In-situ enhanced superhydrophobic composite coating on magnesium alloy surface and preparation method thereof

Abstract

The application provides a magnesium alloy surface hydrotalcite in-situ reinforced super-hydrophobic composite coating and a preparation method thereof. The super-hydrophobic composite coating comprises a magnesium-aluminum hydrotalcite pretreatment layer and a super-hydrophobic coating in-situ reinforced on the surface of the magnesium-aluminum hydrotalcite pretreatment layer. The super-hydrophobic coating is prepared from components including a silicon dioxide precursor, anhydrous ethanol, a long-chain alkoxysilane and ammonia water. The application endows the magnesium alloy with excellent active and passive synergistic corrosion resistance and self-cleaning performance, and realizes long-acting corrosion protection of the magnesium alloy.

Description

Technical Field

[0001] This invention belongs to the field of special functional materials and magnesium alloy surface corrosion protection technology, and in particular relates to the in-situ reinforced superhydrophobic composite coating of hydrotalcite on magnesium alloy surface and its preparation method. Background Technology

[0002] Magnesium alloys, as one of the lightest metallic structural materials, possess advantages such as light weight, high specific strength and specific stiffness, good damping and impact resistance, excellent electromagnetic shielding performance, easy processing and forming, biodegradability, and good biocompatibility. They have significant application value and broad application prospects in marine engineering, aerospace, national defense, automotive and high-speed rail, and medical implant materials, earning them the reputation of "green engineering materials" for the 21st century. However, despite these excellent properties, magnesium alloys have not achieved widespread success in practical applications, primarily due to their poor corrosion resistance. Approximately 90% of magnesium alloys are metallic magnesium. Because magnesium has a relatively low standard potential (-2.37V) and is chemically very reactive, it is easily oxidized or corroded in humid air, marine atmosphere, seawater, and most organic / inorganic acids and their salts. This causes magnesium alloys to lose their original properties and significantly reduce their service life. Therefore, poor corrosion resistance severely restricts the development and application of magnesium alloys.

[0003] In recent years, superhydrophobic coatings have attracted widespread attention from researchers due to their potential applications in self-cleaning, corrosion prevention, anti-icing, and anti-adhesion. Superhydrophobic coatings refer to surfaces with a water contact angle greater than 150° and a roll-off angle less than 10°. Their non-wetting properties significantly reduce the contact area between corrosive media and the coating surface, greatly preventing the diffusion of corrosive ions from the electrolyte into the metal substrate and thus improving corrosion resistance. However, currently reported adhesion between superhydrophobic coatings and substrates remains weak, relying on van der Waals forces, and research on adhesion strength is scarce. Therefore, designing and preparing superhydrophobic coatings with high adhesion strength on magnesium alloy surfaces is of great significance.

[0004] Gen Zhang et al. (In-situ grown super-or hydrophobic Mg-Al layered doublehydroxides films on the anodized magnesium alloy to improve corrosion properties, Surface & Coatings Technology 366(2019)238–247) reported the preparation of magnesium-aluminum layered double hydroxides (MLDs) on the surface of magnesium alloys via an in-situ growth method. The surface of the MLDs was modified with myristic acid and 1H,1H,2H,2H perfluorodecyltrimethoxysilane to obtain a superhydrophobic coating. Characterization confirmed the anti-corrosion properties of this superhydrophobic coating. However, the article only modified the MLD layer, reducing its surface energy. Furthermore, it did not investigate or characterize the mechanical properties of the superhydrophobic coating. Summary of the Invention

[0005] In view of this, the present invention aims to overcome the deficiencies in the prior art and proposes an in-situ reinforced superhydrophobic composite coating of hydrotalcite on the surface of magnesium alloy and its preparation method. The present invention provides a multilayer composite structure, utilizing hydrotalcite loaded with a green corrosion inhibitor (amino acid-based) as a pretreatment layer, and further constructing a micro / nano structure on the surface using nanoparticles as assembly units to prepare a superhydrophobic coating. Through a chemical reaction between the pretreatment layer and the surface superhydrophobic coating, the adhesion between the superhydrophobic coating and the magnesium alloy substrate is enhanced in situ, and the mechanical properties of the coating are characterized. Simultaneously, during the preparation process, a fluorine-free, low surface energy material is selected to modify the nanoparticles, making it environmentally friendly and harmless.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] In a first aspect, the present invention provides a superhydrophobic composite coating for magnesium alloy surface reinforced with hydrotalcite in situ. The superhydrophobic composite coating comprises a magnesium-aluminum hydrotalcite pretreatment layer and a superhydrophobic coating in situ reinforced on the surface of the magnesium-aluminum hydrotalcite pretreatment layer. The superhydrophobic coating is prepared from components including a silica precursor, anhydrous ethanol, long-chain alkoxysilane, and ammonia. The volume fraction of the silica precursor in the superhydrophobic coating is 1-5 parts, the volume fraction of the long-chain alkoxysilane is 2-10 parts, the volume fraction of the anhydrous ethanol is 50-120 parts, and the volume fraction of the ammonia is 3-6 parts. The long-chain alkoxysilane is an alkoxysilane with not less than 16 carbon atoms.

