Bio-based double-layer super-hydrophobic anticorrosive coating for magnesium alloy and preparation method and application of bio-based double-layer super-hydrophobic anticorrosive coating

Abstract

The invention relates to the field of green and environment-friendly anti-corrosion coatings, in particular to a bio-based double-layer super-hydrophobic anti-corrosion coating for magnesium alloy and a preparation method and application thereof.The bio-based double-layer super-hydrophobic anti-corrosion coating comprises an SMT bio-substrate coating and an HS-ATP / SMT super-hydrophobic coating, and the SMT bio-substrate coating comprises a bio-based SMT adhesive, a sulfydryl-containing organic corrosion inhibitor and an organic solvent; the HS-ATP / SMT super-hydrophobic coating comprises HS-ATP, an SMT adhesive and a solvent. When the SMT biological substrate coating is used, the surface of a pretreated magnesium alloy is uniformly coated with the SMT biological substrate coating, and standing is conducted for 10-30 min at the room temperature; drying and curing to obtain an SMT biological substrate coating; the surface of the SMT biological substrate coating is coated with the HS-ATP / SMT super-hydrophobic coating, then standing is conducted for 10-30 min at the room temperature, a sample is dried and cured, and the super-hydrophobic coating is obtained.By means of the scheme, the long-term corrosion resistance and mechanical stability of the magnesium alloy are remarkably improved, meanwhile, use of fluorine-containing compounds and non-degradable resin is reduced, the anti-corrosion effect and environment friendliness are both considered, and the application range is wide. Good application prospects are realized.

Description

Technical Field

[0001] This invention relates to the field of green and environmentally friendly anti-corrosion coatings, specifically to a bio-based double-layer superhydrophobic anti-corrosion coating for magnesium alloys, its preparation method, and its application. Background Technology

[0002] Magnesium alloys possess advantages such as high specific strength, low density, and good vibration damping performance, making them important lightweight structural materials in the automotive, electronics, and aerospace industries. However, due to the high chemical reactivity of magnesium, magnesium alloys are highly susceptible to pitting and crevice corrosion in corrosive environments such as those containing chloride, severely limiting their engineering applications.

[0003] To improve the corrosion resistance of magnesium alloys, various surface protection methods have been proposed in existing technologies, including chemical conversion films, micro-arc oxidation, organic anti-corrosion coatings, and superhydrophobic coatings. Among them, anti-corrosion coatings based on the superhydrophobic effect, by introducing micro / nano rough structures on the metal surface and doping with low surface energy materials, can form a stable air cushion layer at the solid-liquid interface, effectively blocking the penetration of corrosive media, and has become a research hotspot in recent years.

[0004] In existing publicly available technologies, a common approach is to first prepare a dense organic anti-corrosion underlayer, such as epoxy resin, on the magnesium alloy surface. Some methods add corrosion inhibitors to the underlayer to improve the protective performance after coating damage. Subsequently, a superhydrophobic rough structure is constructed on the underlayer surface using fluorinated silanes, fluorinated acrylates, or other fluorinated low surface energy compounds in combination with inorganic particles. While this technology improves the corrosion resistance of magnesium alloys to some extent, it has the following shortcomings: 1. Because a large amount of fluorinated silanes and fluorinated polymers are added to the coating, the product cost is high on the one hand, and there are potential risks to the environment and health on the other hand. Therefore, it cannot be used in fields with high environmental protection and health requirements.

[0005] 2. Thermosetting resin systems such as epoxy resin are difficult to degrade naturally, and they are prone to forming persistent microplastics during coating preparation, use and disposal, which is detrimental to the ecological environment.

[0006] 3. The protection mode is limited. Once the superhydrophobic surface is damaged by mechanical wear, ultraviolet aging or chemical media, the coating is difficult to restore effective protection in time, and the magnesium alloy substrate is prone to corrosion during long-term service.

[0007] 4. Although corrosion inhibitors are introduced into the coating, their distribution and release behavior are difficult to effectively coordinate with the superhydrophobic structure, making it difficult to continue to play a protective role when the coating is damaged, resulting in limited overall corrosion inhibition effect and durability.

[0008] Therefore, it is necessary to develop a green and environmentally friendly technical solution that can significantly improve the long-term corrosion resistance and mechanical stability of magnesium alloys. Summary of the Invention

[0009] The present invention aims to provide a bio-based double-layer superhydrophobic anti-corrosion coating for magnesium alloys, its preparation method and application, which can significantly improve the long-term corrosion resistance and mechanical stability of magnesium alloys while reducing the use of fluorine-containing compounds and non-degradable resins, thus balancing anti-corrosion effect and environmental friendliness, and has good application prospects.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: a bio-based double-layer superhydrophobic anti-corrosion coating for magnesium alloys, comprising an SMT bio-based coating and an HS-ATP / SMT superhydrophobic coating, wherein the SMT bio-based coating comprises 20-60 wt% bio-based SMT adhesive, a thiol-containing organic corrosion inhibitor, and an organic solvent; the HS-ATP / SMT superhydrophobic coating comprises HS-ATP, an SMT adhesive, and a solvent.

[0011] Preferably, as an improvement, the amount of the thiol-containing organic corrosion inhibitor added is 3wt% to 10wt% based on the mass of the bio-based SMT adhesive. Adding too little or too much thiol-containing organic corrosion inhibitor will reduce the corrosion resistance of the coating. In particular, when added in excess, it will not only have little effect on improving the overall corrosion resistance, but may also cause micro-cracks during the curing of the substrate, which will seriously reduce the corrosion resistance of the coating.

[0012] Preferably, as an improvement, the thiol-containing organic corrosion inhibitor is 2-mercaptobenzimidazole corrosion inhibitor, 2-mercaptobenzothiazole, or 2-mercapto-1-methylimidazole; the organic solvent is one or more of butyl butyrate, butyl acetate, and xylene.

