for iron-based soft magnetic alloys and iron-based soft magnetic alloy strips. The method includes: applying a direct current to the iron-based soft magnetic alloy, causing the direct current to generate Joule heating within the iron-based soft magnetic alloy; the Joule heating raises the temperature of the iron-based soft magnetic alloy to below its glass transition temperature or below 300°C for pre-annealing; holding the iron-based soft magnetic alloy at the pre-annealing temperature in an oxygen-containing atmosphere for 3 hours–2 days to generate an oxide layer on the surface of the iron-based soft magnetic alloy; the thickness of the oxide layer is lower than the oxide layer thickness generated under the same oxidation conditions in a control iron-based soft magnetic alloy without direct current treatment, and no SiO2 diffraction peaks appear in the X-ray diffraction pattern of the oxidized iron-based soft magnetic alloy. This method replaces the traditional radiation furnace with "DC Joule self-heating," solving the technical problem of how to improve the oxidation resistance of iron-based soft magnetic alloys.

Description

Technical Field

[0001] This application belongs to the field of heat treatment technology for soft magnetic alloys, and particularly relates to a current pre-annealing method for iron-based soft magnetic alloys and iron-based soft magnetic alloy strips. Background Technology

[0002] Iron-based soft magnetic alloys are widely used in motors, transformers, and inductors due to their high permeability and low coercivity. Traditional annealing requires a vacuum or inert atmosphere to suppress surface oxidation, resulting in complex equipment, high energy consumption, and long cycle times. If annealed directly in air, a loose, SiO2-rich oxide layer quickly forms on the alloy surface, reducing magnetic properties and increasing the cost of subsequent cleaning and coating. Existing technologies attempt to improve oxidation resistance by adding noble metals such as Cr and Al, but this introduces new problems such as compositional drift, reduced magnetic induction, and increased costs. Summary of the Invention

[0003] This application provides a current pre-annealing method for iron-based soft magnetic alloys and iron-based soft magnetic alloy strips to solve the following technical problem: how to improve the oxidation resistance of iron-based soft magnetic alloys.

[0004] In a first aspect, embodiments of this application provide a current pre-annealing method for iron-based soft magnetic alloys, the method comprising: A direct current is applied to the iron-based soft magnetic alloy for pre-annealing. The direct current generates Joule heat inside the iron-based soft magnetic alloy. Within 30s–10min, the Joule heat raises the temperature of the iron-based soft magnetic alloy to below the glass transition temperature of the iron-based soft magnetic alloy or below 300°C. The iron-based soft magnetic alloy after pre-annealing is placed in an oxygen-containing atmosphere and held without current for 3 hours to 2 days at a pre-annealing temperature below the glass transition temperature or below 300°C, so that an oxide layer is formed on the surface of the iron-based soft magnetic alloy. The thickness of the oxide layer is lower than that of the oxide layer generated under the same oxidation conditions in the comparative iron-based soft magnetic alloy without DC current treatment, and the iron-based soft magnetic alloy does not show SiO2 diffraction peaks in the X-ray diffraction pattern after oxidation.

[0005] Optionally, the iron-based soft magnetic alloy is an Fe-Si-B amorphous alloy, and the chemical composition of the Fe-Si-B amorphous alloy, in atomic percentage, is 70≤Fe≤80, 7≤Si≤10, and 10≤B≤14.

[0006] Optionally, the iron-based soft magnetic alloy is an Fe-Si-BC amorphous alloy, and the chemical composition of the Fe-Si-BC amorphous alloy, in atomic percentage, is 75≤Fe≤81, 3≤Si≤5, 13≤B≤19 and 1≤Nb≤2.6.

[0007] Optionally, the iron-based soft magnetic alloy is an Fe-Ni-B-(Si,P,C) amorphous alloy, and the chemical composition of the Fe-Ni-B-(Si,P,C) amorphous alloy, in atomic percentage, is 71≤Fe≤74, 6≤Ni≤10, 10≤B≤15 and 8≤(Si+P+C)≤12.

[0008] Optionally, the iron-based soft magnetic alloy is a Fe-Si-B-Cu-Nb nanocrystalline alloy, wherein the chemical composition of the Fe-Si-B-Cu-Nb nanocrystalline alloy, in atomic percentage, is 73≤Fe≤74, 13≤Si≤14, 8.5≤B≤9.5, 2.8≤Nb≤3.2 and 0.8≤Cu≤1.2.

[0009] Optionally, the iron-based soft magnetic alloy is Fe-Si silicon steel, and the chemical composition of the Fe-Si silicon steel, by weight percentage, is 93.5 ≤ Fe ≤ 99 and 1 ≤ Si ≤ 6.5.

[0010] Optionally, the DC current is applied by passing a continuous DC current along the transverse or longitudinal direction of the iron-based soft magnetic alloy, and the current density of the continuous DC current is 10 A / mm². 2 –40A / mm 2 .

[0011] Optionally, the oxygen-containing atmosphere is an air atmosphere, and the oxygen partial pressure of the air atmosphere is 0.21 bar.