[0008] In some embodiments of the present invention, the silica precursor is one or a mixture of two or more of methyl orthosilicate, ethyl orthosilicate, and butyl orthosilicate.

[0009] In some embodiments of the present invention, the long-chain alkoxysilane is one or a mixture of two or more of hexadecyltriethoxysilane, octadecyltriethoxysilane, docosyltriethoxysilane, hexadecyltrimethoxysilane, octadecyltrimethoxysilane, and docosyltrimethoxysilane.

[0010] In some embodiments of the present invention, the surface of the magnesium-aluminum hydrotalcite pretreated layer is loaded with an amino acid corrosion inhibitor.

[0011] In some embodiments of the present invention, the method for loading an amino acid-based corrosion inhibitor onto the surface of the magnesium-aluminum hydrotalcite pretreated layer includes the following steps:

[0012] Amino acid-based corrosion inhibitors were dissolved in deionized water to obtain corrosion inhibitor solutions with a concentration of 0.02 mol / L to 0.2 mol / L. The pH of the corrosion inhibitor solution was adjusted to 9 to 13. Then, the magnesium alloy with the magnesium-aluminum hydrotalcite pretreated layer was placed in the corrosion inhibitor solution and then placed in a water bath at 40℃ to 80℃ for 18h to 32h to perform corrosion inhibitor intercalation loading, thus obtaining a magnesium-aluminum hydrotalcite pretreated layer loaded with amino acid-based corrosion inhibitors.

[0013] In some embodiments of the present invention, the method for preparing the magnesium-aluminum hydrotalcite pretreatment layer includes the following steps:

[0014] The etched magnesium alloy substrate was placed in the hydrotalcite growth solution and reacted at 100℃-140℃ for 8-16 hours. After the reaction was completed, the substrate was naturally cooled and removed to obtain a magnesium-aluminum hydrotalcite pretreatment layer grown in situ on the magnesium alloy surface.

[0015] In some embodiments of the present invention, the hydrotalcite growth solution is an aqueous solution of aluminum nitrate with a pH value adjusted to 9-13, and the concentration of the aqueous solution of aluminum nitrate is 0.008 mol / L-0.05 mol / L.

[0016] The inventors have innovatively discovered that the concentration of aluminum nitrate affects the stability of the bond between the magnesium-aluminum hydrotalcite pretreatment layer and the superhydrophobic coating. At a suitable concentration, the magnesium-aluminum hydrotalcite pretreatment layer possesses an appropriate specific surface area and microstructure, which is beneficial for constructing a micro / nano structure with a certain degree of surface roughness, thereby achieving superhydrophobic properties. Furthermore, it also facilitates the physical adsorption of the superhydrophobic coating material, thus improving the stability of the bond between the coating and the hydrotalcite.

[0017] In some embodiments of the present invention, the amino acid corrosion inhibitor is one or a mixture of two or more of L-glutamic acid, L-aspartic acid, and L-tryptophan.

[0018] In some embodiments of the present invention, the etching method of the magnesium alloy substrate is as follows: after polishing the magnesium alloy, it is ultrasonically cleaned in anhydrous ethanol for 20 min-60 min, and after cleaning, it is naturally air-dried. Then, it is immersed in an alkaline solution of 4 mol / L-10 mol / L for 1 h-5 h to achieve etching of the magnesium alloy surface. Finally, the magnesium alloy is taken out, cleaned, and dried with cold air to obtain the treated magnesium alloy substrate.

[0019] Secondly, the present invention also provides a method for preparing a hydrotalcite-reinforced superhydrophobic composite coating on a magnesium alloy surface, comprising the following steps:

[0020] S1: Take anhydrous ethanol, ammonia and tetraethoxysilane and stir at room temperature for 12-18 hours to obtain a light blue superhydrophobic sol solution.

[0021] S2: Add hexadecyltrimethoxysilane to the superhydrophobic sol solution prepared in step S1 and stir at room temperature for 2-10 hours. Then place the magnesium alloy with the magnesium-aluminum hydrotalcite pretreated layer loaded with amino acid corrosion inhibitor into it and react at 70℃-110℃ for 10-14 hours to obtain the in-situ reinforced superhydrophobic composite coating of hydrotalcite on the surface of the magnesium alloy.