[0013] The HS-ATP is attapulgite modified with hexadecyltrimethoxysilane and tetraethyl orthosilicate.

[0014] In the HS-ATP / SMT superhydrophobic coating, the mass ratio of HS-ATP to SMT adhesive is 1:(1~3).

[0015] A method for preparing a bio-based double-layer superhydrophobic anti-corrosion coating for magnesium alloys, characterized by comprising: Preparation of SMT bio-based coating: Add 20-60 wt% bio-based SMT adhesive to an organic solvent and stir until an emulsion is formed; add 3%-10% of the bio-based SMT adhesive mass of a thiol-containing organic corrosion inhibitor, and continue stirring or sonicating for 10-60 min to obtain a uniform SMT bio-based coating. Preparation of HS-ATP / SMT superhydrophobic coating: Disperse HS-ATP powder in an alcohol-based organic solvent and sonicate or stir for 10-30 min to form a uniform suspension; add SMT binder at a mass ratio of HS-ATP to SMT of 1:(1-3) and continue stirring for 10-30 min to obtain the HS-ATP / SMT superhydrophobic top coating.

[0016] Preferably, as an improvement, the method for preparing HS-ATP includes the following steps: S1, acid activation S11 Add natural attapulgite to a hydrochloric acid solution with a concentration of 1-4 mol / L and stir the reaction at 60-80 ℃ for 3-6 h; S12 filtration and washing with deionized water until the filtrate is nearly neutral, then drying at 60–100 °C, yields acid-treated attapulgite H-ATP.

[0017] S2, HDTMS Modification S21 disperses H-ATP in an ethanol / ammonia solution to obtain an H-ATP mixture; S22 involves adding a silane mixture to an H-ATP mixture and stirring the mixture to react. 0.8–1.2 mL of the silane mixture is added for every 0.5 g of H-ATP. Adding too much silane mixture will result in poor powder dispersibility (agglomeration), while adding too little may lead to poor hydrophobicity. The silane mixture consists of HDTMS and TEOS. After stirring and reacting with S23, the mixture was centrifuged, washed with ethanol, and dried at 60–80 °C to obtain HS-ATP powder.

[0018] The application of a bio-based double-layer superhydrophobic anti-corrosion coating for magnesium alloys includes the following steps: Substrate treatment: Grind and polish the magnesium alloy substrate, then clean the surface oil and impurities, and dry it for later use; The SMT bio-based coating was uniformly applied to the pretreated magnesium alloy surface and left to stand at room temperature for 10–30 minutes. The sample was then dried and cured to obtain a dense SMT bio-based coating. HS-ATP / SMT superhydrophobic coating was coated on the surface of SMT bio-based coating, and then left to stand at room temperature for 10-30 minutes before drying and curing to obtain HS-ATP / SMT superhydrophobic coating with micro-nano rough structure on the surface. The total thickness of the SMT bio-based coating and the HS-ATP / SMT superhydrophobic coating is 50–120 μm.

[0019] Preferably, as an improvement, during drying and curing, the sample is placed in an oven at 150–200 °C and cured for 4–10 h.

[0020] Preferably, as an improvement, the coating method is spraying, wherein the spraying pressure is 0.1–0.3 MPa and the distance between the spray gun and the substrate is 10–20 cm. Too low a spraying pressure will result in particles being difficult to spray onto the substrate surface, while too high a pressure may lead to an uneven coating. Too short a distance will also result in an uneven coating. Too far a distance will prevent the paint from reaching the substrate.

[0021] Preferably, as an improvement, the thickness of the SMT bio-based coating is 20-60 μm, and the thickness of the HS-ATP / SMT superhydrophobic coating is 30-80 μm.

[0022] The advantages of this solution are as follows: 1. Significantly improved corrosion resistance and good long-term stability: Through the synergistic effect of the SMT bio-based substrate and the HS-ATP / SMT superhydrophobic top layer, the transport of corrosive media to the magnesium alloy surface is significantly inhibited, giving the coating an ultra-high level of corrosion protection for magnesium alloys.

[0023] Electrochemical testing results show that the coating of this invention can reduce the corrosion current density of magnesium alloys by about 5 to 6 orders of magnitude, while significantly increasing the polarization resistance and low-frequency impedance modulus by about 5 to 6 orders of magnitude. It effectively isolates the contact between the corrosive medium and the substrate by increasing the charge transfer resistance of the electrode reaction and constructing a dense physical barrier layer. With its extremely low medium permeability and excellent structural stability, it achieves long-term protection for magnesium alloys and can significantly extend the service life of magnesium alloys in harsh corrosive environments such as marine and industrial atmospheres. It has outstanding application value, especially in fields with stringent requirements for lightweighting and corrosion resistance, such as aerospace, new energy vehicles, and biomedicine.

[0024] The corrosion resistance test results show that the coating of the present invention maintains a high impedance after being immersed in 3.5 wt% NaCl solution for 21 days or more, further demonstrating its excellent long-term corrosion resistance.

[0025] 2. Possesses a synergistic protection mechanism of "superhydrophobic barrier + corrosion-inhibiting self-healing": The top layer, HS-ATP / SMT, forms a micro-nano rough structure and a low surface energy interface, significantly improving the hydrophobicity of the superhydrophobic coating. This results in a contact angle of 157° and a sliding angle of 4.3°. A stable cushion layer is formed at the solid-liquid interface, significantly reducing the contact area with the medium. When the coating is locally damaged or the medium penetrates, the bottom layer, SMT / 2-MBI, gradually releases 2-MBI, forming an adsorption film on the metal surface to inhibit anodic dissolution and achieve corrosion inhibition and self-repair. Therefore, compared to a single organic dense layer or ordinary superhydrophobic layer, the coating of this invention can maintain a better protective effect even under damaged conditions.