[0012] Secondly, embodiments of this application provide an iron-based soft magnetic alloy strip, which is obtained by a current pre-annealing method for an iron-based soft magnetic alloy as described in any one of the first aspects; The thickness of the iron-based soft magnetic alloy strip is 30μm–40μm. The thickness of the surface oxide layer of the iron-based soft magnetic alloy strip after oxidation in air at 300℃ for 3h is ≤200nm. Furthermore, no SiO2 diffraction peaks appear in the X-ray diffraction pattern of the iron-based soft magnetic alloy strip after oxidation.

[0013] Optionally, the iron-based soft magnetic alloy strip is an Fe-Si-B amorphous strip, wherein the chemical composition of the Fe-Si-B amorphous strip is 70≤Fe≤80, 7≤Si≤10 and 10≤B≤14 in atomic percentage, and the effective permeability of the Fe-Si-B amorphous strip at 1kHz is ≥20000.

[0014] The technical solutions provided in this application have the following advantages compared with the prior art: Because iron-based soft magnetic alloys are prone to oxidation and weight gain, as well as surface insulation film deterioration, in low-temperature service environments (≤300℃), the stacking factor decreases and iron loss increases. Traditional pre-annealing (furnace radiation heating) does not provide sufficient relaxation, and during subsequent oxidation, surface Si and B rapidly diffuse outward, forming a loose Fe2O3 / SiO2 mixed oxide layer, resulting in insufficient oxidation resistance.

[0015] First, in the embodiments of this application, the bulk Joule heating generated by the DC current can instantly raise the temperature to below Tg within 30s–10min, with a cooling rate as high as 10²–10³ K / s. This "flash heating-self-quenching" causes short-term structural relaxation in the alloy, reducing the free volume and making it more densely packed at the atomic short-range, thus reducing the diffusion coefficients of surface Si and B by 1–2 orders of magnitude. During subsequent oxidation without current, the outward migration of Si and B is suppressed, and the oxide layer growth rate decreases.

[0016] Secondly, due to the limited supply of Si, the oxide layer is mainly Fe2O3 / Fe3O4, and there is almost no crystalline SiO2 with poor insulation and easy cracking (no SiO2 peak in XRD); the layer thickness can be reduced compared with the traditional furnace annealing control sample, while maintaining a high resistance and reducing eddy current loss.

[0017] The entire current pre-annealing and oxidation stage is kept below 300°C to avoid nanocrystal precipitation and ensure that the strip maintains high Bs and low Hc; and no additional protective atmosphere is required, so the production line can be directly connected to the uncoiling-insulation coating process, saving energy and reducing costs.

[0018] In summary, the embodiments of this application obtain a thinner, SiO2-free, and self-limiting oxide layer on the alloy surface through a two-step method of "first current flash relaxation, then low-temperature current-free oxidation", thereby significantly improving the oxidation resistance and magnetic performance stability of iron-based soft magnetic alloys in low-temperature service environments. Attached Figure Description

[0019] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0021] Figure 1 This is a comparison of the XRD curves of iron-based soft magnetic alloy strips without and after current pre-annealing in Example 1 of this application; Figure 2This is a comparison SEM image of iron-based soft magnetic alloy strips from Embodiment 1 of this application, showing the strips before and after current pre-annealing treatment. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0024] In a first aspect, embodiments of this application provide a current pre-annealing method for iron-based soft magnetic alloys, the method comprising: S1. Apply a direct current to the iron-based soft magnetic alloy for pre-annealing. The direct current generates Joule heat inside the iron-based soft magnetic alloy. Within 30s–10min, the Joule heat raises the temperature of the iron-based soft magnetic alloy to below the glass transition temperature of the iron-based soft magnetic alloy or below 300°C. S2. The iron-based soft magnetic alloy after pre-annealing is placed in an oxygen-containing atmosphere and kept at a pre-annealing temperature below the glass transition temperature or below 300°C without current for 3h–2d to generate an oxide layer on the surface of the iron-based soft magnetic alloy. The thickness of the oxide layer is lower than that of the oxide layer generated under the same oxidation conditions in the comparative iron-based soft magnetic alloy without DC current treatment, and the iron-based soft magnetic alloy does not show SiO2 diffraction peaks in the X-ray diffraction pattern after oxidation.

[0025] The direct current generates Joule heating inside the iron-based soft magnetic alloy. Joule heating causes the iron-based soft magnetic alloy to heat up, so the surface temperature of the iron-based soft magnetic alloy is instantly higher than the core temperature. As a result, the oxygen atom diffusion coefficient on the surface of the iron-based soft magnetic alloy is "frozen" before it can increase sufficiently. Thus, the diffusion depth of oxygen into the interior of the iron-based soft magnetic alloy is limited to ≤200nm, and the oxide layer thickness is suppressed.

[0026] With an extremely short heating time of 30s–10min, the lattice defects and vacancies on the surface of the iron-based soft magnetic alloy do not have enough time to fully relax. As a result, the outward diffusion flux of Fe, Si, and B atoms is lower than that of conventional furnace annealing. Consequently, SiO2 crystal nuclei cannot be formed, and therefore no SiO2 diffraction peaks appear in the X-ray diffraction pattern.

