A preparation method of a micro-arc oxidation composite film layer based on amorphous nano LDHs@SiO2 particles

Abstract

This invention discloses a method for preparing a micro-arc oxidation composite film based on amorphous nano-LDHs@SiO2 particles, belonging to the field of aluminum alloy surface treatment technology. This invention prepares amorphous nano-LDHs@SiO2 particles and uses them as an additive in the micro-arc oxidation electrolyte to create a micro-arc oxidation composite film. The amorphous nano-LDHs@SiO2 particles (ANano-LDHs@SiO2) are uniformly loaded onto the MAO film under the action of an electric field, exhibiting a strong bond with the composite film. This results in a film with excellent internal and external response, dynamic protection, and a long service life, significantly improving the corrosion resistance of aluminum alloys.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy surface treatment technology, specifically relating to a method for preparing a micro-arc oxidation composite film based on amorphous nano-LDHs@SiO2 particles. Background Technology

[0002] Aluminum alloys, due to their low density, high strength, and excellent machinability, are widely used in transportation, shipbuilding, automotive industry, and many other fields. However, this material exhibits poor corrosion resistance in humid and marine environments, making it prone to corrosion failure, which severely limits its widespread application in harsh environments. To address this issue, various surface treatment technologies have been developed, including chemical conversion coatings, micro-arc oxidation (MAO), anodizing, polymer coatings, and electrochemical deposition. Among these, micro-arc oxidation technology offers significant advantages such as improved corrosion resistance, environmental friendliness, and process controllability, making it more promising than other technologies. However, micro-arc oxidation coatings are prone to micropore formation on the surface, and thermal stress changes during preparation can lead to microcracks both inside and on the surface of the coating. These defects become channels for corrosive media such as moisture and chloride ions to penetrate into the substrate, causing substrate corrosion and significantly reducing the protective effectiveness of the coating.

[0003] Layered double hydroxides (LDHs) are a class of layered compounds with high specific surface areas, where these hydroxylated layers are separated by interlayer anions and water molecules. LDHs can act as reservoirs of functional anions, capturing corrosive anions and releasing the loaded anions when exposed to corrosive environments. In-situ growth of LDHs in micro-arc oxidation films has been shown to significantly improve the corrosion resistance of the films. Their unique anion exchange properties and self-healing capabilities make them excellent materials for metal surface modification.

[0004] To address the issue of numerous micropores and cracks in micro-arc oxidation films, many researchers have employed in-situ preparation of low-temperature hydrogen hydride (LDHs) on the micro-arc oxidation film to seal these micropores and cracks, thereby improving corrosion resistance. However, micropores and cracks continuously form during the film's operation, creating new corrosion windows. In-situ prepared LDHs cannot effectively seal these new corrosion windows or capture corrosive ions, and the surface LDHs are also continuously damaged during long-term service without timely replenishment.

[0005] Therefore, effectively sealing these micropores and microcracks is a key technical bottleneck for improving the corrosion resistance of aluminum alloys and expanding their application range in harsh environments, and an efficient and stable solution is urgently needed. Summary of the Invention

[0006] Therefore, the purpose of this invention is to provide a method for preparing a micro-arc oxidation composite film based on amorphous nano-LDHs@SiO2 particles. Based on the characteristics of micro-arc oxidation film and in-situ preparation of LDHs, the prepared amorphous nanoparticles will be uniformly loaded onto the MAO film under the action of an electric field. The MAO / ANano-LDHs@SiO2 (Amorphous NanoLDHs@SiO2) composite film has advantages such as strong bonding, internal and external response, dynamic protection, and long service life, which can significantly improve the corrosion resistance of aluminum alloys.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] In a first aspect, the present invention provides amorphous nano-LDHs@SiO2 particles, which are composed of an encapsulation body and a hybrid body.

[0009] Based on the above technical solution, further, the encapsulation body is sheet-like nano-LDHs wrapped with nano-silica, and the hybrid is an aggregate of the encapsulation body, nano-SiO2 microspheres, and nano-LDHs.

[0010] The encapsulation consists of nano-SiO2 on the outer layer, which encapsulates the inner layer of nano-LDHs; the hybrid consists of the encapsulation, nano-SiO2 microspheres, and nano-LDHs, which are entangled and polymerized by electrostatic adsorption.

[0011] The encapsulation is the main objective of this technical solution. Encapsulation is a small target unit, which is combined into a large unit. The two main parts are intertwined and mixed together and sealed.

[0012] The amorphous nano-LDHs@SiO2 particles were prepared using the following method: S101: Mix nitrate and deionized water, stir and adjust the pH, then place in a high-pressure reactor for constant temperature aging to obtain aged LDHs; S102: The aged LDHs were washed with deionized water and centrifuged. After washing, the nano-LDHs and organosilicon solution extracted by centrifugation were mixed with anhydrous ethanol and ultrasonically dispersed separately. The two ultrasonically dispersed solutions were mixed and placed on a magnetic stirrer for a timed stirring. Then the pH was adjusted and the final aging was carried out. Finally, the amorphous nano-LDHs@SiO2 particles were obtained by centrifugation.

