Composite passivated and insulated coated low-loss FeNi / FeSiAl soft magnetic material as well as preparation method and application of composite passivated and insulated coated low-loss FeNi / FeSiAl soft magnetic material

Abstract

The invention discloses a composite passivated and insulated coated low-loss FeNi / FeSiAl soft magnetic material as well as a preparation method and application thereof. The composite passivated and insulated coated low-loss FeNi / FeSiAl soft magnetic material comprises a FeNi / FeSiAl inner core, a composite phosphate-chromate conversion film attached to the surface of the inner core and a composite layer of kaolin and white carbon black. And the mixed alloy powder is passivated through a phosphoric acid-chromic acid composite passivation solution, and a composite phosphate-chromate conversion film is formed. The preparation method comprises the following steps: mixing a phosphate-chromate film with composite insulating slurry containing kaolin and white carbon black, further carrying out coating treatment, and finally carrying out drying and heat treatment to form a composite insulating structure with the phosphate-chromate film as a bottom layer and the kaolin / white carbon black as an outer layer on the surface of the mixed metal powder. The effective magnetic conductivity of the soft magnetic material under MHz is 80-140, the magnetic core loss is lower than 900mW / cm < 3 >, and the soft magnetic material is particularly suitable for the fields which are extremely sensitive to loss, such as high-frequency switching power supplies, MHz-level power inductors and radio frequency devices.

Description

Technical Field

[0001] This invention belongs to the field of electronic materials technology, and relates to high-frequency soft magnetic composite materials, particularly to a low-loss FeNi / FeSiAl soft magnetic material with composite passivation and insulating coating, its preparation method and application. Background Technology

[0002] As power electronic devices develop towards higher frequencies, higher efficiency, and smaller sizes, extremely stringent requirements are placed on the loss performance of soft magnetic composite materials in the MHz band. Currently, most soft magnetic composite materials in the MHz band are made by pressing a single alloy powder after insulating coating. However, a single soft magnetic alloy system often struggles to simultaneously achieve high saturation magnetic induction, high permeability, and low high-frequency loss.

[0003] Furthermore, traditional insulation methods such as phosphate passivation and chromate passivation, while improving the surface resistivity of materials, often result in passivation layers with insufficient density and generally poor thermal stability, particularly at high frequencies (MHz). Some methods attempt to add inorganic insulating fillers through mechanical mixing, but this results in uneven filler distribution, the formation of weak points in magnetic properties, and poor interfacial bonding between inorganic insulating fillers and metal powder, making them prone to defects under high-pressure forming and thermal stress, leading to increased losses and decreased reliability.

[0004] Therefore, developing a soft magnetic composite material that can combine the advantages of different alloy systems and achieve high permeability, high resistivity and ultra-low total loss in the MHz band has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a low-loss FeNi / FeSiAl soft magnetic material with composite passivation and insulating coating, along with its preparation method and applications. Through optimized blending of FeNi and FeSiAl powders, combined with phosphate-chromate composite passivation and kaolin / fumed silica composite insulation technology, a multi-layered, synergistic insulating system is constructed on the powder surface and between particles, achieving an optimal balance of electrical, magnetic, thermal, and mechanical properties. This invention also provides a soft magnetic composite material with ultra-low core loss, high effective permeability, and excellent frequency stability in the MHz frequency band, along with a method for its scalable production.

[0006] A low-loss FeNi / FeSiAl soft magnetic material with composite passivation and insulating coating comprises a core of FeNi alloy powder and FeSiAl alloy powder, a composite phosphate-chromate conversion film attached to the surface of the core, and a composite layer of kaolin and silica attached to the surface of the conversion film. The soft magnetic material exhibits an effective permeability of 80-140 NmW at 1 MHz and a core loss of less than 900 mW / cm² under 1 MHz, 50 mT testing conditions. 3 .

[0007] A method for preparing a low-loss FeNi / FeSiAl soft magnetic material with composite passivation and insulating coating, the specific steps of which are as follows: Step 1: Mechanically mix FeNi alloy powder and FeSiAl alloy powder, then clean and dry the mixed powder to activate the surface.

[0008] Preferably, the mass ratio of FeNi alloy powder to FeSiAl alloy powder is (30:70) to (90:10).

[0009] Preferably, the FeNi alloy powder is Fe 50 Ni 50 or Fe 45 Ni 55 The particle size D50 is 5~10 μm; the FeSiAl alloy powder is Fe 85 Si9Al5, with a particle size D50 of 5~10 μm.