[0026] 3. Green and environmentally friendly, low cost: This solution does not rely on fluorinated organic compounds, thus avoiding the potential environmental and health risks of fluorinated compounds at the source. At the same time, it does not contain traditional petroleum-based thermosetting resin raw materials such as epoxy resin, reducing the formation of recalcitrant polymers and benefiting the ecological environment. In addition, the raw material costs of each component in this solution are relatively low, thereby reducing the overall cost of this coating and further facilitating market promotion.

[0027] 4. Simple process, scalable for engineering: The preparation process mainly includes conventional substrate pretreatment, coating preparation, spraying and thermosetting, etc. The required equipment is simple and easy to be compatible with existing coating production lines; it is suitable for surface treatment of magnesium alloy components of different shapes and sizes and has good engineering application prospects. Attached Figure Description

[0028] Figure 1 In the image, (a) shows the infrared spectra of HDTMS, H-ATP, and HS-ATP; (b) shows the XPS full spectrum of HS-ATP; and (c) shows the high-resolution C1s spectrum of HS-ATP.

[0029] Figure 2 In the image, a1 and a2 are SEM images of the original H-ATP powder; b1 and b2 are SEM images of the HS-ATP powder.

[0030] Figure 3 In the image, (ab) shows the surface and (c) cross-section SEM images of the HASM coating, and (d) shows the EDS energy spectrum of the HASM coating and the corresponding elemental distribution diagram (ei).

[0031] Figure 4 In the image, (a) shows the self-cleaning ability of the HASM coating; (b) shows the self-cleaning mechanism; (c) shows digital photographs of different droplets on the prepared HASM coating; and (d) shows the "silver mirror" phenomenon.

[0032] Figure 5In the image, (a) is a schematic diagram of the sandpaper abrasion test and its corresponding optical photograph; (b) shows the changes in the water contact angle and sliding angle of the HASM coating after different abrasion cycles; (c) is a schematic diagram of the tape peeling test; and (d) shows the changes in the water contact angle and sliding angle of the HASM coating after different peeling cycles.

[0033] Figure 6 The test results of magnesium alloy, SMT / 2-MBI and HASM coating after immersion in 3.5 wt% NaCl solution for 2 h are as follows: (a) polarization curve, (b) Bode modulus curve, (c) Bode phase angle curve, (d) Nyquist curve.

[0034] Figure 7 The test results of SMT / 2-MBI and HASM coatings after immersion in 3.5 wt% NaCl solution for different times are shown in the following figures: (a, d) are Bode modulus curves, (b, e) are Bode phase angle curves, and (c, f) are Nyquist curves; (g) is the equivalent circuit model of magnesium alloy, SMT / 2-MBI and HASM coating; (h) is the |Z| of each sample under different conditions. f = 0.01 R ct and R coat value. Detailed Implementation

[0035] The following detailed description illustrates the specific implementation method: Example 1 A bio-based double-layer superhydrophobic anti-corrosion coating for magnesium alloys, used in green and environmentally friendly fields, includes an SMT bio-based coating and an HS-ATP / SMT superhydrophobic coating. The SMT bio-based coating comprises a bio-based SMT adhesive, a thiol-containing organic corrosion inhibitor, and an organic solvent. The bio-based SMT adhesive is an adhesive prepared from biomass raw materials, with a preferred solid content of 20–60 wt%. The thiol-containing organic corrosion inhibitor is 2-mercaptobenzimidazole (2-MBI) corrosion inhibitor, etc., with 2-MBI being preferred in this embodiment. The organic solvent is one or more of butyl butyrate, butyl acetate, and xylene; butyl acetate is used as an example in this embodiment. The amount of organic corrosion inhibitor added is preferably 3%–10 wt% by weight of SMT, more preferably 5%–8 wt%. In this embodiment, 6.7 wt% is preferred; values ​​exceeding this amount have little effect on improving the coating's corrosion resistance and increase raw material costs. In this embodiment, the masses of SMT and 2-MBI are 3 g and 0.2 g, respectively, and the organic solvent is 10 mL of butyl acetate.

[0036] The HS-ATP / SMT superhydrophobic coating comprises HS-ATP, SMT adhesive, and solvent. HS-ATP is attapulgite modified with hexadecyltrimethoxysilane (HDTMS) and tetraethyl orthosilicate (TEOS). The SMT adhesive is a bio-based adhesive used to bind HS-ATP, forming a continuous coating on the substrate surface; the solvent is ethanol, isopropanol, etc. The mass ratio of HS-ATP to SMT adhesive is 1:(1-3), preferably 1:2. In this embodiment, the masses of HS-ATP and SMT adhesive are 0.5 g and 1 g, respectively, and the solvent ethanol is 20 mL.

[0037] A method for preparing a bio-based double-layer superhydrophobic anti-corrosion coating for magnesium alloys is as follows: Preparation of SMT bio-based coating: Take 3 g of SMT adhesive and add it to 10 mL of butyl acetate. Stir until a homogeneous solution or emulsion is formed. Add 0.2 g of 2-MBI and continue stirring or sonicating for 30 min to obtain SMT / 2-MBI undercoat. Preparation of HS-ATP / SMT superhydrophobic coating: 1g of HS-ATP powder was dispersed in 20mL of ethanol or ethanol / water mixed solvent and stirred for 20min to form a uniform suspension; 0.2g of SMT binder was added and stirred for another 20min to obtain the HS-ATP / SMT superhydrophobic top coating.