[0027] When the pre-annealing temperature is lower than the glass transition temperature of the iron-based soft magnetic alloy or lower than 300°C, the amorphous structure of the iron-based soft magnetic alloy does not crystallize, thus maintaining the high permeability of the iron-based soft magnetic alloy and preventing the soft magnetic properties of the iron-based soft magnetic alloy from deteriorating. At the same time, the low temperature reduces the solubility of oxygen in the iron-based soft magnetic alloy, thereby exponentially decreasing the growth rate of the oxide layer and further reducing the thickness of the oxide layer. Glass transition temperature: The measured value for Fe-Si-B amorphous alloys is approximately 510℃, therefore the pre-annealing temperature is <510℃; the measured value for Fe-Si-BC amorphous alloys is approximately 520℃, therefore the pre-annealing temperature is <520℃; the measured value for Fe-Ni-B-(Si,P,C) amorphous alloys is approximately 530℃, therefore the pre-annealing temperature is <530℃; the measured value for Fe-Si-B-Cu-Nb nanocrystalline alloys is approximately 540℃, therefore the pre-annealing temperature is <540℃; there is no glass transition temperature for Fe-Si silicon steel, therefore the pre-annealing temperature is <300℃.

[0028] A 3-hour–2-day holding time provides a sufficiently long oxidation period, allowing a continuous and dense Fe2O3 / Fe3O4 film to form on the surface of the iron-based soft magnetic alloy. This oxide film then acts as a diffusion barrier for subsequent oxygen diffusion inward, thereby reducing the rate of oxide layer thickness growth by an order of magnitude during subsequent service.

[0029] The oxide layer thickness is lower than that of the comparative iron-based soft magnetic alloy without DC current treatment. The DC current pre-annealing method makes the oxide layer thickness on the surface of the iron-based soft magnetic alloy ≤200nm. Thus, the surface oxide layer thickness of the iron-based soft magnetic alloy after oxidation in air atmosphere at 300℃ for 3h is ≤200nm. Consequently, the high-frequency eddy current loss of the iron-based soft magnetic alloy does not increase, and the efficiency of the iron-based soft magnetic alloy device does not decrease.

[0030] In some embodiments, the iron-based soft magnetic alloy is an Fe-Si-B amorphous alloy, wherein the chemical composition of the Fe-Si-B amorphous alloy, in atomic percentage, is 70≤Fe≤80, 7≤Si≤10, and 10≤B≤14.

[0031] With an Fe atom percentage of 70–80%, Fe atoms provide a high saturation magnetic induction intensity Bs, resulting in an effective permeability of ≥20000 at 1kHz for the iron-based soft magnetic alloy strip. Consequently, iron-based soft magnetic alloy devices can withstand higher magnetic flux densities, thus allowing for a reduction in device size.

[0032] With a Si atomic percentage of 7–10, Si atoms increase the resistivity ρ of iron-based soft magnetic alloys, thereby reducing eddy current losses and consequently decreasing high-frequency losses Pcv, thus reducing the temperature rise of iron-based soft magnetic alloys.

[0033] With a boron atom percentage of 10–14, boron atoms enhance the amorphous formation capability of iron-based soft magnetic alloys. As a result, iron-based soft magnetic alloys remain amorphous even during rapid cooling of 30s–10min, and consequently, the permeability of iron-based soft magnetic alloys does not decrease, thus preserving the soft magnetic properties of iron-based soft magnetic alloys.

[0034] Fe, by atomic percentage: 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80; Si, by atomic percentage: 7, 7.5, 8, 8.5, 9, 9.5, 10; B, by atomic percentage: 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14.

[0035] In some embodiments, the iron-based soft magnetic alloy is an Fe-Si-BC amorphous alloy, wherein the chemical composition of the Fe-Si-BC amorphous alloy, in atomic percentage, is 75≤Fe≤81, 3≤Si≤5, 13≤B≤19, and 1≤Nb≤2.6.

[0036] The percentage of Nb atoms is 1–2.6. Nb atoms form Nb-B clusters with B atoms, which makes the amorphous structure of the iron-based soft magnetic alloy more compact. This leads to a reduction in the free volume of the iron-based soft magnetic alloy, which in turn reduces the oxygen diffusion coefficient by an order of magnitude, resulting in an oxide layer thickness of ≤200nm.

[0037] The trace solid solution of C atoms occupies the interstitial space of the octahedron in the iron-based soft magnetic alloy, thereby increasing the lattice distortion of the iron-based soft magnetic alloy. Consequently, the solubility of oxygen in the iron-based soft magnetic alloy decreases, thus increasing the SiO2 nucleation energy. As a result, no SiO2 diffraction peaks appear in the X-ray diffraction pattern.

[0038] Fe, by atomic percentage: 75, 76, 77, 78, 79, 80, 81; Si, by atomic percentage: 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5; B, by atomic percentage: 13, 14, 15, 16, 17, 18, 19; Nb, by atomic percentage: 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6.

[0039] In some embodiments, the iron-based soft magnetic alloy is an Fe-Ni-B-(Si,P,C) amorphous alloy, wherein the chemical composition of the Fe-Ni-B-(Si,P,C) amorphous alloy, in atomic percentage, is 71≤Fe≤74, 6≤Ni≤10, 10≤B≤15, and 8≤(Si+P+C)≤12.

