Magnesium alloy surface MOF coated LDH / SLIPS self-repairing composite coating and preparation method and application thereof

Abstract

The invention discloses a preparation method of a magnesium alloy surface MOF coated LDH / SLIPS self-repairing composite coating, which comprises the following steps: a, immersing a cleaned magnesium alloy matrix in a sodium nitrate aqueous solution for in-situ hydrothermal reaction to obtain a magnesium alloy on which an LDH coating grows; and b, placing the magnesium alloy on which the LDH coating is grown in a 2, 5-dihydroxy terephthalic acid aqueous solution, and carrying out hydrothermal reaction to obtain the magnesium alloy on which the MOF-coated LDH composite structure is grown. According to the preparation method, a sodium nitrate solution is used as an in-situ growth solution, the LDH coating with a lamellar structure distributed randomly is prepared, metal cations (such as Mg < 2 + > and Al < 3 + >) controllably released by the LDH coating in a specific slow-release environment are used as a metal source required by MOF crystal growth, in-situ self-supply ion nucleation and growth of MOF are induced on the LDH surface, and the MOF crystal is prepared. And the interface bonding strength between the MOF and the LDH is effectively enhanced. According to the self-repairing composite coating, the service life of the magnesium alloy is remarkably prolonged, and wide application of the magnesium alloy in the fields of aerospace, automobiles, electronics and the like can be promoted.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment technology, specifically relating to a self-healing composite coating of magnesium alloy surface MOF@LDH / SLIPS, its preparation method and application. Background Technology

[0002] Magnesium alloys, as one of the lightest structural metal materials, possess advantages such as low density, high specific strength, good electromagnetic shielding performance, easy recycling, and abundant reserves. However, magnesium and its alloys have inherent defects, such as high chemical reactivity, making them highly reactive with water or electrolytes in humid or corrosive environments, leading to rapid corrosion. Their naturally formed surface oxide film is loose and porous, making it difficult to serve as an effective barrier layer to prevent the penetration of corrosive media, and it is easily destroyed in common media such as chlorides. Furthermore, magnesium alloys often contain multiple alloying elements and second-phase structures, which easily form galvanic corrosion under corrosive media, accelerating the localized corrosion process and manifesting as various failure modes such as pitting corrosion, intergranular corrosion, and crevice corrosion, greatly limiting their reliability and durability in harsh service environments. Therefore, improving the corrosion resistance and service reliability of magnesium alloys has become one of the current research focuses in the field of magnesium alloys.

[0003] Currently, the main corrosion protection strategies include alloying, surface coating technology, and electrochemical treatment. Among these, surface coating technology is considered one of the most effective means to improve the corrosion resistance of magnesium alloys. In recent years, self-healing coatings have received widespread attention due to their ability to effectively repair themselves after being damaged or destroyed in the external environment. With the continuous development of materials science and engineering technology, self-healing coatings have been increasingly widely used in many research fields. Therefore, there is an urgent need to develop new, efficient, stable, engineering-feasible, and self-healing surface modification technologies for magnesium alloys. By constructing multifunctional composite structures, the comprehensive performance improvement of magnesium alloys in terms of corrosion resistance and long service life can be achieved. For example, in recent years, some scholars have attempted to grow metal-organic frameworks (MOFs) in situ on the surface of layered bimetallic hydroxides (LDH) to construct multifunctional protective coatings. Although this type of structure integrates the ion exchange capacity of LDH and the pore loading function of MOF to a certain extent, the following key technical shortcomings still exist: 1) The interfacial bonding between MOF and LDH is weak, and there is a lack of strong chemical bond between them. They mainly rely on electrostatic or physical adsorption, which makes the composite layer prone to delamination and warping during service, seriously affecting the protection life. 2) The overall water stability of the coating is poor. MOF materials are sensitive to moisture and ion erosion. The coating is prone to crystal swelling or erosion in corrosive environments, making it difficult to maintain the integrity of the structure in complex environments, which limits its widespread application in practical engineering environments. 3) The MOF growth process has poor controllability. The in-situ growth process of MOF on LDH surface lacks a precise control mechanism, often resulting in problems such as uneven crystal size distribution, low packing density, and insufficient exposure of active sites, which affect coating consistency and functional release efficiency. 4) The coating preparation process is complex and has poor repeatability. The existing MOF@LDH coating preparation steps are cumbersome, the parameters are sensitive, and the process is not repeatable, making it unsuitable for large-scale continuous production. 5) In actual service environments, the slow-release efficiency and response triggering mechanism of MOFs often lag behind the occurrence of corrosion, making it difficult to achieve proactive protection with "preemptive awareness," resulting in insufficient protection effectiveness. Therefore, further in-depth research on existing self-healing coatings is essential. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the main objective of this invention is to provide a MOF@LDH / SLIPS self-healing composite coating for magnesium alloy surfaces. This coating not only exhibits excellent bonding strength with the magnesium alloy substrate but also possesses excellent internal bonding strength and good self-healing capabilities.

[0005] This invention also provides a method for preparing the MOF@LDH / SLIPS self-healing composite coating on the magnesium alloy surface. First, an LDH coating is grown in situ on the magnesium alloy surface. The LDH layer serves as an ion source for MOF growth, enabling in-situ growth of the MOF layer based on the LDH coating, thus constructing the MOF@LDH composite structure. A corrosion inhibitor is loaded onto the MOF@LDH coating. The MOF@LDH coating with the corrosion inhibitor is then treated with silane to achieve a low surface energy, resulting in a superhydrophobic layer. Finally, a lubricant is injected into the low-surface-energy-modified MOF@LDH composite structure to form a stable liquid-infused smooth porous surface (SLIPS), thus constructing the MOF@LDH / SLIPS self-healing composite coating and further improving the coating's corrosion resistance and self-healing ability.

[0006] This invention also provides the application of the MOF@LDH / SLIPS self-healing composite coating on the magnesium alloy surface.