[0038] The preparation method of HS-ATP includes the following steps: S1, acid activation S11. Add 10g of natural attapulgite to 100mL of 3mol / L hydrochloric acid solution and stir at 70℃ for 4h. S12. Filter and wash with deionized water until the filtrate is nearly neutral, dry at 60°C to obtain acid-treated attapulgite H-ATP; S2, HDTMS Modification S21. Disperse 1g of H-ATP in 100mL of ethanol / ammonia solution to obtain H-ATP mixture; S22. Add 2 mL of a silane mixture to the H-ATP mixture and stir to react. The silane mixture consists of HDTMS and TEOS, with a volume ratio of HDTMS to TEOS of (6~8):3. Within this range, the final coating performance is optimized. Too large a volume ratio will lead to agglomeration, while too small a volume ratio will result in poor hydrophobicity of the coating. In this embodiment, the preferred volume ratio of HDTMS to TEOS is 7:3.

[0039] S23. After stirring the reaction under greenhouse conditions for 4 hours, the mixture was centrifuged, washed three times with ethanol, and dried at 60-80℃ to obtain HS-ATP powder.

[0040] The application of a bio-based double-layer superhydrophobic anti-corrosion coating for magnesium alloys is as follows: Substrate treatment: AZ31B magnesium alloy plate with dimensions of 20 mm × 20 mm × 3 mm was selected; it was polished with 800, 1200 and 2000 grit sandpaper in sequence; it was ultrasonically cleaned with acetone and anhydrous ethanol for 10 min each, rinsed with deionized water and air-dried for later use. Two coats of SMT bio-based coating were uniformly sprayed onto the surface of a magnesium alloy plate. After standing at room temperature for 10–30 min, the sample was placed in an oven at 180 ℃ for 8 h to cure, resulting in a dense SMT / 2-MBI coating of approximately 40 μm.

[0041] Spray HS-ATP / SMT superhydrophobic coating 2-3 times on the SMT / 2-MBI coating surface, and then let it stand at room temperature for 10-30 min before placing the sample in an oven at 180 ℃ for 8 h to obtain an HS-ATP / SMT superhydrophobic coating with a micro-nano rough structure on a surface of about 40 μm. The thickness of the SMT bio-based coating is 20–60 μm, the thickness of the HS-ATP / SMT superhydrophobic coating is 30–80 μm, and the total thickness of the two coatings is 50–120 μm. In this embodiment, the thickness of each coating is 40 μm.

[0042] Coatings on other substrates (such as wrought or die-cast magnesium alloys containing Al and Zn) are prepared using the same process.

[0043] Example 2 Unlike Example 1: 3 g of SMT adhesive was added to 10 mL of butyl butyrate and stirred until a homogeneous solution or emulsion was formed; 0.1 g of 2-MBI was added and stirred or sonicated for 30 min to obtain an SMT / 2-MBI undercoat; 0.5 g of HS-ATP powder was dispersed in 20 mL of ethanol mixed solvent and stirred for 12 min to form a homogeneous suspension; 0.5 g of SMT adhesive was added and stirred for 20 min to obtain an HS-ATP / SMT superhydrophobic topcoat.

[0044] Two coats of SMT bio-based coating were uniformly sprayed onto the surface of a magnesium alloy plate. After standing at room temperature for 20 minutes, the sample was cured in an oven at 150°C for 10 hours to obtain a dense SMT bio-based coating. Then, 2-3 coats of HS-ATP / SMT superhydrophobic coating were sprayed onto the SMT / 2-MBI coating surface. After standing at room temperature for 20 minutes, the sample was cured in an oven at 150°C for 10 hours to obtain an HS-ATP / SMT superhydrophobic coating with a micro-nano rough structure on the surface.

[0045] Example 3 Unlike Example 1: 3 g of SMT adhesive was added to 10 mL of butyl butyrate and stirred until a homogeneous solution or emulsion was formed; 0.3 g of 2-MBI was added and stirred or sonicated for 50 min to obtain an SMT / 2-MBI undercoat; 0.5 g of HS-ATP powder was dispersed in 20 mL of ethanol or an ethanol / water mixture and stirred for 30 min to form a homogeneous suspension; 1.5 g of SMT adhesive was added and stirred for 20 min to obtain an HS-ATP / SMT superhydrophobic topcoat.

[0046] Two coats of SMT bio-based coating were uniformly sprayed onto the surface of a magnesium alloy plate. After standing at room temperature for 30 minutes, the sample was cured in an oven at 200°C for 4 hours to obtain a dense SMT bio-based coating. Then, 2-3 coats of HS-ATP / SMT superhydrophobic coating were sprayed onto the SMT / 2-MBI coating surface. After standing at room temperature for 30 minutes, the sample was cured in an oven at 200°C for 4 hours to obtain an HS-ATP / SMT superhydrophobic coating with a micro-nano rough structure on the surface.

[0047] Comparative Example 1 The difference from Example 1 is that HS-ATP in the superhydrophobic coating is replaced with H-ATP; Comparative Example 2 Unlike Example 1, the mass ratio of HS-ATP to SMT adhesive is 1:0.5, which is 0.5g and 0.25g respectively.

[0048] Comparative Example 3 Unlike Example 1, the mass ratio of HS-ATP to SMT adhesive is 1:4, which is 0.5g and 2g respectively.

[0049] Comparative Example 4 Unlike Example 1, the amount of 2-MBI added was 1 wt%, or 0.03 g, based on the mass of the bio-based SMT adhesive.

[0050] Comparative Example 5 Unlike Example 1, the coating was cured by placing the sample in an oven at 220 °C for 3 hours during the drying process.

[0051] Comparative Example 6 Unlike Example 1, the coating was cured by placing the sample in an oven at 120 °C for 12 h during the drying process.

[0052] experiment The test results of hydrophobicity and abrasion resistance are shown in Table 1. In Table 1, the number of abrasion cycles refers to the number of rubbing cycles the coating undergoes before its contact angle fails. The test method is as follows: the sample is placed on 1000-grit sandpaper and rubbed back and forth for 10 cm under a 100 g load, constituting one cycle (the contact angle is recorded every five abrasion cycles). The standard for contact angle failure is: after several friction cycles, if the contact angle is <150° and the sliding angle is greater than 10°, then the contact angle is considered to have failed.