[0040] With a Ni atomic percentage of 6–10, Ni atoms increase the resistivity ρ of iron-based soft magnetic alloys, thereby reducing high-frequency eddy current losses and ensuring that the effective permeability of the iron-based soft magnetic alloy strip remains ≥20000 at 1kHz.

[0041] P atoms and C atoms coexist, forming a phosphate-carbonate composite film on the surface of the iron-based soft magnetic alloy. This composite film, together with the Fe2O3 film, synergistically blocks oxygen diffusion inward, resulting in an oxide layer thickness of ≤200nm.

[0042] Fe, by atomic percentage: 71, 71.5, 72, 72.5, 73, 73.5, 74; Ni, by atomic percentage: 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10; B, by atomic percentage: 10, 11, 12, 13, 14, 15; Si+P+C, by atomic percentage: 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12.

[0043] In some embodiments, the iron-based soft magnetic alloy is a Fe-Si-B-Cu-Nb nanocrystalline alloy, wherein the chemical composition of the Fe-Si-B-Cu-Nb nanocrystalline alloy, in atomic percentage, is 73≤Fe≤74, 13≤Si≤14, 8.5≤B≤9.5, 2.8≤Nb≤3.2 and 0.8≤Cu≤1.2.

[0044] With a Cu atomic percentage of 0.8–1.2%, Cu atoms form Cu clusters in the iron-based soft magnetic alloy, which then become heterogeneous nucleation sites for α-FeSi nanocrystals. Subsequently, after current pre-annealing, uniform nanocrystals of 10–20 nm are formed inside the iron-based soft magnetic alloy, thereby averaging the magnetocrystalline anisotropy of the iron-based soft magnetic alloy, resulting in an effective magnetic permeability of ≥20000.

[0045] With a Nb atomic percentage of 2.8–3.2, Nb atoms inhibit the growth of α-FeSi grains, thus keeping the grain size ≤20nm. Consequently, the high-frequency loss of the iron-based soft magnetic alloy does not increase, and low loss is maintained even when the oxide layer thickness is ≤200nm.

[0046] Fe, by atomic percentage: 73, 73.2, 73.4, 73.6, 73.8, 74; Si, by atomic percentage: 13, 13.2, 13.4, 13.6, 13.8, 14; B, by atomic percentage: 8.5, 8.6, 8.7, 8.8, 8.9, 9, 9.1, 9.2, 9.3, 9.4, 9.5; Nb, by atomic percentage: 2.8, 2.9, 3, 3.1, 3.2; Cu, by atomic percentage: 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2.

[0047] In some embodiments, the iron-based soft magnetic alloy is Fe-Si silicon steel, wherein the chemical composition of the Fe-Si silicon steel is 93.5 ≤ Fe ≤ 99 and 1 ≤ Si ≤ 6.5 by weight percentage.

[0048] With a Si weight percentage of 1–6.5, Si atoms increase the resistivity ρ of iron-based soft magnetic alloys, thereby reducing eddy current losses and resulting in an effective permeability of ≥20000 for iron-based soft magnetic alloy strips at 1 kHz.

[0049] The current pre-annealing method is carried out below 300℃. Fe-Si silicon steel does not precipitate the ordered phase Fe3Si, so the permeability of the iron-based soft magnetic alloy does not decrease. As a result, the iron-based soft magnetic alloy still maintains low iron loss when the oxide layer thickness is ≤200nm.

[0050] Fe, by atomic percentage, is: 93.5, 94, 94.5, 95, 95.5, 96, 96.5, 97, 97.5, 98, 98.5, 99; Si, by atomic percentage, is: 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5.

[0051] In some embodiments, the direct current is applied by passing a continuous direct current along the transverse or longitudinal direction of the iron-based soft magnetic alloy, wherein the current density of the continuous direct current is 10 A / mm². 2 –40A / mm 2 .

[0052] With a current density of 10–40 A / mm² and a Joule heat power density of Q=ρj², the surface temperature rise rate of the iron-based soft magnetic alloy is ≥10℃ / s. Consequently, the pre-annealing temperature below 300℃ can be reached within 30s–10min, thus preventing grain growth in the iron-based soft magnetic alloy and resulting in an oxide layer thickness ≤200nm.

[0053] When current is introduced laterally or longitudinally along the iron-based soft magnetic alloy, the current path length is maximized, resulting in the lowest voltage drop. Consequently, industrial power supplies can be used directly without increasing production costs.

[0054] Current densities include, but are not limited to, 10, 12, 15, 18, 20, 22, 25, 28, 30, 32, 35, 38, and 40 A / mm². 2 .

[0055] In some embodiments, the oxygen-containing atmosphere is an air atmosphere with an oxygen partial pressure of 0.21 bar.

[0056] With an oxygen partial pressure of 0.21 bar and an oxidation potential of μO = μO0 + RTln(0.21), the amount of oxygen adsorbed on the surface of the iron-based soft magnetic alloy is sufficient to form an Fe2O3 film. The Fe2O3 film then becomes a diffusion barrier, which reduces the subsequent rate of oxide layer thickness growth, resulting in an oxide layer thickness ≤ 200 nm.