[0010] Step 2: Immerse the pretreated mixed powder in the phosphate-chromate composite passivation solution and stir at 50~80℃ for 10~60 minutes to cause oxidation-passivation reaction on the powder surface, forming a dense and strongly adherent composite phosphate-chromate conversion film with a thickness of 30~100 nm on the surface.

[0011] The pH value of the phosphoric acid-chromic acid composite passivation solution is 1.5~3.5, wherein the concentration of phosphoric acid is 0.5~5 wt% and the concentration of chromic acid is 0.5~5 wt%.

[0012] Preferably, the phosphoric acid-chromic acid composite passivation solution further includes deionized water and an accelerator, wherein the accelerator is sodium nitrate or sodium fluoride.

[0013] Step 3: Disperse kaolin and nano-silica in a solvent, add a silane coupling agent to prepare a composite insulating slurry, and coat the mixed powder after insulation passivation in Step 2 to ensure that the composite insulating slurry adheres uniformly to the powder surface and fills the gaps between particles. The total mass of the kaolin and nano-silica accounts for 0.5% to 3.0% of the mass of the FeNi / FeSiAl mixed powder.

[0014] Preferably, the silane coupling agent is KH550, and the amount added is 0.5% to 3% of the mass of the FeNi / FeSiAl mixed powder.

[0015] Preferably, the mass ratio of kaolin to nano-silica is (1~5):1.

[0016] Step 4: Dry and heat-treat the coated material to finally form a composite insulating structure on the surface of the mixed powder, with a phosphate-chromate film as the bottom layer and kaolin / fumed silica as the outer layer.

[0017] Preferably, the material is dried at a low temperature of 80~150℃, and then heat-treated at an inert atmosphere of 300~450℃ for 0.5~2 hours to allow the silane coupling agent to crosslink, the composite insulating slurry to cure, and to form a stable bond with the composite phosphate-chromate conversion film.

[0018] An application of a low-loss FeNi / FeSiAl soft magnetic material with composite passivation and insulating coating involves pressing and annealing mixed FeNi and FeSiAl alloy powder with insulating coating obtained by the above method to prepare a soft magnetic core.

[0019] Preferably, the composite powder with insulation coating is mixed evenly with lubricant and pressed into a magnetic core blank under 1600~2000MPa. Then, it is annealed in a reducing atmosphere at 600~750℃ for 1~3 hours to eliminate internal stress, reduce some of the excessively oxidized metal phase, and further improve the density and stability of the insulation layer.

[0020] A power electronic device comprising the aforementioned soft magnetic core, wherein the power electronic device operates at a frequency of 1 MHz or higher.

[0021] The present invention has the following beneficial effects: 1. Synergistic Optimization of Magnetic Properties: By blending FeNi and FeSiAl, the advantages of high permeability and low high-frequency loss characteristics are complemented at the material level. Furthermore, by adjusting the mixing ratio of FeNi and FeSiAl, the saturation magnetic induction, permeability, and loss characteristics of the soft magnetic material can be flexibly designed to meet the needs of different MHz application scenarios.

[0022] 2. Synergistic Effect of Multilayer Composite Insulation System: The inner passivation film formed by phosphoric acid-chromic acid composite passivation has strong adhesion to the metal substrate, good density, provides the first high-resistivity barrier, and effectively inhibits interfacial diffusion. The composite addition of flake kaolin and nanoparticle silica forms a point-to-surface bonded three-dimensional insulation network between particles. The kaolin flakes effectively block eddy current paths, while silica fills the voids, improves packing density, and enhances insulation reliability. The use of silane coupling agents greatly improves the interfacial compatibility and adhesion between the inorganic insulator and the metal passivation layer. The multilayer composite insulation system achieves extremely high overall resistivity with limited addition amounts, while minimizing the disruption effect on the magnetic circuit and exhibiting weak magnetic dilution.