[0007] The purpose of the present invention is achieved through the following technical solutions: A method for preparing a MOF@LDH / SLIPS self-healing composite coating on a magnesium alloy surface includes the following steps: a. The cleaned magnesium alloy substrate is immersed in an in-situ growth solution for in-situ hydrothermal reaction to obtain a magnesium alloy with an LDH coating; wherein the in-situ growth solution is an aqueous sodium nitrate solution; b. The magnesium alloy with the LDH coating was placed in an aqueous solution of 2,5-dihydroxyterephthalic acid and subjected to a hydrothermal reaction to obtain a magnesium alloy with a MOF@LDH composite structure.

[0008] In some specific embodiments, the method for preparing the MOF@LDH / SLIPS self-healing composite coating on the magnesium alloy surface of the present invention further includes the following steps: c. Magnesium alloys with MOF@LDH composite structures are immersed in an aqueous solution containing corrosion inhibitors to carry out the corrosion inhibitor loading reaction. d. Immerse the magnesium alloy obtained in step c in an anhydrous ethanol solution of silane for low surface energy modification treatment, clean and dry to obtain a superhydrophobic magnesium alloy. e. Add lubricant droplets onto the surface of the superhydrophobic magnesium alloy, then tilt the alloy to allow excess lubricant to flow out from the surface, forming a lubricant layer, thus obtaining a magnesium alloy with a MOF@LDH / SLIPS self-healing composite coating.

[0009] The preparation method of this application, by using only sodium nitrate solution as the in-situ growth solution, not only forms an LDH coating with a randomly distributed lamellar structure, but also has the following effects: 1) Strong interfacial bonding: The metal ions required for MOF growth are directly derived from LDH sheets, and the generated MOF crystals can be firmly anchored in the LDH structure, which significantly improves the interfacial bonding force. 2) Uniform and controllable structure: It avoids the problems of impurity deposition and uncontrolled nucleation caused by external metal sources, and forms a MOF coating with regular structure and uniform distribution; 3) Environmentally friendly and simplified process: The process does not require the introduction of exogenous metal salts, reducing environmental burden and synthesis complexity, and has good scalability; In some specific embodiments, the hydrothermal reaction conditions in steps a and b are both: hydrothermal reaction at 90ºC~120ºC for 6-10 hours.

[0010] In some specific embodiments, the concentration of the sodium nitrate aqueous solution is 0.01-0.05M.

[0011] In some specific embodiments, the concentration of the 2,5-dihydroxyterephthalic acid aqueous solution in step b is 0.01-0.1M.

[0012] In some specific embodiments, the corrosion inhibitor in step c is salicylic acid ester with a concentration of 0.01-0.05M.

[0013] In some specific embodiments, the process conditions for the corrosion inhibitor loading reaction in step c are: reacting at 50-70°C for 1-2 hours.

[0014] In some specific embodiments, the silane in step d is one or more of perfluoroquaternary ammonium silane, fluorinated polyether-modified trimethoxysilane, or trifluoropropyltrimethoxysilane, and the lubricant in step e is one or more of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, fluorinated polyether-modified polydimethylsiloxane, or perfluoropolyether.

[0015] As part of the same inventive concept, this invention also provides a MOF@LDH / SLIPS self-healing composite coating for magnesium alloy surfaces.

[0016] As part of the same inventive concept, this invention also provides the application of the MOF@LDH / SLIPS self-healing composite coating on the magnesium alloy surface in the fields of aerospace, automotive, and electronics.

[0017] Furthermore, the method for preparing the MOF@LDH / SLIPS self-healing composite coating on the magnesium alloy surface provided by the present invention is not only applicable to magnesium alloys, but also to a variety of solid substrates other than magnesium alloys, such as aluminum alloys, titanium alloys, zinc alloys, and steel, and has good versatility.

[0018] Compared with the prior art, the present invention has at least the following advantages: 1) The preparation method provided by this invention uses sodium nitrate solution as an in-situ growth solution to prepare an LDH coating with a randomly distributed lamellar structure. This LDH coating can controllably release metal cations (such as Mg) in a specific slow-release environment (such as acidic or alkaline environments). 2+ As a metal source required for MOF crystal growth, MOF@LDH is induced to undergo in-situ self-donated ion nucleation and growth on the LDH surface, effectively enhancing the interfacial bonding strength between MOF and LDH. Simultaneously, based on the micro / nano structure constructed by the MOF@LDH coating, liquid lubricant is infused into it to form a liquid-infused smooth porous surface (SLIPS), ultimately constructing a MOF@LDH / SLIPS composite coating in situ on the magnesium alloy surface. This composite coating exhibits excellent corrosion resistance, slow-release response, structural stability, and active self-healing properties, demonstrating promising engineering application prospects. This coating can further promote the large-scale application of magnesium alloys in green manufacturing and high-end equipment. Furthermore, the development of this magnesium alloy surface protection technology not only addresses a technical bottleneck in improving its engineering practicality but also represents a crucial step in promoting the green development of new materials.

[0019] 2) The preparation method of this invention is simple, environmentally friendly, and low-cost. No toxic or harmful chemical reagents are used in the entire preparation process, and there is no waste liquid discharge, truly achieving clean production and green manufacturing. At the same time, this preparation method is highly efficient, possesses good industrial adaptability and mass production capability, and meets the current technological demand for green high-performance materials.

[0020] 3) The MOF@LDH / SLIPS self-healing composite coating on the magnesium alloy surface of this invention has two main advantages. First, the coating structure is dense, uniform, and layered, effectively preventing the penetration of harmful ions such as chloride ions in corrosive media, thereby significantly improving the corrosion resistance of the magnesium alloy. Second, the lubricant injected into the coating has good physical fluidity, and the loaded corrosion inhibitor can be released as needed. Therefore, when the coating is scratched, the lubricant and corrosion inhibitor self-repair the defects in the coating through rapid physical flow and chemical reaction, respectively, ensuring that the coating is always in an intact state, thus providing reliable and long-lasting corrosion resistance for the magnesium alloy; further promoting its widespread application in high-end manufacturing fields such as aerospace, automotive, and electronics. Attached Figure Description

[0021] In order to more clearly illustrate the specific embodiments of the present invention, the following briefly introduces the drawings required for the specific embodiments or the description of the prior art.