[0022] In some embodiments of the present invention, the method for loading an amino acid-based corrosion inhibitor onto the surface of the magnesium-aluminum hydrotalcite pretreated layer includes the following steps:

[0023] Amino acid-based corrosion inhibitors were dissolved in deionized water to obtain corrosion inhibitor solutions with a concentration of 0.02 mol / L to 0.2 mol / L. The pH of the corrosion inhibitor solution was adjusted to 9 to 13. Then, the magnesium alloy with the magnesium-aluminum hydrotalcite pretreated layer was placed in the corrosion inhibitor solution and then placed in a water bath at 40℃ to 80℃ for 18h to 32h to perform corrosion inhibitor intercalation loading, thus obtaining a magnesium-aluminum hydrotalcite pretreated layer loaded with amino acid-based corrosion inhibitors.

[0024] In some embodiments of the present invention, the method for preparing the magnesium-aluminum hydrotalcite pretreatment layer includes the following steps:

[0025] The etched magnesium alloy substrate was placed in the hydrotalcite growth solution and reacted at 100℃-140℃ for 8-16 hours. After the reaction was completed, the substrate was naturally cooled and removed to obtain a magnesium-aluminum hydrotalcite pretreatment layer grown in situ on the magnesium alloy surface.

[0026] This invention provides long-lasting corrosion protection to magnesium alloys by preparing a hydrotalcite pretreatment layer loaded with a green amino acid-based corrosion inhibitor on the surface, followed by a superhydrophobic coating. This also improves the adhesion between the coating and the magnesium alloy. The main reason is:

[0027] (1) Due to its superhydrophobic properties, the in-situ reinforced superhydrophobic composite coating of hydrotalcite can significantly reduce the contact area between the corrosive medium and the coating, thus playing a passive anti-corrosion role for magnesium alloys. In addition, the corrosion inhibitor loaded in the hydrotalcite pretreatment layer can react at the defect site to form a new passivation film after the coating wears and forms defects. This further isolates the contact between the corrosive medium and the magnesium alloy substrate, thereby achieving an active anti-corrosion effect.

[0028] (2) In the preparation of the magnesium-aluminum hydrotalcite pretreatment layer, the magnesium element comes from the magnesium alloy. Therefore, the pretreatment layer obtained by the in-situ growth method is directly grown on the surface of the magnesium alloy and has a strong bonding force. Through the chemical reaction between the functional groups on the surface of hydrotalcite and the silica nanoparticle building units of the superhydrophobic coating, chemical bonding between layers is achieved, which improves the bonding force between the superhydrophobic coating and the magnesium alloy substrate.

[0029] In summary, the preparation of a superhydrophobic composite coating reinforced by in-situ hydrotalcite achieves synergistic active and passive corrosion protection, and the bonding force between the composite coating and the magnesium alloy substrate is greatly improved. Therefore, long-term corrosion protection of magnesium alloys can be achieved.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] (1) The present invention prepares a double-layer composite coating on the surface of magnesium alloy and optimizes the preparation steps of the two coatings. Specifically, a hydrotalcite pretreatment layer is first grown in situ on the surface of magnesium alloy, and then a superhydrophobic coating with silica nanoparticles as the building unit is grown on the surface of the hydrotalcite pretreatment layer. This gives the magnesium alloy excellent active and passive synergistic anti-corrosion performance and self-cleaning performance, and achieves long-term corrosion protection of magnesium alloy.

[0032] (2) In designing the double-layer coating system, the present invention increases the chemical reaction between the hydrotalcite pretreatment layer and the superhydrophobic coating on the surface to achieve a strong bond between the coating and the magnesium alloy substrate in the form of chemical bonds.

[0033] (3) In preparing the hydrotalcite pretreatment layer, the present invention uses a green and environmentally friendly amino acid corrosion inhibitor as an insert for the hydrotalcite layer, avoiding the low toxicity and environmental pollution of inorganic corrosion inhibitors.

[0034] (4) In preparing the superhydrophobic coating, the present invention uses green, fluorine-free hexadecyltrimethoxysilane as a low surface energy material to reduce the surface energy of the coating and overcome fluorine pollution. Attached Figure Description

[0035] Figure 1 A scanning electron microscope image of the in-situ enhanced superhydrophobic composite coating of hydrotalcite prepared in Example 1 of the present invention;

[0036] Figure 2 The water contact angle and roll-off angle of the hydrotalcite in-situ reinforced superhydrophobic composite coating prepared in Example 1 of this invention;

[0037] Figure 3 Tafel curves of the coatings prepared for the examples and comparative examples. Detailed Implementation

[0038] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0039] In this document, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0040] In this document, when values ​​are described as ranges, it should be understood that such disclosure includes disclosure of all possible subranges within that range, as well as the specific numerical values ​​falling within that range, regardless of whether the specific numerical value or specific subrange is explicitly specified.

[0041] In this article, the terms "multiple" or "more than" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0042] In this document, the terms "preferred" and "more preferred" are used only to describe implementation methods or embodiments with better effects, and should be understood as not constituting a limitation on the scope of protection of this invention.