[0013] Secondly, the present invention provides a method for preparing a micro-arc oxidation composite film based on amorphous nano-LDHs@SiO2 particles, comprising the following steps: S1: Sodium salt, potassium salt and the above-mentioned amorphous nano-LDHs@SiO2 particles are mixed in deionized water to prepare micro-arc oxidation electrolyte; S2: The pretreated aluminum alloy substrate is placed in the micro-arc oxidation electrolyte and reacted by passing an electric current to obtain a sample; S3: Rinse and dry the sample to form a MAO / ANano-LDHs@SiO2 composite coating.

[0014] Based on the above technical solution, further, the potassium salt is potassium hydroxide at a concentration of 0.5~3 g / L, and the sodium salt is sodium silicate at a concentration of 2~10 g / L.

[0015] Based on the above technical solution, the volume ratio of the amorphous nano-LDHs@SiO2 particle sol to the micro-arc oxidation electrolyte is 1:20~100.

[0016] The preferred volume ratio of the amorphous nano-LDHs@SiO2 particle sol to the micro-arc oxidation electrolyte is 1:100.

[0017] Based on the above technical solution, the pretreatment specifically involves cleaning and polishing the aluminum alloy substrate.

[0018] Based on the above technical solution, the energized reaction adopts a constant voltage mode, with the following electrical parameters: positive voltage 520~550V, negative voltage 60~100V, positive and negative duty cycles of 30~50%, pulse frequency 100~300Hz, electrolyte temperature maintained at 25~60℃, and reaction time 10-15min.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention provides a method and application for preparing a micro-arc oxidation composite film based on amorphous nano-LDHs@SiO2 particles. Based on the characteristics of micro-arc oxidation films and in-situ LDH preparation, amorphous nano-LDHs@SiO2 particles are pre-prepared. These nanoparticles consist of an encapsulation body and a hybrid. The encapsulation body consists of sheet-like nano-LDHs encapsulated in a layer of silica. The hybrid is an electrostatically entangled polymer of the encapsulation body, silica microspheres, and sheet-like LDHs. Under the influence of an electric field, the amorphous nano-LDHs@SiO2 particles migrate towards the anode and are uniformly loaded onto the MAO film. The irregularly shaped nanoparticles can be more firmly embedded inside and outside the film. During film growth, some nanoparticles in the film will rupture under the thermal stress of micro-arc oxidation, gaining greater ion exchange opportunities. During subsequent service, the formation of new corrosion windows also activates the surrounding nano-LDHs@SiO2 particles. For encapsulated components embedded in the film, the internal LDHs can exchange ions through cracks or gaps in the nano-SiO2 shell. For hybrids bombarded by MAO plasma, although some exposed LDHs will fail, some hybrids will survive and be successfully loaded inside and outside the film, retaining their ion exchange capacity. The prepared amorphous nanoparticles are uniformly loaded onto the MAO film under the action of an electric field. The MAO / ANano-LDHs@SiO2 composite film has a strong bond, internal and external response, dynamic protection, and long service life, which can significantly improve the corrosion resistance of aluminum alloys.

[0020] 2. The amorphous nano-LDHs@SiO2 particles prepared in this invention are uniformly distributed inside and outside the film layer, which has the effect of sealing micropores and microcracks. They will be continuously activated during subsequent long-term service, dynamically responding to corrosion windows. The preparation of MAO / ANano-LDHs@SiO2 composite film layers on valve metal surfaces such as aluminum alloys can effectively improve the corrosion resistance of the substrate. The coating performance and long-term service performance are better than those of ordinary MAO in-situ grown LDHs. The preparation method is simple and is not affected by the size and shape of the specimen. Attached Figure Description

[0021] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0022] Figure 1 The electron microscope images of Example 1 of the present invention are as follows: (a) is an electron microscope image of Example 1 magnified 150 times; (b) is an electron microscope image of Example 1 magnified 1000 times; and (c) is an electron microscope image of Example 1 magnified 30000 times. Figure 2 This is a fluorescence staining result diagram of Example 6 of the present invention; Figure 3This is a graph showing the electrochemical test results of Example 7 of the present invention; Figure 4 This is a graph showing the salt spray test results of Example 8 of the present invention. Detailed Implementation

