A magnesium-aluminum alloy surface gas-liquid dual-repellent anti-corrosion composite coating and a preparation method thereof

Abstract

The application discloses a magnesium-aluminum alloy surface gas-liquid dual-repellent anti-corrosion composite coating and a preparation method thereof. The method comprises the following steps: immersing a pretreated magnesium-aluminum alloy with alpha phase and beta phase organizational structures into a phosphoric acid-chromate mixed etching solution without external current, and performing selective etching by using a two-phase natural potential difference, so that the alpha phase is preferentially dissolved to construct a micron-level "valley" part, and a phosphoric acid-chromate conversion film is in-situ deposited on the surface of a continuous network beta phase "peak" part skeleton, thereby obtaining a "peak-valley" multi-level micro-nano composite structure which is closely intertwined; and then, the magnesium-aluminum alloy is immersed into a fluorine-containing silane ethanol solution for treatment, and the composite coating is obtained after drying. The coating and the substrate are integrated, and have excellent gas-liquid dual-repellent performance, long-acting anti-corrosion performance and good mechanical stability. The method is simple, low in cost, safe and controllable, and is suitable for fields of marine equipment corrosion prevention and underwater transmission parts, and has great industrial application potential.

Description

Technical Field

[0001] This application relates to the field of alloy surface treatment technology, and mainly to a gas-liquid dual-repellent anti-corrosion composite coating for magnesium-aluminum alloy surface and its preparation method. Background Technology

[0002] Magnesium-aluminum alloys possess significant advantages such as high specific strength, good shock absorption, strong electromagnetic shielding capabilities, and ease of recycling, leading to their widespread application in aerospace, electronic devices, and marine equipment. However, the chemically reactive nature of magnesium-aluminum alloys and the naturally formed porous oxide film on their surface make them difficult to provide lasting protection in harsh environments containing salt spray or humidity, making them highly susceptible to severe corrosion. This has become a bottleneck limiting the further application of magnesium-aluminum alloys. In recent years, constructing super-amphotropic (both hydrophobic and oleophobic) coatings on metal surfaces, utilizing the stable air layer they trap to block the penetration of corrosive media such as water and oil, has become a promising method for improving the corrosion resistance of magnesium-aluminum alloys.

[0003] Currently, the mainstream approach to constructing superhydrophobic or superamphophobic coatings on magnesium-aluminum alloy surfaces involves first building micro-nano rough structures on the surface using physical or chemical methods, and then modifying them with low surface energy materials. However, existing technologies still present numerous challenges. For techniques using chemical or electrochemical etching to construct rough surfaces, corrosion products remain on the surface after the etchant reacts with the magnesium-aluminum alloy. These corrosion products often exhibit a potential difference with the substrate, which can easily trigger galvanic corrosion in corrosive environments, accelerating localized corrosion and leading to decreased corrosion resistance and shortened functional service life of the coating. This has become a key technical challenge hindering the transition of superamphophobic functional coatings for magnesium-aluminum alloys from laboratory applications to practical use. On the other hand, besides etching, common methods for achieving superhydrophobicity on material surfaces include sol-gel methods and synthetic spraying methods. These methods generally suffer from complex processes, cumbersome procedures, and parameter sensitivity, resulting in low efficiency in large-scale production. Furthermore, they often rely on high-power lasers, specialized lithography machines, and other high-end equipment, leading to high purchase and maintenance costs and high barriers to technology promotion. In addition, these methods often involve harmful chemicals such as toxic organic solvents, strong acids and alkalis, and volatile organic compounds, which endanger the health of operators and easily cause environmental pollution.

[0004] In summary, existing magnesium-aluminum alloy surface modification technologies lack an effective balance between achieving superhydrophobic and dihydrophobic properties, long-term corrosion resistance, and process economy. Therefore, developing a coating capable of in-situ construction of multi-level micro / nano composite structures while simultaneously achieving the aforementioned properties, along with its low-cost, safe, controllable, and efficient preparation method, has significant engineering application value and urgent market demand. Summary of the Invention

[0005] To address the technical problem of existing magnesium-aluminum alloy surface modification technologies lacking an effective balance between achieving superhydrophobic and hydrophobic properties, long-term corrosion resistance, and process economy, this application proposes a gas-liquid hydrophobic and hydrophobic composite coating for magnesium-aluminum alloy surfaces and its preparation method.

[0006] According to one aspect of the present invention, a method for preparing a gas-liquid dual-repellent anti-corrosion composite coating on a magnesium-aluminum alloy surface is provided, comprising the following steps: S1. Grind and clean the magnesium-aluminum alloy containing α and β phases; S2. The magnesium-aluminum alloy treated in S1 is immersed in a phosphate-chromium salt mixed etching solution for etching for more than 30 seconds without an external current; the etching temperature is 60-90℃; the phosphate-chromium salt mixed etching solution includes water, phosphoric acid and chromium trioxide; the volume ratio of water to phosphoric acid is (4~5):1; the concentration of chromium trioxide is 1~5g / L; S3. Immerse the magnesium-aluminum alloy treated in S2 into an ethanol solution containing fluorosilane; after immersion, remove and rinse to obtain the gas-liquid dual-repellent anti-corrosion composite coating on the surface of the magnesium-aluminum alloy; the mass-volume concentration of the fluorosilane is 0.4~5.0 g / L; the immersion time is 40~720 min.