[0043] In this document, terms such as "further" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this invention.

[0044] In this article, the term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0045] In this document, the term "about" means a specified value of + / - 10%, preferably + / - 5%, and more preferably + / - 1%.

[0046] In this article, the terms “include,” “including,” “have,” “contain,” etc., are all open-ended terms, meaning that they include but are not limited to.

[0047] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0048] The present invention will be described in detail below with reference to the embodiments.

[0049] Example 1

[0050] (1) Prepare AZ31B magnesium alloy, and clean and etch the magnesium alloy. The specific methods are as follows:

[0051] The magnesium alloy was cut into pieces 7 cm long and 2.5 cm wide. Then, it was polished with 400 grit, 800 grit, 1200 grit and 1500 grit sandpaper in sequence. After that, it was ultrasonically cleaned in anhydrous ethanol for 20 minutes. After cleaning, it was air-dried. Then, it was immersed in an alkaline solution of 4 mol / L for 1 hour to etch the surface of the magnesium alloy. Finally, the magnesium alloy was removed, cleaned and dried with cold air to obtain the treated magnesium alloy substrate.

[0052] (2) The specific method for preparing a hydrotalcite pretreatment layer loaded with green corrosion inhibitor (amino acid type) on the etched magnesium alloy surface is as follows:

[0053] Raw materials: Aluminum nitrate nonahydrate, L-glutamic acid corrosion inhibitor, sodium hydroxide, deionized water.

[0054] First, prepare the hydrotalcite growth solution. Add 0.8 g of aluminum nitrate nonahydrate to 105 mL of deionized water and stir for 10 minutes until the aluminum nitrate nonahydrate is completely dissolved. Slowly add an appropriate amount of 0.5 mol / L sodium hydroxide aqueous solution to adjust the pH of the solution to 9. Then, pour the mixed solution into a reaction vessel, and vertically place the magnesium alloy substrate etched in the first step into the solution in the reaction vessel. Finally, place the reaction vessel in an oven at 100 degrees Celsius and react for 8 hours. After the reaction is complete, allow the reaction vessel to cool naturally, and then remove the magnesium alloy to obtain the magnesium-aluminum hydrotalcite pretreated layer grown in situ on the magnesium alloy surface. Further, an appropriate amount of amino acid-based corrosion inhibitor is dissolved in deionized water to prepare a corrosion inhibitor solution with a concentration of 0.02 mol / L. The pH of the corrosion inhibitor solution is adjusted to 9 using a 1 mol / L sodium hydroxide solution. Then, the magnesium alloy with magnesium aluminum hydrotalcite grown on it is placed in the solution and then placed in a 40°C water bath for 18 hours to perform intercalation loading of the corrosion inhibitor, thus obtaining a magnesium aluminum hydrotalcite pretreatment layer with amino acid-based corrosion inhibitor loaded on the magnesium alloy surface.

[0055] (3) The specific method for preparing an environmentally friendly superhydrophobic coating on the surface of the magnesium aluminum hydrotalcite pretreated layer is as follows:

[0056] Raw materials: tetraethoxysilane, anhydrous ethanol, hexadecyltrimethoxysilane, ammonia.

[0057] The superhydrophobic coating was prepared using a chemical deposition method. First, a superhydrophobic sol was prepared by weighing 50 mL of anhydrous ethanol, 3 mL of ammonia, and 1 mL of tetraethoxysilane into an Erlenmeyer flask and stirring at room temperature for 12 hours to obtain a light blue sol. Then, 2 mL of hexadecyltrimethoxysilane was added, and stirring continued at room temperature for 2 hours to obtain the superhydrophobic sol. The superhydrophobic sol was then placed in a reaction vessel, and a magnesium alloy with a magnesium-aluminum hydrotalcite pretreatment layer loaded with amino acid-based corrosion inhibitors was placed vertically within it. The reaction was carried out at 70°C for 10 hours to obtain an in-situ hydrotalcite-reinforced superhydrophobic composite coating on the magnesium alloy surface.

[0058] Scanning electron microscope images of the in-situ enhanced superhydrophobic composite coating of hydrotalcite prepared in Example 1 are shown below. Figure 1 As shown.

[0059] Example 2

[0060] (1) Prepare AZ31B magnesium alloy, and clean and etch the magnesium alloy. The specific methods are as follows:

[0061] The magnesium alloy was cut into pieces 7 cm long and 2.5 cm wide. Then, it was polished with 400 grit, 800 grit, 1200 grit and 1500 grit sandpaper in sequence. After that, it was ultrasonically cleaned in anhydrous ethanol for 60 minutes. After cleaning, it was air-dried. Then, it was immersed in 6 mol / L alkaline solution for 3 hours to etch the surface of the magnesium alloy. Finally, the magnesium alloy was removed, cleaned and dried with cold air to obtain the treated magnesium alloy substrate.

