Zinc-aluminum-magnesium coated steel containing corrosion-resistant coating and preparation method of zinc-aluminum-magnesium coated steel

Abstract

The invention discloses zinc-aluminum-magnesium coating steel containing a corrosion-resistant coating and a preparation method of the zinc-aluminum-magnesium coating steel, and belongs to the technical field of metal material surface protection. An LDH ZIF-8 composite coating is formed on the surface of the zinc-aluminum-magnesium coating steel through a step-by-step in-situ growth method. The preparation method comprises the following steps: placing zinc-aluminum-magnesium coating steel in an LDH seed crystal solution containing zinc nitrate, aluminum nitrate and urea, reacting at 80-100 DEG C for 12-24 hours, and growing an LDH coating in situ; and putting the composite coating into ZIF-8 seed crystal liquid containing 2-methylimidazole and sodium formate, and reacting at 40-80 DEG C for 3-12 hours to finally form the composite coating. According to the composite coating, the layered structure and anion exchange capacity of LDH and the physical shielding and pH responsive corrosion inhibitor release functions of ZIF-8 are combined, and the corrosion resistance is remarkably improved through the synergistic effect. Experiments show that the corrosion resistance of the zinc-aluminum-magnesium coating steel is improved by 1-2 orders of magnitude through the coating, and the coating is simple in preparation process, low in cost, environmentally friendly and suitable for long-acting protection in high-corrosion environments such as the ocean.

Description

Technical Field

[0001] This invention relates to the field of surface protection technology for metallic materials, specifically to a zinc-aluminum-magnesium coated steel containing a corrosion-resistant coating and its preparation method. Background Technology

[0002] Zinc-aluminum-magnesium coated steel has been widely used in marine engineering, transportation, and building structures due to its excellent comprehensive corrosion resistance and cost advantages. However, the marine environment is characterized by high salt spray, high humidity, and high temperature. Corrosive media such as chloride ions in the marine environment can severely corrode the metal surface, placing extremely stringent requirements on the long-term durability of the materials.

[0003] Although zinc-aluminum-magnesium coated steel possesses a certain degree of corrosion protection, its coating can still experience pitting and uniform corrosion under long-term harsh environments, rendering its protective performance insufficient to meet the long-life requirements of high-end equipment. Therefore, constructing a denser, more stable composite coating with active protection on the surface of zinc-aluminum-magnesium coated steel has become a key technical approach to improve its service performance.

[0004] Currently, researchers have attempted to enhance the corrosion resistance of metals by adding surface coatings. For example, adding a layered double hydroxide (LDH) coating to the surface of zinc-aluminum-magnesium coated steel can enhance the anti-corrosion effect; however, a single LDH coating still provides insufficient corrosion protection. Other methods involve adding corrosion-resistant functional powders as fillers to organic coatings to prepare anti-corrosion coatings, which are then applied to the substrate surface for corrosion protection. However, this coating preparation method suffers from complex processes, multiple reactions, and long processing times, increasing not only process costs and environmental burden but also potentially affecting the adhesion between the coating and the metal substrate, as well as the uniformity of the coating, resulting in insufficient corrosion resistance.

[0005] Therefore, how to construct a composite coating with excellent corrosion resistance in situ on the surface of zinc-aluminum-magnesium coated steel using a simple, efficient, and environmentally friendly process has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] In view of the above-mentioned shortcomings of the existing technology, the purpose of this invention is to provide a zinc-aluminum-magnesium coated steel with a corrosion-resistant coating and its preparation method, so as to solve the technical problems of insufficient corrosion resistance of existing zinc-aluminum-magnesium coated steel in harsh corrosive environments, and the complex, costly and limited effect of existing protective coating preparation processes.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A zinc-aluminum-magnesium coated steel containing a corrosion-resistant coating, wherein the surface of the zinc-aluminum-magnesium coated steel has an LDH@ZIF-8 composite coating formed by in-situ growth, wherein the composite coating consists of LDH as the bottom layer and ZIF-8 covering the surface of the LDH.