[0007] Preferably, the etching solution preferentially etches the α phase while retaining the β phase, and simultaneously generates a phosphate-chromium salt conversion film in situ on the surface of the magnesium-aluminum alloy, forming a multi-level micro-nano composite structure interwoven with the β phase and the phosphate-chromium salt conversion film.

[0008] More preferably, the fluorosilane is modified on the surface of the multi-level micro-nano composite structure to form a gas-phase trapping layer.

[0009] This invention achieves deep integration of structure and function through selective etching under mild conditions without applied current. It cleverly utilizes the natural potential difference between the α and β phases in the magnesium-aluminum alloy matrix, ensuring the complete preservation of the β phase network as a "reinforcing rib," thereby constructing a multi-level micro / nano framework with atomic-level bonding to the matrix and extremely high peel strength in situ. During this process, etching and film formation are coupled simultaneously. The phosphate-chromium salt system dissolves the α phase to construct the morphology while simultaneously depositing a dense phosphate-chromium salt conversion film in situ on the framework surface, achieving the dual goals of morphology roughening and chemical passivation in a single step. This structure, interwoven with the "peaks" of the β phase and the "valleys" formed by the conversion layer, after modification with low surface energy fluorosilanes, effectively constructs a stable gas-phase trapping layer on the composite coating surface. This not only endows the surface with excellent gas-liquid dual-repellency properties but also constructs a dual protection system from both physical and chemical perspectives, significantly improving the mechanical stability and service life of the magnesium-aluminum alloy under harsh environments.

[0010] Preferably, the magnesium-aluminum alloy comprises AZ91D magnesium-aluminum alloy. AZ series alloys exhibit distinct α- and β-phase distribution characteristics, with a stable and moderate potential difference between the two phases. This provides excellent compatibility with the present invention, enabling the stable achievement of the desired selective etching effect. This allows for the in-situ construction of a "peak-valley" multi-level rough skeleton with optimal mechanical support strength, excellent indentation resistance, and wear resistance, providing the best material carrier for subsequently obtaining long-lasting, highly stable superhydrophobic properties.

[0011] Preferably, the fluorosilane comprises 1H,1H,2H,2H-perfluorooctyltriethoxysilane. Fluorosilanes utilize the extremely low surface free energy of the CF bond to endow multi-level micro / nano structures with excellent superhydrophobic and superoleophobic properties, comprehensively constructing a dual-hydrophobic system for all media (gas-liquid), suitable for extreme and harsh conditions such as corrosion protection of marine equipment. The aforementioned fluorosilane molecules have relatively long perfluoroalkyl chains (C8), providing extremely low surface energy. Their ethoxy (-OCH2CH3) groups readily hydrolyze in the presence of trace amounts of water and undergo a condensation reaction with the hydroxyl groups on the magnesium-aluminum alloy surface, forming a strong Si-OM bond.

[0012] According to a second aspect of the present invention, a magnesium-aluminum alloy is provided, the surface of which has a gas-liquid dual-hydrophobic anti-corrosion composite coating prepared by the above method; the gas-liquid dual-hydrophobic anti-corrosion composite coating includes a multi-level micro-nano composite structure interwoven with a β phase and a phosphate-chromium salt conversion film, and a fluorosilane layer modified on the surface of the multi-level micro-nano composite structure.

[0013] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes a multi-level micro / nano composite structure constructed in situ through selective etching, combined with low surface energy modification using fluorosilanes. The resulting coating exhibits both superhydrophobic and superoleophobic properties, effectively blocking the penetration of water, oil, and corrosive media. Simultaneously, the β-phase framework acts as a physical barrier, while the phosphate-chromium salt conversion film serves as a chemical protective layer. The synergistic effect of these two elements significantly enhances the electrochemical impedance of the coating compared to the substrate, resulting in a substantial improvement in its corrosion resistance.

[0014] This invention utilizes the potential difference between the α and β phases of magnesium-aluminum alloys for in-situ selective etching. The β phase framework is atomically bonded to the substrate, eliminating the interface peeling problem common with traditional external coatings. The resulting coating exhibits extremely high bonding strength and resistance to mechanical damage. Even after being subjected to external forces such as friction, scratching, and peeling, it maintains stable gas-liquid dual-repellency properties, making it suitable for dynamic operating conditions during long-term service.

[0015] This invention requires no external current, no vacuum or high-voltage equipment, and no expensive devices such as high-power lasers or lithography machines. It only requires conventional heating and immersion operations, resulting in significantly lower equipment investment and operating costs compared to existing technologies. The etching solution has a simple composition, is free of halide ions and strong acids and alkalis, and the etching process is gentle and controllable, with high operational safety, a wide tolerance for process parameters, and is easy to scale up for mass production.

[0016] This invention can be directly applied to the surface of commonly used magnesium-aluminum alloys such as the AZ series. It has strong adaptability to the shape of the substrate and can process plates, bars, complex curved surfaces, and small precision parts. The resulting coating has comprehensive properties of strong adhesion, gas-liquid dual repellency, and long-term corrosion protection. It can be widely used in marine equipment corrosion protection, microfluidic devices, underwater transmission components, petrochemicals, and aerospace, and has great industrial application value. Attached Figure Description

[0017] The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and, together with the description, serve to explain the principles of this application. Other embodiments and many anticipated advantages of these embodiments will be readily recognized as they become better understood through reference to the following detailed description. Elements in the drawings are not necessarily to scale. The same reference numerals refer to corresponding similar parts.