[0062] (2) The specific method for preparing a hydrotalcite pretreatment layer loaded with green corrosion inhibitor (amino acid type) on the etched magnesium alloy surface is as follows:

[0063] Raw materials: Aluminum nitrate nonahydrate, L-glutamic acid corrosion inhibitor, sodium hydroxide, deionized water.

[0064] First, prepare the hydrotalcite growth solution. Add 0.8 g of aluminum nitrate nonahydrate to 265 mL of deionized water and stir for 30 minutes until the aluminum nitrate nonahydrate is completely dissolved. Slowly add an appropriate amount of 5 mol / L sodium hydroxide aqueous solution to adjust the pH of the solution to 13. Then, pour the mixed solution into a reaction vessel, and vertically place the magnesium alloy substrate etched in the first step into the solution in the reaction vessel. Finally, place the reaction vessel in an oven at 140 degrees Celsius and react for 16 hours. After the reaction is complete, allow the reaction vessel to cool naturally, and then remove the magnesium alloy to obtain the magnesium-aluminum hydrotalcite pretreated layer grown in situ on the magnesium alloy surface. Furthermore, an appropriate amount of amino acid-based corrosion inhibitor is dissolved in deionized water to prepare a corrosion inhibitor solution with a concentration of 0.2 mol / L. The pH of the corrosion inhibitor solution is adjusted to 13 using a 5 mol / L sodium hydroxide solution. Then, the magnesium alloy with magnesium aluminum hydrotalcite grown on it is placed in the solution and then placed in an 80°C water bath for 32 hours to perform intercalation loading of the corrosion inhibitor, thereby obtaining a magnesium aluminum hydrotalcite pretreatment layer with amino acid-based corrosion inhibitor loaded on the magnesium alloy surface.

[0065] (3) The specific method for preparing an environmentally friendly superhydrophobic coating on the surface of the magnesium aluminum hydrotalcite pretreated layer is as follows:

[0066] Raw materials: methyl orthosilicate, anhydrous ethanol, octadecyltrimethoxysilane, ammonia.

[0067] The superhydrophobic coating was prepared using a chemical deposition method. First, a superhydrophobic sol was prepared by weighing 120 mL of anhydrous ethanol, 6 mL of ammonia, and 5 mL of methyl orthosilicate into an Erlenmeyer flask and stirring at room temperature for 18 hours to obtain a light blue sol. Then, 10 mL of octadecyltrimethoxysilane was added, and stirring continued at room temperature for another 10 hours to obtain the superhydrophobic sol. The superhydrophobic sol was then placed in a reaction vessel, and a magnesium alloy with a magnesium-aluminum hydrotalcite pretreatment layer loaded with amino acid-based corrosion inhibitors was placed vertically within it. The reaction was carried out at 110°C for 14 hours to obtain an in-situ hydrotalcite-reinforced superhydrophobic composite coating on the magnesium alloy surface.

[0068] Example 3

[0069] (1) Prepare AZ31B magnesium alloy, and clean and etch the magnesium alloy. The specific methods are as follows:

[0070] The magnesium alloy was cut into pieces 7 cm long and 2.5 cm wide. Then, it was polished with 400 grit, 800 grit, 1200 grit and 1500 grit sandpaper in sequence. After that, it was ultrasonically cleaned in anhydrous ethanol for 60 minutes. After cleaning, it was air-dried. Then, it was immersed in 10 mol / L alkaline solution for 5 hours to etch the surface of the magnesium alloy. Finally, the magnesium alloy was removed, cleaned and dried with cold air to obtain the treated magnesium alloy substrate.

[0071] (2) The specific method for preparing a hydrotalcite pretreatment layer loaded with green corrosion inhibitor (amino acid type) on the etched magnesium alloy surface is as follows:

[0072] Raw materials: Aluminum nitrate nonahydrate, L-glutamic acid corrosion inhibitor, sodium hydroxide, deionized water.

[0073] First, prepare the hydrotalcite growth solution. Add 2 grams of aluminum nitrate nonahydrate to 105 ml of deionized water and stir for 20 minutes until the aluminum nitrate nonahydrate is completely dissolved. Slowly add an appropriate amount of 2.5 mol / L sodium hydroxide aqueous solution to adjust the pH of the solution to 13. Then, pour the mixed solution into a reaction vessel, and vertically place the magnesium alloy substrate etched in the first step into the solution in the reaction vessel. Finally, place the reaction vessel in an oven at 120 degrees Celsius and react for 12 hours. After the reaction is complete, allow the reaction vessel to cool naturally, and then remove the magnesium alloy to obtain the magnesium-aluminum hydrotalcite pretreated layer grown in situ on the magnesium alloy surface. Further, an appropriate amount of amino acid-based corrosion inhibitor is dissolved in deionized water to prepare a corrosion inhibitor solution with a concentration of 0.1 mol / L. The pH of the corrosion inhibitor solution is adjusted to 10 using a 3 mol / L sodium hydroxide solution. Then, the magnesium alloy with magnesium aluminum hydrotalcite grown on it is placed in the solution and then placed in a 55°C water bath for 24 hours to perform intercalation loading of the corrosion inhibitor, thus obtaining a magnesium aluminum hydrotalcite pretreatment layer with amino acid-based corrosion inhibitor loaded on the magnesium alloy surface.