[0008] The preparation method of the above-mentioned zinc-aluminum-magnesium coated steel containing a corrosion-resistant coating includes the following steps: (1) The zinc-aluminum-magnesium coated steel was placed in LDH seed solution and allowed to stand for reaction. After the reaction was completed, zinc-aluminum-magnesium coated steel with LDH coating grown in situ on the surface was obtained. (2) After cleaning and drying, the zinc-aluminum-magnesium coated steel with LDH coating grown in situ on the surface is placed in ZIF-8 seed solution for static reaction. After the reaction is completed, zinc-aluminum-magnesium coated steel with LDH@ZIF-8 composite coating is obtained.

[0009] Furthermore, before placing the zinc-aluminum-magnesium coated steel in the LDH seed solution, the zinc-aluminum-magnesium coated steel is pretreated. The pretreatment includes cleaning with acetone to remove oil, and then ultrasonically cleaning the zinc-aluminum-magnesium coated steel in an ethanol solution and drying it.

[0010] Furthermore, the LDH seed solution is prepared by dissolving zinc nitrate, aluminum nitrate and urea in deionized water, wherein the concentration of zinc nitrate is 0.02-0.04 mol / L, the concentration of aluminum nitrate is 0.005-0.01 mol / L, and the concentration of urea is 0.0125-0.025 mol / L.

[0011] Furthermore, the molar ratio of zinc nitrate to aluminum nitrate in the LDH seed solution is 4:1-2.

[0012] Furthermore, the ZIF-8 seed solution is prepared by dissolving 2-methylimidazole and sodium formate in methanol, wherein the concentration of 2-methylimidazole is 0.1-0.4 mol / L and the concentration of sodium formate is 0.1-0.2 mol / L.

[0013] Furthermore, the zinc-aluminum-magnesium coated steel is subjected to a static reaction in LDH seed solution at a temperature of 80-100℃.

[0014] Furthermore, the zinc-aluminum-magnesium coated steel is allowed to stand in the LDH seed solution for 12-24 hours.

[0015] Furthermore, the zinc-aluminum-magnesium coated steel with LDH coating grown in situ on the surface is subjected to a static reaction in ZIF-8 seed solution at a temperature of 40-80℃.

[0016] Furthermore, the zinc-aluminum-magnesium coated steel with LDH coating grown in situ on the surface is allowed to stand in ZIF-8 seed solution for 3-12 hours.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention provides a zinc-aluminum-magnesium coated steel containing a corrosion-resistant LDH@ZIF-8 composite coating. By constructing a composite coating of hydrotalcite (LDH) and zeolite imidazole ester framework material-8 (ZIF-8) in situ on the substrate surface, a highly efficient synergistic effect of multiple anti-corrosion mechanisms is achieved. In this composite coating, LDH, with its unique layered structure, can significantly extend the penetration path of corrosive media and improve the physical barrier performance of the substrate. Simultaneously, products such as zinc oxide generated in situ during corrosion by LDH can be further deposited on the coating surface, achieving self-sealing of the LDH microstructure and enhancing its barrier effect. Furthermore, LDH possesses excellent anion exchange capacity, actively capturing and fixing corrosive media such as chloride ions in the environment, thereby slowing down the corrosion process. On the other hand, the ZIF-8 coating not only provides excellent physical shielding and hydrophobic protection but also decomposes and releases 2-methylimidazolium corrosion inhibitors in acidic corrosive environments, achieving active inhibition and repair of localized corrosion areas. Experimental results show that the composite coating improves the corrosion resistance of zinc-aluminum-magnesium coated steel by 1 to 2 orders of magnitude and significantly extends its service life in harsh marine environments.

[0018] 2. The preparation method provided by this invention employs a stepwise in-situ growth technique to directly construct LDH and ZIF-8 coatings sequentially on the surface of zinc-aluminum-magnesium coated steel. This process requires no complex pretreatment or posttreatment, is simple in procedure, convenient to operate, and highly efficient. Furthermore, the entire reaction system is simple in composition, environmentally friendly, and does not use toxic or harmful reagents, resulting in low cost. This method cleverly utilizes the substrate itself as the reaction source, achieving a strong chemical bond between the coating and the substrate. It overcomes the problems of cumbersome processes, weak adhesion, or reliance on organic resins as carriers in traditional composite coating preparations, making it highly suitable for large-scale industrial production and application. Attached Figure Description

[0019] Figure 1 These are comparison images of the microstructure of the workpiece surface in Embodiment 1 of the present invention with those in Comparative Examples 1 and 2.