[0018] Figure 1 A flowchart illustrating the preparation process of a gas-liquid dual-repellent anti-corrosion composite coating for magnesium-aluminum alloy surfaces according to the present invention is shown. Figure 2 A diagram illustrating the formation mechanism of a gas-liquid dual-repellent anti-corrosion composite coating on a magnesium-aluminum alloy surface according to the present invention is shown. Figure 3 The image shows the stable floating state of the composite coating material prepared according to the embodiment of the present invention on the water surface and the water contact angle test image; Figure 4 The image shows the stable floating state of the composite coating material prepared according to the embodiment of the present invention on the surface of peanut oil and the oil contact angle test image. Figure 5 The image shown illustrates the sandpaper friction performance test of the composite coating material prepared according to an embodiment of the present invention; Figure 6 The graphs showing the changes in water contact angle and roll-off angle of the composite coating material prepared according to an embodiment of the present invention with the number of friction cycles are shown. Figure 7 The graphs showing the changes in oil contact angle and roll-off angle of the composite coating material prepared according to an embodiment of the present invention with the number of friction cycles are shown. Figure 8 The image shown is an image of a tape peeling test performed on the composite coating material prepared according to an embodiment of the present invention; Figure 9 The image shown illustrates the scraping performance test of the composite coating material prepared according to an embodiment of the present invention; Figure 10 The figure shows a comparison of the electrochemical impedance modulus spectra of the composite coating material and the untreated magnesium-aluminum alloy substrate according to an embodiment of the present invention. Figure 11 The electrochemical impedance Nyquist plot and equivalent circuit fitting model diagram of the untreated magnesium-aluminum alloy matrix are shown. Figure 12 The electrochemical impedance Nyquist plot and equivalent circuit fitting model diagram of the composite coating material prepared according to the embodiments of the present invention are shown. Figure 13 The diagram shows the practical application effect of the underwater transmission component of Embodiment 4 of the present invention in a mixed medium. Detailed Implementation

[0019] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0020] Where there is no conflict, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] This invention provides a method for preparing a gas-liquid dual-repellent anti-corrosion composite coating on the surface of magnesium-aluminum alloys, such as... Figure 1 As shown, Figure 2 Here is a mechanism diagram for this method, see reference. Figure 1 and Figure 2 Specifically, it includes the following steps: S1. Grind and clean the magnesium-aluminum alloy containing α and β phases.

[0022] S2. The magnesium-aluminum alloy treated in S1 is immersed in a phosphate-chromium salt mixed etching solution for more than 30 seconds without an external current. The etching temperature is 60-90℃. The phosphate-chromium salt mixed etching solution includes water, phosphoric acid and chromium trioxide (CrO3). The volume ratio of water to phosphoric acid is (4~5):1. The concentration of chromium trioxide is 1~5g / L.

[0023] This invention utilizes the α phase (magnesium-rich matrix, with a low potential) and β phase (Mg) in a magnesium-aluminum alloy matrix under conditions without external applied current. 17 Al 12 The natural potential difference between the α and β phases leads to the spontaneous formation of countless tiny galvanic cells on the surface. In these cells, the α phase acts as the anode, undergoing an oxidation reaction where magnesium atoms in the matrix lose electrons and become Mg. 2+The β phase preferentially dissolves upon entering the solution; the β phase, acting as the cathode, is preserved intact under galvanic protection, forming a continuous network framework structure. Simultaneously, a reduction reaction occurs in the cathode region (β phase or phase boundary), releasing hydrogen gas, leading to the formation of H+ in the interface layer near the metal surface. + As the concentration decreased, the local pH value rapidly increased. This increase in pH disrupted the original chemical equilibrium of the etching solution, inducing the reaction of phosphate ions in the solution with Mg dissolved from the substrate. 2+ Al 3+ And the reduced Cr 3+ A synergistic precipitation reaction occurs, resulting in the in-situ deposition of a dense hydroxyl-rich phosphate-chromium salt conversion film on the substrate surface. This conversion film preferentially fills and grows in the dissolved α-phase regions (valleys) and simultaneously coats the surface of the retained network β-phase (peaks). Ultimately, through the coupling of this selective etching and in-situ deposition, a multi-level "peak-valley" micro-nano composite structure is constructed, consisting of a tightly interwoven β-phase network and the conversion film.

[0024] Specifically, this phosphate-chromium salt mixed etching solution has a simple composition. Phosphoric acid provides a suitable acidic environment to promote the dissolution of the α-phase, while CrO3 forms chromic acid in the aqueous solution, which can inhibit excessive hydrogen evolution and participate in the formation of the conversion film. Compared with the halogen salts or mixtures of multiple phosphates commonly used in the prior art, the etching solution of this invention does not contain halide ions, avoiding the risk of secondary corrosion caused by residual chloride or bromide ions after etching. At the same time, the formulation does not contain any additional free phosphates, making the subsequent in-situ conversion film composition purer and its growth more controlled.

[0025] More specifically, a water-to-phosphoric acid volume ratio of (4-5):1 and a chromium trioxide concentration of 1-5 g / L are key parameter windows for ensuring the precise construction of the "peak-valley" framework. Within this range, the acidity of the etching solution is moderate, ensuring a preferential etching rate for the α-phase without excessively eroding the β-phase or causing the conversion film to become loose and detach. If the phosphoric acid ratio is too high, the etching reaction is too vigorous, easily causing localized damage to the β-phase framework; if the phosphoric acid ratio is too low, the etching kinetics are insufficient, the α-phase is not fully dissolved, and it is difficult to form a micro / nano structure with sufficient roughness. Simultaneously, an appropriate concentration of CrO3 can steadily induce the in-situ formation of the phosphate-chromium salt conversion film at a suitable passivation rate, ensuring not only uniform coating of the morphological framework but also avoiding cracking or detachment caused by excessive chromate deposition leading to an overly thick film and increased internal stress.

