Preparation method of low-loss heat-resistant magnetic powder core

Abstract

This application provides a method for preparing a low-loss, heat-resistant magnetic powder core, relating to the field of magnetic powder core preparation. The method involves placing a proportioned raw material in a vacuum induction melting furnace and melting it at 1350–1450°C under argon protection, casting it into an ingot. The ingot is then mechanically crushed and ground in a ball mill to obtain alloy powder of 100–400 mesh. The alloy powder is mixed with an insulating coating agent in a specific ratio and stirred until a uniform coating layer is formed. After drying, the coated powder is obtained and filled into a mold. The green magnetic powder core was pressed under a pressure of 2-1.8 GPa. This application achieved precise control of the proportion of Cu, Nb and C elements in the alloy composition and precise control of the nanocrystalline microstructure during the heat treatment process. The resulting magnetic powder core had a power loss as low as 187.8 mW / cm³ under 50 kHz and 0.1 T conditions, which is significantly better than Comparative Example 1 (412.5 mW / cm³) without the addition of Nb and C and Comparative Example 2 (276.3 mW / cm³) without two-stage heat treatment.

Description

Technical Field

[0001] This invention relates to the field of magnetic powder core preparation, and more specifically, to a method for preparing a low-loss, heat-resistant magnetic powder core. Background Technology

[0002] The advent of the 5G era has placed higher demands on electronic components in terms of high frequency, miniaturization, and high current, leading to an explosive growth in related research and applications. Soft magnetic composite materials are important materials used in electronic components. They are formed by pressing magnetic powder after coating the surface with a high resistivity insulating layer. They are widely used in transformers, filters, sensors, molded inductors, etc. To improve the energy conversion efficiency of the magnetic powder core, reduce eddy current losses caused by high frequencies, and alleviate device heat generation, the magnetic powder core usually needs to be insulated.

[0003] With the development of power electronic devices towards higher frequencies and greater integration, higher requirements are being placed on magnetic powder core materials. These materials not only need to possess high saturation magnetic induction and low loss, but also good thermal stability and DC superposition characteristics. While traditional Fe-Si based magnetic powder cores have high permeability, they suffer from high high-frequency losses and poor thermal stability. In recent years, Fe-based nanocrystalline alloys have attracted widespread attention due to their excellent soft magnetic properties, especially the ability to significantly reduce losses and improve thermal stability by controlling nanocrystal nucleation and growth using Cu and Nb elements. Summary of the Invention

[0004] The purpose of this invention is to solve the current problems of high power consumption and insufficient stability.

[0005] In order to achieve the above-mentioned objectives and improve the above-mentioned problems, the present invention provides a method for preparing a low-loss heat-resistant magnetic powder core, wherein the proportioned raw materials are placed in a vacuum induction melting furnace and melted at 1350-1450°C under argon protection, and then cast into an ingot. After the ingot is mechanically crushed, it is ground in a ball mill and sieved to obtain alloy powder with a mesh size of 100-400. The alloy powder is mixed with an insulating coating agent in a certain proportion, stirred until a uniform coating layer is formed, and then dried to obtain the coated powder. The coated powder is filled into a mold and pressed into a green magnetic powder core under a pressure of 1.2-1.8 GPa. The green magnetic powder core is placed in a protective atmosphere furnace for heat treatment. First stage (nanocrystalline annealing): Heat to 480-550℃ at 510℃ / min, and hold at 30-60℃ for 3 minutes; Second stage (thermal stabilization annealing): heat up to 580-620℃, hold for 1030℃ minutes; after heat treatment, cool with the furnace to below 300℃ and then air cool to obtain a low-loss heat-resistant magnetic powder core.

[0006] As a preferred technical solution of this application, the preferred composition of the alloy is: Fe81.3Si4B10Cu1.5Nb1.5C1.7Fe81.3Si4B10Cu1.5Nb1.5C1.7.

[0007] As a preferred technical solution of this application, the insulating coating agent is tetraethyl orthosilicate, and its mass mixing ratio with the alloy powder is 1:101:20.

[0008] As a preferred technical solution of this application, the first stage annealing temperature is located between the first crystallization initiation temperature (Tx1) and the second crystallization initiation temperature (Tx2) of the alloy, so as to fully precipitate Cu clusters and induce the nucleation of α-Fe nanocrystals.

[0009] As a preferred technical solution of this application, the second-stage annealing temperature is higher than the complete precipitation temperature of Cu clusters but lower than the precipitation temperature of the non-magnetic second phase, and the enrichment effect of Nb atoms at the grain boundaries is used to suppress the growth of nanocrystals.

[0010] As a preferred technical solution of this application, the average size of α-Fe nanocrystals in the prepared magnetic powder core is controlled to be between 1525 nm.

[0011] As a preferred technical solution of this application, the obtained magnetic powder core has a power loss P < 200mW / cm3 under the conditions of a test frequency of 50kHz and a magnetic induction intensity of 0.1T.