[0022] Figure 1 Here is a scanning electron microscope image of the LDH coating on the magnesium alloy surface in Example 1; Figure 2 Here is a scanning electron microscope image of the MOF@LDH coating on the magnesium alloy surface in Example 1; Figure 3 This is a scanning electron microscope image of the MOF@LDH coating with corrosion inhibitor loaded on the magnesium alloy surface in Example 1; Figure 4 This is a scanning electron microscope image of the MOF@LDH / SLIPS composite coating on the magnesium alloy surface in Example 1; Figure 5 This is the X-ray diffraction pattern of the LDH coating on the magnesium alloy surface in Example 1; Figure 6 This is the X-ray diffraction pattern of the MOF@LDH coating on the magnesium alloy surface in Example 1; Figure 7 This is the X-ray diffraction pattern of the MOF@LDH coating with corrosion inhibitor loaded on the magnesium alloy surface in Example 1; Figure 8 It is the Tafel polarization curve of the exposed magnesium alloy; Figure 9 This is the Tafel polarization curve of the LDH coating on the magnesium alloy surface in Example 1; Figure 10 The Tafel polarization curve of the MOF@LDH coating on the magnesium alloy surface in Example 1 is shown. Figure 11 The Tafel polarization curve of the MOF@LDH coating with corrosion inhibitor loaded on the magnesium alloy surface in Example 1 is shown. Figure 12 The Tafel polarization curve of the superhydrophobic coating on the magnesium alloy surface in Example 1 is shown. Figure 13 The Tafel polarization curve of the MOF@LDH / SLIPS composite coating on the magnesium alloy surface in Example 1 is shown. Figure 14 These are metallographic microscope images and SVET response voltages of the MOF@LDH / SLIPS composite coating on the magnesium alloy surface after scratches appeared in Example 1. Figure 15 These are metallographic micrographs and SVET response voltages of the MOF@LDH / SLIPS composite coating on the magnesium alloy surface of Example 1 12 hours after self-healing. Figure 16 The images show metallographic micrographs and SVET response voltages of the MOF@LDH / SLIPS composite coating on the magnesium alloy surface in Example 1 24 hours after self-healing. Figure 17 This is the Tafel polarization curve of the MOF@LDH / SLIPS composite coating on the magnesium alloy surface in Example 1 after scratches appeared; Figure 18 This is the Tafel polarization curve of the magnesium alloy surface after 12 hours of self-healing with the MOF@LDH / SLIPS composite coating in Example 1. Figure 19 This is the Tafel polarization curve of the magnesium alloy surface after 24 hours of self-healing with the MOF@LDH / SLIPS composite coating in Example 1. Figure 20 This is a scanning electron microscope image of the LDH coating on the surface of the magnesium alloy in Comparative Example 1; Figure 21 This is a scanning electron microscope image of the MOF@LDH / SLIPS composite coating on the surface of magnesium alloy in Comparative Example 1. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The following embodiments are merely descriptive and not limiting, and should not be construed as limiting the scope of protection of the present invention.

[0024] When a quantity, concentration, or other value or parameter is described as a range, preferred range, or preferred upper and lower limits, it should be understood that it is equivalent to specifically disclosing any range by combining any pair of upper or preferred values ​​with any lower or preferred values, regardless of whether the range is specifically disclosed. Unless otherwise stated, the numerical range values ​​listed herein include the endpoints of the range and all integers and fractions within that range.

[0025] Unless otherwise stated, all percentages, parts, ratios, etc. in this document are by weight.

[0026] The materials, methods, and embodiments described herein are exemplary and should not be construed as limiting unless otherwise stated.

[0027] Example 1 This embodiment provides a method for preparing a MOF@LDH / SLIPS self-healing composite coating on a magnesium alloy surface, including the following steps: 1. In-situ growth of LDH coating Hydrothermal reaction steps: First, pour a 0.01M sodium nitrate solution into the inner liner of the reactor, and then place the magnesium alloy sample into the sodium nitrate solution; after sealing the reactor, place it in an electric oven for in-situ growth, the reaction temperature is 110±5ºC, and the constant temperature reaction time is set to 8 hours to obtain a magnesium alloy with an LDH coating on the surface. 2. In-situ growth of MOF layers Magnesium alloy samples with grown LDH layers were placed in an aqueous solution of 2,5-dihydroxyterephthalic acid (concentration 0.05M, pH 9) and hydrothermally reacted at 100ºC for 9 hours. The samples were then removed and washed repeatedly with deionized water to obtain magnesium alloys with grown MOF@LDH composite structures. 3. Loaded corrosion inhibitor Magnesium alloy samples with MOF@LDH layers were immersed in an aqueous solution of 0.03 M salicylic acid ester and subjected to a corrosion inhibitor loading reaction at 60 ºC for 1.5 hours. 4. Superhydrophobic layer The magnesium alloy treated in step 3 was immersed in an anhydrous ethanol solution of silane (perfluoroquaternary ammonium silane, concentration 0.01 M) for low surface energy modification treatment for 1 hour, and then dried after cleaning to obtain a superhydrophobic magnesium alloy. 5. Lubricating fluid layer Lubricant (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide) was dropped onto the surface of the superhydrophobic magnesium alloy, and then placed at a 15º angle to allow excess lubricant to flow out from the surface of the magnesium alloy, forming a lubricant layer, and finally obtaining a magnesium alloy with a MOF@LDH / SLIPS self-healing composite coating.

