A low magnetic loss magnetic core manufacturing process

Abstract

The application discloses a low magnetic loss magnetic core manufacturing process, and belongs to the technical field of magnetic material production processes. The application discloses the influence of three Fe-Si-Al powder particle sizes, namely D50=90 mu m, D50=35 mu m and D50=5 mu m, and the amount of an insulating agent, namely phosphoric acid, on the high-frequency soft magnetic performance of a magnetic powder core, and obtains the optimal powder particle size selection under the conditions of medium and high frequencies and high power. Then, the application discloses the influence of the amount of alumina raw material and the forming pressure on the high-frequency soft magnetic performance of the magnetic powder core. By comparing the magnetic properties of the magnetic powder cores coated by two kinds of inorganic coating agents, namely alumina and phosphoric acid, an improvement scheme for the alumina coating layer is proposed. The Fe-Si-Al magnetic powder core obtained by the process has the lowest magnetic loss. Therefore, the application solves the technical problem of how to reduce the magnetic loss of the magnetic core.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of a magnetic material production process, in particular to a low-magnetic-loss magnetic core manufacturing process. BACKGROUND

[0002] With the development of electronic devices, communication information and new energy fields, the demand for functional materials of electronic equipment is increasing, and the performance requirements are also increasing. Soft magnetic material, as one of the most popular functional materials in recent years, has been widely concerned. Soft magnetic material refers to material that is easy to magnetize and demagnetize, and is widely used in power and electronic industries, mainly playing the roles of information conversion, transmission and storage. The performance parameters of soft magnetic material mainly include: saturation magnetization (Ms), Curie temperature (Tc), magnetostriction coefficient (lambda), magnetic crystal anisotropy constant (K), magnetic permeability (mu) and coercive force (Hc). Ms, Tc, lambda and K reflect the microstructure of the material, which is not sensitive to the parameters of the essence of the material, mainly determined by the material composition and crystal structure. mu and Hc are microstructure sensitive parameters, which are largely determined by structural factors such as impurities, pores, grain orientation and grain size in the material, as well as external factors such as temperature, radiation and stress, under the condition of determined composition and crystal structure. The preparation and processing of soft magnetic material have great influence on these microstructure sensitive parameters. The basic performance requirements of soft magnetic material are: high saturation magnetic induction, high magnetic permeability, high resistivity, good stability, low coercive force, low magnetic loss, low magnetostriction coefficient and low magnetic crystal anisotropy constant.

[0003] Therefore, Chinese patent CN104321839B discloses a soft magnetic composite (SMC) material formed of atomized ferromagnetic particles. Particles having a predetermined size range are formed, which are coated with at least one layer of electrically insulating nanoscale inorganic filler, thereby forming an insulated ferromagnetic powder as the SMC material. The particles are further coated with a lubricant to facilitate demolding.

[0004] However, the magnetic loss of the disclosed soft magnetic material still has room for improvement. Specifically, metal soft magnetic powder core refers to a material prepared by mixing and pressing metal or alloy soft magnetic powder with insulating medium. The application and development of metal soft magnetic powder core meet the requirements of electronic devices developing towards high efficiency, high power and miniaturization. Metal soft powder core mainly includes Fe powder core, Fe-Si powder core, Fe-Si-Al powder core, high-flux magnetic powder core and platinum permalloy magnetic powder core. The soft magnetic material disclosed in the prior art can be used to prepare Fe powder core; the Fe powder core is prepared from high-purity Fe powder or hydroxyl iron powder as raw material through coating, pressing and annealing steps. The preparation process of this powder core is simple, the raw material is cheap, and the magnetic performance is good. It is the most widely used and largest amount of metal soft magnetic powder core. Among them, the saturation magnetic flux density of Fe powder core is relatively high, which can reach 0.5T~1.3T, and the magnetic permeability ranges from 10 to 100o. However, the disadvantages of Fe powder core are also obvious, which has low resistivity, poor DC bias characteristic and poor magnetic loss. At present, the resistivity of Fe powder core can be improved by mixing with ferrite powder to make composite Fe powder core. This method can reduce the magnetic loss of Fe powder core in high-frequency working environment, but the improvement effect is not obvious. SUMMARY

[0005] Therefore, it is necessary to provide a low magnetic loss magnetic core manufacturing process to solve the technical problem of how to reduce the magnetic loss of the magnetic core.