[0023] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0024] Example 1 This embodiment prepares a MAO / LDHs@SiO2 composite film on the surface of an aluminum alloy, and the specific method is as follows: (1) Amorphous nano-LDHs@SiO2 particles were prepared in advance; (2) Drill holes and tap the 2024 aluminum alloy substrate with dimensions of 20x20x2 and then polish it with 400 grit sandpaper; (3) Prepare electrolyte: potassium hydroxide 0.5~1g / L, sodium silicate 2~5g / L, and the volume of amorphous nano LDHs@SiO2 particle sol and electrolyte is 8L; (4) The treated aluminum alloy substrate is connected to the anode and suspended in the electrolyte. The specimen is 50 mm away from the liquid surface. The electrical parameters are: positive voltage 520 V, negative voltage 60 V, positive and negative duty cycle 30%, pulse frequency 100 Hz, energized reaction for 10 min, and electrolyte temperature maintained at 25 ℃. (5) Rinse and dry the specimen after step (4) to obtain MAO / ANano-LDHs@SiO2 composite film.

[0025] Example 2 The difference between this embodiment and embodiment 1 is that: The electrolyte volume in step (3) is 5L.

[0026] Example 3 This embodiment prepares a MAO / LDHs@SiO2 composite film on the surface of an aluminum alloy, and the specific method is as follows: (1) Amorphous nano-LDHs@SiO2 particles were prepared in advance; (2) Drill holes and tap the 2024 aluminum alloy substrate with dimensions of 20x20x2 and then polish it with 400 grit sandpaper; (3) Prepare electrolyte: potassium hydroxide 0.5 g / L, sodium silicate 2 g / L, and the volume of amorphous nano LDHs@SiO2 particle sol and electrolyte is 8 L; (4) The treated aluminum alloy substrate is connected to the anode and suspended in the electrolyte. The specimen is 50 mm away from the liquid surface. The electrical parameters are: positive voltage 550 V, negative voltage 100 V, positive and negative duty cycle 50%, pulse frequency 300 Hz, energized reaction for 15 min, and electrolyte temperature maintained at 60 ℃. (5) Rinse and dry the specimen after step (4) to obtain MAO / ANano-LDHs@SiO2 composite film.

[0027] Example 4 The difference between this example and Example 3 is that: The electrolyte volume in step (3) is 5L.

[0028] Comparative Example 1 This comparative example uses a technique to prepare the film layer without adding amorphous nano-LDHs@SiO2 particles to the electrolyte. The specific steps are as follows: (1) Drill holes and tap the 2024 aluminum alloy substrate with dimensions of 20x20x2 and then polish it with 400 grit sandpaper; (2) Prepare the electrolyte: potassium hydroxide 0.5~3g / L, sodium silicate 2~10g / L; (3) The treated aluminum alloy substrate is connected to the anode and suspended in the electrolyte. The specimen is 50 mm away from the liquid surface. The electrical parameters are: positive voltage 520~550V, negative voltage 60~100V, positive and negative duty cycle 30~50%, pulse frequency 100~300Hz, energizing reaction for 10-15 min, and electrolyte temperature maintained at 25~60℃. (4) Rinse and dry the specimen after step (4) to make MAO film sample.

[0029] Comparative Example 2 The difference between this comparative example and Example 1 is that LDHs are grown in situ on a pre-prepared MAO film layer. The specific steps are as follows: (1) Drilling, tapping and polishing with 400 grit sandpaper on a 2024 aluminum alloy substrate with dimensions of 20x20x2. (2) Prepare the electrolyte: potassium hydroxide 0.5~3g / L, sodium silicate 2~10g / L; (3) The treated aluminum alloy substrate is connected to the anode and suspended in the electrolyte. The specimen is 50 mm away from the liquid surface. The electrical parameters are: positive voltage 520~550V, negative voltage 60~100V, positive and negative duty cycle 30~50%, pulse frequency 100~300Hz, energizing reaction for 10-15 min, and electrolyte temperature maintained at 25~60℃. (4) Rinse and dry the sample after step (5) to make a MAO film sample; (5) The MAO membrane sample was suspended in the inner liner of the reactor. The original solution of 1 mol / L zinc nitrate and aluminum nitrate was prepared to have a molar ratio of divalent to trivalent metal cations of (2~3):1. Then it was mixed with deionized water and poured into the inner liner of the reactor to cover the MAO membrane sample. The pH was adjusted to 9~10 with 25~28% ammonia water. The sample was aged at 110~120℃ in a high-pressure reactor for 12~24h. (6) After 12-24 hours, the sample was taken out, rinsed with deionized water and dried to obtain MAO / LDHs-Situ.

[0030] Example 5 The morphology of the films prepared in Example 1 and Comparative Example 1 was observed by scanning electron microscopy. The results are as follows: Figure 1 As shown, compared with ordinary MAO film, the MAO / ANano-LDHs@SiO2 composite film has many uniform protrusions on its surface instead of ordinary crater-like micropores. Further magnification revealed that these micro-protrusions embedded in the film are large encapsulation clusters formed by the aggregation of many encapsulation bodies. Figure 1 c shows magnified observation of the micropores. There are some fine flocculent substances around the micropores, which are even smaller hybrids. There are many flaky and flocculent substances in the micropores. These substances are mainly larger hybrids. Therefore, it can be known that the amorphous nano LDHs@SiO2 particles effectively block the micropores and are uniformly loaded inside and outside the film.