[0053] Corrosion resistance test method: Immerse the sample in a 3.5 wt% NaCl solution. Corrosion resistance failure criterion: Impedance modulus in the low-frequency region is below 10. 3 If so, the corrosion resistance is deemed to have failed.

[0054]

[0055] Table 1 As can be seen from the test results in Table 1, the synergistic effect of the SMT bio-based substrate and the HS-ATP / SMT superhydrophobic top layer in Examples 1-3, along with the balanced configuration of each component and the control of process parameters, enabled the coating to maintain high impedance even after immersion in 3.5 wt% NaCl solution for 21 days or more, demonstrating that the coating possesses an ultra-high level of corrosion protection for magnesium alloys. Simultaneously, it also achieved high levels of superhydrophobicity and wear resistance, with an average contact angle as high as 157° and a wear resistance of up to 55 cycles. This fully demonstrates that this solution significantly improves the long-term corrosion resistance and mechanical stability of magnesium alloys.

[0056] Comparative Example 1, coated only with SMT bio-based coating, exhibited extremely poor corrosion resistance, superhydrophobicity, and abrasion resistance. In Comparative Example 2, the mass ratio of HS-ATP to SMT adhesive was too high, resulting in a significant improvement in superhydrophobicity but relatively low corrosion and abrasion resistance. In Comparative Example 3, the mass ratio was too low, leading to poor performance across all coating properties. In Comparative Example 4, insufficient 2-MBI resulted in better abrasion resistance but lower corrosion resistance. In Comparative Examples 5 and 6, tests were conducted on excessively high or low temperatures during drying and curing. The experiments showed that adjusting the temperature range, even with simultaneous adjustments to the curing time, reduced both abrasion and corrosion resistance.

[0057] I. HS-ATP Test To analyze the chemical composition of HS-ATP, the ATP powders before and after modification were characterized by FTIR and XPS.

[0058] like Figure 1 As shown in a, for H-ATP, 3607cm -1 and 3548cm -1 The absorption peak at 975 cm⁻¹ corresponds to the stretching vibration of -OH. -1 The strong peak at [value missing] corresponds to the stretching vibration of the Si-O bond. In comparison, HS-ATP shows several new characteristic peaks, including one at 2920 cm⁻¹. -1 and 2850 cm -1 The peak at 1465 cm⁻¹ corresponds to the stretching vibrations of -CH₃ and -CH₂. -1 The peak at 1016 cm⁻¹ is attributed to the bending vibration of CH, while the peak at 1016 cm⁻¹ is attributed to the bending vibration of CH. -1 and 805 cm -1 The characteristic peaks at these locations are attributed to the asymmetric stretching vibrations of Si-O-Si and C-Si, respectively. These results collectively indicate that HDTMS has been successfully grafted onto the H-ATP surface.

[0059] XPS full spectrum results of HS-ATP ( Figure 1 b) shows four main peaks, corresponding to O1s, C1s, Si2s, and Si2p, with binding energies of 532.2 eV, 284.8 eV, 150 eV, and 102.96 eV, respectively. The high-resolution spectrum of C1s ( Figure 1 c) It can be decomposed into two characteristic peaks: CH / CC (284.8 eV) and C-Si (285.4 eV), indicating that the carbon element on the HS-ATP surface mainly exists in the form of alkane chains. Combined with FTIR results, this further confirms that a hydrophobic hexadecyl chain (-C...) has been successfully grafted onto the HS-ATP surface. 16 H 33 ).

[0060] The surface morphology and elemental composition of the ATP nanoparticles before and after modification, as well as the HASM bilayer coating, were characterized by SEM and EDS.

[0061] like Figure 2 As shown in a1 and a2, H-ATP exhibits a dense, bundled, interwoven nanorod morphology, with fiber lengths mainly distributed between 0.1 and 1 μm. The crystal edges are clear and sharp, and the surface is free of coating, fully demonstrating its inherent nanofiber bundle microstructure. In contrast, HS-ATP retains the basic rod / fiber morphological units (…). Figure 2 b1 and b2), but the bundle structure is significantly dispersed, the degree of fiber interweaving is reduced, and some single fibers are in a separated state; at the same time, the surface roughness is slightly reduced and the crystal edge clarity is weakened, which can be attributed to the regulatory effect of HDTMS modification on its surface and aggregation morphology.

[0062] II. Testing of Composite Dual-Coating (HASM Coating) 1. Microstructure HASM coating surface ( Figure 3 a) Composed of continuous micron-scale aggregates stacked together, forming a uniform microframework and exhibiting a typical micro-nano dual-scale structure. Under high magnification, it can be observed that HS-ATP nanoparticles are tightly embedded and firmly fixed by SMT adhesive. This structure helps to form a stable micro-nano composite roughness, thereby achieving excellent superhydrophobic properties and mechanical stability. EDS spectra and elemental distribution maps show ( Figure 3 d) C, O, Mg, Al, and Si elements are uniformly and densely distributed on the coating surface, with contents of 55.68 wt%, 23.35 wt%, 1.17 wt%, 1.11 wt%, and 18.69 wt%, respectively. Furthermore, the cross-sectional morphology of the HASM bilayer coating ( Figure 3 c) indicates that the thickness of the bottom SMT / 2-MBI coating is approximately 39.1 μm, the thickness of the top superhydrophobic layer is approximately 41.8 μm, and the total thickness is approximately 80.9 μm. The interface between the two layers is smooth and dense, with no obvious pores or delamination, indicating that the SMT substrate forms good bonding and transition between layers, which helps to improve the overall mechanical stability and long-term protective performance of the coating.