[0026] Specifically, the etching time is limited to 30 seconds or more. From the perspective of microscopic reaction kinetics, 30 seconds is the minimum critical reaction time for in-situ construction of a complete multi-level micro / nano structure and obtaining the initial passivation shielding layer. After exceeding this critical time, on the one hand, the dense phosphate-chromium salt composite barrier layer generated by the in-situ surface reaction can produce a self-limiting effect, effectively inhibiting further mass transfer of corrosive ions into the depth of the substrate, allowing the growth of microstructures and surface passivation function to spontaneously enter a stable plateau period; on the other hand, the moderate thinning of the macroscopic substrate due to the extended reaction time is functionally decoupled from the microscopic surface morphology construction. This does not lead to a degradation of the long-term anti-corrosion performance and superhydrophobic properties of the resulting composite coating, but rather gives the material the freedom to achieve adaptive positioning of complex microstructures through interface morphology density control. Therefore, the selective etching process does not have a substantial upper limit on the reaction time at the functional construction level.

[0027] S3. Immerse the magnesium-aluminum alloy treated by S2 in an ethanol solution containing fluorine silane at room temperature for 40~720 minutes; after immersion, remove and rinse, and dry at 100℃ for 15 minutes, or air dry naturally, thus obtaining a gas-liquid dual-repellent anti-corrosion composite coating on the surface of the magnesium-aluminum alloy.

[0028] In specific embodiments, the fluorosilane includes 1H,1H,2H,2H-perfluorooctyltriethoxysilane. The fluorosilane molecule undergoes hydrolysis to generate silanol groups, which then undergo a dehydration condensation reaction with the active hydroxyl groups (-OH) on the surface of the phosphate-chromium salt conversion film. Through chemical bonding, long fluorocarbon segments are firmly grafted onto the surface of the "peak-valley" hierarchical micro / nano composite structure. After drying, a dense, self-assembled low surface energy layer is formed on the surface of the hierarchical framework. Due to the extremely low surface free energy of the fluorocarbon segments, combined with the supporting effect of the hierarchical micro / nano structure on the droplets, a stable gas-phase trapping layer is captured and locked between the liquid and the surface, thereby obtaining a gas-liquid dual-repellent anti-corrosion composite coating with excellent anti-corrosion performance and mechanical stability on the magnesium-aluminum alloy surface.

[0029] This invention also provides a magnesium-aluminum alloy product in which the coating and substrate are integrally integrated, preventing large-area peeling failure during use. Even if the surface fluorosilane layer is partially damaged due to long-term wear, the exposed multi-level micro-nano structure still maintains a certain degree of hydrophobicity, oleophobicity, and physical protection. This product combines strong adhesion, dual gas-liquid repellency, and long-term corrosion resistance, making it suitable for harsh working conditions such as corrosion protection of marine equipment, microfluidic devices, and underwater transmission components, and possessing great potential for industrial applications.

[0030] Example 1 A method for preparing a gas-liquid dual-repellent anti-corrosion composite coating on a magnesium-aluminum alloy surface, comprising the following specific steps: S101. Take 90 mL of deionized water, 20 mL of phosphoric acid (85 wt%), and 0.3 g of chromium trioxide (CrO3), and stir to mix evenly to obtain an etching solution. The volume ratio of deionized water to phosphoric acid is 4.5:1, and the concentration of CrO3 is 3 g / L.

[0031] S102. After surface pretreatment, the AZ91D magnesium-aluminum alloy sample (20mm×20mm×5mm) was immersed in the above-mentioned etching solution without external current. The etching temperature was 80℃, the etching time was 60s, and the etching thickness was approximately 0.3mm. During the etching process, the etching solution preferentially etched the α phase while retaining the β phase. Simultaneously, a phosphate-chromium salt conversion film was generated in situ on the surface, forming a multi-level micro-nano composite structure interwoven with the β phase and the conversion film. After etching, the sample was removed, rinsed with deionized water, and dried.

[0032] S103. Prepare a fluorosilane ethanol solution by dissolving 1.0 g of 1H,1H,2H,2H-perfluorooctyltriethoxysilane in 50 mL of anhydrous ethanol and stirring magnetically for 5 min to obtain a fluorosilane solution with a mass-volume concentration of 2.0 g / L. Immerse the sample obtained in S102 into this solution and soak at room temperature for 360 min. After removal, gently rinse with anhydrous ethanol, dry in a 60℃ oven for 20 min, and cool to room temperature to obtain a gas-liquid dual-repellent anti-corrosion composite coating.

[0033] Example 2 A method for preparing a gas-liquid dual-repellent anti-corrosion composite coating on a magnesium-aluminum alloy surface, comprising the following specific steps: S201. Take 80 mL of deionized water, 20 mL of phosphoric acid (85 wt%), and 0.3 g of chromium trioxide (CrO3), and stir to mix evenly to obtain an etching solution. The volume ratio of deionized water to phosphoric acid is 4:1, and the concentration of CrO3 is 3 g / L.

[0034] S202. After surface pretreatment, the AZ91D magnesium-aluminum alloy sample (20mm×20mm×5mm) is immersed in the above etching solution without external current. The etching temperature is 60℃, the etching time is 30s, and the etching thickness is approximately 0.2mm. After etching, the sample is removed, rinsed with deionized water, and dried.