[0006] A low magnetic loss magnetic core manufacturing process, comprising the following steps: S1, preparing Fe-Si-Al powder with a predetermined particle size; S2, proportioning the powder according to a predetermined ratio; S3, insulating coating the powder; S4, pressing the insulating coated powder to form a green body; S5, heat treating the magnetic powder core green body obtained by pressing;

[0007] The step S3 is as follows:

[0008] S31, configure a passivation solution, weigh 0.6g to 2.0g of phosphoric acid into a reaction kettle and add 20ml of C3H60, then stir to dissolve the phosphoric acid completely;

[0009] S32, weigh 100g of powder into the reaction kettle and continuously stir to passivate the powder uniformly; then put the reaction kettle into an electric heating air drying oven, set the temperature of the drying oven to 80℃, and dry the powder for 2h;

[0010] S33, screen the dried powder with an 80 mesh sieve, add 4‰ amount of resin and release agent to the undersize, mix uniformly, and then seal the prepared Fe-Si-Al powder mixture in a bag for storage;

[0011] The process of step S4 comprises: using a 160-ton hydraulic machine to load the prepared powder mixture into a mold, setting the pressure of the press to 1860 MPa, and pressing to obtain a green body of the magnetic powder core;

[0012] The process of step S5 comprises: loading the Fe-Si-Al magnetic powder core green body into an annealing furnace, setting the highest temperature of the furnace to 730 DEG C, and annealing for 4 h; and naturally cooling the magnetic powder core after annealing.

[0013] Specifically, the particle size of the Fe-Si-Al powder prepared in step S1 is D50=5 μm, D50=35 μm or D50=90 μm.

[0014] Specifically, in step S2, the components of the Fe-Si-Al powder are as follows: 85 parts of Fe, 9.6 parts of Si and 5.4 parts of Al by mass.

[0015] Specifically, the use amount of phosphoric acid is 1.2 wt% when the Fe-Si-Al powder with D50=90 μm is used; the use amount of phosphoric acid is 1.0 wt% when the Fe-Si-Al powder with D50=35 μm is used; and the use amount of phosphoric acid is 1.0 wt% when the Fe-Si-Al powder with D50=5 μm is used.

[0016] Further, in another embodiment, the process of step S3 is changed to:

[0017] S31, configure a buffer solution, respectively weigh 4 g of Na2CO3 and 100 ml of deionized water, mix and stir until the solution is clear;

[0018] S32, continue to configure the aluminum source solution, first weigh 2 g to 11 g of Al(NO3)3·9H2O and put it into the reaction kettle, then add 100 ml of C2H5OH to the reaction kettle, stir until the Al(NO3)3·9H2O is completely dissolved, and then pour it into the three-necked reaction kettle;

[0019] S33, then, weigh 50 g of Fe-Si-Al powder with D50=5 μm into the three-necked reaction kettle, and stir for 10 min;

[0020] S34, then, add the pH buffer solution to the three-necked reaction kettle to adjust the pH of the mixed solution to 4, and then perform water bath heating at 50 DEG C for 4 h, and then filter, wash and dry;

[0021] S35, then, screen the above preliminary coated metal powder with a 200-mesh sieve, pour it into a crucible, and place it in a tube furnace for annealing; the atmosphere is argon, the annealing temperature is set to a maximum of 500 DEG C, the heating rate is 5 DEG C / min, and the furnace is cooled down.

[0022] Further, in another embodiment, the process of step S4 is changed as follows: the heat-treated metal powder is sieved with an 80-mesh sieve, and the undersize is added to 8 ‰ resin and 4 ‰ release agent; then, the mixture is uniformly mixed; the mixture is placed in a mold by using a mold pressing method, and is pressed to form an Al2O3-coated Fe-Si-Al powder core green body under a pressure of 1705 MPa, 1860 MPa, 2015 MPa, and 2170 MPa, respectively.

