Coating with in-situ plugging and active protection functions, and preparation method and application thereof

Abstract

This invention discloses a coating with both in-situ plugging and active protection functions, its preparation method, and its application, belonging to the field of metal material surface treatment technology. This invention proposes an innovative electrolyte design scheme, which achieves film growth and in-situ chemical plugging of micropores in a one-step process by performing micro-arc oxidation on commercial 5083 aluminum alloy in a phosphate system containing specific cerium salts and complexing agents. The process is simple, and the resulting coating exhibits excellent plugging strength and corrosion resistance, as well as active protection functions, providing a new solution for improving the durability of 5083 aluminum alloy in harsh marine environments.

Description

Technical Field

[0001] This invention belongs to the field of metal material surface treatment technology, specifically relating to a coating with both in-situ sealing and active protection functions, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] 5083 aluminum alloy possesses high specific strength, excellent formability and weldability, and relatively good corrosion resistance in chloride-containing media, making it an important material for shipbuilding, marine engineering, and offshore structural components. However, under prolonged exposure to harsh marine atmospheric and immersion environments, chloride ions can still induce pitting corrosion, crevice corrosion, and stress corrosion cracking, directly affecting structural safety and service life. Therefore, strengthening and protecting the surface of this alloy is crucial.

[0004] Micro-arc oxidation is an electrochemical surface treatment method that grows ceramic oxide films in situ on valve metal surfaces such as aluminum, magnesium, and titanium through high-voltage discharge. The resulting coating forms a metallurgical bond with the substrate, exhibiting high hardness, high wear resistance, and good corrosion resistance, making it an effective means of surface modification for aluminum alloys. However, in the micro-arc oxidation of 5083 aluminum alloy, the intense plasma discharge during the process leads to numerous micropores and microcracks in the generated ceramic film. These defects create corrosive media (such as Cl-). - The rapid penetration of water and other pollutants into the 5083 alloy substrate severely weakens the long-term protective barrier effect of the coating, becoming a major bottleneck limiting the application of micro-arc oxidation technology to improve the high corrosion resistance of 5083 aluminum alloy. Furthermore, during actual service, the coating inevitably suffers damage. After damage, the coating usually cannot continue to protect the substrate and may even accelerate substrate corrosion.

[0005] Currently, the main methods for addressing micropores and microcracks in micro-arc oxidation films are post-treatment sealing or electrolyte addition. Post-treatment sealing methods, such as preparing composite coatings through paint spraying, suffer from problems including cumbersome processes, increased costs, weak adhesion between the sealing agent and the substrate, and susceptibility to aging and detachment. Electrolyte modification methods focus on adding nanoparticles (such as TiO2) to the electrolyte, allowing them to co-deposit into the film or block pores during discharge. However, nanoparticles are prone to agglomeration, exhibit poor dispersion stability in the electrolyte, and their interfacial bonding with the ceramic substrate is mostly physical-mechanical, making them susceptible to failure under thermal or mechanical stress. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a coating, its preparation method, and its application that combine in-situ sealing and active protection functions.

[0007] This invention proposes an innovative electrolyte design scheme. By performing micro-arc oxidation on commercial 5083 aluminum alloy in a phosphate system containing specific cerium salts and complexing agents, film growth and in-situ chemical sealing of micropores are completed in one step. The process is simple, and the obtained film has both excellent sealing strength and corrosion resistance, as well as active protection function, providing a new solution for improving the durability of 5083 aluminum alloy in harsh marine environments.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing a coating that combines in-situ sealing and active protection functions, comprising the following steps: Using aluminum alloy as the anode and stainless steel electrolytic cell as the cathode, the anode, cathode and electrolyte constitute an electrochemical reaction system. A coating with both in-situ sealing and active protection functions is formed on the surface of aluminum alloy using micro-arc oxidation process. The electrolyte comprises phosphate, complexing agent, alkali, cerium salt and water.

[0009] Secondly, the present invention provides a coating that combines in-situ sealing and active protection functions, which is prepared by the above-mentioned preparation method.

[0010] Thirdly, the present invention provides a micro-arc oxidation system, using an aluminum alloy as the anode and a stainless steel electrolytic cell as the cathode, wherein the anode, cathode and electrolyte constitute an electrochemical reaction system; wherein the electrolyte is the electrolyte described above.

[0011] Fourthly, the present invention provides a coating prepared by the above-mentioned method that combines in-situ sealing and active protection functions, or the above-mentioned coating that combines in-situ sealing and active protection functions, for corrosion resistance in shipbuilding and marine engineering.