[0035] S203. Prepare a fluorosilane ethanol solution by dissolving 0.2 g of 1H,1H,2H,2H-perfluorooctyltriethoxysilane in 50 mL of anhydrous ethanol and stirring magnetically for 5 min to obtain a fluorosilane solution with a mass-volume concentration of 0.4 g / L. Immerse the sample obtained in S202 into this solution and soak at room temperature for 40 min. After removal, gently rinse with anhydrous ethanol, dry in a 60℃ oven for 20 min, and cool to room temperature to obtain a gas-liquid dual-repellent anti-corrosion composite coating.

[0036] Example 3 A method for preparing a gas-liquid dual-repellent anti-corrosion composite coating on a magnesium-aluminum alloy surface, comprising the following specific steps: S301. Take 100 mL of deionized water, 20 mL of phosphoric acid (85 wt%), and 0.3 g of chromium trioxide (CrO3), and stir to mix evenly to obtain an etching solution. The volume ratio of deionized water to phosphoric acid is 5:1, and the concentration of CrO3 is 3 g / L.

[0037] S302. After surface pretreatment, the AZ91D magnesium-aluminum alloy sample (20mm×20mm×5mm) is immersed in the above etching solution without external current. The etching temperature is 90℃, the etching time is 30s, and the etching thickness is approximately 0.4mm. After etching, the sample is removed, rinsed with deionized water, and dried.

[0038] S303. Prepare a fluorosilane ethanol solution by dissolving 2.5 g of 1H,1H,2H,2H-perfluorooctyltriethoxysilane in 50 mL of anhydrous ethanol and stirring magnetically for 5 min to obtain a fluorosilane solution with a mass-volume concentration of 5 g / L. Immerse the sample obtained in S302 into this solution and soak at room temperature for 720 min. After removal, gently rinse with anhydrous ethanol, dry in a 60℃ oven for 20 min, and cool to room temperature to obtain a gas-liquid dual-repellent anti-corrosion composite coating.

[0039] Example 4 An underwater transmission component has a surface coated with a gas-liquid dual-hydrophobic anti-corrosion composite coating by the preparation method of the magnesium-aluminum alloy surface gas-liquid dual-hydrophobic anti-corrosion composite coating of the present invention. The specific preparation method is the same as in Example 1.

[0040] Comparative Example 1 A method for preparing an anti-corrosion coating on a magnesium-aluminum alloy surface. The only difference between this comparative example and Example 1 is that the ratio of water to phosphoric acid is 3:1.

[0041] Comparative Example 2 A method for preparing an anti-corrosion coating on a magnesium-aluminum alloy surface. The only difference between this comparative example and Example 1 is that the ratio of water to phosphoric acid is 6:1.

[0042] Comparative Example 3 A method for preparing an anti-corrosion coating on a magnesium-aluminum alloy surface. The only difference between this comparative example and Example 1 is that the concentration of CrO3 is 0.5 g / L.

[0043] Comparative Example 4 A method for preparing an anti-corrosion coating on a magnesium-aluminum alloy surface. The only difference between this comparative example and Example 1 is that the concentration of CrO3 is 7 g / L.

[0044] Comparative Example 5 A method for preparing an anti-corrosion coating on a magnesium-aluminum alloy surface, the only difference between this comparative example and Example 1 is that the etching temperature is 50°C.

[0045] Comparative Example 6 A method for preparing an anti-corrosion coating on a magnesium-aluminum alloy surface, the only difference between this comparative example and Example 1 is that the etching temperature is 100℃.

[0046] Comparative Example 7 A method for preparing an anti-corrosion coating on a magnesium-aluminum alloy surface. The only difference between this comparative example and Example 1 is that the etching time is 20s.

[0047] Comparative Example 8 A method for preparing an anti-corrosion coating on a magnesium-aluminum alloy surface. The only difference between this comparative example and Example 1 is that the mass-volume concentration of fluorosilane is 0.3 g / L.

[0048] Comparative Example 9 A method for preparing an anti-corrosion coating on a magnesium-aluminum alloy surface. The only difference between this comparative example and Example 1 is that the mass-volume concentration of fluorosilane is 6 g / L.

[0049] Comparative Example 10 A method for preparing an anti-corrosion coating on a magnesium-aluminum alloy surface. The only difference between this comparative example and Example 1 is that the immersion time of the sample in the fluorosilane solution is 30 min.

[0050] Comparative Example 11 A method for preparing an anti-corrosion coating on a magnesium-aluminum alloy surface. The only difference between this comparative example and Example 1 is that the immersion time of the sample in the fluorosilane solution is 800 min.

[0051] The above embodiments and comparative examples were tested for gas-liquid double hydrophobicity, mechanical stability, and chemical stability. The test methods are as follows: Contact angle testing: An optical contact angle meter was used at room temperature. The sample to be tested was placed horizontally on the sample stage, and deionized water and test oil (such as peanut oil) were added dropwise using a microsyringe, with a droplet volume of 5-8 μL. After the droplets stabilized, the static contact angle was measured using the conic method with image analysis software. At least 5 different locations were selected for testing for each sample, and the average value was taken.

[0052] Roll-off angle test: Fix the sample horizontally on the tilting stage of the optical contact angle measuring instrument. After adding the test droplet, increase the tilting angle slowly and uniformly, and record the critical angle at which the droplet begins to roll, which is the roll-off angle. Each sample should be tested at least 3 times, and the average value should be taken.