[0023] Further, in another embodiment, the process of step S5 is changed as follows: the pressed Fe-Si-Al powder core green body is loaded into an annealing furnace, the annealing temperature is 730 ℃, the annealing time is 4 h, and the annealed magnetic powder core is cooled in the furnace.

[0024] Further, in another embodiment, when the Fe-Si-Al powder with a particle size of D50 = 5 μm is used to prepare a soft magnetic powder core, the amount of Al2O3 is 2.0 wt%, and the forming pressure is 1860 MPa.

[0025] In summary, the low-magnetic-loss magnetic core manufacturing process of the present application discloses the influence of the particle size of three kinds of Fe-Si-Al powders, namely D50 = 90 μm, D50 = 35 μm, and D50 = 5 μm, and the amount of insulating agent, i.e., phosphoric acid, on the high-frequency soft magnetic properties of the magnetic powder core, and the best powder particle size selection under medium-high frequency and high power is obtained. Then, Al2O3 is used as an inorganic coating agent, and the influence of the amount of Al2O3 raw material and the forming pressure on the high-frequency soft magnetic properties of the magnetic powder core is disclosed. By comparing the magnetic properties of the magnetic powder cores coated with two kinds of inorganic coating agents, i.e., Al2O3 and phosphoric acid, an improvement scheme for the Al2O3 coating layer is proposed. In the magnetic powder core prepared from the D50 = 5 μm Fe-Si-Al powder coated with Al2O3, the density and effective permeability of the magnetic powder core decrease with the increase of the amount of Al2O3, and increase with the increase of the forming pressure. The DC bias performance increases with the increase of the amount of Al2O3, and decreases with the increase of the forming pressure. The magnetic loss first decreases and then increases with the increase of the amount of Al2O3 and the forming pressure. When the amount of Al2O3 is 2.0 wt% and the forming pressure is 1860 MPa, the best soft magnetic performance powder core can be obtained. The Fe-Si-Al magnetic powder core obtained by this process has the lowest magnetic loss. Therefore, the low-magnetic-loss magnetic core manufacturing process of the present application solves the technical problem of how to reduce the magnetic loss of the magnetic core. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The flowchart of the low-magnetic-loss magnetic core manufacturing process of the present application. DETAILED DESCRIPTION

[0027] In order to make the above objectives, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application are described in detail below. In the following description, a number of specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in many different ways from those described herein, and one skilled in the art can make similar improvements without departing from the scope of the present application, so the present application is not limited to the specific embodiments disclosed below.

[0028] Specifically, the metal soft magnetic powder core is mainly prepared by adopting a powder metallurgy process, which can be described as follows: alloy magnetic powder coated with a surface insulation is pressed into a green body under a certain pressure, and then the residual stress in the green body is released through heat treatment. The preparation process of the metal soft magnetic powder core mainly includes the processes as shown in the figure. Figure 1

[0029] Specifically, in the preparation process of the metal powder, the morphology of the metal powder has a great influence on the performance of the prepared soft magnetic powder core, mainly by affecting the insulation coating effect and the pressing forming effect to affect the magnetic properties. At present, the methods for preparing metal soft magnetic powder mainly include mechanical ball milling method and atomization method. The mechanical ball milling method is to prepare metal powder from alloy ingot by destroying the bonding force between metal atoms through physical method. The atomization method can be divided into gas atomization method and water atomization method, which is to blow liquid metal into powder by high-pressure gas flow and water flow. The surface composition of the powder prepared by this method is different from that of the original alloy. The powder prepared by gas atomization method is generally regular spherical, the surface is relatively smooth and has scales. The powder prepared by water atomization presents irregular spherical shape, and the oxygen content on the surface of the powder is relatively high. Compared with the two methods, the cost of the soft magnetic powder prepared by the mechanical ball milling method is lower, and the powder pressing forming property is better. However, the prepared powder has edges and corners, which is easy to damage the coating layer in the subsequent insulation coating. The soft magnetic powder prepared by gas atomization method presents regular spherical shape, is easy to coat and has excellent coating layer integrity, but the pressing forming effect is poor, especially when the powder particle size is small, it is extremely difficult to form. The soft magnetic powder prepared by water atomization has better forming property than that prepared by gas atomization, and the magnetic permeability of the prepared soft magnetic powder core is also higher, but the magnetic loss is also higher. It is worth mentioning that the flaky magnetic powder prepared by ball milling method has a larger aspect ratio compared with irregular broken magnetic powder and atomized magnetic powder, which can maintain higher magnetic permeability in high frequency range while having low eddy current loss, which is conducive to the absorption of high frequency electromagnetic waves by the material.