[0012] As a preferred technical solution of this application, after the magnetic powder core is aged at 150°C for 100 hours, the attenuation rate of its effective magnetic permeability is less than 5%.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: In the scheme of this application: 1. This invention achieves precise control over the microstructure of nanocrystals during heat treatment by precisely controlling the ratio of Cu, Nb, and C elements in the alloy composition, particularly using the preferred Fe81.3Si4B10Cu1.5Nb1.5C1.7Fe81.3Si4B10Cu1.5Nb1.5C1.7 composition. During the first stage of annealing, Cu atoms preferentially precipitate to form high-density, diffusely distributed Cu-rich clusters (approximately 5–8 nm in size), providing numerous heterogeneous nucleation sites for α-Fe nanocrystals. During the second stage of annealing, Nb atoms accumulate at grain boundaries, forming diffusion barriers and effectively suppressing excessive grain growth. The final average size of the obtained α-Fe nanocrystals is stably controlled between 15 and 25 nm. According to the random anisotropy model, when the grain size is smaller than the ferromagnetic exchange coupling length, the effective magnetocrystalline anisotropy constant is proportional to the sixth power of the grain size. Therefore, grain refinement can significantly reduce coercivity and hysteresis loss. Experimental results show that the power loss of the magnetic powder core prepared by this invention is as low as 187.8 mW / cm under 50 kHz and 0.1 T conditions, which is significantly better than that of Comparative Example 1 (412.5 mW / cm) without the addition of Nb and C and Comparative Example 2 (276.3 mW / cm) without two-stage heat treatment. 2. The two-stage heat treatment process adopted in this invention not only achieves nanocrystallization, but more importantly, the high-temperature annealing in the second stage promotes the full segregation of Nb elements with larger atomic radii and slower diffusion rates towards the grain boundaries. This Nb-rich region formed at the grain boundaries has high thermal stability and can effectively hinder the long-range diffusion of Fe atoms and grain boundary migration under high-temperature service conditions, thereby suppressing the coarsening of nanocrystals at high temperatures. Experiments show that after continuous aging at 150°C for 100 hours, the effective permeability of the magnetic powder core of this invention decreases by only 3.5%, which is much lower than that of Comparative Example 1 (18.2% decrease) without Nb and Comparative Example 2 (9.8% decrease) without the second-stage heat treatment. This proves that the magnetic powder core prepared by this invention has excellent heat aging resistance and can work stably for a long time under harsh conditions such as high temperature and high current. 3. This invention uses tetraethyl orthosilicate as an insulating coating agent to form a uniform and dense high-resistivity coating layer on the surface of the alloy powder, effectively blocking the eddy current path between particles and further reducing high-frequency eddy current loss. At the same time, by controlling the pressing pressure within a wide range of 1.2 to 1.8 GPa, while ensuring that the magnetic powder core has sufficient density and high permeability, it avoids the damage to the insulation layer caused by excessive pressure. Thanks to the fine nanocrystalline structure and optimized grain boundary characteristics, the magnetic powder core of this invention exhibits excellent DC superposition characteristics: under an applied 100 Oe DC bias magnetic field, the effective permeability can still maintain more than 72% of the initial value, which is significantly better than the comparative example. It is suitable for power inductors, filters and other devices that need to maintain high inductance values ​​under high current.

[0014] 4. This invention abandons expensive elements such as Co and Zr, and mainly uses common industrial raw materials such as Fe, Si, B, Cu and Nb. Among them, the C element is added in the form of inexpensive Fe-C master alloy, which effectively controls the cost of raw materials. The entire preparation process is clear, has good compatibility with existing magnetic powder core production lines, requires no special equipment modification, and has good prospects for industrial promotion. Attached Figure Description

[0015] Figure 1 One of the flowcharts for the preparation method of the low-loss heat-resistant magnetic powder core provided in this application; Figure 2 The second flowchart of the preparation method of the low-loss heat-resistant magnetic powder core provided in this application; Figure 3 The third flowchart of the preparation method of the low-loss heat-resistant magnetic powder core provided in this application; Figure 4 The fourth flowchart of the preparation method of the low-loss heat-resistant magnetic powder core provided in this application; Figure 5 The fifth flowchart of the preparation method of the low-loss heat-resistant magnetic powder core provided in this application; Figure 6 The sixth flowchart of the preparation method of the low-loss heat-resistant magnetic powder core provided in this application.

[0016] Figure 7 Performance comparison chart of the low-loss heat-resistant magnetic powder core provided in this application.

[0017] Figure 8 X-ray diffraction pattern of the low-loss heat-resistant magnetic powder core provided in this application.

[0018] Figure 9 TEM images of alloys at different heat treatment stages for the low-loss heat-resistant magnetic powder core provided in this application. Detailed Implementation

[0019] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0020] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0021] It should be noted that, unless otherwise specified, the embodiments and features and technical solutions in the present invention can be combined with each other.

[0022] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0023] Example 1 Please refer to Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 , Figure 9 A method for preparing a low-loss, heat-resistant magnetic powder core, comprising: The composition was weighed according to the atomic percentages: Fe 8 1.3 Si 4 B 10 Cu 1.5 Nb 1.5 C 1.7. C was added as an Fe-C master alloy.