[0012] One or more of the above technical solutions have the following advantages or beneficial effects: This invention provides a coating that combines in-situ plugging and active protection functions: a micro-arc oxidation ceramic film for aluminum alloys. It utilizes a specific electrolyte system of "exogenous cerium-EDTA-2Na-phosphate" and leverages the localized high-temperature and high-pressure environment of micro-arc discharge to induce an in-situ reaction between exogenous cerium ions and electrolyte components within the film pores, generating a thermodynamically stable plugging material (such as cerium phosphate). This achieves in-situ chemical plugging of the micropores. This method integrates film preparation and pore sealing, simplifying the process; the plugging material bonds firmly to the ceramic substrate; it significantly improves the barrier performance of the film and endows it with active protection functions, resulting in an order-of-magnitude improvement in the corrosion resistance of aluminum alloys (such as commercially available 5083 aluminum alloy). Attached Figure Description

[0013] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0014] Figure 1 This is a schematic diagram of the micro-arc oxidation equipment used in this invention; Figure 2 XRD patterns are shown below; (a) shows the XRD patterns of the micro-arc oxidation ceramic film layer with in-situ sealing and active protection functions on the surface of commercial 5083 aluminum alloy prepared in Examples 1 to 3 and the typical porous micro-arc oxidation ceramic film layer on the surface of commercial 5083 aluminum alloy prepared in Comparative Example 1; (b) is a longitudinally stretched magnified view of (a). Figure 3 The images shown are SEM images of the micro-arc oxidation ceramic films prepared in Examples 1 to 3 and Comparative Example 1 of the present invention; wherein, (a) is an SEM image of the micro-arc oxidation ceramic film prepared in Comparative Example 1, (b) is an SEM image of the micro-arc oxidation ceramic film prepared in Example 1, (c) is an SEM image of the micro-arc oxidation ceramic film prepared in Example 2, and (d) is an SEM image of the micro-arc oxidation ceramic film prepared in Example 3. Figure 4 The Tafel curves are obtained from electrochemical tests of Examples 1 to 3, Comparative Example 1, and commercial 5083 aluminum alloy substrates in 3.5wt% NaCl solution. Figure 5 The images shown are SEM images of Comparative Example 1 after it has been artificially scratched and then immersed in a 3.5 wt% NaCl solution for 120 hours. (a) shows the initial morphology of Comparative Example 1 after scratching; (b) is a magnified view of the area within the frame of (a); (c) shows the corrosion morphology of Comparative Example 1 after immersion in the scratched solution for 120 hours; and (d) is a magnified view of the area within the frame of (c). The orange arrows in the images indicate coating debris, and the red arrows indicate corrosion products. Figure 6 This is an EDS analysis of Comparative Example 1 of the present invention after being artificially scratched and immersed in 3.5 wt% NaCl solution for 120 hours; wherein, (a) is the morphology after corrosion, (b) is a partial magnified view of the area within the frame of (a), (c) is the line scan analysis result of the yellow line area in (b), and (d) is the EDS surface scan analysis result of (b); the yellow line in the figure represents the EDS line scan analysis area; Figure 7 The images are SEM images of Example 2 of the present invention after being artificially scratched and then immersed in 3.5wt% NaCl solution for 120 hours. Among them, (a) is the initial morphology of Example 2 after scratching, (b) is a partial enlarged view of the framed area in (a), (c) is the corrosion morphology of Example 2 after being immersed in 3.5wt% NaCl solution for 120 hours after scratching, and (d) is a partial enlarged view of the framed area in (c). The orange arrows in the images indicate coating debris. Figure 8 The above are the EDS analysis results of Example 2 of the present invention after being artificially scratched and soaked in 3.5 wt% NaCl solution for 120 hours; wherein, (a) is the corrosion morphology, (b) is the EDS surface scan result of (a), and (c) is the EDS line scan result of the yellow line area in (a), where the yellow line is the EDS line scan analysis area. Detailed Implementation

[0015] In this invention, unless otherwise specified, all other test materials and instruments are conventional test materials in the field and can be purchased through commercial channels.

[0016] This invention discloses a coating that combines in-situ sealing and active protection functions. Its preparation method includes the following steps: first, pretreating the surface of commercial 5083 aluminum alloy; then, preparing a cerium-containing micro-arc oxidation electrolyte; performing micro-arc oxidation treatment on the commercial 5083 aluminum alloy using a micro-arc oxidation power source; continuously stirring the electrolyte during the oxidation process; finally, obtaining a micro-arc oxidation ceramic film layer with both in-situ sealing and active protection functions on the surface of the commercial 5083 aluminum alloy; rinsing with deionized water; and air-drying. By designing the composition of the micro-arc oxidation electrolyte and the micro-arc oxidation process parameters, in-situ sealing of the micro-arc oxidation ceramic film layer and its active protection function are achieved, significantly improving the corrosion resistance of commercial 5083 aluminum alloy, and possessing practical application value.