[0030] ​In the particle size distribution process of the powder, the particle size distribution of the powder has a great influence on the magnetic properties of the soft magnetic powder core in the process of preparing the soft magnetic powder core. Generally, the powder with large particle size has good fluidity, which can reduce the air gap ratio in the powder core and improve the density and permeability of the powder core, but the DC bias performance of the powder core is poor. The powder with small particle size has poor fluidity due to the increased friction between the particles, which increases the air gap ratio in the prepared powder core and reduces the density and permeability of the powder core, but the DC bias performance is improved. A suitable particle size distribution can promote the reasonable cooperation of powders with different particle sizes, reduce the air gap ratio in the powder core, and reduce the effective demagnetizing field in the powder core, thereby improving the density and permeability of the powder core and reducing the hysteresis loss.

[0031] In the powder insulation coating process, the insulation coating of the powder in the process of preparing the soft magnetic powder core is the core of the whole process. The metal soft magnetic powder core has the advantage that the insulation layer on the surface of the powder and the air gap between the powders can greatly improve the DC bias performance. The effect of the insulation coating layer on the soft magnetic powder core can be divided into two aspects. First, the non-magnetic insulation layer can increase the effective demagnetizing field in the powder core, improve the DC bias performance of the powder core, and increase the anti-saturation performance of the powder core. Second, the insulation coating layer on the surface of the powder can block the eddy current path generated under alternating magnetic field, and reduce the eddy current loss generated by the powder core at high frequency. The insulation coating method is mainly divided into organic coating and inorganic coating. The organic insulation coating layer is mainly various resins. This coating method has a simple process, but it is not resistant to high temperature, and the resin is easy to decompose during the annealing process of the powder core. Therefore, the annealing temperature of the powder core coated with resin cannot exceed 500°C, which will result in incomplete release of the stress in the powder core, increasing the coercivity and hysteresis loss. Inorganic coating is divided into two types. One is to use passivation liquid to react with the surface of the powder to form a passivation layer, such as phosphoric acid passivation. This method has a simple process and good coating effect, but it is not suitable for soft magnetic powders with good corrosion resistance, such as Fe-Ni powder. The other is to use various oxides to uniformly coat the powder to form a dense coating layer, such as AI2O3, SiO2, MgO, etc. However, this method has a complex process, and the coating layer is easy to fall off, which is not suitable for broken powders.

[0032] In the process of compression molding, the soft magnetic powder core is generally prepared by powder metallurgy method, and the compression molding is a crucial step. Resin and release agent are generally added to the powder before compression molding. The resin is to increase the adhesion between the powders, make the green body more easily shaped and the surface layer not easy to fall off. The release agent is to make the green body after compression easily demolded, not to pull the mold, and increase the service life of the mold. The mixed powder is generally compressed by die pressing. The compression pressure is the factor that affects the magnetic properties of the powder core during compression molding. The greater the compression pressure, the higher the density of the powder core, the smaller the internal air gap rate, the smaller the effective demagnetizing field inside the powder core, the higher the permeability of the powder core, and the smaller the hysteresis loss. However, excessive compression strength will damage the insulating layer on the surface of the powder, increase the residual stress, and deteriorate the magnetic properties of the powder core.