[0057] Using an air atmosphere eliminates the need for a vacuum or inert gas, thus reducing production costs by ≥50% compared to vacuum annealing. Consequently, the current pre-annealing method for iron-based soft magnetic alloys can be used for continuous online production, thereby improving production efficiency.

[0058] Secondly, embodiments of this application provide an iron-based soft magnetic alloy strip, which is obtained by a current pre-annealing method for an iron-based soft magnetic alloy as described in any one of the first aspects; The thickness of the iron-based soft magnetic alloy strip is 30μm–40μm. The thickness of the surface oxide layer of the iron-based soft magnetic alloy strip after oxidation in air at 300℃ for 3h is ≤200nm. Furthermore, no SiO2 diffraction peaks appear in the X-ray diffraction pattern of the iron-based soft magnetic alloy strip after oxidation.

[0059] With a thickness of 30–40 μm, the eddy current skin depth of the iron-based soft magnetic alloy strip is δ≈30 μm@1 kHz, thus the entire iron-based soft magnetic alloy strip participates in magnetization, resulting in an effective permeability ≥20000, thereby reducing the size of the device.

[0060] The surface oxide layer thickness is ≤200nm, and the resistivity of the oxide layer is much higher than that of the iron-based soft magnetic alloy matrix. As a result, the eddy current path is not cut off by the oxide layer, and the high-frequency loss of the iron-based soft magnetic alloy strip does not increase, thus the temperature rise is ≤30℃.

[0061] The X-ray diffraction pattern does not show SiO2 diffraction peaks. Since SiO2 is a high-resistivity brittle phase, the bending fatigue life of the iron-based soft magnetic alloy strip is ≥1000 cycles. Furthermore, the iron-based soft magnetic alloy strip can be wound into a toroidal magnetic core, thereby improving the reliability of the device.

[0062] Thicknesses include, but are not limited to, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, and 40 μm.

[0063] In some embodiments, the iron-based soft magnetic alloy strip is an Fe-Si-B amorphous strip, wherein the chemical composition of the Fe-Si-B amorphous strip is 70≤Fe≤80, 7≤Si≤10 and 10≤B≤14 in atomic percentage, and the effective permeability of the Fe-Si-B amorphous strip at 1kHz is ≥20000.

[0064] With a chemical composition of 70–80 at.% Fe, 7–10 at.% Si, and 10–14 at.% B, and an amorphous forming capability of ≥80%, the iron-based soft magnetic alloy strip remains amorphous after current pre-annealing, resulting in zero anisotropy. Consequently, the effective permeability at 1 kHz is ≥20000, and the magnetization power consumption of the iron-based soft magnetic alloy strip is ≤0.2 W / kg, thus saving energy in the device.

[0065] Fe, by atomic percentage: 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80; Si, by atomic percentage: 7, 7.5, 8, 8.5, 9, 9.5, 10; B, by atomic percentage: 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14.

[0066] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0067] I. Implementation Examples Example 1 A method for current pre-annealing of iron-based soft magnetic alloys, the method comprising: A continuous direct current is applied to an Fe-Si-B amorphous ribbon with a composition of Fe78Si9B13, and the current density of the continuous direct current is 25 A / mm². 2 This causes the continuous DC current to generate Joule heating inside the Fe-Si-B amorphous ribbon. The Joule heating raises the Fe-Si-B amorphous ribbon to a pre-annealing temperature of 280°C within 120 seconds. The pre-annealing temperature is lower than the glass transition temperature of the Fe-Si-B amorphous ribbon, which is 510°C. Fe-Si-B amorphous ribbon was kept at 280℃ for 24 hours in air atmosphere to generate an oxide layer on the surface of Fe-Si-B amorphous ribbon. The thickness of the oxide layer is 180 nm, which is lower than the thickness of the oxide layer of the Fe-Si-B amorphous ribbon generated under the same oxidation conditions without continuous DC current treatment (420 nm). Furthermore, no SiO2 diffraction peak appears in the X-ray diffraction pattern of the Fe-Si-B amorphous ribbon after oxidation.

[0068] Example 2 A method for current pre-annealing of iron-based soft magnetic alloys, the method comprising: A continuous direct current is applied to an Fe-Si-BC amorphous ribbon with a composition of Fe76Si4B16Nb2. The current density of the continuous direct current is 20A / mm2, so that the continuous direct current generates Joule heating inside the Fe-Si-BC amorphous ribbon. The Joule heating process raises the Fe-Si-BC amorphous ribbon to a pre-annealing temperature of 290°C within 90 seconds. The pre-annealing temperature is lower than the glass transition temperature of the Fe-Si-BC amorphous ribbon, which is 520°C. Fe-Si-BC amorphous ribbon was kept at 290℃ for 12 hours in air atmosphere to generate an oxide layer on the surface of the Fe-Si-BC amorphous ribbon. The thickness of the oxide layer is 160 nm, which is lower than the thickness of the oxide layer of the Fe-Si-BC amorphous ribbon generated under the same oxidation conditions without continuous DC current treatment (400 nm). Furthermore, no SiO2 diffraction peak appears in the X-ray diffraction pattern of the Fe-Si-BC amorphous ribbon after oxidation.

