Environment-friendly micro-arc oxidation in-situ growth ceramic protective coating applied to aviation aluminum alloy structural part and corrosion-resistant / wear-resistant modification method of environment-friendly micro-arc oxidation in-situ growth ceramic protective coating

Abstract

The invention relates to the field of aluminum alloy, in particular to a method for in-situ growth of an environment-friendly ceramic protective coating for an aviation aluminum alloy structural part through micro-arc oxidation and various coatings prepared through the method. Firstly, a micro-arc oxidation ceramic layer is prepared on the surface of an aluminum alloy, then a wave-absorbing coating is compounded on the surface of the oxidation ceramic layer, and the aluminum alloy wave-absorbing functional coating with the corrosion protection performance and the wave-absorbing function is prepared. The ceramic layer with a compact microstructure is prepared, and the corrosion resistance of the aluminum alloy is remarkably improved. The wave-absorbing coating compounding technology has the effect of sealing the porous ceramic layer, the corrosion resistance of the ceramic layer is further improved, meanwhile, the ceramic layer has the wave-absorbing function, and the absorption strength and the absorption peak frequency interval can be effectively changed by adjusting the type, content and electromagnetic parameters of a wave-absorbing agent and the thickness of the coating. The comprehensive coating prepared by the invention has the characteristics of excellent corrosion resistance, firm surface bonding, wide electromagnetic wave absorption frequency band and the like, and can be widely applied to the fields of aviation, aerospace, military industry, electronic products and the like.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloys, specifically to an environmentally friendly micro-arc oxidation in-situ grown ceramic protective coating for aerospace aluminum alloy structural components and its corrosion / wear resistance modification method. Background Technology

[0002] Stealth technology has developed rapidly in developed countries and has been applied to advanced weaponry, posing a significant threat to my country's military security. As a primary high technology in the military field, it has been listed as a fundamental element of "competitive strategy." In recent years, the emergence of advanced infrared / ultraviolet detectors, millimeter-wave radars, and other new advanced detectors, along with the urgent need to improve the effectiveness of integrated defense systems, has presented even more severe challenges to the stealth technology of existing equipment. Furthermore, the dramatic increase in space electromagnetic waves in recent years has had a significant impact on personal safety and equipment stability. Radar absorption technology, as an effective means to improve the stealth capabilities of weapon systems and reduce the impact of electromagnetic waves on the human body and electronic equipment, has significant application needs in the fields of weaponry and electronic products.

[0003] Aluminum alloys possess advantages such as low specific gravity, high thermal and electrical conductivity, good corrosion resistance and plasticity, beautiful color, no low-temperature brittleness, and ease of forming. They have long been the most widely used metal structural material in aerospace and are the preferred lightweight structural material for weight reduction. They are used to manufacture aircraft skins, frames, beams, slats, and structural components for launch vehicles and spacecraft. Besides their extensive use in the aerospace industry, aluminum alloys are also widely applied in various sectors of the national economy and people's daily lives, such as transportation, construction, and electrical industries.

[0004] If a surface-absorbing protective coating can be developed on aluminum alloys, and aluminum alloy components with electromagnetic wave absorption function, comprehensive surface protection performance, and load-bearing capacity can be manufactured, it will have immeasurable strategic significance for aluminum alloys in aerospace, weaponry, civilian products and other fields. Summary of the Invention

[0005] The purpose of this invention is to provide an environmentally friendly micro-arc oxidation in-situ grown ceramic protective coating for aerospace aluminum alloy structural parts, and a method for modifying its corrosion resistance and wear resistance. The coating and its preparation method aim to improve the corrosion resistance of the aluminum alloy surface and give it a microwave absorption function. This includes using micro-arc oxidation technology to prepare an oxide ceramic layer to improve the corrosion resistance of the aluminum alloy surface, and using a microwave absorption coating composite technology to further improve the corrosion resistance of the micro-arc oxidation layer and give the coating a microwave absorption function.

[0006] The technical solutions of the present invention are as follows: An environmentally friendly micro-arc oxidation in-situ grown ceramic protective coating for aerospace aluminum alloy structural parts and its corrosion / wear resistance modification method coating, the bottom layer is a porous ceramic layer prepared by micro-arc oxidation technology, and a gradient structure microwave absorbing coating is coated on the porous ceramic layer.

[0007] In this invention, the technical parameter range of the porous ceramic layer is as follows: The ceramic layer thickness is 30-80 μm, the salt spray test (ASTM B117 standard) is ≥5000h, the porosity is 5-10%, the average pore size is 100-200 nm, the bonding strength is ≥70 MPa, and the microhardness is 800-1500 HV0.1.

[0008] In this invention, the technical parameter range of the microwave absorbing coating is as follows: The coating thickness is 1-2 mm, the absorber particle size is 20-100 nm, and the absorption bandwidth (reflection loss < -10 dB) is ≥ 3 GHz.