[0023] 3. Excellent processability and reliability: The composite passivation and slurry coating processes are mature and controllable, suitable for industrial production. The resulting material has high compact strength, and the insulation layer remains stable after high-temperature annealing, ensuring long-term reliability of the product under high-temperature and high-frequency conditions. Experimental data demonstrates that the material of this invention exhibits high effective permeability ( ) under test conditions of 1MHz and 50mT. e ) greater than 100, core loss (Pcv) less than 900mW / cm 3 . Attached Figure Description

[0024] Figure 1 This is a TEM image of the FeNi powder surface after passivation in Example 1; Figure 2 This is a TEM image of the FeSiAl powder surface after passivation in Example 1; Figure 3 The permeability of sample C1 in Example 1 at different frequencies; Figure 4 The loss curves of sample C1 in Example 1 at different frequencies are shown. Detailed Implementation

[0025] The present invention will be further explained below with reference to the accompanying drawings; Example 1 This embodiment provides a method for preparing low-loss FeNi / FeSiAl composite soft magnetic materials for the MHz band, the specific steps of which are as follows: Step 1: Weigh 60g of Fe with a particle size D50=5μm. 50 Ni 50 Powder and 40g of Fe with a particle size D50=5μm 85 Si9Al5 powder was mechanically mixed for one hour, then washed and dried.

[0026] Step 2: Prepare a composite passivation solution containing 1 wt% H3PO4 and 0.5 wt% CrO3. Immerse the mixed powder in the composite passivation solution and stir at 70°C for 30 minutes. Wash with water and dry to obtain passivation powder. Figure 1 , 2 The images are TEM images of FeNi and FeSiAl powders after passivation. It can be seen that the passivation layer on the surface of the metal powder is uniform and dense, with a thickness of approximately 80 nm to 85 nm.

[0027] Step 3: Weigh 1g of calcined modified kaolin, 1g of nano-silica, and 0.09g of KH550, disperse them in 50mL of ethanol solvent, and sonicate to obtain a composite insulating slurry. Mix the composite insulating slurry with the passivation powder, stirring to ensure the composite insulating slurry adheres evenly to the powder surface and fills the gaps between particles.

[0028] Step 4: Dry the coated material at 80°C, and then heat-treat it in N2 at 350°C for 1 hour. Finally, a composite insulating structure with a phosphate-chromate film as the bottom layer and kaolin / fumed silica as the outer layer is formed on the surface of the mixed powder.

[0029] Add 0.5% zinc stearate to the obtained composite insulating soft magnetic material, then press it into a toroidal core at 1800 MPa. Anneal the core sample C1 at 650 °C for 1 hour in a N2 / H2 mixed atmosphere. The permeability and loss curves at different frequencies are shown below. Figure 3 , 4 As shown, the permeability of the magnetic core sample C1 does not change significantly with increasing frequency, remaining stable above 100. The loss curve increases with increasing frequency, but remains below 900 mW / cm². 3 It can meet the usage requirements of power electronic equipment in the MHz band.

[0030] Example 2 This embodiment provides a method for preparing low-loss FeNi / FeSiAl composite soft magnetic materials for the MHz band. Based on Example 1, Fe... 50 Ni 50 The weight of the powder was changed to 70g, Fe 85 The weight of Si9Al5 powder was modified to 30g. The mass ratio of calcined modified kaolin to nano-silica in the composite insulating slurry was 3:1, and the total addition amount accounted for 2.5wt% of the mixed powder mass.

[0031] Finally, pressing and annealing were performed to obtain the magnetic core sample C2.

[0032] Example 3 This embodiment provides a method for preparing low-loss FeNi / FeSiAl composite soft magnetic materials for the MHz band. Based on Example 1, Fe... 50 Ni 50 The weight of the powder was changed to 30g, Fe 85 The weight of Si9Al5 powder was modified to 70g. A composite passivation solution containing 2wt% H3PO4 and 1wt% CrO3 was prepared, with a total insulation addition of 1.5wt%.

[0033] After pressing, the sample was annealed at 700℃ for 1 hour to obtain magnetic core sample C3.

[0034] Comparative Example 1 This comparative example uses the method of Example 1 to passivate and coat 100g of FeSiAl powder, with a total insulation addition of 3wt%, and obtains magnetic core sample D1 after pressing and annealing.

[0035] Comparative Example 2 In this comparative example, 100g of FeNi powder was passivated with phosphoric acid solution, then 1.0wt% of silicone resin was added for insulation treatment, and magnetic core sample D2 was prepared after pressing and annealing.

[0036] The magnetic core samples obtained above were measured, and the results are shown in Table 1: Table 1 As shown in Table 1, compared to a single FeSiAl core sample, the FeNi mixture effectively improves the overall permeability and saturation magnetic induction. Furthermore, as the FeNi content in the mixed powder increases, the permeability and saturation magnetic induction of the sample also increase accordingly. Therefore, the proportion of FeNi in the mixed powder can be adjusted according to the needs of different application scenarios.