[0069] Example 3 A method for current pre-annealing of iron-based soft magnetic alloys, the method comprising: A continuous DC current with a current density of 18 A / mm² is applied to a Fe-Ni-B-(Si,P,C) amorphous ribbon with a composition of Fe73Ni8B12Si4P2C2, causing the continuous DC current to generate Joule heating inside the Fe-Ni-B-(Si,P,C) amorphous ribbon. The Joule heating process raises the temperature of the Fe-Ni-B-(Si,P,C) amorphous ribbon to a pre-annealing temperature of 285°C within 150 seconds. The pre-annealing temperature is lower than the glass transition temperature of the Fe-Ni-B-(Si,P,C) amorphous ribbon, which is 530°C. Fe-Ni-B-(Si,P,C) amorphous ribbon was kept at 285℃ for 18 hours in an air atmosphere to generate an oxide layer on the surface of the Fe-Ni-B-(Si,P,C) amorphous ribbon. The thickness of the oxide layer is 170 nm, which is lower than the thickness of the oxide layer of the Fe-Ni-B-(Si,P,C) amorphous ribbon generated under the same oxidation conditions without continuous DC current treatment (410 nm). Furthermore, no SiO2 diffraction peak appears in the X-ray diffraction pattern of the Fe-Ni-B-(Si,P,C) amorphous ribbon after oxidation.

[0070] Example 4 A method for current pre-annealing of iron-based soft magnetic alloys, the method comprising: A continuous direct current is applied to a Fe-Si-B-Cu-Nb nanocrystalline ribbon with the composition Fe73.5Si13.5B9Nb3Cu1. The current density of the continuous direct current is 22A / mm2, so that the continuous direct current generates Joule heating inside the Fe-Si-B-Cu-Nb nanocrystalline ribbon. The Joule heating process raises the temperature of the Fe-Si-B-Cu-Nb nanocrystalline ribbon to a pre-annealing temperature of 295°C within 100 seconds. The pre-annealing temperature is lower than the glass transition temperature of the Fe-Si-B-Cu-Nb nanocrystalline ribbon, which is 540°C. Fe-Si-B-Cu-Nb nanocrystalline ribbons were kept at 295℃ for 15 hours in an air atmosphere to generate an oxide layer on the surface of the Fe-Si-B-Cu-Nb nanocrystalline ribbons. The thickness of the oxide layer is 155 nm, which is lower than the thickness of the oxide layer of the Fe-Si-B-Cu-Nb nanocrystalline ribbon generated under the same oxidation conditions without continuous DC current treatment (390 nm). Furthermore, no SiO2 diffraction peak appears in the X-ray diffraction pattern of the Fe-Si-B-Cu-Nb nanocrystalline ribbon after oxidation.

[0071] Example 5 A method for current pre-annealing of iron-based soft magnetic alloys, the method comprising: A continuous direct current is applied to Fe-Si silicon steel strip with a composition of Fe-6.0wt%Si. The current density of the continuous direct current is 15A / mm2, so that the continuous direct current generates Joule heat inside the Fe-Si silicon steel strip. The Joule heating process raises the Fe-Si silicon steel strip to a pre-annealing temperature of 300°C within 60 seconds, wherein the pre-annealing temperature is below 301°C. Fe-Si silicon steel strip was kept at 300℃ for 10 hours in an air atmosphere to generate an oxide layer on the surface of the Fe-Si silicon steel strip. The thickness of the oxide layer is 190 nm, which is lower than the thickness of the oxide layer of the Fe-Si silicon steel strip without continuous DC current treatment, which is 450 nm thick under the same oxidation conditions. Furthermore, no SiO2 diffraction peaks appear in the X-ray diffraction pattern of the Fe-Si silicon steel strip after oxidation.

[0072] II. Comparative Example Comparative Example 1 Fe-Si-B amorphous ribbon with composition Fe78Si9B13 was placed directly in air at 280℃ for 24 hours without applying a continuous DC current. The resulting Fe-Si-B amorphous ribbon had an oxide layer thickness of 420 nm, and SiO2 diffraction peaks appeared in the X-ray diffraction pattern of the oxidized Fe-Si-B amorphous ribbon.

[0073] Comparative Example 2 Fe-Si-BC amorphous ribbon with composition Fe76Si4B16Nb2 was placed directly in air at 290℃ for 12 hours without applying a continuous DC current. The resulting comparative Fe-Si-BC amorphous ribbon had an oxide layer thickness of 400 nm, and SiO2 diffraction peaks appeared in the X-ray diffraction pattern of the oxidized Fe-Si-BC amorphous ribbon.

[0074] Comparative Example 3 Fe-Ni-B-(Si,P,C) amorphous ribbons with the composition Fe73Ni8B12Si4P2C2 were placed directly in an air atmosphere at 285℃ for 18 hours without applying a continuous DC current. The resulting Fe-Ni-B-(Si,P,C) amorphous ribbon had an oxide layer thickness of 410 nm, and the oxide layer of the Fe-Ni-B-(Si,P,C) amorphous ribbon showed SiO2 diffraction peaks in the X-ray diffraction pattern after oxidation.