[0020] Figure 2 This is a graph showing the change of the electrochemical impedance spectral modulus of the workpieces in Example 1, Comparative Examples 1 and 2 of the present invention over time. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the scope of the invention.

[0022] I. Examples and Comparative Examples Example 1 A method for preparing zinc-aluminum-magnesium coated steel containing a corrosion-resistant LDH@ZIF-8 composite coating, the specific steps of which are as follows: (1) Pretreatment of workpiece: The zinc-aluminum-magnesium coated steel is processed into a rectangular sample of 50mm×30mm×3mm. A hole with a diameter of 3mm is drilled directly above the top of the sample to form the workpiece. The workpiece is cleaned and degreased with acetone, and then ultrasonically cleaned in an ethanol solution for 30 seconds. The cleaning is repeated 5 times. Finally, it is dried with compressed air and set aside for use. Cleaning the workpiece before coating can remove impurities on the workpiece, improve the fixing effect of the coating on the workpiece, and thus improve the corrosion resistance.

[0023] (2) Preparation of LDH seed solution: Weigh 1.48g zinc nitrate (Zn(NO3)2·6H2O), 0.468g aluminum nitrate (Al(NO3)3·9H2O), and 0.75g urea (CO(NH2)2), and dissolve them sequentially in 250mL of deionized water. Stir magnetically for 5 minutes to ensure thorough mixing and obtain the LDH seed solution. In this seed solution, the concentration of zinc nitrate is approximately 0.02 mol / L, the concentration of aluminum nitrate is approximately 0.005 mol / L, the concentration of urea is approximately 0.025 mol / L, and the molar ratio of zinc nitrate to aluminum nitrate is 4:1.

[0024] (3) In-situ growth of LDH coating: The zinc-aluminum-magnesium coated steel workpiece pretreated in step (1) is completely immersed in the LDH seed solution prepared in step (2). The reaction system is placed in a constant temperature water bath at 80°C and allowed to stand for 12 hours. After the reaction is completed, the workpiece is removed, the surface is rinsed with deionized water to remove loosely attached particles, and then dried with compressed air to obtain an intermediate workpiece with an LDH coating on the surface.

[0025] (4) Preparation of ZIF-8 seed solution: Weigh 4.11 g of 2-methylimidazole and 1.844 g of sodium formate (NaCOOH), and dissolve them in 200 mL of methanol. Stir magnetically for 5 minutes to ensure complete dissolution, thus obtaining the ZIF-8 seed solution. In this seed solution, the concentration of 2-methylimidazole is approximately 0.25 mol / L, and the concentration of sodium formate is approximately 0.113 mol / L.

[0026] (5) In-situ growth of ZIF-8 coating to form composite coating: The intermediate workpiece with LDH coating prepared in step (3) is completely immersed in the ZIF-8 seed solution prepared in step (4). The reaction system is placed in a constant temperature water bath at 60°C and allowed to stand for 6 hours. After the reaction is completed, the workpiece is taken out, rinsed with methanol and deionized water in sequence, and finally dried with compressed air to obtain the zinc-aluminum-magnesium coated steel containing the corrosion-resistant LDH@ZIF-8 composite coating.

[0027] Example 2 A method for preparing zinc-aluminum-magnesium coated steel containing a corrosion-resistant LDH@ZIF-8 composite coating is basically the same as that in Example 1, except for the process parameters: (1) In the LDH seed solution, the concentration of zinc nitrate was adjusted to 0.03 mol / L, the concentration of aluminum nitrate was adjusted to 0.0075 mol / L, and the concentration of urea was adjusted to 0.01875 mol / L.

[0028] (2) The LDH growth reaction temperature was adjusted to 90℃ and the reaction time was adjusted to 18 hours.

[0029] (3) In the ZIF-8 seed solution, the concentration of 2-methylimidazole was adjusted to 0.2 mol / L and the concentration of sodium formate was adjusted to 0.15 mol / L.

[0030] (4) The growth reaction temperature of ZIF-8 was adjusted to 50℃ and the reaction time was adjusted to 9 hours.