[0009] The method for preparing the microwave-absorbing functional protective coating on the surface of aluminum alloy in this invention includes the following steps: A. The surface of the aluminum alloy to be processed is placed in an electrolyte. Depending on the aluminum alloy, the electrolyte comprises the following components: sodium silicate at a concentration of 5–30 g / L, sodium hydroxide at a concentration of 1–10 g / L, urea at a concentration of 1–5 g / L, and the remainder is water. Then, the surface of the alloy to be processed is used as the electrode, and an inert conductor (graphite) is used as the counter electrode. These two electrodes, together with a power supply, form an electrolytic circuit. A DC or AC pulse voltage is applied to the power supply. The process parameters are as follows: The pulse frequency is adjusted within the range of 20–3000 Hz. When the alloy surface to be processed is anodic (anodic), the electrolytic voltage varies within the range of 20–800 V; when the alloy surface is cathodic (cathodic), the electrolytic voltage varies within the range of 20–400 V. This step can be further refined as follows: AC pulse voltages are applied simultaneously. The amplitudes of the anodizing and cathodic voltage pulses can be the same or different, and can be stably controlled at a certain level within the voltage variation range. They can also be increased or decreased simultaneously, or changed in opposite directions, with the application time controlled from 1 to 5 hours. This results in the formation of a porous ceramic layer with a thickness of 30–80 μm on the aluminum alloy surface.

[0010] B. The microwave absorbing coating is mainly composed of microwave absorbing agent and resin. The microwave absorbing agent is added to the adhesive in a mass ratio of (1-4): (1-4). The temperature is raised to 50-90℃ and stirred to make it evenly dispersed.

[0011] The microwave absorbing agent is strontium ferrite powder, carbonyl iron powder, barium titanate powder, or carbon black powder, and the particle size of the microwave absorbing agent is 20-100 nm. The binder is epoxy resin.

[0012] The mass ratio of microwave absorber to adhesive is: (1) Strontium ferrite powder : epoxy resin = (2-4) : (1-3); (2) Carbonyl iron powder : epoxy resin = (1-4) : (1-3); (3) Barium titanate powder : epoxy resin = (1-4) : (1-3); (4) Carbon black powder: epoxy resin = (2-3): (3-4).

[0013] C. Add polyamide curing agent to the coating prepared in step B. The mass ratio of polyamide to epoxy resin is (0.2-0.5):(0.5-1.5). Coat the coating evenly (by spraying or brushing) to form a coating with a gradient of components on the surface of the material prepared in step A. The curing temperature is 20-90℃, the curing time is 5-12h, and the coating thickness is 1-2mm.

[0014] The beneficial effects of this invention are: 1. This invention forms micro-plasma on the surface of the aluminum alloy to be processed, and prepares a dense microstructured ceramic layer on the alloy surface, which significantly improves the corrosion resistance of the aluminum alloy. A microwave-absorbing coating is then applied to the ceramic layer. This coating serves two purposes: firstly, it seals the ceramic layer, further improving its protective properties; secondly, it imparts microwave-absorbing functionality. Furthermore, the absorption intensity and absorption peak frequency range can be effectively altered by adjusting the type, content, electromagnetic parameters, and coating thickness of the absorbing agent.

[0015] 2. This invention is the first to propose the concept of preparing a microwave-absorbing functional protective coating on the surface of aluminum alloys. The research aims to further functionalize the surface of aluminum alloys while achieving corrosion protection, forming a protective coating with microwave-absorbing capabilities, which is bound to demonstrate unique application value. Currently, this field is still unexplored both domestically and internationally. Therefore, the preparation technology of microwave-absorbing functional coating materials for aluminum alloy surfaces has significant implications and promising application prospects for the promotion and application of aluminum alloys.

[0016] 3. The comprehensive coating prepared by this invention has the characteristics of excellent corrosion resistance, strong surface adhesion, and wide electromagnetic wave absorption frequency band. It can be widely used in aviation, aerospace, military, electronic products and other fields, and has significant social and economic value. Detailed Implementation

[0017] Example 1

[0018] Step 1: Using aluminum alloy sheet, LY12 aluminum alloy is selected for processing. The surface of the aluminum alloy to be processed is placed in an electrolyte. The electrolyte includes sodium silicate at a concentration of 5-30 g / L (30 g / L in this example), sodium hydroxide at a concentration of 1-10 g / L (5 g / L in this example), urea at a concentration of 1-5 g / L (5 g / L in this example), and the remainder is water. The surface of the alloy to be processed is used as the electrode, and an inert conductor is used as the counter electrode of the alloy surface to be processed. The two electrodes and the power supply form an electrolytic circuit. The inert conductor mentioned here is a conductor that is inert to the specific electrolyte in this example (graphite in this example).