[0037] Meanwhile, compared to the single passivation insulation method, although the double-layer composite insulation structure sacrifices some magnetic permeability and saturation magnetic induction intensity, the core loss is significantly reduced, and it can simultaneously achieve high magnetic permeability, high saturation magnetic induction intensity and low loss characteristics.

Claims

1. A low-loss FeNi / FeSiAl soft magnetic material with composite passivation and insulating coating, characterized in that: The FeNi / FeSiAl soft magnetic material comprises a core of FeNi alloy powder and FeSiAl alloy powder, a composite phosphate-chromate conversion film attached to the surface of the core, and a composite layer of kaolin and silica attached to the surface of the conversion film. The soft magnetic material has an effective permeability of 80-140 NmW at 1 MHz and a core loss of less than 900 mW / cm² under 1 MHz, 50 mT testing conditions. 3 .

2. A method for preparing a low-loss FeNi / FeSiAl soft magnetic material with composite passivation and insulating coating, characterized in that: Prepare a phosphoric acid-chromic acid composite passivation solution with a phosphoric acid concentration of 0.5~5 wt% and a chromic acid concentration of 0.5~5 wt%. Kaolin and nano-silica are dispersed in a solvent, and a silane coupling agent is added to prepare a composite insulating slurry. After cleaning and activating the mixed FeNi alloy powder and FeSiAl alloy powder, they are immersed in a phosphate-chromic acid composite passivation solution to cause an oxidation-passivation reaction on the powder surface, forming a composite phosphate-chromate conversion film. Then, they are mixed with a composite insulating slurry and further coated. Finally, they are dried and heat-treated to form a composite insulating structure on the surface of the mixed powder, with a phosphate-chromate film as the bottom layer and kaolin / fumed silica as the outer layer.

3. The preparation method of a low-loss FeNi / FeSiAl soft magnetic material with composite passivation and insulating coating as described in claim 2, characterized in that: The FeNi alloy powder is Fe 50 Ni 50 or Fe 45 Ni 55 The particle size D50 is 5~10 μm; the FeSiAl alloy powder is Fe 85 Si9Al5, with a particle size D50 of 5~10 μm; the mass ratio of FeNi alloy powder to FeSiAl alloy powder is (30:70)~(90:10).

4. The preparation method of a low-loss FeNi / FeSiAl soft magnetic material with composite passivation and insulating coating as described in claim 2, characterized in that: The mixed powder is immersed in a phosphate-chromate composite passivation solution and stirred at 50-80°C for 10-60 minutes to induce an oxidation-passivation reaction on the powder surface, forming a composite phosphate-chromate conversion film with a thickness of 30-100 nm.

5. The preparation method of a low-loss FeNi / FeSiAl soft magnetic material with composite passivation and insulating coating as described in claim 4, characterized in that: The phosphoric acid-chromic acid composite passivation solution also includes deionized water and an accelerator, wherein the accelerator is sodium nitrate or sodium fluoride.

6. The preparation method of a low-loss FeNi / FeSiAl soft magnetic material with composite passivation and insulating coating as described in claim 2, characterized in that: In the composite insulating slurry, the mass ratio of kaolin to nano-silica is (1~5):

1.

7. The preparation method of a low-loss FeNi / FeSiAl soft magnetic material with composite passivation and insulating coating as described in claim 2, characterized in that: The total mass of the kaolin and nano-silica accounts for 0.5% to 3.0% of the mass of the mixed powder, and the total mass of the silane coupling agent accounts for 0.5% to 3% of the mass of the mixed powder.

8. The preparation method of a low-loss FeNi / FeSiAl soft magnetic material with composite passivation and insulating coating as described in claim 2, characterized in that: The material coated with the composite insulating slurry is dried at low temperature at 80~150℃, and then heat-treated at 300~450℃ in an inert atmosphere for 0.5~2 hours to allow the silane coupling agent to crosslink, the composite insulating slurry to cure, and to form a stable bond with the composite phosphate-chromate conversion film.

9. An application of a low-loss FeNi / FeSiAl soft magnetic material with composite passivation and insulating coating, characterized in that: The FeNi / FeSiAl soft magnetic material of claim 1 or the FeNi / FeSiAl soft magnetic material prepared by any of the methods of claims 2 to 8 is mixed evenly with a lubricant and pressed into a core blank. Then, it is annealed in a reducing atmosphere to prepare a soft magnetic core.

10. A power electronic device with an operating frequency of 1MHz or higher, characterized in that: It includes the soft magnetic core as described in claim 9.

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