[0031] Example 3 A method for preparing zinc-aluminum-magnesium coated steel containing a corrosion-resistant LDH@ZIF-8 composite coating is basically the same as that in Example 1, except for the process parameters: (1) In the LDH seed solution, the concentration of zinc nitrate was adjusted to 0.04 mol / L, the concentration of aluminum nitrate was adjusted to 0.01 mol / L, and the concentration of urea was adjusted to 0.0125 mol / L.

[0032] (2) The LDH growth reaction temperature was adjusted to 100℃ and the reaction time was adjusted to 24 hours.

[0033] (3) In the ZIF-8 seed solution, the concentration of 2-methylimidazole was adjusted to 0.4 mol / L and the concentration of sodium formate was adjusted to 0.2 mol / L.

[0034] (4) The growth reaction temperature of ZIF-8 was adjusted to 80℃ and the reaction time was adjusted to 3 hours.

[0035] Comparative Example 1 To compare performance, zinc-aluminum-magnesium coated steel samples without any composite coating were prepared. The specific method was as follows: the zinc-aluminum-magnesium coated steel was processed into workpieces of the same size as in Example 1, cleaned with acetone to remove oil, then ultrasonically cleaned in ethanol solution for 30 seconds (repeated 5 times), and finally dried to obtain blank control samples.

[0036] Comparative Example 2 A zinc-aluminum-magnesium coated steel with a corrosion-resistant LDH coating is prepared as follows: The zinc-aluminum-magnesium coated steel is processed into a rectangular sample of 50mm × 30mm × 3mm. A 3mm diameter hole is drilled directly above the top of the sample to obtain the zinc-aluminum-magnesium coated steel workpiece. The workpiece is cleaned and degreased with acetone, then ultrasonically cleaned in an ethanol solution for 30 seconds, repeated 5 times, and dried for later use. 1.48g of zinc nitrate, 0.468g of aluminum nitrate, and 0.75g of urea are dissolved sequentially in 250mL of deionized water and stirred for 5 minutes to prepare an LDH seed solution. The cleaned zinc-aluminum-magnesium coated steel workpiece is then placed in the LDH seed solution and allowed to react at 90℃ for 12 hours. Afterward, it is removed, cleaned with deionized water, and dried to obtain the zinc-aluminum-magnesium coated steel with a corrosion-resistant LDH coating.

[0037] II. Performance Testing and Effect Verification To verify the superior performance of the LDH@ZIF-8 composite coating prepared in this invention, the workpieces prepared in Example 1, Comparative Example 1, and Comparative Example 2 were subjected to the following tests: (1) Microscopic morphological characterization: The surface morphology of the samples was observed using scanning electron microscopy (SEM). The results are as follows: Figure 1 As shown, the coating obtained in Example 1 clearly shows that the ZIF-8 rhombic dodecahedral structure is uniformly and densely covered on the LDH layered structure, forming a good composite structure. This indicates that the LDH@ZIF-8 composite coating was successfully prepared in situ on the surface of zinc-aluminum-magnesium coated steel. In contrast, the sample surface of Comparative Example 1 only shows the original zinc-aluminum-magnesium coating morphology, while Comparative Example 2 shows the morphology of zinc-aluminum-magnesium coated steel with the LDH composite coating.

[0038] (2) Corrosion resistance test: Electrochemical impedance spectroscopy (EIS) was performed using an electrochemical workstation in a 3.5 wt% sodium chloride (NaCl) solution. The test results are as follows: Figure 2 As shown, the workpiece with the LDH@ZIF-8 composite coating prepared in Example 1 has a low-frequency impedance modulus (|Z|). 0.01Hz The value remained at approximately 1~1.5×10 throughout the entire testing period. 4The low-frequency impedance modulus of the blank zinc-aluminum-magnesium coated steel workpiece in Comparative Example 1 was significantly lower than this value. Although the low-frequency impedance modulus of Comparative Example 2 was initially comparable to that of the present invention, it decreased over time and became significantly lower than that of the present invention. The results show that after preparing the LDH@ZIF-8 composite coating on the surface of zinc-aluminum-magnesium coated steel using the method of the present invention, its corrosion resistance is improved by 1 to 2 orders of magnitude compared to untreated zinc-aluminum-magnesium coated steel. Moreover, compared to zinc-aluminum-magnesium coated steel with a single LDH coating, the durability of the present invention is greatly improved. It is evident that the composite coating of the present invention has excellent corrosion resistance.