[0028] Example 2 This embodiment provides a method for preparing a MOF@LDH / SLIPS self-healing composite coating on a magnesium alloy surface, including the following steps: 1. In-situ growth of LDH coating Hydrothermal reaction steps: First, pour a 0.03M sodium nitrate solution into the inner liner of the reactor, and then place the magnesium alloy sample into the sodium nitrate solution; after sealing the reactor, place it in an electric oven for in-situ growth, the reaction temperature is 95±5ºC, and the constant temperature reaction time is set to 10 hours to obtain a magnesium alloy with an LDH coating on the surface. 2. In-situ growth of MOF layers Magnesium alloy samples with grown LDH layers were placed in an aqueous solution of 2,5-dihydroxyterephthalic acid (concentration 0.03M, pH 8.5) and hydrothermally reacted at 110ºC for 8 hours. The samples were then removed and washed repeatedly with deionized water to obtain magnesium alloys with MOF@LDH composite structures. 3. Loaded corrosion inhibitor Magnesium alloy samples with MOF@LDH layers were immersed in an aqueous solution of 0.03 M salicylic acid ester and subjected to a corrosion inhibitor loading reaction at 60 ºC for 1.5 hours. 4. Superhydrophobic layer The magnesium alloy treated in step 3 was immersed in an anhydrous ethanol solution of silane (trifluoropropyltrimethoxysilane, concentration is 0.01 M) for low surface energy modification treatment for 1 hour, and then dried after cleaning to obtain a superhydrophobic magnesium alloy. 5. Lubricating fluid layer Lubricant (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide) was dropped onto the surface of the superhydrophobic magnesium alloy, and then placed at a 20º angle to allow excess lubricant to flow out from the surface of the magnesium alloy, forming a lubricant layer, and finally obtaining a magnesium alloy with a MOF@LDH / SLIPS self-healing composite coating.

[0029] Example 3 This embodiment provides a method for preparing a MOF@LDH / SLIPS self-healing composite coating on a magnesium alloy surface, including the following steps: 1. In-situ growth of LDH coating Hydrothermal reaction steps: First, pour a 0.2M sodium nitrate solution into the inner liner of the reactor, and then place the magnesium alloy sample into the sodium nitrate solution; after sealing the reactor, place it in an electric oven for in-situ growth, the reaction temperature is 110±5ºC, and the constant temperature reaction time is set to 8 hours to obtain a magnesium alloy with an LDH coating on the surface. 2. In-situ growth of MOF layers Magnesium alloy samples with grown LDH layers were placed in an aqueous solution of 2,5-dihydroxyterephthalic acid (concentration 0.01M, pH 9.5) and hydrothermally reacted at 120ºC for 7 hours. The samples were then removed and washed repeatedly with deionized water to obtain magnesium alloys with MOF@LDH composite structures. 3. Loaded corrosion inhibitor Magnesium alloy samples with MOF@LDH layers were immersed in an aqueous solution of 0.03M salicylic acid ester and subjected to a corrosion inhibitor loading reaction at 60 ºC for 1.5 hours. 4. Superhydrophobic layer The magnesium alloy treated in step 3 was immersed in an anhydrous ethanol solution of silane (perfluoroquaternary ammonium silane, concentration 0.02 M) for low surface energy modification treatment for 2 hours, and then dried after cleaning to obtain a superhydrophobic magnesium alloy. 5. Lubricating fluid layer Lubricant (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide) was dropped onto the surface of the superhydrophobic magnesium alloy, and then placed at a 10º angle to allow excess lubricant to flow out from the surface of the magnesium alloy, forming a lubricant layer, and finally obtaining a magnesium alloy with a MOF@LDH / SLIPS self-healing composite coating.

[0030] Comparative Example 1 This comparative example provides a method for preparing a MOF@LDH / SLIPS self-healing composite coating on a magnesium alloy surface. The preparation method is basically the same as in Example 1, except that the in-situ growth solution used is a mixed aqueous solution of 0.1 M sodium nitrate, 0.05 M aluminum nitrate, and 0.001 M lanthanum nitrate. Specifically: 1. In-situ growth of LDH coating Hydrothermal reaction steps: First, a mixed aqueous solution of 0.1 M sodium nitrate, 0.05 M aluminum nitrate and 0.001 M lanthanum nitrate was poured into the inner liner of the reactor. Then, the magnesium alloy sample was placed in the in-situ growth solution. After sealing the reactor, it was placed in an electric oven for in-situ growth. The reaction temperature was 115±5ºC and the constant temperature reaction time was set to 12 hours to obtain a magnesium alloy with an LDH coating on the surface. Steps 2)-5) are the same as in Example 1; Performance characterization: This application uses Example 1 as an example to conduct performance tests on the preparation process or the prepared sample, specifically: 1) Appearance and morphology The magnesium alloy samples obtained during the preparation process in Example 1 were observed using a scanning electron microscope, among which... Figure 1 This is a scanning electron microscope (SEM) image of a magnesium alloy surface after an LDH coating has been grown. It exhibits a typical lamellar stacked structure, reflecting its layered crystal characteristics. The image shows clearly defined nanosheets randomly arranged in different orientations, demonstrating a certain three-dimensional effect. This morphological feature is closely related to its layered structure, providing ample interlayer space and specific surface area for the subsequent containment of liquid lubricant.

[0031] Figure 2This is a scanning electron microscope (SEM) image of the surface of a magnesium alloy after a MOF@LDH coating has been grown. The SEM image of the MOF shows a regular hexagonal prismatic crystal morphology with a smooth surface and clear edges, demonstrating good crystallinity. The crystals exhibit a long columnar or rod-like structure, with lengths generally ranging from several hundred nanometers to several micrometers, while the diameter is relatively small, exhibiting a high aspect ratio, thus constructing a micro / nanostructured MOF@LDH coating. The particle size is relatively uniform, densely distributed but without obvious agglomeration, indicating that the MOF synthesis process was well controlled. Furthermore, the long axis of the MOF@LDH coating is aligned along the crystal growth direction, exhibiting good monodispersity, thus providing space for subsequent liquid lubricant infusion.