[0019] A DC or AC pulse voltage is applied to the control power supply, with the pulse frequency adjusted within the range of 20–3000 Hz (1000 Hz in this embodiment). When the alloy to be processed is anodized (anodized), the electrolytic voltage varies within the range of 20–800 V; when the alloy is cathodic (cathodicized), the electrolytic voltage varies within the range of 20–400 V. This step can be further refined as follows: AC pulse voltages are applied simultaneously. The amplitudes of the anodizing and cathodic voltage pulses can be the same or different, and can be stably controlled at a certain level within the voltage variation range, or they can be increased or decreased simultaneously, or they can change in opposite directions. The application time is controlled to be 1–5 hours (in this embodiment, the anodizing voltage pulse amplitude is 600 V and the cathodic voltage pulse amplitude is 400 V, and the application time is 4 hours).

[0020] Thus, a porous ceramic layer with a thickness of about 60μm, a salt spray test (ASTM B117 standard) of ≥5000h, a porosity of 5%, an average pore size of about 100nm, a bonding strength of about 70MPa, and a microhardness of about 1200HV0.1 is formed on the aluminum alloy surface.

[0021] Step 2: Mix strontium ferrite and epoxy resin at a mass ratio of 60:40. The size of the microwave absorber particles should be 50-100 nm. Heat to 80°C and stir to ensure uniform dispersion. The surface of the aluminum alloy micro-arc oxidation layer has small pores. To allow the microwave absorber particles to enter the pores and form a gradient coating, the particle size must be controlled within a small range.

[0022] Step 3: Add polyamide curing agent (mass ratio of 1:2 to epoxy resin) to the coating prepared in step 2, coat it evenly with the ceramic layer prepared in step 1, and then cure it with a thickness of 1 mm or 2 mm, a curing temperature of 70℃, and a curing time of 6 h.

[0023] The aluminum alloy sample coated with this coating has a neutral salt spray resistance time (ASTM B117 standard) of ≥6000h. When the coating thickness is 1mm, the reflection loss of electromagnetic waves between 3 and 7GHz is less than -10dB, the absorption bandwidth is 4GHz, and the absorption peak is -27dB. When the coating thickness is 2mm, the reflection loss of electromagnetic waves between 1.5 and 7GHz is less than -10dB, the absorption bandwidth is 5.5GHz, and the absorption peak is -34dB.

[0024] The bottom layer of the microwave-absorbing functional protective coating on the aluminum alloy surface is a porous ceramic layer (about 60 μm thick) prepared by micro-arc oxidation technology. A polymer layer with microwave-absorbing agent particles is coated on the porous ceramic layer. The polymer layer partially penetrates into the pores of the porous ceramic layer to form a gradient structure microwave-absorbing coating.

[0025] Example 2

[0026] Step 1: Perform the same steps as in Step 1 of Example 1.

[0027] Step 2: Mix barium titanate and epoxy resin at a mass ratio of 55:45. The size of the microwave absorber particles is 50-100 nm. Heat to 80°C and stir to make them evenly dispersed.

[0028] Step 3: Add polyamide curing agent (mass ratio of 1:2 to epoxy resin) to the coating prepared in step 2, coat it evenly with the ceramic layer prepared in step 1, and dry it to a thickness of 1 or 2 mm. The curing temperature is 70℃ and the curing time is 6 hours.

[0029] The aluminum alloy sample coated with this coating has a neutral salt spray resistance time (ASTM B117 standard) of ≥6000h. When the coating thickness is 1mm, the reflection loss of electromagnetic waves between 11 and 14GHz is less than -10dB, the absorption bandwidth is 3GHz, and the absorption peak is -27dB. When the coating thickness is 2mm, the reflection loss of electromagnetic waves between 9 and 13.5GHz is less than -10dB, the absorption bandwidth is 4.5GHz, and the absorption peak is -30dB. Example

[0030] Step 1: Perform the same steps as in Step 1 of Example 1.

[0031] Step 2: Mix carbonyl iron powder and epoxy resin at a mass ratio of 70:30. The size of the microwave absorber particles is 50-100 nm. Heat to 80°C and stir to make them evenly dispersed.

[0032] Step 3: Add polyamide curing agent (mass ratio of 1:2 to epoxy resin) to the coating prepared in step 2, coat it evenly with the ceramic layer prepared in step 1, and dry it to a thickness of 1 or 2 mm. The curing temperature is 70℃ and the curing time is 6 hours.

[0033] The aluminum alloy sample coated with this coating has a neutral salt spray resistance time (ASTM B117 standard) of ≥5500h. When the coating thickness is 1mm, the reflection loss of electromagnetic waves between 4.5 and 7.5GHz is less than -10dB, the absorption bandwidth is 3GHz, and the absorption peak is -29dB. When the coating thickness is 2mm, the reflection loss of electromagnetic waves between 3 and 7.2GHz is less than -10dB, the absorption bandwidth is 4.2GHz, and the absorption peak is -35dB.