[0053] Friction test: A cyclic linear friction tester was used. The sample was fixed on the worktable, and an appropriate friction medium was selected. Reciprocating friction was performed under a set load (100g). After the set number of friction cycles was reached, surface debris was removed with compressed air. The contact angle and roll-off angle of the friction area were measured according to the test method described above to evaluate the wear resistance of the coating.

[0054] Tape peel test: Apply standard pressure-sensitive tape smoothly to the coating surface, and apply even pressure with a roller or your fingers to ensure tight contact. After standing for 30 seconds, peel the tape evenly off the coating surface at a 180° angle. Repeat the above operation up to the set number of times. After each peel, test the contact angle and roll-off angle of the coating surface and observe the change in coating wettability.

[0055] Scratch test: Apply appropriate pressure with the tip of a blade to scratch the coating surface to create obvious scratches. Observe whether the coating peels off or the substrate is exposed in the scratched area. Test the contact angle and roll-off angle near the scratched area to evaluate whether the coating can still maintain its gas-liquid bihydrophobic properties after damage.

[0056] Electrochemical impedance spectroscopy (EIS) was performed using a three-electrode system with 3.5 wt.% NaCl aqueous solution as the electrolyte and the sample to be tested as the working electrode (exposed area 1 cm²). 2 The reference electrode was Ag / AgCl (saturated KCl), and the auxiliary electrode was a platinum plate. Before testing, the samples were immersed in the electrolyte and allowed to stand for 30 minutes to reach a stable state. Measurements were taken at room temperature, with impedance spectra acquired at open-circuit potential. The EIS curves of the samples were determined using CView software. The initial potential for the potential scan was set to 0.5V, the terminal potential to 1V, and the data acquisition interval was 0.5mV. For comparison, the same corrosion test was performed on the untreated magnesium-aluminum alloy substrate. To ensure the repeatability and accuracy of the experimental results, at least three parallel tests were performed on all samples.

[0057] The test results are shown in Tables 1 and 2.

[0058] Table 1 Summary of test data for each embodiment

[0059] Table 2 Summary of test data for each comparative example

[0060] As shown in Table 1, the composite coatings prepared in Examples 1-3 not only exhibit ultra-high static contact angles of 161.3°~169.1° with water, and roll-off angles all controlled below 1.8°, but also show significantly higher static contact angles (up to 156.3°) with low surface tension organic oils (peanut oil), exceeding 142°, demonstrating excellent gas-liquid dual hydrophobic wetting characteristics. Specifically, taking the composite coating material prepared in Example 1 as an example... Figure 3and Figure 4 As shown, this material exhibits extremely excellent broad liquid-spectrum non-wetting properties, and can penetrate water surfaces (…). Figure 3 ) and peanut oil surface ( Figure 4 It achieves a long-lasting and highly stable floating state, with a static water contact angle as high as 169.1°. Figure 3 (Embedded image), peanut oil contact angle reaches up to 156.3° ( Figure 4 The embedded image objectively confirms the technical effectiveness of the intrinsic multi-level micro-nano structure for locking and stabilizing the air cushion.

[0061] In core service life assessments, the composite coating, after undergoing high-load reciprocating linear friction and repeated peeling of standard pressure-sensitive tape at large angles, showed no macroscopic damage to its multi-level composite micro-nano morphology and low surface energy modification layer. Even when subjected to severe scratches from extremely sharp and hard objects, the scratches and the exposed deep skeleton still maintained excellent hydrophobic properties, demonstrating outstanding scratch resistance and durability. Figure 5 As shown, the friction test involved continuously linearly rubbing the coated surface of Example 1 with a 100g standard weight loaded on sandpaper. As the number of friction cycles increased, Figure 6 and Figure 7 The dynamic evolution curves of the water and oil contact angles and roll-off angles of this material are shown respectively. From... Figure 6 As can be seen, after up to 200 sandpaper friction cycles, the water contact angle (WCA) still maintains a superhydrophobic state of over 154.5°; from Figure 7 As can be seen, after 100 friction cycles, the oil contact angle (OCA) remained stable at 150.3°, which fully demonstrates the "reinforcing" support role of the β-phase mesh skeleton, which is integrated with the matrix, in the anti-wear layer. Furthermore, Figure 8 The process and results of a large-angle repeated peel test of standard pressure-sensitive tape are shown. After 100 peels, the surface can still achieve high droplet bounce and non-wetting. Figure 9 The image shows a test image of severe scratches inflicted by a sharp blade. The scratches and the deep areas exposing the skeleton remained intact and spherical after the liquid droplet was applied, without any wetting or spreading. This further confirms the unique structural toughness and in-situ service durability of the coating of this invention from an experimental perspective.