[0032] Figure 3 This is a scanning electron microscope (SEM) image of a magnesium alloy surface after a MOF@LDH coating has been loaded with a corrosion inhibitor. The SEM image shows a significant change in the original regular rod-like structure, transforming it into a loose, lamellar morphology. This structural transformation is mainly attributed to the partial hydrolysis of the MOF during the corrosion inhibitor loading process, which disrupted its original crystal framework. The previously dense, regular hexagonal prismatic crystal surface gradually became rough, exhibiting peeling and expansion, ultimately forming a lamellar or stacked structure. The gaps between the lamellars facilitate the further release and diffusion of the corrosion inhibitor, indicating that the MOF not only provides an effective carrier function but also provides a channel for the release of the corrosion inhibitor during the structural transformation process.

[0033] Figure 4 The MOF@LDH coating on the magnesium alloy surface, after being infused with lubricant, forms a MOF@LDH / SLIPS composite coating. Scanning electron microscopy (SEM) images show that after infusion with liquid lubricant, the original lamellar porous structure of the MOF@LDH is uniformly covered by the liquid, and the sharp boundaries between the pores become blurred, exhibiting a relatively smooth and continuous surface feature. This change indicates that the lubricant fully fills the pores and surface depressions of the MOF@LDH, forming a typical liquid-infused layer, giving it excellent smoothness and liquid sealing ability. At the same time, the overall structure still retains a certain degree of micro / nano-scale roughness, which is beneficial for the stable retention of the lubricant.

[0034] In addition, the scanning electron microscope image of the magnesium alloy with an LDH coating prepared in step 1) of Comparative Example 1 is shown below. Figure 20 As shown in the figure, compared to the magnesium alloy with an LDH coating grown on its surface in Example 1 ( Figure 1 Using a mixed in-situ growth solution can yield an LDH coating with better density.

[0035] And the scanning electron microscope images of the MOF@LDH coatings prepared in steps 1) and 2) of Comparative Example 1 are as follows: Figure 21As shown in the figure, the MOF@LDH coating on the magnesium alloy surface has uneven size distribution, low packing density, and discontinuous coating formation.

[0036] This indicates that the LDH coating surface, with its lower density, contains more pores, defects, and rough regions. These structural features provide a larger specific surface area and more available active sites, which is beneficial for the penetration, adsorption, and crystallization of MOF precursors. Furthermore, the porous structure promotes the deep penetration of metal ions and organic ligands in the precursor solution, thereby facilitating the in-situ formation of MOF crystals on and within the LDH layer. Therefore, MOFs are more easily grown in situ on low-density LDH, and their nuclei preferentially nucleate at these defect sites, thus promoting the formation of continuous, dense MOF coatings. On the dense LDH surface, which is flat and has few pores, there is a lack of effective nucleation sites, making it difficult for MOF crystals to adhere and grow, resulting in discontinuous film formation, poor adhesion, or limited growth. This dense surface may also hinder the diffusion of MOF precursors, thereby inhibiting the uniform growth of MOF layers.

[0037] Therefore, the poorly dense LDH substrate actually provides a more favorable microstructural environment for the in-situ construction of MOFs.

[0038] 2) Composition or structural characterization The magnesium alloy samples obtained in the preparation process of Example 1 were characterized by XRD, wherein Figure 5 The X-ray diffraction pattern of the magnesium alloy surface after growing an LDH coating shows distinct diffraction peaks at 2θ ≈ 11º and 23º, corresponding to the (003) and (006) crystal planes, respectively. These are characteristic diffraction planes in the LDH structure. The (003) crystal plane's diffraction peak is strong and sharp, indicating that the LDH has a good layered structure and highly ordered interlayer stacking. Furthermore, magnesium hydroxide-related diffraction peaks also appear in the X-ray diffraction pattern, suggesting that the coating formed on the magnesium alloy surface after hydrothermal treatment is mainly composed of LDH and magnesium hydroxide.

[0039] Figure 6The X-ray diffraction pattern of the magnesium alloy surface after growing the MOF@LDH coating shows a series of new diffraction peaks, such as 2θ ≈ 6.8º, 11.8º, 18.1º, and 26.8º, which can be attributed to the characteristic diffraction peaks of Mg-MOF and correspond to its characteristic crystal planes (e.g., (100), (110), (200), and (220)). The appearance of the Mg-MOF diffraction peaks proves that it has been successfully grown in situ on the LDH matrix, forming a MOF@LDH composite structure. Among them, the low-angle strong diffraction peaks of MOF (such as those near 6.8º) are typical signs of its ordered pore structure, indicating that the synthesized MOF material has good crystallinity and regularity. In addition, no obvious impurity peaks were observed, indicating that the synthesized MOF@LDH composite coating is relatively pure.

[0040] Figure 7 After loading a corrosion inhibitor, the X-ray diffraction pattern of the MOF@LDH coating on the magnesium alloy surface still shows the characteristic diffraction peaks of LDH and Mg-MOF, indicating that the crystal framework of the composite structure has not been destroyed. Compared with the state before loading the corrosion inhibitor, the main characteristic diffraction peak of LDH on the (003) crystal plane showed a slight leftward shift (shifted to a lower angle), indicating an increase in interlayer spacing, which is related to the entry of corrosion inhibitor molecules into the interlayer channels of the layered structure. The peak intensity of some MOF characteristic peaks was slightly weakened or slightly broadened, which may be due to a certain degree of crystal distortion or diffraction interference caused by the entry of corrosion inhibitor molecules into the pores or interlayer structure of MOF. In addition, no impurity peaks were observed, indicating that the corrosion inhibitor successfully entered the MOF@LDH composite coating structure and no secondary phases were precipitated.

[0041] 3) Corrosion resistance test This embodiment also tested the electrochemical performance of bare AZ31 magnesium alloy and magnesium alloys with different coatings during the preparation process. Specifically, the polarization curves of AZ31 magnesium alloy samples and magnesium alloy samples with different coatings on their surfaces were tested in 3.5 wt.% sodium chloride solution using an electrochemical workstation (Princeton 4000A).