[0031] Example 6 ANano-LDHs@SiO2 was fluorescently stained with FITC staining agent. This staining agent binds to the hydroxyl groups on the LDHs layer but not to the silanol groups on the silica. FITC staining agent is more sensitive to the MAO environment than LDHs. Therefore, the presence of fluorescence under a confocal fiber microscope proves that ANano-LDHs@SiO2 exists in the film layer.

[0032] The results are as follows Figure 2 As shown, a~c are bright field images, and d~f are microscopic fluorescence images. a is the image of ANano-LDHs@SiO2 without electrolyte doping, and no fluorescence is observed under the microscope. b is the image of ANano-LDHs@SiO2 after doping and staining, and abundant green fluorescence can be seen. c is the image of b after polishing to remove the 20μm thick MAO film layer, and relatively abundant fluorescence is still observed under confocal fluorescence microscopy.

[0033] Example 7 Electrochemical tests were performed on Examples 1, 2, 1, and 2, and the results are as follows: Figure 3 As shown.

[0034] Figure 3a represents the open-circuit voltage for each example. The open-circuit voltage of the embodiment is corrected to indicate that the embodiment has better thermal stability. Figure 3 b shows the Tafel polarization curves for each example. The self-corrosion potential, self-corrosion current density, Tafel anodic slope, Tafel cathodic slope, polarization resistance, porosity, and suppression effect data are shown in Table 1. The examples have a more positive self-corrosion potential and a lower self-corrosion current density. The suppression effect of Example 2 is 96%, which is better than that of Comparative Example 2 (93%). Figure 3 c and d represent EIS impedance tests. Table 2 shows the electrical parameters of the equivalent circuit elements for EIS testing. Low-frequency impedance can reflect the comprehensive performance of the film. The low-frequency impedance of the example is better than that of the comparative example 2.

[0035] Table 1

[0036] Table 2

[0037] In the table, Substrate is the aluminum alloy substrate, MAO is the specimen prepared in Comparative Example 1, MAO-5L is the specimen prepared in Example 2, MAO-8L is the specimen prepared in Example 1, and MAO-In-situ is the specimen prepared in Comparative Example 2.

[0038] Example 8 Each case underwent a copper-accelerated acetic acid spray (CASS) test, where 1 hour of experimental salt spray is equivalent to 8 hours of ordinary salt spray. Figure 4 (The English text in the figure has the same meaning as in Example 5) As shown: Comparative Examples 1 and 2 showed corrosion under salt spray on the first day, while the Example showed no significant change. The Example only showed significant corrosion on the fifth day, indicating that ANano-LDHs@SiO2 plays a significant role in corrosion resistance in the MAO film. The corrosion resistance effect of the present invention is significantly better than that of traditional in-situ grown LDHs on the MAO surface.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An amorphous nano-LDHs@SiO2 particle, characterized in that, It consists of an encapsulation body and a hybrid body.

2. The amorphous nano-LDHs@SiO2 particles according to claim 1, characterized in that, The encapsulation body is a sheet-like nano-LDHs encapsulated in nano-silica, and the hybrid is an aggregate of the encapsulation body, nano-SiO2 microspheres, and nano-LDHs.

3. A method for preparing a micro-arc oxidation composite film based on amorphous nano-LDHs@SiO2 particles, characterized in that, Includes the following steps: S1: Sodium salt, potassium salt and the amorphous nano-LDHs@SiO2 particles as described in claim 1 or 2 are mixed in deionized water to prepare a micro-arc oxidation electrolyte. S2: The pretreated aluminum alloy substrate is placed in the micro-arc oxidation electrolyte and reacted by passing an electric current to obtain a sample; S3: Rinse and dry the sample to form a MAO / ANano-LDHs@SiO2 composite coating.

4. The application according to claim 1, characterized in that, The potassium salt is potassium hydroxide at a concentration of 0.5-3 g / L, and the sodium salt is sodium silicate at a concentration of 2-10 g / L.

5. The application according to claim 3, characterized in that, The volume ratio of the prepared amorphous nano-LDHs@SiO2 particle sol to the micro-arc oxidation electrolyte is 1:20~100.

6. The application according to claim 3, characterized in that, The energizing reaction adopts a constant voltage mode, with the following electrical parameters: positive voltage 520~550V, negative voltage 60~100V, positive and negative duty cycles of 30~50%, pulse frequency 100~300Hz, electrolyte temperature maintained at 25~60℃, and reaction time 10-15min.

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