[0062] Furthermore, this invention employs electrochemical impedance spectroscopy (EIS) in a 3.5 wt% NaCl solution to further elucidate the microscopic corrosion kinetics of the obtained composite coating. Figure 10 The electrochemical impedance spectroscopy (EIS) comparison results of the composite coating material prepared in Example 1 and the untreated magnesium-aluminum alloy substrate are shown. From... Figure 10 As can be seen intuitively, at the low frequency end (10... - 2Magnesium-aluminum alloys with a gas-liquid dual-hydrophobic anti-corrosion composite coating on their surface exhibit impedance moduli values ​​more than three orders of magnitude higher than those of the untreated substrate. To further analyze the microscopic electrochemical protection mechanism, this invention performs equivalent circuit modeling and analysis of the interfacial charge transfer process. Figure 11 and Figure 12 Impedance Nyquist plots and corresponding equivalent circuit fitting model diagrams are shown for the untreated substrate and the composite coating material of Example 1, respectively. Figure 11 As shown, the untreated substrate has a loose natural oxide film structure on its surface, and its corresponding fitting circuit includes the equivalent inductance parameter (R) characterizing anodic dissolution and local pitting corrosion. l (and L), indicating the corrosive medium Cl - Ions have penetrated the surface and caused corrosion; while... Figure 12 As shown, the capacitive arc diameter of the composite coating material prepared in Example 1 of this invention increases significantly, and the equivalent inductance parameter (R) in the fitted circuit also increases. l The L and L completely disappear, exhibiting an extremely high charge transfer resistance, thus effectively suppressing the electrochemical degradation process at the interface.

[0063] This unprecedented, ultra-high corrosion resistance and passivation shielding performance stems from the unique chemical and physical synergistic shielding mechanism of this invention. Regarding the chemical barrier, such as... Figure 2 As shown in the schematic diagram of the formation mechanism, during the selective etching stage of mixed acid, due to the preferential dissolution of the anodic α phase in the substrate, a dense, chemically inert network of magnesium phosphate is generated and deposited in situ, directly blocking the penetration path of the corrosive medium. Simultaneously, the intrinsically inert β phase is perfectly preserved and strengthened during the etching process through the in-situ deposition of a highly dense CrPO4 ceramic layer. Both together construct a robust, multi-level intrinsic anti-corrosion passivation layer at the microscopic level. Regarding the physical barrier, firstly, the hierarchical "peak-valley" micro-nano topology, formed by the interweaving of "peaks" constructed from the continuous network of β phases and "valleys" formed by the preferential etching of the α phase, intrinsically restricts the mechanical transfer of solution charge in geometric space. Crucially, the subsequent modification with low surface energy modifiers imparts superhydrophobicity to the surface, which, in conjunction with the multi-level framework, establishes a long-lasting and stable solid-liquid-gas composite interface on the surface of the composite coating. This continuous air layer, captured and locked by the multi-level topological structure, separates the underlying substrate from the corrosive Cl-. - The ions are macroscopically physically isolated, greatly reducing the actual solid-liquid contact area between the corrosive medium and the skeleton surface. Ultimately, this invention achieves a leap in global corrosion resistance and durability through the physicochemical synergy of the microscopic intrinsic passivation layer and the macroscopic gas film effect.

[0064] By systematically comparing the comparative schemes with process parameters deviating from the window, the decisive influence of the proportion of each core component and the operating conditions on the construction of multi-level micro-nano morphology and the quality of chemical passivation in the mixed acid selective etching stage is further revealed intuitively.

[0065] On the one hand, there is a strong interlocking effect between the mixed acid ratio and the skeletal structure construction. When the volume ratio of water to phosphoric acid is too low, as in Comparative Example 1, the excessive acidity leads to an overly vigorous reaction, dissolving the β-phase network that acts as a "reinforcing rib," resulting in a significant degradation of the structural durability after wear and scratch tests. On the other hand, when the volume ratio is too high, as in Comparative Example 2, insufficient etching power leads to incomplete dissolution of the α-phase, making it impossible to construct a micro-nano "valley" structure with sufficient gas phase retention capacity, which greatly limits the improvement of long-term corrosion resistance due to air pad retention.

[0066] On the other hand, when the concentration of CrO3, a key component for film formation inhibition and passivation, is too low, as in Comparative Example 3, it cannot induce the formation of a continuous and consistent dense passivation barrier layer in situ, resulting in a sharp drop in corrosion resistance. When its concentration is too high, as in Comparative Example 4, it will lead to oversaturation of interfacial reactants and cause excessive disordered deposition of the conversion film. During the subsequent drying and curing process, the thick film is prone to micro-cracks or even large-area dry cracking and peeling due to strong internal stress caused by volume shrinkage, resulting in a severe limitation on its cycle life of reciprocating friction and tape peeling.

[0067] In addition, the synergy between etching thermodynamic conditions and time is also crucial. When the temperature is too low (Comparative Example 5), the natural potential difference between the two phases cannot be effectively activated. When the temperature is too high (Comparative Example 6) or the reaction time is too short (Comparative Example 7), the network structure is over-etched and dissolved or the development of the passivation film is defective. After mechanical damage, the stable gas phase retention layer cannot be locked, resulting in the loss of dynamic low roll-off angle performance.

[0068] Further investigation into subsequent surface chemical modification and interfacial film formation kinetics reveals that the material properties of low surface energy modifiers, like the immersion time window, exhibit precise critical thresholds.

[0069] At the level of modifier concentration, when the concentration of low surface energy modifier is too low (as in Comparative Example 8), a dense monomolecular full-coverage layer cannot be formed on the surface of the multi-level composite network, resulting in a low initial wetting angle and a complete loss of the ability to repel low surface tension oils; while when the concentration is too high (as in Comparative Example 9), the modifier molecules undergo disordered multilayer physical accumulation on the micro-nano surface. When these non-chemically bonded accumulation layers are subjected to strong tearing of tape and scratching by sharp hard objects, they are prone to overall brittle collapse and delamination due to weak interlayer shear force, and their mechanical service durability is significantly degraded, which is significantly worse than that of Examples 1-3.