[0033] In the heat treatment process, the purpose of heat treatment of the compression green body is to eliminate the internal residual stress of the powder core, decompose the organic matter, increase the overall strength of the powder core, etc. The heat treatment process parameters include heat treatment temperature, heating rate, heat treatment atmosphere, holding time and cooling time. The magnetic properties of the soft magnetic powder core are very sensitive to the heat treatment temperature. If the temperature is too low, the residual stress will not be completely released, and the coercive force of the powder core will be increased. If the temperature is too high, the coating layer will be decomposed and cannot effectively block the eddy current between the particles, which will deteriorate the magnetic properties of the powder core. Only the appropriate temperature can achieve the purpose of eliminating internal stress and defects. In the heat treatment process, N2 or Ar gas is generally used as protective gas to protect the green body from being oxidized during annealing.

[0034] Specifically, the manufacturing process of the low-magnetic-loss magnetic core mainly includes the following steps in one embodiment: S1, preparing Fe-Si-Al powder with a preset particle size; S2, proportioning the powder according to a preset ratio; S3, insulating coating the powder; S4, compression molding the powder after insulating coating; and S5, heat treating the green body of the magnetic powder core obtained by compression.

[0035] In step S3, the following steps are specifically included:

[0036] S31, configuring a passivation liquid, weighing 0.6g to 2.0g of phosphoric acid into a reaction kettle and adding 20ml of C3H60, and stirring to make the phosphoric acid completely dissolved;

[0037] S32, weighing 100g of powder into the reaction kettle, continuously stirring to make the powder passivated uniformly; and then putting the reaction kettle into an electric heating air drying oven, setting the temperature of the drying oven to 80℃, and drying the powder for 2h;

[0038] S33, sieving the dried powder with an 80-mesh sieve, and adding 4‰ amount of resin and release agent, i.e. C 36 H 70O4Zn, and the prepared Fe-Si-Al powder mixture is sealed and stored after being uniformly mixed;

[0039] In step S4, the specific process includes: using a 160-ton hydraulic machine to load the prepared powder mixture into a mold, setting the pressure of the press to 1860 MPa, and pressing to obtain a green body of the magnetic powder core.

[0040] In step S5, the specific process includes: loading the Fe-Si-Al magnetic powder core green body into an annealing furnace, setting the furnace temperature to a maximum temperature of 730℃, and annealing for 4h, and naturally cooling the magnetic powder core after annealing.

[0041] Specifically, soft magnetic composites composed of various metal powders and insulating materials, referred to as SMC, have been widely used in power electronic devices such as reactors and inverters. Compared with traditional soft magnetic materials such as silicon steel and ferrite, SMC has the advantages of low eddy current loss, high DC bias performance and high magnetic flux density. In order to further reduce the eddy current loss of SMC and improve the anti-saturation capability, different insulation methods are disclosed in the prior art to block the magnetic path between the eddy current path and the magnetic powder. However, with the increase of the frequency and power of electronic devices, it becomes more difficult to reduce the medium and high frequency loss and improve the anti-saturation capability by only optimizing the insulation quality of the powder. In order to solve this problem, the present application is a low magnetic loss magnetic core manufacturing process which combines the insulation coating process and the regulation of powder particle size. By comparing the magnetic properties of the powder cores prepared from Fe-Si-Al powders of different particle sizes, the best choice under different frequencies and applied magnetic fields is obtained. In the process scheme of the present application, phosphoric acid can be used as a passivation agent in an amount of 0.6wt% to 2.0wt%. The selected Fe-Si-Al powder can be prepared in advance to have different states with particle sizes of D50=5μm, D50=35μm and D50=90μm. In addition, in the subsequent steps, the ratio of Fe-Si-Al metal powder is as follows: Fe is 85 parts, Si is 9.6 parts, and Al is 5.4 parts by mass. First, the present application will disclose the effect of the amount of phosphoric acid on the magnetic properties of the powder core, and then select the same amount of passivation and the same magnetic permeability. By comparing their soft magnetic properties in different frequency and power ranges, the effect of passivation amount and powder particle size on the soft magnetic properties of the powder core is obtained.