[0042] The Tafel polarization curves of the exposed AZ31 magnesium alloy and the magnesium alloys with different coatings during the preparation process in this application are shown on the same coordinate system. Figure 8 The image shows the Tafel polarization curve of exposed AZ31 magnesium alloy. The corrosion voltage of the exposed AZ31 magnesium alloy is -1.47 V, and the corrosion current density is 5.52 × 10⁻⁶. -5 A cm -2 ; Figure 9 The figures show the Tafel polarization curves of a magnesium alloy with an LDH coating (LDH). The corrosion voltage of the LDH-coated magnesium alloy is -1.39 V, and the corrosion current density is 5.05 × 10⁻⁶.-6 A cm -2 ; Figure 10 The figures show the Tafel polarization curves of a magnesium alloy with a MOF@LDH coating (MOF@LDH). The corrosion voltage of the MOF@LDH coated magnesium alloy is -1.29 V, and the corrosion current density is 7.38 × 10⁻⁶. -7 A cm -2 ; Figure 11 The images show the Tafel polarization curves of a MOF@LDH coated magnesium alloy with a corrosion inhibitor. The corrosion voltage of the MOF@LDH coated magnesium alloy with the corrosion inhibitor is -1.26 V, and the corrosion current density is 3.87 × 10⁻⁶. -8 A cm -2 ; Figure 12 The Tafel polarization curves are for magnesium alloys with superhydrophobic coatings grown after low surface energy modification. The corrosion voltage of the magnesium alloy with the superhydrophobic coating is -1.23 V, and the corrosion current density is 1.39 × 10⁻⁶. -8 A cm -2 ; Figure 13 These are Tafel polarization curves of a magnesium alloy with a MOF@LDH / SLIPS composite coating (MOF@LDH / SLIPS) after lubrication. The corrosion voltage of the MOF@LDH / SLIPS composite coating magnesium alloy is -0.81 V, and the corrosion current density is 2.15 × 10⁻⁶. -10 A cm -2 .

[0043] Therefore, compared to the exposed AZ31 magnesium alloy substrate, the preparation of each coating (LDH, MOF@LDH, MOF@LDH with corrosion inhibitor, superhydrophobic surface, and MOF@LDH / SLIPS) significantly increased the corrosion voltage, increasing sequentially from -1.47 V to -1.39 V, -1.29 V, -1.26 V, -1.23 V, and -0.81 V. From a thermodynamic perspective, the construction of the protective coatings led to a positive shift in the electrode potential of the magnesium alloy surface, indicating improved thermodynamic stability of the system and a reduced free energy driving force for the corrosion reaction, thereby significantly reducing the corrosion susceptibility of the magnesium alloy. In particular, the preparation of the MOF@LDH / SLIPS composite coating significantly improved the corrosion resistance of the magnesium alloy.

[0044] On the other hand, compared to the bare AZ31 magnesium alloy substrate, the corrosion current density of magnesium alloy samples with protective coatings (LDH, MOF@LDH, MOF@LDH with corrosion inhibitor, superhydrophobic surface, and MOF@LDH / SLIPS) decreased significantly, from 5.52 × 10⁻⁶. -5 A cm -2 It decreased sequentially to 5.05 × 10 -6 A cm -2 7.38 × 10 -7 A cm -2 3.87 × 10 -8 A cm -2 1.39 × 10 -8 A cm -2 2.15 × 10 -10 A cm -2 The corrosion current density decreased by one, two, three, three, and five orders of magnitude, respectively. Therefore, from a kinetic perspective, the decrease in corrosion current density after the protective coating is grown on the magnesium alloy substrate indicates that the electrochemical corrosion reaction rate is significantly suppressed. This phenomenon is attributed to the coating's ability to effectively block the diffusion path of the corrosive medium, significantly increase the interfacial charge transfer impedance, and reduce anodic reactivity, thereby greatly improving the kinetic corrosion resistance of the magnesium alloy substrate. In particular, the preparation of the MOF@LDH / SLIPS composite coating resulted in a five-order-of-magnesium decrease in corrosion current density, demonstrating that this composite coating can significantly improve the corrosion resistance of magnesium alloys and effectively protect the magnesium alloy substrate from corrosion.

[0045] Table 1. Test results of corrosion resistance of the protective coating prepared in Example 1 As shown in Table 1, the corrosion potential gradually increases with the gradual formation of the coating, while the corrosion current density continuously decreases. This indicates a significant inhibitory effect of the coating on the corrosion behavior of the substrate. The increase in corrosion potential signifies improved thermodynamic stability of the metal matrix, indicating that oxidation reactions are more difficult to occur on the metal surface. The coating effectively blocks direct contact between the corrosive medium and the substrate, slowing down the initiation of the corrosion process. The decrease in corrosion current density reflects the slowdown of the corrosion reaction rate. The coating provides a good physical barrier, limiting the transport of electrons and ions. Especially after introducing layered structures (such as LDH) and porous structures (such as MOF) into the coating, the diffusion path of the corrosive medium is prolonged, making it difficult for corrosive active substances to quickly reach the metal surface. The loading of corrosion inhibitors and low surface energy modification further enhance the self-healing ability and hydrophobicity of the coating, preventing the penetration of moisture and corrosive ions, thereby reducing the corrosion current. After the lubricant is injected, a stable and continuous liquid film is formed on the surface, which can effectively block the direct contact of corrosive media (moisture, ions, etc.) with the substrate surface, greatly reducing the possibility of corrosion. Furthermore, the lubricant imparts extremely low surface energy to the surface, making it difficult for droplets and contaminants to adhere, thus reducing the retention of contaminants and corrosion sources. The fluidity and smoothness of the lubricant layer hinder the deposition of corrosive salts, preventing salt bloom and scale formation, and effectively extending the coating life. In summary, the positive shift in corrosion potential and the reduction in corrosion current density together indicate that the coating system achieves dual protection at both the thermodynamic and kinetic levels, effectively improving the corrosion resistance of the magnesium alloy substrate.