[0070] Regarding the immersion reaction time, when the immersion time is too short, as in Comparative Example 10, due to the limitation of microscopic interface diffusion kinetics, the reactant monomers cannot be fully spread, penetrate, and grafted within the complex and highly curved three-dimensional "peak-valley" multi-level network. As a result, the active hydroxyl groups on the surface of the conversion film are not completely passivated and eliminated, and the film exhibits a large number of chemical defects on a macroscopic scale, making it unable to resist continuous and long-term chemical erosion by fluids. However, when the immersion time is excessively extended, as in Comparative Example 11, it not only fails to bring about a linear leap in the hydrophobic limit performance, but also causes severe interfacial stress concentration and strain accumulation in the local micro-regions due to excessive mutual polymerization of the modifier molecules. This makes the modified layer extremely prone to microscopic brittle fracture and loss under reciprocating friction damage, resulting in a precipitous drop in its performance maintenance life.

[0071] Furthermore, to further verify the structural toughness and macroscopic service applicability of the method of the present invention on the surface of actual engineering components, Embodiment 4 of the present invention utilizes the method of Embodiment 1 to in-situ construct a composite coating on the surface of an underwater transmission component substrate. Combined with... Figure 13 Based on the actual application effect diagrams and relevant assessment data, it can be seen that the underwater transmission component achieves uniform coating of the "peak-valley" multi-level micro-nano framework and low surface energy modification layer even on complex three-dimensional irregular surface structures. Macroscopically, it exhibits extremely excellent broad liquid spectrum non-wetting properties and all-media gas-liquid dual-repellency characteristics. After long-term dynamic fluid uninterrupted shearing and high-speed rotational transmission tests in simulated sewage and oily mixed media, its key working surfaces and irregular corner areas exhibit excellent low adhesion characteristics and self-cleaning capabilities. There are no pollutants or oil deposits remaining on the surface, and due to the integrated interface bonding between the multi-level framework and the substrate, the coating did not experience any micro-cracks, loss, or peeling. The above results strongly confirm that the preparation process of this invention not only has excellent coating adaptability to actual engineering components with complex shapes, but also exhibits unparalleled ultra-high service stability under dynamic and complex multi-media harsh conditions, possessing great industrial practical value.

[0072] In summary, this invention achieves a substantial technological breakthrough in "structure-function integration" through precise control of the selective etching kinetics of mixed acids and the low surface energy dense assembly behavior. This not only enables the magnesium-aluminum alloy composite coating to exhibit extremely excellent and stable gas-liquid dual-repellency properties and a very high electrochemical impedance barrier on a macroscopic scale, but also endows it with unique structural toughness and in-situ service durability in the face of severe mechanical damage such as friction, peeling, and knife scratches. Thus, it provides the substrate with an extremely safe, reliable, and long-lasting protective effect in complex, multi-media, and harsh corrosive environments.

[0073] The specific embodiments of this application have been described above, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A method for preparing a gas-liquid dual-repellent anti-corrosion composite coating on a magnesium-aluminum alloy surface, characterized in that, Includes the following steps: S1. Grind and clean the magnesium-aluminum alloy containing α and β phases; S2. The magnesium-aluminum alloy treated in S1 is immersed in a phosphate-chromium salt mixed etching solution for etching for more than 30 seconds without an external current; the etching temperature is 60-90℃; the phosphate-chromium salt mixed etching solution includes water, phosphoric acid and chromium trioxide; the volume ratio of water to phosphoric acid is (4~5):1; the concentration of chromium trioxide is 1~5g / L; S3. Immerse the magnesium-aluminum alloy treated in S2 into an ethanol solution containing fluorosilane; after immersion, remove and rinse to obtain the gas-liquid dual-repellent anti-corrosion composite coating on the surface of the magnesium-aluminum alloy; the mass-volume concentration of the fluorosilane is 0.4~5.0 g / L; the immersion time is 40~720 min.

2. The method for preparing the gas-liquid dual-repellent anti-corrosion composite coating on the surface of magnesium-aluminum alloy according to claim 1, characterized in that, The etching solution preferentially etches the α phase while retaining the β phase, and at the same time generates a phosphate-chromium salt conversion film in situ on the surface of the magnesium-aluminum alloy, forming a multi-level micro-nano composite structure interwoven with the β phase and the phosphate-chromium salt conversion film.

3. The method for preparing the gas-liquid dual-repellent anti-corrosion composite coating on the surface of magnesium-aluminum alloy according to claim 2, characterized in that, The fluorosilane is modified on the surface of the multi-level micro-nano composite structure to form a gas phase trapping layer.

4. The method for preparing the gas-liquid dual-repellent anti-corrosion composite coating on the surface of magnesium-aluminum alloy according to claim 1, characterized in that, The magnesium-aluminum alloy includes AZ91D magnesium-aluminum alloy.

5. The method for preparing the gas-liquid dual-repellent anti-corrosion composite coating on the surface of magnesium-aluminum alloy according to claim 1, characterized in that, The fluorosilanes include 1H,1H,2H,2H-perfluorooctyltriethoxysilane.

6. A magnesium-aluminum alloy, characterized in that, Its surface has a gas-liquid dual-repellent anti-corrosion composite coating prepared by the method described in any one of claims 1-5; The gas-liquid dual-repellent anti-corrosion composite coating includes a multi-level micro-nano composite structure interwoven with a β phase and a phosphate-chromium salt conversion film, and a fluorosilane layer modified on the surface of the multi-level micro-nano composite structure.

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