[0074] (3) The specific method for preparing an environmentally friendly superhydrophobic coating on the surface of the magnesium aluminum hydrotalcite pretreated layer is as follows:

[0075] Raw materials: butyl orthosilicate, anhydrous ethanol, docosyltriethoxysilane, ammonia.

[0076] The superhydrophobic coating was prepared using a chemical deposition method. First, a superhydrophobic sol was prepared by weighing 100 mL of anhydrous ethanol, 4 mL of ammonia, and 3 mL of tetrabutyl orthosilicate into a conical flask and stirring at room temperature for 15 hours to obtain a light blue sol. Then, 5 mL of docosyltriethoxysilane was added, and stirring continued at room temperature for 8 hours to obtain the superhydrophobic sol. The superhydrophobic sol was placed in a reaction vessel, and a magnesium alloy with a magnesium-aluminum hydrotalcite pretreatment layer loaded with amino acid corrosion inhibitors was placed vertically inside. The reaction was carried out at 90 degrees Celsius for 12 hours to obtain an in-situ hydrotalcite-reinforced superhydrophobic composite coating on the magnesium alloy surface.

[0077] Comparative Example 1: Superhydrophobic coating sprayed onto magnesium alloy substrate

[0078] Compared to Example 1, Comparative Example 1 involves directly applying a superhydrophobic coating to the etched magnesium alloy surface using a spraying method, without a hydrotalcum powder pretreatment layer. The cleaning and etching of the magnesium alloy are the same as in Example 1, and the preparation method of the superhydrophobic sol is also the same as step (3) in Example 1. The difference lies in the use of a spraying method to directly prepare the coating on the etched magnesium alloy surface. The specific method is as follows:

[0079] The prepared superhydrophobic sol was uniformly sprayed onto the etched magnesium alloy surface using an air compressor. The spraying pressure was 40 psi and the spraying distance was 15 cm. Finally, the sprayed magnesium alloy was dried at room temperature to obtain the superhydrophobic coating.

[0080] Comparative Example 2: Magnesium alloy substrate coated with a hydrotalcite-reinforced superhydrophobic coating

[0081] Compared to Example 1, Comparative Example 2 involved spraying a hydrotalcite coating onto a magnesium alloy surface, followed by chemical deposition to prepare a superhydrophobic coating on the hydrotalcite surface. The cleaning and etching of the magnesium alloy were the same as in Example 1, as was the method for preparing the superhydrophobic coating via chemical deposition. The difference was that the in-situ grown hydrotalcite layer in Example 1 was replaced with a sprayed hydrotalcite layer, and the loading of the subsequent corrosion inhibitor was also the same as in Example 1. The specific preparation method is as follows:

[0082] Raw materials: Magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, deionized water, sodium hydroxide.

[0083] First, a magnesium-aluminum hydrotalcite solution was prepared. Then, a magnesium-aluminum hydrotalcite coating was applied to the etched magnesium alloy surface using a spraying method. 100 mL of 0.5 mol / L magnesium nitrate hexahydrate and 0.25 mol / L aluminum nitrate nonahydrate were mixed together in a round-bottom flask. Then, 2 mol / L sodium hydroxide solution was slowly added dropwise to adjust the pH of the mixture to approximately 10. To avoid introducing carbon dioxide, nitrogen gas was continuously bubbled into the solution. After the addition was complete, the suspension was aged in a 65°C water bath for 24 hours to obtain a magnesium-aluminum hydrotalcite suspension. This suspension was then sprayed onto the etched magnesium alloy surface under the following conditions: pressure 40 psi, spraying distance 15 cm, ensuring the magnesium-aluminum hydrotalcite suspension was evenly sprayed onto the substrate surface.

[0084] The corrosion inhibitor loading and the preparation of the superhydrophobic coating were then carried out using the same method as in Example 1.

[0085] Comparative Example 3

[0086] Compared to Example 1, Comparative Example 3 involves preparing an in-situ reinforced superhydrophobic coating of hydrotalcite without corrosion inhibitor intercalation on the surface of a magnesium alloy. That is, steps (1) and (3) are the same as in Example 1, and the specific method for step (2) is as follows:

[0087] Raw materials: aluminum nitrate nonahydrate, sodium hydroxide, deionized water.