[0046] 4) Wetting test The water contact angle of the coating surface was measured using a contact angle meter (KRÜSS) to evaluate the wettability of the coating surface. The test droplet volume was 5 μL, and each sample was titrated at least three times in parallel to ensure the reliability of the test results. The test results are shown in the table below: Table 2. Wetting performance test results of the protective coating prepared in Example 1 To evaluate the wetting properties of the prepared coating, water contact angle tests were conducted on samples at different stages. The results are shown in Table 2. The results in the table show that the contact angle of the LDH coating is higher than that of the bare magnesium alloy substrate, indicating that its surface roughness and micro / nano structure enhance hydrophobicity. However, further growth of the MOF structure leads to a decrease in the contact angle, which may be attributed to the enhanced hydrophilicity of the MOF pore structure, which enhances the wetting behavior of water droplets. Subsequently, the contact angle rebounded after the introduction of a corrosion inhibitor, possibly because the hydrophobic groups of the organic corrosion inhibitor molecules are exposed on the surface, weakening the hydrophilicity of the interface. Further modification with low surface energy materials further increases the contact angle, demonstrating excellent hydrophobic properties. Finally, after the surface is infused with lubricant, the contact angle decreases significantly, mainly because the smooth flow interface of the lubricant changes the solid / liquid interfacial tension, causing the surface to exhibit neutral wetting similar to a lubricated state. This series of contact angle changes indicates that the wettability of the coating can be effectively controlled through a multi-step construction strategy, thus providing a basis for subsequent functionalization (such as self-healing and corrosion protection).

[0047] 5) Self-healing test Artificial scratches were prepared on the surface of magnesium alloy samples with MOF@LDH / SLIPS composite coating using a standard scratch instrument. The scratched samples were then immersed in a 3.5 wt.% sodium chloride solution, and the scratch morphology was photographed periodically (0 h, 12 h, 24 h) using a metallographic microscope to assess the degree of repair at the scratches.

[0048] From metallographic microscope images (such as Figures 14-16 As can be seen, at the initial moment (0 h), the scratch edges were distinct, and the exposed substrate area was clearly visible, indicating that the coating had been damaged at this point and could not provide effective protection. After a certain period of time (12 h), the scratched area showed partial filling, and the edges became blurred, indicating that the lubricant or corrosion inhibitor in the coating began to be released and migrate to the damaged area, resulting in preliminary self-healing behavior. After 24 h, the scratch was basically covered by the newly formed material, and the micrograph showed that the continuity of the new coating was enhanced, and the substrate was re-encapsulated. The scratched area was almost indistinguishable, and the surface tended to be intact and smooth, indicating that the coating has good self-healing ability.

[0049] This series of microscopic images clearly demonstrates that the coating possesses time-dependent self-healing characteristics after damage. Through the material's own diffusion, release, and reconstruction mechanisms, it can effectively restore the protective function of the damaged area, thereby extending the coating's service life and improving its overall corrosion resistance.

[0050] On the other hand, to further reveal the electrochemical process of the coating's self-healing behavior, a micro-area scanning electrochemical testing system (SVET) was used to monitor the scratched area in real time. By placing microelectrodes at the damaged site, the change in electrochemical response voltage over time was continuously recorded, allowing for a direct evaluation of the self-healing effect of the scratched area. The results are shown in Table 3. Table 3. Test results of the self-healing performance of the MOF@LDH / SLIPS composite coating prepared in Example 1. As shown in Table 3, at the initial moment of the scratch (t = 0): due to the exposed substrate, the scratched area is in direct contact with the corrosive medium, resulting in a significant corrosion reaction, manifested as a high electrochemical response voltage. Over time: the voltage signal gradually decreases, indicating a reduction in corrosion activity. This process can be attributed to the release and migration of self-healing components (such as corrosion inhibitors or lubricants) from the coating to the damaged area, blocking the contact between the corrosive medium and the metal. In the stable phase (e.g., after 24 hours): the voltage tends to stabilize and remains at a low level (the response voltage decreased by two orders of magnitude compared to the initial moment), indicating that the scratched area has essentially achieved self-healing, forming a new protective layer, thus effectively restoring the electrochemical stability of the coating.

[0051] This process demonstrates that self-healing coatings can not only repair surface damage macroscopically, but also restore their electrochemical impedance properties at the microscale. The micro-area electrochemical testing system provides a sensitive and high-resolution means for evaluating the real-time repair behavior of the coating.

[0052] Furthermore, to further evaluate the corrosion resistance of magnesium alloy samples with MOF@LDH / SLIPS composite coating at different self-healing stages, samples from the initial, partial, and complete self-healing stages were selected and subjected to potentiodynamic polarization tests using an electrochemical workstation to assess their corrosion resistance. The test results are as follows: Figure 17 , Figure 18 and Figure 19 As shown, detailed corrosion potential and corrosion current density data are shown in Table 4: Table 4. Test results of corrosion resistance of the self-healing MOF@LDH / SLIPS composite coating prepared in Example 1. As shown in Table 4, the corrosion potential gradually shifts to the positive direction: with the progress of the self-healing process, the corrosion potential gradually shifts from the initial -1.34 V to the positive direction, indicating that the thermodynamic stability of the metal surface gradually increases, suggesting a reduction in corrosion tendency. The corrosion current density continues to decrease, and with the extension of the self-healing time, the corrosion current density decreases significantly, reflecting a substantial decrease in the corrosion rate of the system, indicating that the coating gradually forms an effective protective barrier in the damaged area. This trend can be attributed to the following aspects: Release and coverage of self-healing components: In the scratched area, as self-healing components such as corrosion inhibitors or lubricants are gradually released and migrate to the defect, they prevent the corrosive medium from contacting the metal substrate; Re-formed passivation layer or protective film: The self-healing products form a new covering layer at the scratch, effectively improving the shielding performance of the local area; Recovery of overall electrochemical performance: As the degree of self-healing continues to increase, the entire coating system restores its integrity, thereby stabilizing the electrochemical behavior. Therefore, the positive shift in corrosion voltage and the decrease in corrosion current density jointly demonstrate the continuous improvement in the corrosion protection performance of the coating during the self-healing process, verifying its excellent self-healing ability.