[0039] In summary, this invention successfully constructed an LDH@ZIF-8 composite coating on the surface of zinc-aluminum-magnesium coated steel using a stepwise in-situ growth method. This preparation method is simple, environmentally friendly, and low-cost. The resulting composite coating combines the advantages of LDH in extending the corrosion path and facilitating anion exchange, with the physical shielding effect of ZIF-8 and its ability to release corrosion inhibitors (2-methylimidazole) under acidic conditions. This synergistic effect significantly improves the long-term corrosion resistance of zinc-aluminum-magnesium coated steel in harsh marine environments.

[0040] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A zinc-aluminum-magnesium coated steel containing a corrosion-resistant coating, characterized in that, The zinc-aluminum-magnesium coated steel surface has an LDH@ZIF-8 composite coating formed by in-situ growth. The composite coating consists of LDH as the bottom layer and ZIF-8 covering the surface of LDH.

2. The method for preparing zinc-aluminum-magnesium coated steel containing a corrosion-resistant coating as described in claim 1, characterized in that, Includes the following steps: (1) The zinc-aluminum-magnesium coated steel was placed in LDH seed solution and allowed to stand for reaction. After the reaction was completed, zinc-aluminum-magnesium coated steel with LDH coating grown in situ on the surface was obtained. (2) After cleaning and drying, the zinc-aluminum-magnesium coated steel with LDH coating grown in situ on the surface is placed in ZIF-8 seed solution for static reaction. After the reaction is completed, zinc-aluminum-magnesium coated steel with LDH@ZIF-8 composite coating is obtained.

3. The method for preparing zinc-aluminum-magnesium coated steel containing a corrosion-resistant coating according to claim 2, characterized in that, Before being placed in the LDH seed solution, the zinc-aluminum-magnesium coated steel is pretreated. The pretreatment includes cleaning with acetone to remove oil, and then ultrasonically cleaning the zinc-aluminum-magnesium coated steel in an ethanol solution and drying it.

4. The method for preparing zinc-aluminum-magnesium coated steel containing a corrosion-resistant coating according to claim 2, characterized in that, The LDH seed solution is prepared by dissolving zinc nitrate, aluminum nitrate and urea in deionized water, wherein the concentration of zinc nitrate is 0.02-0.04 mol / L, the concentration of aluminum nitrate is 0.005-0.01 mol / L, and the concentration of urea is 0.0125-0.025 mol / L.

5. The method for preparing zinc-aluminum-magnesium coated steel containing a corrosion-resistant coating according to claim 4, characterized in that, The molar ratio of zinc nitrate to aluminum nitrate in the LDH seed solution is 4:1-2.

6. The method for preparing zinc-aluminum-magnesium coated steel containing a corrosion-resistant coating according to claim 2, characterized in that, The ZIF-8 seed solution is prepared by dissolving 2-methylimidazole and sodium formate in methanol, wherein the concentration of 2-methylimidazole is 0.1-0.4 mol / L and the concentration of sodium formate is 0.1-0.2 mol / L.

7. The method for preparing zinc-aluminum-magnesium coated steel containing a corrosion-resistant coating according to claim 2, characterized in that, The zinc-aluminum-magnesium coated steel is subjected to a static reaction in LDH seed solution at a temperature of 80-100℃.

8. The method for preparing zinc-aluminum-magnesium coated steel containing a corrosion-resistant coating according to claim 2, characterized in that, The zinc-aluminum-magnesium coated steel is allowed to stand in LDH seed solution for 12-24 hours for reaction.

9. The method for preparing zinc-aluminum-magnesium coated steel containing a corrosion-resistant coating according to claim 2, characterized in that, The zinc-aluminum-magnesium coated steel with an in-situ grown LDH coating is subjected to a static reaction in ZIF-8 seed solution at a temperature of 40-80℃.

10. The method for preparing zinc-aluminum-magnesium coated steel containing a corrosion-resistant coating according to claim 2, characterized in that, The zinc-aluminum-magnesium coated steel with an in-situ grown LDH coating was allowed to stand in ZIF-8 seed solution for 3-12 hours.

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