[0063] 2. Self-cleaning performance Figure 4The self-cleaning properties of the prepared superhydrophobic HASM coating are demonstrated. To simulate surface contamination caused by solid particles, silica powder was selected as the solid contaminant and uniformly sprinkled on the coating surface with an inclination angle of less than 10°. When water droplets fall on the surface, they can roll freely over a very small contact area, carrying away the contaminant particles. Ultimately, all solid particles are removed, and the coating surface remains clean and residue-free, demonstrating the coating's excellent self-cleaning ability. The figure also illustrates the self-cleaning mechanism of the HASM coating. This mechanism originates from the synergistic effect of the surface micro / nano dual roughness structure and low surface energy chemical modification, giving the water droplets an extremely high static contact angle and an extremely low sliding angle. In this state, the water droplets exist in a Cassie-Baxter mode, forming only a very small contact area on the surface and easily rolling under gravity. During the rolling process, the water droplets can encapsulate and carry away surface dust or contaminant particles, thus achieving a self-cleaning behavior similar to the lotus leaf effect. In addition, the figure shows the wetting behavior of common liquids such as water, milk, cola, and tea on the HASM coating surface. It is clearly observed that these liquids are all spherically distributed, indicating that the coating exhibits excellent hydrophobic properties in a variety of liquid systems. Furthermore, the figure shows the typical "silver mirror" phenomenon exhibited by the HASM coating in water, indicating that a stable air film has been successfully deposited on its surface. This air film forms a complete optical reflection interface between the coating and the liquid, causing total internal reflection rather than transmission of incident light, thus producing a specular reflection effect. These phenomena demonstrate the coating's excellent superhydrophobicity and underwater moisture resistance, providing strong evidence for its superior performance in waterproofing and corrosion-resistant applications.

[0064] 3. Superhydrophobic properties Because superhydrophobic coatings possess a multi-scale rough structure at the micron / nanoscale, they are susceptible to wear and tear during use, leading to surface structural damage and degradation of their hydrophobic properties. Studies have shown that sandpaper abrasion testing and tape peeling testing are effective methods for evaluating the mechanical stability of superhydrophobic protective coatings. In this study, the mechanical durability of the HASM coating was evaluated using a sandpaper abrasion test.

[0065] In the test, the sample was placed on 1000-grit sandpaper and rubbed back and forth for 10 cm under a 100 g load as one cycle (see...). Figure 5(a) A total of 60 cycles were performed, with WCA and SA recorded every 5 cycles. The HASM coating exhibited superior wear resistance and stability. Its hydrophobicity improved slightly in the early stages of wear, possibly due to the more uniform surface roughness distribution caused by slight wear, or the exposure of new low surface energy regions, thus enhancing the stability of the Cassie–Baxter state, leading to a slight increase in WCA and a decrease in SA. With increasing wear cycles, the hydrophobicity of the HASM coating gradually decreased. After 55 wear cycles, its WCA decreased from 156.1°±1° to 151.6±1.9°, while SA increased from 4.9±0.2° to 7.1±0.3°. Despite the slight decrease in hydrophobicity, the coating maintained a superhydrophobic level, indicating excellent mechanical stability and durable superhydrophobic properties under repeated friction.

[0066] Figure 5 Figure c illustrates the schematic procedure of the tape peel test. 3M tape was uniformly applied to the HASM coating surface and rolled under a 100 g weight to ensure full contact. The tape was then quickly peeled off, and the changes in WCA and SA after tape peel cycles were recorded to evaluate the coating's adhesion stability and surface structure durability. The results are shown in the figure. In the initial stage of the tape peel test, the hydrophobicity of the HASM coating slightly increased, consistent with the phenomenon observed in the sandpaper abrasion test. This is mainly attributed to the slight mechanical disturbance making the surface roughness distribution more uniform, thus further stabilizing the Cassie–Baxter state. As the number of tape peel cycles increased, the coating's WCA gradually decreased, while SA slowly increased. After 65 tape peel cycles, the HASM coating's WCA decreased to 153.9 ± 0.7°, and SA increased to 9.6 ± 0.4°, still maintaining superhydrophobicity.

[0067] 4. Corrosion resistance To systematically evaluate the corrosion resistance of the samples, common electrochemical analysis methods such as electrochemical impedance spectroscopy (EIS) and Tafel polarization curve testing were used as quantitative evaluation methods for three types of samples: bare magnesium alloy, magnesium alloy coated with SMT / 2-MBI coating, and magnesium alloy coated with HASM coating of this scheme. Tafel polarization curve can quickly compare the corrosion behavior of magnesium alloys under different coating systems.

[0068] Table 2 and Figure 6 a shows the Tafel polarization curves and corresponding electrochemical parameters of different samples after immersion in 3.5 wt% sodium chloride solution for 2 h.

[0069]

[0070] Table 2. Polarization curve parameters of different samples after immersion in 3.5 wt% NaCl solution for 2 h. Table 2 shows the slope (β) of the anode Tafel. a ), cathode Tafel slope (β) c ), corrosion potential (E) corr ) and corrosion current density ( i corr All values ​​were obtained through fitting using CHI software. Polarization resistance (R) p This reflects the coating's ability to hinder the migration of corrosive media; a higher value indicates a more significant protective effect. Furthermore, R p and corrosion inhibition efficiency ( η p It can be calculated using the following formula:

[0071] Studies have shown that lower i corr Values ​​and corrections E corr These values ​​correspond to lower dynamic corrosion inhibition rates and more stable thermodynamic corrosion resistance trends, respectively. Compared to bare magnesium alloys ( i corr = 7.67×10 -4 A·cm -2 Two types of coatings i corr The values ​​were all significantly reduced. Among them, the SMT / 2-MBI coating... i corr 3.59×10 -7 A·cm -2 The corrosion rate decreased by approximately three orders of magnitude, indicating that the underlying anti-corrosion coating has a significant corrosion-inhibiting effect; while the HASM double-layer coating... i corr Further reduced to 5.68×10 -10 A·cm -2 Compared to bare magnesium alloys, it reduces costs by six orders of magnitude, exhibiting superior protective performance. Meanwhile, the HASM coating... E corr Compared to bare magnesium alloys, the surface shift is 400 mV, significantly improving the thermodynamic stability of the substrate. Furthermore, the Rp value of bare magnesium alloys is only 1.26 × 10⁻⁶ mV. 3 Ω·cm 2 The Rp values ​​of the SMT / 2-MBI coating and the HASM coating reached 2.99 × 10⁻⁶ respectively. 6 and 1.90×10 9 Ω·cm 2This represents an improvement of approximately 3 and 6 orders of magnitude, respectively. Calculations show that the HASM composite coating... η p The corrosion resistance is as high as 99.99%. The HASM double-layer coating significantly enhances the corrosion resistance of magnesium alloys, mainly due to the gas film formed on its superhydrophobic surface, which effectively blocks the intrusion of corrosive media. Furthermore, the naturally occurring multi-layered porous structure of ATP extends the penetration path of corrosive substances, thus forming a natural barrier on the coating surface. Therefore, the prepared HASM coating provides excellent corrosion protection for magnesium alloys.

[0072] The corrosion resistance characteristics of different coated samples were tested using electrochemical impedance spectroscopy (EIS). Typically, the impedance modulus (|Z|) in the low-frequency region... f = 0.01 The higher the value, the larger the diameter of the capacitor ring, indicating that the coating has better corrosion resistance.

[0073] like Figure 6 As shown in b, after immersion in 3.5 wt% NaCl solution for 2 hours, the |Z| of the HASM double-layer coating and the SMT / 2-MBI coating... f = 0.01 The values ​​are 9.07 × 10 7 and 8.44×10 6 Ω·cm 2 This is significantly higher than the 2.63 × 10⁻⁶ of bare magnesium alloy. 2 Ω·cm 2 This indicates that both coatings significantly improved the corrosion resistance of the substrate. The Nyquist plot shows ( Figure 6 d) The capacitor ring diameters of the HASM double-layer coating and SMT / 2-MBI are significantly larger than those of the bare magnesium alloy. This can be attributed to the high hydrophobicity of the superhydrophobic coating and its dense and uniform structure, making it difficult for water molecules and corrosive substances to penetrate the coating. (In the phase diagram...) Figure 6 c) The bare magnesium alloy exhibits a single peak, corresponding to the corrosion process occurring directly on its surface. The HASM double-layer coating, however, shows a maximum phase angle close to 90°, exhibiting characteristics approaching ideal capacitance, and forms a broad phase angle plateau in the mid-to-high frequency region, indicating that it can stably function as a physical barrier under different corrosion rates.

[0074] Further long-term immersion tests were conducted on the samples to evaluate their long-term corrosion resistance. With prolonged immersion time, the |Z| of the SMT / 2-MBI coating increased. f = 0.01 The value gradually decreased to 5.58 × 10 on the ninth day. 3 Ω·cm 2 ( Figure 7 a) This is consistent with the decreasing trend of the capacitance loop in the Nyquist plot. Figure 7 c). Phase diagram shows ( Figure 7(b) In the initial immersion stage (first three days), the phase angle gradually decreased, indicating that initial voids may have formed on the coating surface, and the corrosion inhibitor 2-MBI began to migrate to the metal interface, forming a chemisorption film to inhibit corrosion. However, in the later immersion stage, the peak phase angle dropped below 60°, suggesting a decrease in the integrity of the protective film and a gradual weakening of its corrosion-inhibiting effect. In contrast, after 21 days of immersion, the |Z| of the HASM double-layer coating... f = 0.01 The value remains at 1.16 × 10 4 Ω·cm 2 ( Figure 7 d), which is about two orders of magnitude higher than that of bare magnesium alloy, and the diameter of the capacitor ring is still significantly larger than that of the bare substrate. Figure 7 f). The phase diagram shows ( Figure 7 e) During the first week, the phase angle remained consistently high, indicating that the superhydrophobic coating effectively blocked the penetration of corrosive media. The appearance of a mid-frequency peak on the seventh day suggests that the low surface energy structure of the superhydrophobic layer may have developed micro-defects after being eroded by the media, allowing for gradual penetration and transforming the system from a single capacitive behavior to a resistive-capacitive composite behavior. After longer immersion, the phase angle peak further decreased to below 20°, and the high-frequency response weakened, indicating that the top hydrophobic barrier had essentially failed, allowing a large amount of corrosive media to reach the coating / substrate interface. Overall, the HASM dual-layer coating exhibits superior long-term corrosion resistance compared to the SMT / 2-MBI single-layer coating. This is mainly due to the highly efficient barrier effect of its superhydrophobic top layer, which delays the penetration of corrosive media and provides secondary protection to the bottom layer containing corrosion inhibitors when the media reaches a localized area, thus achieving a more durable synergistic protective effect.