[0034] Example 3

[0035] Step 1: Perform the same steps as in Step 1 of Example 1.

[0036] Step 2: Mix carbon black, epoxy resin and polyurethane at a mass ratio of 40:60. The size of the microwave absorber particles is 20-80 nm. Heat to 80°C and stir to make them evenly dispersed.

[0037] Step 3: Add polyamide curing agent (mass ratio of 1:2 to epoxy resin) to the coating prepared in step 2, coat it evenly with the ceramic layer prepared in step 1, and then dry it to a thickness of 1 or 2 mm. The curing temperature is 50℃.

[0038] The aluminum alloy sample coated with this coating has a neutral salt spray resistance time (ASTM B117 standard) of ≥6000h. When the coating thickness is 1mm, the reflection loss of electromagnetic waves between 9 and 13GHz is less than -10dB, the absorption bandwidth is 4GHz, and the absorption peak is -27dB. When the coating thickness is 2mm, the reflection loss of electromagnetic waves between 7.5 and 12.5GHz is less than -10dB, the absorption bandwidth is 5GHz, and the absorption peak is -33dB.

[0039] It should be noted that the specific embodiments described above enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the present invention in any way. Therefore, although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention; and all technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. An environmentally friendly micro-arc oxidation in-situ grown ceramic protective coating for use in aerospace aluminum alloy structural components, characterized in that, The bottom layer is a porous ceramic layer prepared by micro-arc oxidation technology, and a gradient structure microwave absorbing coating is coated on the porous ceramic layer; the microwave absorbing coating includes microwave absorbing agent and resin, with the microwave absorbing agent: binder = (1~4): (1~4) by mass.

2. The microwave-absorbing functional protective coating on the aluminum alloy surface according to claim 1, characterized in that, The porous ceramic layer has a thickness of 30–80 μm, a porosity of 5–10%, and an average pore size of 100–200 nm.

3. The microwave-absorbing functional protective coating on the aluminum alloy surface according to claim 1, characterized in that, The thickness of the microwave absorbing coating is 1-2 mm, and the particle size of the microwave absorbing agent is 20 nm-100 nm.

4. A method for preparing the microwave-absorbing functional protective coating on an aluminum alloy surface as described in claim 1, characterized in that it comprises the following steps: A. The surface of the aluminum alloy to be processed is placed in an electrolyte, the surface of the alloy to be processed is used as an electrode, and an inert conductor is used as the counter electrode of the surface of the alloy to be processed. The two electrodes and the power supply form an electrolytic circuit. The power supply applies a DC or AC pulse voltage to form a porous ceramic layer on the surface of the aluminum alloy. B. Mix various microwave absorbing agents and adhesives in proportion, heat to 50-90℃, and stir to make them evenly dispersed; C. Add polyamide curing agent to the coating prepared in step B. The mass ratio of polyamide to epoxy resin is (0.2-0.5):(0.5-1.5). Coat the surface of the material prepared in step A uniformly to form a coating with a gradient of components. The curing temperature is 20-90℃, the curing time is 5-12h, and the coating thickness is 1-2mm.

5. The method for preparing the microwave-absorbing functional protective coating on the aluminum alloy surface according to claim 4, characterized in that, The electrolyte in step A includes the following components: sodium silicate at a concentration of 5–30 g / L, sodium hydroxide at a concentration of 1–10 g / L, urea at a concentration of 1–5 g / L, and the remainder is water.

6. The method for preparing the microwave-absorbing functional protective coating on the aluminum alloy surface according to claim 4, characterized in that the pulse frequency is adjusted in the range of 10 to 2000 Hz, the electrolysis voltage varies in the range of 20 to 800 V when the surface of the alloy to be processed is the anode, and the electrolysis voltage varies in the range of 20 to 400 V when the surface of the alloy to be processed is the cathode, and the application time is controlled to be 1 to 5 h.

7. The method for preparing the microwave-absorbing functional protective coating on the aluminum alloy surface according to claim 4, characterized in that the microwave-absorbing agent in step B is strontium ferrite powder, carbonyl iron powder, barium titanate powder or carbon black powder, the particle size of the microwave-absorbing agent is 20-100 nm, and the binder is epoxy resin.

8. The method for preparing the microwave-absorbing functional protective coating on the aluminum alloy surface according to claim 7, characterized in that the mass ratio of the microwave-absorbing agent to the binder is: (1) Strontium ferrite powder : epoxy resin = (2-4) : (1-3); (2) Carbonyl iron powder : epoxy resin = (1-4) : (1-3); (3) Barium titanate powder : epoxy resin = (1-4) : (1-3); (4) Carbon black powder: epoxy resin = (2-3): (3-4).