[0088] First, prepare the hydrotalcite growth solution. Add 0.8 g of aluminum nitrate nonahydrate to 105 mL of deionized water and stir for 10 minutes until the aluminum nitrate nonahydrate is completely dissolved. Slowly add an appropriate amount of 0.5 mol / L sodium hydroxide aqueous solution to adjust the pH of the solution to 9. Then, pour the mixed solution into a reaction vessel, and vertically place the magnesium alloy substrate etched in the first step into the solution in the reaction vessel. Finally, place the reaction vessel in an oven at 100 degrees Celsius and react for 8 hours. After the reaction is complete, allow the reaction vessel to cool naturally, and then remove the magnesium alloy to obtain the magnesium-aluminum hydrotalcite pretreated layer grown in situ on the magnesium alloy surface.

[0089] Comparative Example 4

[0090] Compared to Example 1, in Comparative Example 4, hexadecyltrimethoxysilane was replaced with dodecyltrimethoxysilane. The other steps were the same as in Example 1.

[0091] Comparative Example 5

[0092] Compared to Example 1, in step (2) of Comparative Example 5, 2 grams of aluminum nitrate nonahydrate were added to 80 ml of deionized water.

[0093] Performance testing:

[0094] 1. Morphological analysis:

[0095] The surface morphology of the composite coating was observed using scanning electron microscopy. The in-situ hydrotalcite-reinforced superhydrophobic composite coating for magnesium alloy prepared in Example 1 was as follows: Figure 1 As shown in the figure, the sheet-like structure is composed of hydrotalcite sheets, and silica nanoparticles are deposited on the surface of the hydrotalcite, forming a two-layer composite system.

[0096] 2. Wettability characteristics:

[0097] The water contact angle and roll-off angle of the prepared coating were characterized using an optical contact angle meter. Table 1 shows the water contact angle and roll-off angle of the examples and comparative examples. Figure 2 The water contact angle and roll-off angle of the hydrotalcite in-situ reinforced superhydrophobic composite coating prepared in Example 1.

[0098] Table 1. Water contact angle and roll-off angle of the hydrotalcite-reinforced superhydrophobic composite coatings prepared in the examples and comparative examples.

[0099] Example 1 153° 6° Comparative Example 1 152° 5° Comparative Example 2 56° —The water droplet cannot roll Comparative Example 3 152° 5° Comparative Example 4 143° —The water droplet cannot roll Comparative Example 5 138° —The water droplet cannot roll

[0100] 3. Characterization of corrosion resistance;

[0101] Tafel curve tests were performed on the treated magnesium alloy substrates of Comparative Examples 1-5 and the hydrotalcite-reinforced superhydrophobic composite coating obtained in Example 1 using an electrochemical method. Figure 3 As shown in the figure, generally speaking, a lower corrosion current and a higher corrosion potential indicate that the coating has strong anti-corrosion performance. It can be seen from the figure that the in-situ reinforced superhydrophobic composite coating with hydrotalcite on the magnesium alloy surface (Example 1) has low corrosion current and high corrosion potential, indicating that the composite coating prepared in Example 1 has the best anti-corrosion performance.

[0102] 4. Mechanical property characterization:

[0103] According to the national standard GB / T 6739-2022 "Paints and Varnishes—Pencil Method for Determining Hardness of Paint Films," standardized pencils were used to conduct tests using a pencil hardness tester that met the standard requirements, following standard procedures. Table 2 shows the pencil hardness grades for the examples and comparative examples. Hardness grades are typically HB, B, 3H, etc., where H represents hardness and B represents blackness; the higher the number, the more pronounced the corresponding characteristic. Higher pencil hardness indicates greater paint film hardness, signifying stronger adhesion between the coating and the substrate.

[0104] Table 2 shows the adhesion between the coatings prepared in the examples and comparative examples and the magnesium alloy substrate.

[0105] Example 1 4H Comparative Example 1 1H Comparative Example 2 3H Comparative Example 3 4H Comparative Example 4 4H Comparative Example 5 1H

[0106] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A superhydrophobic composite coating with in-situ hydrotalcite reinforcement on the surface of a magnesium alloy, characterized in that: The superhydrophobic composite coating comprises a magnesium aluminum hydrotalcite pretreatment layer and a superhydrophobic coating in situ reinforced on the surface of the magnesium aluminum hydrotalcite pretreatment layer. The superhydrophobic coating is prepared from components including a silica precursor, anhydrous ethanol, long-chain alkoxysilane, and ammonia. The volume fraction of the silica precursor in the superhydrophobic coating is 1-5 parts, the volume fraction of the long-chain alkoxysilane is 2-10 parts, the volume fraction of the anhydrous ethanol is 50-120 parts, and the volume fraction of the ammonia is 3-6 parts. The long-chain alkoxysilane is an alkoxysilane with not less than 16 carbon atoms. The surface of the magnesium-aluminum hydrotalcite pretreated layer is loaded with an amino acid corrosion inhibitor. The preparation method of the magnesium-aluminum hydrotalcite pretreated layer includes the following steps: The etched magnesium alloy substrate was placed in the hydrotalcite growth solution and reacted at 100℃-140℃ for 8-16 hours. After the reaction was completed, the substrate was naturally cooled and removed to obtain a magnesium-aluminum hydrotalcite pretreatment layer grown in situ on the magnesium alloy surface.