[0075] To further evaluate the corrosion resistance of the coating, an equivalent circuit fitting analysis was performed on the EIS data. Figure 7 g provides equivalent circuit models to describe the electrochemical responses of bare magnesium alloys, SMT / 2-MBI coatings, and HASM bilayer coatings. In the fitted model, R... L L and CPE represent inductive reactance and inductance, respectively; c With R coat Characterizing the non-ideal capacitive response and coating resistance of the coating, respectively; CPE dl With R ct These are used to fit the non-ideal capacitance response and charge transfer resistance of the electric double layer, respectively. Where R... ct It is inversely proportional to the corrosion rate and can be used as an important indicator for evaluating the protective performance of a coating. For example... Figure 7 As shown in h, after 21 days of immersion in the HASM double-layer coating, its R... ct Although the value decreased to 1.66 × 10 4 Ω·cm 2 But still better than bare magnesium alloy R ct (3.79×10) 2 Ω·cm2 The value is about two orders of magnitude higher, indicating that it still maintains good corrosion resistance. coat This reflects the coating's ability to impede electrolyte penetration and corrosive media transport; its value is positively correlated with the coating's shielding ability. As immersion time increases, the R value of the HASM double-layer coating... coat From 8.76×10 7 Ω·cm 2 Decreased to 2.81×10 3 Ω·cm 2 In contrast, after 9 days of immersion in the SMT / 2-MBI coating, R... coat It has decreased to 3.18×10 3 Ω·cm 2 In summary, the HASM coating combines physical barrier effects with chemical inhibition mechanisms. Relying on the cushion effect of the superhydrophobic surface and the auxiliary protection of the underlying corrosion inhibition system, it exhibits excellent long-term corrosion resistance.

[0076] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A bio-based double-layer superhydrophobic anticorrosive coating for magnesium alloys, characterized by: The SMT bio-substrate coating and the HS-ATP / SMT super-hydrophobic coating are included, wherein the SMT bio-substrate coating includes 20-60 wt% bio-based SMT binder, thiol-containing organic corrosion inhibitor and organic solvent; the HS-ATP / SMT super-hydrophobic coating includes HS-ATP, SMT binder and solvent.

2. The bio-based double-layer superhydrophobic anticorrosive coating for magnesium alloys according to claim 1, characterized in that: The thiol-containing organic corrosion inhibitor is added in an amount of 3 wt%-10 wt% based on the mass of the bio-based SMT binder.

3. The bio-based double-layer superhydrophobic anticorrosive coating for magnesium alloys according to claim 2, characterized in that: The thiol-containing organic corrosion inhibitor is 2-mercaptobenzimidazole corrosion inhibitor, 2-mercaptobenzothiazole or 2-mercapto-1-methylimidazole; the organic solvent is one or more of butyl butyrate, butyl acetate and dimethylbenzene.

4. The bio-based double-layer superhydrophobic anticorrosive coating for magnesium alloys according to claim 1, characterized in that: The HS-ATP is attapulgite modified by hexadecyltrimethoxysilane and tetraethyl orthosilicate.

5. The bio-based dual-layer superhydrophobic anticorrosive coating for magnesium alloys according to claim 1, characterized in that: In the HS-ATP / SMT super-hydrophobic coating, the mass ratio of HS-ATP to SMT binder is 1:(1-3).

6. A process for the preparation of a bio-based double layer superhydrophobic anticorrosive coating for magnesium alloys characterized by: The preparation method includes the following steps: The SMT bio-substrate coating is prepared by adding 20-60 wt% bio-based SMT binder into an organic solvent and stirring to form a milky liquid; 3%-10% thiol-containing organic corrosion inhibitor based on the mass of the bio-based SMT binder is added, and stirring or ultrasonic treatment is continued for 10-60 min to obtain a uniform SMT bio-substrate coating; The HS-ATP / SMT super-hydrophobic coating is prepared by dispersing HS-ATP powder in an alcoholic organic solvent, ultrasonic treatment or stirring for 10-30 min to form a uniform suspension; SMT binder is added in a mass ratio of HS-ATP to SMT of 1:(1-3), and stirring is continued for 10-30 min to obtain a HS-ATP / SMT super-hydrophobic top coating.

7. A process for the preparation of a bio-based double layer superhydrophobic anticorrosive coating for magnesium alloys according to claim 6, characterized by: The preparation method of the HS-ATP includes the following steps: S1, acid activation S11, natural attapulgite is added into a hydrochloric acid solution with a concentration of 1-4 mol / L, and stirring reaction is carried out at 60-80 ℃ for 3-6 h; S12, filtration and washing with deionized water until the filtrate is close to neutral, and drying at 60-100 ℃ to obtain acid-treated attapulgite H-ATP; S2, HDTMS modification S21, H-ATP is dispersed in an ethanol / ammonia water mixed solution to obtain an H-ATP mixed solution; S22, a silane mixture is added into the H-ATP mixed solution for stirring reaction, wherein 0.8-1.2 mL of the silane mixture is added per 0.5 g of H-ATP, and the silane mixture is composed of HDTMS and TEOS; S23, after stirring reaction, centrifugal separation, ethanol washing and drying, HS-ATP powder is obtained.

8. Use of a bio-based double-layer superhydrophobic anticorrosive coating for magnesium alloys, characterized in that: The preparation method includes the following steps: Substrate treatment: the magnesium alloy substrate is polished, and then the surface oil stains and impurities are cleaned, and the substrate is dried for use; The SMT bio-substrate coating is uniformly coated on the surface of the pretreated magnesium alloy, and after standing at room temperature for 10-30 min, the coating is dried and cured to obtain a dense SMT bio-substrate coating. The HS-ATP / SMT super-hydrophobic coating is coated on the surface of the SMT bio-based primer, and then is dried and cured after standing at room temperature for 10-30 min, to obtain a HS-ATP / SMT super-hydrophobic coating layer with micro-nano rough structure on the surface. The thickness of the SMT bio-based primer is 20-60 μm, and the thickness of the HS-ATP / SMT super-hydrophobic coating layer is 30-80 μm.

9. Use of a bio-based double-layer superhydrophobic anticorrosive coating for magnesium alloys according to claim 8, characterized in that: The coating method is spraying, wherein the spraying pressure is 0.1-0.3 MPa, and the distance between the spray gun and the substrate is 10-20 cm.

10. Use of a bio-based double-layer superhydrophobic anticorrosive coating for magnesium alloys according to claim 8, characterized in that: During the drying and curing, the sample is placed in an oven at 150-200 ℃ for 4-10 h.

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