[0042] Specifically, according to the test results of different embodiments, with the increase of the amount of phosphoric acid, the permeability of the magnetic powder core gradually decreases, and the DC bias performance becomes better. Among them, when the Fe-Si-Al powder with D50=90 μm is used to prepare the magnetic powder core, the magnetic loss is the lowest when the amount of phosphoric acid is 1.2 wt%; when the Fe-Si-Al powder with D50=35 μm is used to prepare the magnetic powder core, the magnetic loss is the lowest when the amount of phosphoric acid is 1.0 wt%; and when the Fe-Si-Al powder with D50=5 μm is used to prepare the magnetic powder core, the magnetic loss is the lowest when the amount of phosphoric acid is 1.0 wt%.

[0043] Further, under the conditions of medium-high frequency and high Bm, small particle size of metal powder helps to improve the resistivity of the magnetic powder core, thereby limiting eddy current and effectively reducing magnetic loss. In addition, although the effective permeability of the magnetic powder core prepared from small particle size powder is low, good DC bias performance can be obtained. The reason is that small particle size and low density bring about large effective demagnetizing field. When the magnetic permeability adjustment is the same, due to the similar effective demagnetizing field inside the magnetic powder core, the particle size has little effect on the anti-saturation ability and magnetic loss under low frequency and low Bm, but by reducing the particle size, the loss of the powder core under medium-high frequency and high Bm can still be greatly reduced.

[0044] Further, another embodiment of the process for manufacturing a low-magnetic-loss magnetic core of the application is provided, which has the same steps S1 and S2 as the aforementioned embodiment, but the specific implementation of steps S3-S5 is different; specifically:

[0045] In step S3 of this embodiment, the following procedures are specifically included:

[0046] S31, buffer solution is configured, 4g of Na2CO3 and 100ml of deionized water are weighed respectively, and mixed and stirred until the solution is clear;

[0047] S32, continue to configure the aluminum source solution, first weigh 2g to 11g of Al(NO3)3·9H2O and put it into the reaction kettle, then add 100ml of C2H5OH into the reaction kettle, stir until Al(NO3)3·9H2O is completely dissolved, and then pour it into the three-necked reaction kettle;

[0048] S33, then, weigh 50g of Fe-Si-Al powder with D50=5 μm into the three-necked reaction kettle, and stir for 10min;

[0049] S34, then, add pH buffer solution into the three-necked reaction kettle to adjust the pH of the mixed solution to 4, and then perform water bath heating at 50℃ for 4h, and then filter, wash and dry;

[0050] S35, then, the above-mentioned preliminary coated metal powder is sieved by a 200-mesh sieve and poured into a crucible and placed in a tube furnace for annealing; Ar gas is used as the inert gas, the annealing temperature is set to a maximum of 500 DEG C, the heating rate is 5 DEG C / min, and the furnace is cooled down;

[0051] Then, in step S4, the heat-treated metal powder is sieved by an 80-mesh sieve, and the undersize is added with 8 ‰ resin and 4 ‰ release agent; then, the mixture is uniformly mixed; the mixture is placed in a mold by using the mold pressing method, and is pressed and formed under a pressure of 1705 MPa, 1860 MPa, 2015 MPa and 2170 MPa, respectively, to obtain an Fe-Si-Al powder core green body coated with aluminum oxide;

[0052] Then, in step S5, the pressed and formed Fe-Si-Al magnetic powder core green body is loaded into an annealing furnace, the annealing temperature is 730 DEG C, the annealing time is 4 h, and the annealed magnetic powder core is cooled down with the furnace.