[0075] Comparative Example 4 Fe-Si-B-Cu-Nb nanocrystalline ribbons with the composition Fe73.5Si13.5B9Nb3Cu1 were placed directly in an air atmosphere at 295℃ for 15 hours without applying a continuous DC current. The resulting comparative Fe-Si-B-Cu-Nb nanocrystalline ribbons had an oxide layer thickness of 390 nm, and SiO2 diffraction peaks appeared in the X-ray diffraction pattern of the oxidized Fe-Si-B-Cu-Nb nanocrystalline ribbons.

[0076] Comparative Example 5 Fe-Si silicon steel strip with a composition of Fe-6.0wt%Si was placed directly in an air atmosphere at 300℃ for 10h without applying a continuous DC current. The resulting comparative Fe-Si silicon steel strip had an oxide layer thickness of 450nm, and SiO2 diffraction peaks appeared in the X-ray diffraction pattern of the oxidized Fe-Si silicon steel strip.

[0077] III. Results Data Experimental methods for evaluating results: Oxide layer thickness measurement: Each strip was cut into 10mm×10mm pieces and X-ray reflectance (XRR) was used to measure the thickness at the point where the electron density of the oxide layer / substrate interface changed abruptly. The testing equipment was a Bruker D8 Discover with a scanning step size of 0.005°. Three points were tested for each sample and the arithmetic mean was taken.

[0078] SiO2 diffraction peak determination: Using a CuK α-ray X-ray diffractometer, the scanning range is 2θ = 15°–80° with a step size of 0.02°. If the diffraction peak corresponding to α-quartz PDF#46-1045 appears in the 2θ = 20–30° range for each sample, it is recorded as "appeared"; otherwise, it is recorded as "not appearing".

[0079] Effective permeability at 1 kHz: Tested using a WayneKerr3260B impedance analyzer at B=1mT and 25℃. Each sample was wound with 10 turns of a toroidal sample, and the arithmetic mean of 3 tests was taken.

[0080] Table 1. Results data for both the examples and comparative examples.

[0081] As shown in Table 1, the technological advancements of this application's technical solution include: 1. The oxide layer thickness in Examples 1-5 is 155-190nm, and the oxide layer thickness in Comparative Examples 1-5 is 390-450nm, with a reduction range of 53%-65%; continuous DC current Joule self-heating for 30s-10min + pre-annealing temperature < glass transition temperature of each system or <300℃, inhibits oxygen diffusion inward, thereby quantitatively reducing the oxide layer thickness.

[0082] 2. The X-ray diffraction patterns of Examples 1-5 all showed "no SiO2 diffraction peaks", while those of Comparative Examples 1-5 all showed "SiO2 diffraction peaks"; current density 10-40 A / mm 2 Short-term heating prevents surface Si atoms from migrating over long distances, thus reducing the SiO2 nucleation rate to zero.

[0083] 3. The effective magnetic permeability of Examples 1-5 is 20500-23000, and the effective magnetic permeability of Comparative Examples 1-5 is 16500-18500, representing an improvement of 14%-39%; the pre-annealing temperature is < glass transition temperature or < 300℃ to ensure that the amorphous / nanocrystalline structure is not crystallized, thereby maintaining high magnetic permeability.

[0084] 4. The heating time for current pre-annealing is 30s-10min, which is ≥50 times shorter than that of traditional radiant furnace heating time of ≥5h. The DC current directly heats the iron-based soft magnetic alloy itself, eliminating the radiation heat transfer link, thus shortening the heating time by orders of magnitude.

[0085] 5. Using air atmosphere instead of vacuum or inert gas protection eliminates the need for vacuum systems and gas costs, resulting in a production cost reduction of ≥50%; in the embodiments of this application, a dense oxide layer can be achieved with an oxygen partial pressure of 0.21 bar in the air atmosphere, thereby eliminating the need for expensive atmospheres.

[0086] In summary, the data in Table 1 demonstrates that the technical solution of this application achieves five quantifiable technological advancements in addressing the technical problem of "improving the oxidation resistance of iron-based soft magnetic alloys": thinner oxide layer, no SiO2 precipitation, higher magnetic permeability, shorter processing time, and lower cost.

[0087] Further explanation of the attached diagram: Figure 1 This is a comparison of the XRD curves of iron-based soft magnetic alloy strips without and after current pre-annealing in Example 1 of this application; Figure 2 This is a comparison SEM image of iron-based soft magnetic alloy strips from Embodiment 1 of this application, showing the strips before and after current pre-annealing treatment.

[0088] Depend on Figure 1 Results: The initial state sample without current pre-annealing showed obvious SiO2 diffraction peaks at 2θ≈22°, 28°, and 36°, with peak intensities ≥30 counts; the iron-based soft magnetic alloy strip with current pre-annealing showed no SiO2 diffraction peaks in the same angular range, and the peak intensity dropped to 0 counts. Therefore, the current pre-annealing method completely suppresses the precipitation of SiO2 crystal phase, satisfying the requirement that "no SiO2 diffraction peaks appear".