[0053] In summary, the MOF@LDH / SLIPS self-healing composite coating for magnesium alloy surfaces prepared in this invention exhibits excellent corrosion resistance and shows great application potential. This invention uses a hydrothermal method to grow layered double hydroxide (LDH) and metal-organic framework (MOF) materials in situ on the magnesium alloy surface, preparing a MOF@LDH composite structure. Based on the MOF@LDH composite structure, a slippery liquid-infused porous surface (SLIPS) with good stability, hydrophobicity, and self-healing properties is combined to form the MOF@LDH / SLIPS self-healing composite coating. This composite coating effectively isolates the magnesium alloy substrate from external corrosive media, improving the corrosion resistance of the magnesium alloy.

[0054] When the coating surface suffers minor damage or scratches, the liquid lubricant, driven by capillary force, reflows to fill the scratched or defective areas, quickly restoring its original smoothness and hydrophobic properties. Furthermore, the injected liquid is in a dynamic equilibrium state, spontaneously rearranging and redistributing itself after localized loss, thus achieving "imperceptible" self-repair. Even if significant lubricant loss occurs during service, its surface function can be restored through re-injection, demonstrating "maintainable" self-healing properties. On the other hand, the corrosion inhibitors loaded in the composite coating can also achieve chemical self-healing performance through chemical reactions: when the coating is damaged, exposing the metal surface, changes in the local corrosion potential, pH, and ion concentration of the substrate induce the release of the corrosion inhibitor from the LDH and MOF support; subsequently, the corrosion inhibitor can migrate to the defective area, adsorbing on the metal surface to form a protective film (complex film), inhibiting anodic or cathodic reactions and slowing down the corrosion process.

[0055] Therefore, the MOF@LDH / SLIPS composite coating prepared by this invention effectively reduces production costs and significantly improves the corrosion resistance of magnesium alloys. Compared to the bare magnesium alloy substrate, its corrosion current density decreases by five orders of magnitude. After damage occurs, the composite coating, through the physical self-healing properties of its lubricant and the chemical self-healing properties of its corrosion inhibitor, gradually reduces its response voltage with increasing immersion time, exhibiting excellent self-healing effects. The self-healed coating still provides excellent corrosion resistance for the magnesium alloy, with the corrosion current density remaining five orders of magnitude lower than that of the bare magnesium alloy substrate, and the impedance modulus at low frequencies recovering to a level comparable to that of the unscratched sample.

[0056] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention.

Claims

1. A method for preparing a MOF@LDH / SLIPS self-healing composite coating on a magnesium alloy surface, characterized in that, The steps include: a. The cleaned magnesium alloy substrate is immersed in an in-situ growth solution for in-situ hydrothermal reaction to obtain a magnesium alloy with an LDH coating; wherein the in-situ growth solution is an aqueous sodium nitrate solution; b. The magnesium alloy with the LDH coating was placed in an aqueous solution of 2,5-dihydroxyterephthalic acid and subjected to a hydrothermal reaction to obtain a magnesium alloy with a MOF@LDH composite structure.

2. The method for preparing the MOF@LDH / SLIPS self-healing composite coating on the magnesium alloy surface according to claim 1, characterized in that, It also includes the following steps: c. The magnesium alloy with the MOF@LDH composite structure was immersed in an aqueous solution containing a corrosion inhibitor to carry out the corrosion inhibitor loading reaction; d. Immerse the magnesium alloy obtained in step c in an anhydrous ethanol solution of silane for low surface energy modification treatment, clean and dry to obtain a superhydrophobic magnesium alloy. e. Add lubricant droplets onto the surface of the superhydrophobic magnesium alloy, then tilt the alloy to allow excess lubricant to flow out from the surface, forming a lubricant layer, thus obtaining a magnesium alloy with a MOF@LDH / SLIPS self-healing composite coating.

3. The method for preparing the MOF@LDH / SLIPS self-healing composite coating on the magnesium alloy surface according to claim 1, characterized in that, The conditions for the hydrothermal reaction described in steps a and b are: hydrothermal reaction at 90ºC~120ºC for 6-10 hours.

4. The method for preparing the MOF@LDH / SLIPS self-healing composite coating on the magnesium alloy surface according to claim 1, characterized in that, The concentration of the sodium nitrate aqueous solution is 0.01-0.05M.

5. The method for preparing the MOF@LDH / SLIPS self-healing composite coating on the magnesium alloy surface according to claim 4, characterized in that, The concentration of the 2,5-dihydroxyterephthalic acid aqueous solution in step b is 0.01-0.1M.

6. The method for preparing the MOF@LDH / SLIPS self-healing composite coating on the magnesium alloy surface according to claim 1, characterized in that, The corrosion inhibitor mentioned in step c is salicylic acid ester with a concentration of 0.01-0.05M.

7. The method for preparing the MOF@LDH / SLIPS self-healing composite coating on the magnesium alloy surface according to claim 4, characterized in that, The process conditions for the corrosion inhibitor loading reaction in step c are: reacting at 50-70℃ for 1-2 hours.

8. The method for preparing the MOF@LDH / SLIPS self-healing composite coating on the magnesium alloy surface according to claim 1, characterized in that, The silane mentioned in step d is one or more of perfluoroquaternary ammonium silane, fluorinated polyether-modified trimethoxysilane, or trifluoropropyltrimethoxysilane, and the lubricant mentioned in step e is one or more of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, fluorinated polyether-modified polydimethylsiloxane, or perfluoropolyether.

9. A self-healing composite coating of magnesium alloy surface MOF@LDH / SLIPS prepared by the preparation method according to any one of claims 1-8.

10. The application of the MOF@LDH / SLIPS self-healing composite coating on magnesium alloy surfaces according to claim 9 in the fields of aerospace, automotive, and electronics.

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