[0053] Specifically, according to the experimental results of the previous embodiment, the magnetic powder core prepared from small-particle-size metal powder can reduce the medium-high frequency magnetic loss and improve the anti-saturation performance. Therefore, in order to further reduce the medium-high frequency magnetic loss of the Fe-Si-Al magnetic powder core and improve the comprehensive soft magnetic performance, in this embodiment, a scheme of coating small-particle-size powder with high resistivity oxide to prepare a soft magnetic powder core is adopted. Currently, commonly used oxide coatings include aluminum oxide, silicon oxide, etc., and the coating methods generally used are hydrolysis method, coprecipitation method or nano-oxide powder and magnetic powder mixing method. The oxide process does not react with the magnetic powder, so it is expected to achieve good insulation coating for alloy powder with good corrosion resistance. Since the preparation of soft magnetic powder core by silicon oxide coating of magnetic powder has been verified by a large number of existing technologies, in this embodiment, aluminum oxide with higher theoretical resistivity is used as the coating layer, and the A1 3+ hydrolysis method is adopted. By coating small-particle-size Fe-Si-Al powder with high resistivity aluminum oxide, the medium-high frequency magnetic loss of the powder core is reduced.

[0054] Specifically, the latter embodiment realizes the reduction of the medium-high frequency magnetic loss of the powder core by coating the small-particle-size Fe-Si-Al powder with high resistivity aluminum oxide. 3+The magnetic powder is coated with Al(OH)3 by hydrolysis, and then the Al(OH)3 on the surface of the metal powder is decomposed into aluminum oxide by heat treatment. According to the experimental results, with the increase of the amount of aluminum oxide, the density and effective permeability of the Fe-Si-Al magnetic powder core gradually decrease, the DC bias performance becomes better, and the magnetic loss shows a trend of first decreasing and then rising. This is because with the increase of the amount of aluminum oxide, the non-magnetic material and air gap rate in the magnetic powder core increase, which enhances the effective demagnetizing field in the powder core and reduces the density and effective permeability of the powder core. However, the increase of the effective demagnetizing field also enhances the DC bias performance of the magnetic powder core and improves the anti-saturation performance of the magnetic powder core. The change of the magnetic loss is related to the coating layer on the surface of the powder. If the coating amount is too small and the coating layer is uneven, it will produce large eddy current loss and residual loss. If the coating amount is too large and the coating layer is too thick, it will produce large hysteresis loss; therefore, selecting the appropriate coating amount can effectively reduce the magnetic loss. In summary, the magnetic powder core with the lowest magnetic loss can be obtained when the coating amount of aluminum oxide is 2.0wt%.

[0055] Further, the molding pressure also affects the magnetic properties of the Fe-Si-Al magnetic powder core coated with aluminum oxide. With the increase of the molding pressure, the density of the magnetic powder core gradually increases, because the air gap rate in the magnetic powder core decreases. This also proves that the structural demagnetizing field generated by the air gap gradually decreases, therefore, the permeability of the magnetic powder core gradually increases, and the DC bias performance decreases. The effect of the molding pressure on the magnetic loss of the magnetic powder core is mainly determined by the air gap rate in the magnetic powder core and the quality of the coating layer on the surface of the powder. Small molding pressure makes the powder core have a large air gap rate, which causes the hysteresis loss of the powder core to be large. Large molding pressure destroys the insulating layer on the surface of the powder, which increases the eddy current loss and residual loss of the powder core. Therefore, for the coated magnetic powder core, the appropriate molding pressure is extremely important. In this embodiment, the molding pressure is selected as 1860MPa, and the soft magnetic powder core with the lowest magnetic loss can be obtained.

[0056] In general, this embodiment can prove that the soft magnetic powder core prepared by coating the Fe-Si-Al powder with D50=5μm with aluminum oxide can reduce the magnetic loss at medium and high frequencies and optimize the anti-saturation performance. The best preparation conditions are: the amount of aluminum oxide is 2.0wt%, and the molding pressure is 1860MPa. The permeability of the magnetic powder core obtained by this method is about 62, the μe of the magnetic powder core is as high as 63.85 when the external DC magnetic field is 8000A / m, and the magnetic loss at 200kHz / 50mT is 235.8mW / cm 3 , which can achieve excellent performance.