2. The in-situ reinforced superhydrophobic composite coating of hydrotalcite on magnesium alloy surface according to claim 1, characterized in that: The silica precursor is one or a mixture of two or more of methyl orthosilicate, ethyl orthosilicate, and butyl orthosilicate.

3. The in-situ reinforced superhydrophobic composite coating with hydrotalcite on the surface of magnesium alloy according to claim 1, characterized in that: The long-chain alkoxysilane is one or a mixture of two or more of hexadecyltriethoxysilane, octadecyltriethoxysilane, docosyltriethoxysilane, hexadecyltrimethoxysilane, octadecyltrimethoxysilane, and docosyltrimethoxysilane.

4. The in-situ reinforced superhydrophobic composite coating of hydrotalcite on magnesium alloy surface according to claim 1, characterized in that: The amino acid corrosion inhibitor is one or a mixture of two or more of L-glutamic acid, L-aspartic acid, and L-tryptophan.

5. The in-situ reinforced superhydrophobic composite coating with hydrotalcite on the surface of magnesium alloy according to claim 1, characterized in that: The method for loading an amino acid-based corrosion inhibitor onto the surface of the magnesium-aluminum hydrotalcite pretreated layer includes the following steps: Amino acid-based corrosion inhibitors were dissolved in deionized water to obtain corrosion inhibitor solutions with a concentration of 0.02 mol / L to 0.2 mol / L. The pH of the corrosion inhibitor solution was adjusted to 9 to 13. Then, the magnesium alloy with the magnesium-aluminum hydrotalcite pretreated layer was placed in the corrosion inhibitor solution and then placed in a water bath at 40℃ to 80℃ for 18h to 32h to perform corrosion inhibitor intercalation loading, thus obtaining a magnesium-aluminum hydrotalcite pretreated layer loaded with amino acid-based corrosion inhibitors.

6. The in-situ reinforced superhydrophobic composite coating of hydrotalcite on magnesium alloy surface according to claim 1, characterized in that: The hydrotalcite growth solution is an aqueous solution of aluminum nitrate with a pH adjusted to 9-13, and the concentration of the aqueous solution of aluminum nitrate is 0.008 mol / L-0.05 mol / L.

7. The method for preparing the in-situ reinforced superhydrophobic composite coating of hydrotalcite on the surface of magnesium alloy according to any one of claims 1-6, characterized in that: Includes the following steps: S1: Take anhydrous ethanol, ammonia and tetraethoxysilane and stir at room temperature for 12-18 hours to obtain a light blue superhydrophobic sol solution. S2: Add hexadecyltrimethoxysilane to the superhydrophobic sol solution prepared in step S1 and stir at room temperature for 2-10 hours. Then place the magnesium alloy with the magnesium-aluminum hydrotalcite pretreated layer loaded with amino acid corrosion inhibitor into it and react at 70℃-110℃ for 10-14 hours to obtain the in-situ reinforced superhydrophobic composite coating of hydrotalcite on the surface of the magnesium alloy.

8. The method for preparing the in-situ reinforced superhydrophobic composite coating of hydrotalcite on the surface of magnesium alloy according to claim 7, characterized in that: The method for loading an amino acid-based corrosion inhibitor onto the surface of the magnesium-aluminum hydrotalcite pretreated layer includes the following steps: Amino acid-based corrosion inhibitors were dissolved in deionized water to obtain corrosion inhibitor solutions with a concentration of 0.02 mol / L to 0.2 mol / L. The pH of the corrosion inhibitor solution was adjusted to 9 to 13. Then, the magnesium alloy with the magnesium-aluminum hydrotalcite pretreated layer was placed in the corrosion inhibitor solution and then placed in a water bath at 40℃ to 80℃ for 18h to 32h to perform corrosion inhibitor intercalation loading, thus obtaining a magnesium-aluminum hydrotalcite pretreated layer loaded with amino acid-based corrosion inhibitors.

9. The method for preparing the in-situ reinforced superhydrophobic composite coating of hydrotalcite on the surface of magnesium alloy according to claim 7, characterized in that: The preparation method of the magnesium-aluminum hydrotalcite pretreated layer includes the following steps: The etched magnesium alloy substrate was placed in the hydrotalcite growth solution and reacted at 100℃-140℃ for 8-16 hours. After the reaction was completed, the substrate was naturally cooled and removed to obtain a magnesium-aluminum hydrotalcite pretreatment layer grown in situ on the magnesium alloy surface.

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