[0024] A vacuum induction melting furnace was used. The furnace was evacuated to 5×103 Pa and filled with argon gas to 0.6 atm. The furnace was melted at 1400℃ for 15 minutes and then cast into ingots.

[0025] The ingots are coarsely crushed by a jaw crusher and then placed in a planetary ball mill, where they are ball-milled at 200 rpm for 4 hours and then sieved to obtain powder of 200-400 mesh.

[0026] Mix powder and tetraethyl orthosilicate in a mass ratio of 15:1, add an appropriate amount of ethanol, stir for 30 minutes, and dry at 80°C for 2 hours.

[0027] Press the annular magnetic powder core (outer diameter 20mm, inner diameter 12mm, height 5mm) under a pressure of 1.5GPa for 2 minutes.

[0028] First stage of heat treatment: Heat to C520℃ at 8℃ / min and hold for 45 minutes.

[0029] Second stage: Increase the temperature to C600℃ at a rate of 5℃ / min, hold for 20 minutes, cool with the furnace to 250℃, and then air cool.

[0030] Example 2 The preparation method of the low-loss heat-resistant magnetic powder core provided in Example 1 is further optimized, specifically, as follows: Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 , Figure 9 As shown: Comparative Example 1, which is C-free and low in Nb, is Fe84Si4B11Cu1 (containing no Nb or C). The remaining preparation steps are the same as in Example 1.

[0031] Comparative Example 2, which uses low Cu and no second-stage annealing, has the composition Fe82Si4B12Nb1.5Cu0.5. The heat treatment only involves one-step annealing at 520℃ for 60 min, and the remaining steps are the same as in Example 1.

[0032] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0033] Obviously, the embodiments described above are merely some embodiments of the present invention, not all embodiments. The accompanying drawings show preferred embodiments of the present invention, but do not limit the patent scope of the present invention. The present invention can be implemented in many different forms; rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing specific embodiments, or make equivalent substitutions for some of the technical features. Any equivalent structures made using the content of this specification and drawings, directly or indirectly applied to other related technical fields, are similarly within the patent protection scope of this invention.

Claims

1. A method for preparing a low-loss, heat-resistant magnetic powder core, characterized in that, include: The proportioned raw materials are placed in a vacuum induction melting furnace and melted at 1350-1450℃ under argon protection, and then cast into ingots. After the ingot is mechanically crushed, it is ground in a ball mill and sieved to obtain alloy powder with a mesh size of 100-400. The alloy powder is mixed with an insulating coating agent in a certain proportion, stirred until a uniform coating layer is formed, and then dried to obtain the coated powder. The coated powder is filled into a mold and pressed into a green magnetic powder core under a pressure of 1.2-1.8 GPa. The green magnetic powder core is placed in a protective atmosphere furnace for heat treatment. First stage (nanocrystalline annealing): Heat to 480-550℃ at 510℃ / min, and hold at 30-60℃ for 3 minutes; Second stage (thermal stabilization annealing): heat up to 580-620℃, hold for 1030℃ minutes; after heat treatment, cool with the furnace to below 300℃ and then air cool to obtain a low-loss heat-resistant magnetic powder core.

2. The method for preparing a low-loss heat-resistant magnetic powder core according to claim 1, characterized in that, The preferred composition of the alloy is: Fe81.3Si4B10Cu1.5Nb1.5C1.7Fe81.3Si4B10Cu1.5Nb1.5C1.

7.

3. The method for preparing a low-loss, heat-resistant magnetic powder core according to claim 2, characterized in that, The insulating coating agent is tetraethyl orthosilicate, and its mass mixing ratio with the alloy powder is 1:101:

20.

4. The method for preparing a low-loss heat-resistant magnetic powder core according to claim 3, characterized in that, The first stage annealing temperature is located between the first crystallization initiation temperature (Tx1) and the second crystallization initiation temperature (Tx2) of the alloy, so as to fully precipitate Cu clusters and induce the nucleation of α-Fe nanocrystals.

5. The method for preparing a low-loss heat-resistant magnetic powder core according to claim 4, characterized in that, The second-stage annealing temperature is higher than the complete precipitation temperature of Cu clusters but lower than the precipitation temperature of the non-magnetic second phase, utilizing the enrichment effect of Nb atoms at the grain boundaries to suppress the growth of nanocrystals.

6. The method for preparing a low-loss heat-resistant magnetic powder core according to claim 5, characterized in that, The average size of the α-Fe nanocrystals in the prepared magnetic powder core is controlled to be between 1525 nm.

7. The method for preparing a low-loss heat-resistant magnetic powder core according to claim 6, characterized in that, The obtained magnetic powder core exhibits a power loss P < 200 mW / cm3 under test conditions of 50 kHz frequency and 0.1 T magnetic induction intensity.

8. The method for preparing a low-loss heat-resistant magnetic powder core according to claim 7, characterized in that, After aging at 150°C for 100 hours, the effective permeability of the prepared magnetic powder core decreases by less than 5%.

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