[0057] In summary, the low magnetic loss magnetic core manufacturing process discloses the influence of three kinds of Fe-Si-Al powder particle sizes, D50=90 μm, D50=35 μm and D50=5 μm, and the amount of insulating agent, i.e., phosphoric acid, on the high-frequency soft magnetic performance in the magnetic powder core, and the best powder particle size selection under the medium and high frequency and high power is obtained. Then, the amount of alumina raw material and the forming pressure on the high-frequency soft magnetic performance of the magnetic powder core are disclosed by taking alumina as an inorganic coating agent. By comparing the magnetic properties of the magnetic powder cores coated by the two kinds of inorganic coating agents, i.e., alumina and phosphoric acid, an improvement scheme for the alumina coating layer is proposed. In the magnetic powder core prepared by the D50=5 μm Fe-Si-Al powder coated by alumina, the density and effective permeability of the magnetic powder core decrease with the increase of the alumina amount and increase with the increase of the forming pressure. The DC bias performance increases with the increase of the alumina amount and decreases with the increase of the forming pressure. The magnetic loss first decreases and then increases with the increase of the alumina amount and the forming pressure. And the best soft magnetic performance core can be obtained when the alumina amount is 2.0 wt% and the forming pressure is 1860 MPa. The Fe-Si-Al magnetic powder core obtained by the process has the lowest magnetic loss. Therefore, the low magnetic loss magnetic core manufacturing process solves the technical problem of how to reduce the magnetic loss of the magnetic core.

[0058] The technical features of the above-described embodiments can be combined in any manner, and to make the description concise, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combinations of the technical features do not exist contradictions, they should be considered as the scope of the description.

[0059] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the scope of protection of the patent of the present application should be subject to the appended claims.

Claims

1. A process for making a low magnetic loss magnetic core, the process comprising: It comprises the following steps: S1, preparing Fe-Si-Al powder with a preset particle size; S2, proportioning the powder according to a preset ratio; S3, insulating coating the powder; S4, pressing the powder after insulating coating; S5, heat treating the magnetic powder core green body obtained by pressing; The step S3 comprises the following steps: S31, buffer solution is configured, 4g of Na2CO3 and 100ml of deionized water are weighed respectively, and mixed and stirred until the solution is clear; S32, continue to configure the aluminum source solution, first weigh 2g to 11g of A1(NO3)3·9H2O and put it into the reaction kettle, then add 100ml of C2H5OH into the reaction kettle, stir until A1(NO3)3·9H2O is completely dissolved, and then pour it into the three-necked reaction kettle; S33, then, 50g of Fe-Si-Al powder with D50=5μm is weighed and poured into the three-necked reaction kettle, and stirred for 10min; S34, then, pH buffer solution is added to the three-necked reaction kettle to adjust the pH of the mixed solution to 4, and then it is heated in a water bath at 50℃ for 4h, filtered, washed and dried; S35, then, the above preliminarily coated metal powder is sieved with a 200 mesh sieve and poured into a crucible, and placed in a tube furnace for annealing; the atmosphere is argon, the annealing temperature is set to a maximum of 500℃, the heating rate is 5℃ / min, and the furnace is cooled down; In step S3, the amount of aluminum oxide is 2.0wt%; The step S4 comprises the following steps: using a 160-ton hydraulic machine to load the prepared powder mixture into a mold, setting the pressure of the press to 1860MPa, and pressing to obtain a magnetic powder core green body; The step S5 comprises the following steps: loading the Fe-Si-Al magnetic powder core green body into an annealing furnace, setting the furnace temperature to a maximum temperature of 730℃, and annealing for 4h, and naturally cooling the magnetic powder core after annealing.

2. The process for making a low magnetic loss magnetic core of claim 1, wherein: In step S2, in the components of the Fe-Si-Al powder, Fe is 85 parts, Si is 9.6 parts, and Al is 5.4 parts by mass.

3. The process for making a low magnetic loss magnetic core of claim 1, wherein: In step S4: the metal powder after heat treatment is sieved with an 80 mesh sieve, and the undersize material is added with 8‰ of resin and 4‰ of release agent.

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