[0089] Depend on Figure 2 Results: The surface of the initial sample without current pre-annealing was covered with loose oxide particles ≥1μm, and the oxide layer thickness was ≈420nm; the surface of the iron-based soft magnetic alloy strip after current pre-annealing had only a dense oxide layer ≤200nm, with no visible loose particles. Therefore, the current pre-annealing method reduces the oxide layer thickness by ≥50%, and changes the oxide layer morphology from loose to dense, satisfying the requirement of "oxide layer thickness ≤200nm".

[0090] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for pre-annealing iron-based soft magnetic alloys using current, characterized in that, The method includes: A direct current is applied to the iron-based soft magnetic alloy for pre-annealing. The direct current generates Joule heat inside the iron-based soft magnetic alloy. Within 30s–10min, the Joule heat raises the temperature of the iron-based soft magnetic alloy to below the glass transition temperature of the iron-based soft magnetic alloy or below 300°C. The iron-based soft magnetic alloy after pre-annealing is placed in an oxygen-containing atmosphere and held without current for 3 hours to 2 days at a pre-annealing temperature below the glass transition temperature or below 300°C, so that an oxide layer is formed on the surface of the iron-based soft magnetic alloy. The thickness of the oxide layer is lower than that of the oxide layer generated under the same oxidation conditions in the comparative iron-based soft magnetic alloy without DC current treatment, and the iron-based soft magnetic alloy does not show SiO2 diffraction peaks in the X-ray diffraction pattern after oxidation.

2. The current pre-annealing method for iron-based soft magnetic alloys according to claim 1, characterized in that, The iron-based soft magnetic alloy is an Fe-Si-B amorphous alloy, and the chemical composition of the Fe-Si-B amorphous alloy, in atomic percentage, is 70≤Fe≤80, 7≤Si≤10, and 10≤B≤14.

3. The current pre-annealing method for iron-based soft magnetic alloys according to claim 1, characterized in that, The iron-based soft magnetic alloy is an Fe-Si-BC amorphous alloy, and the chemical composition of the Fe-Si-BC amorphous alloy, in atomic percentage, is 75≤Fe≤81, 3≤Si≤5, 13≤B≤19 and 1≤Nb≤2.

6.

4. The current pre-annealing method for iron-based soft magnetic alloys according to claim 1, characterized in that, The iron-based soft magnetic alloy is an Fe-Ni-B-(Si,P,C) amorphous alloy, and the chemical composition of the Fe-Ni-B-(Si,P,C) amorphous alloy, in atomic percentage, is 71≤Fe≤74, 6≤Ni≤10, 10≤B≤15 and 8≤(Si+P+C)≤12.

5. The current pre-annealing method for iron-based soft magnetic alloys according to claim 1, characterized in that, The iron-based soft magnetic alloy is a Fe-Si-B-Cu-Nb nanocrystalline alloy, and the chemical composition of the Fe-Si-B-Cu-Nb nanocrystalline alloy, in atomic percentage, is 73≤Fe≤74, 13≤Si≤14, 8.5≤B≤9.5, 2.8≤Nb≤3.2 and 0.8≤Cu≤1.

2.

6. The current pre-annealing method for iron-based soft magnetic alloys according to claim 1, characterized in that, The iron-based soft magnetic alloy is Fe-Si silicon steel, and the chemical composition of the Fe-Si silicon steel, by weight percentage, is 93.5 ≤ Fe ≤ 99 and 1 ≤ Si ≤ 6.

5.

7. The current pre-annealing method for iron-based soft magnetic alloys according to claim 1, characterized in that, The DC current is applied by continuously supplying a DC current along the transverse or longitudinal direction of the iron-based soft magnetic alloy, and the current density of the continuous DC current is 10 A / mm². 2 –40A / mm 2 .

8. The current pre-annealing method for iron-based soft magnetic alloys according to claim 1, characterized in that, The oxygen-containing atmosphere is an air atmosphere, and the oxygen partial pressure of the air atmosphere is 0.21 bar.

9. A type of iron-based soft magnetic alloy strip, characterized in that, The iron-based soft magnetic alloy strip is obtained by current pre-annealing of an iron-based soft magnetic alloy according to any one of claims 1 to 8; The thickness of the iron-based soft magnetic alloy strip is 30μm–40μm. The thickness of the surface oxide layer of the iron-based soft magnetic alloy strip after oxidation in air at 300℃ for 3h is ≤200nm. Furthermore, no SiO2 diffraction peaks appear in the X-ray diffraction pattern of the iron-based soft magnetic alloy strip after oxidation.

10. The iron-based soft magnetic alloy strip according to claim 9, characterized in that, The iron-based soft magnetic alloy strip is an Fe-Si-B amorphous strip. The chemical composition of the Fe-Si-B amorphous strip, in atomic percentage, is 70≤Fe≤80, 7≤Si≤10, and 10≤B≤14. The effective permeability of the Fe-Si-B amorphous strip at 1kHz is ≥20000.

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