[0017] A first typical embodiment of the present invention provides a method for preparing a coating that combines in-situ sealing and active protection functions, comprising the following steps: Using aluminum alloy as the anode and stainless steel electrolytic cell as the cathode, the anode, cathode and electrolyte constitute an electrochemical reaction system. A coating with both in-situ sealing and active protection functions is formed on the surface of aluminum alloy using micro-arc oxidation process. The electrolyte comprises phosphate, complexing agent, alkali, cerium salt and water.

[0018] In some embodiments of this implementation, the concentration of phosphate in the electrolyte is 5-25 g / L, specifically 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 10 g / L, 11 g / L, 12 g / L, 13 g / L, 14 g / L, 15 g / L, 16 g / L, 17 g / L, 18 g / L, 19 g / L, 20 g / L, 21 g / L, 22 g / L, 23 g / L, 24 g / L, 25 g / L, and other values ​​between these ranges. The concentration of the complexing agent is 2-8 g / L, specifically 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, and other values ​​between these ranges. The concentration of the alkali is 0.25~2.0 g / L, specifically 0.25 g / L, 0.5 g / L, 1 g / L, 1.5 g / L, 2 g / L, etc., and specific values ​​between these ranges. The concentration of the cerium salt is 1~20 g / L, specifically 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 10 g / L, 11 g / L, 12 g / L, 13 g / L, 14 g / L, 15 g / L, 16 g / L, 17 g / L, 18 g / L, 19 g / L, 20 g / L, etc., and specific values ​​between these ranges. Preferably, to obtain the best in-situ plugging effect and electrolyte stability, the concentration of the phosphate is 10~20 g / L; the concentration of the complexing agent is 4~6 g / L; the concentration of the alkali is 0.5~1.5 g / L; and the concentration of the cerium salt is 2.5~15 g / L.

[0019] Furthermore, the complexing agent is EDTA-2Na (C 10 H 14 (N2O8·2H2O). EDTA cannot be added directly as a complexing agent because EDTA acid (H4EDTA) has very low solubility in water. This invention requires complexing a high concentration of cerium ions. If EDTA acid is added directly, it is difficult to dissolve, causing the complexation reaction to fail, and the cerium ions will react directly with the alkali to form a precipitate.

[0020] In this invention, EDTA-2Na plays a chelating and stabilizing role. 3+ It readily undergoes hydrolysis and precipitation in alkaline phosphate systems (provided by NaOH). EDTA-2Na acts as a chelating agent, reacting with Ce... 3+Formation of stable complexes, ensuring a large amount of Ce 3+ It can remain stable in high-pH electrolytes until it is transported to the discharge channel to participate in the reaction. If EDTA-2Na is removed, Ce... 3+ It will immediately precipitate in an alkaline environment, the electrolyte will fail, and uniform doping will be impossible to achieve.

[0021] Furthermore, phosphates include sodium phosphate (Na4P2O7).

[0022] In this invention, phosphates are used instead of other salts because the film formed by the phosphate system is relatively dense, and phosphate ions can undergo a specific precipitation reaction with cerium ions, which is a chemical match that is difficult to achieve with silicate or citrate systems.

[0023] At high temperatures, Ce 3+ With PO4 3- This results in the formation of cerium phosphate (CePO4), a chemically stable substance with a unique crystal structure. Its melting point and fluidity allow it to be mixed with molten Al2O3 for backfilling within the discharge channel.

[0024] If a silicate system is used, although films can be formed, the behavior of compounds formed by silicon and cerium (such as cerium-silicon compounds) at high temperatures is completely different from that of CePO4. This may not achieve the self-sealing effect of melt backfilling, or the sealing material formed may not have the chemical stability of CePO4.

[0025] If a citrate system is used, citric acid, being an organic acid, will directly carbonize or vaporize under high-temperature electric arc, failing to provide the anions required to form a stable inorganic sealing material. Therefore, the "in-situ self-sealing" of this invention cannot be achieved.

[0026] Regarding specific forms of sodium phosphate, such as Na4P2O7 (sodium pyrophosphate), it hydrolyzes in solution to provide PO4. 3- Sodium salt was chosen because Na... + It is the most "inert" cation in the system and will not participate in the reaction to introduce impurities. Replacing it with a calcium salt (such as calcium phosphate) will introduce Ca. 2+ It may generate calcium phosphate precipitate, which may damage the stability of the electrolyte, or even be incorporated into the coating and affect its semiconductor properties.

[0027] Furthermore, the base includes NaOH.

[0028] In this invention, the role of alkali (NaOH) is twofold: First, it regulates conductivity. As a supporting electrolyte (a strong electrolyte added to the solution primarily to increase its conductivity, but which does not directly participate in the main electrode reaction), it increases the conductivity of the solution, reduces the arc-starting voltage, and makes the arc starting more uniform. If the alkalinity is too low, it will be detrimental to the micro-arc oxidation arc starting; if it is too high, the 5083 aluminum alloy will react, leading to a violent MAO process and substrate burning. Second, it maintains the pH environment to ensure that the complexation reaction between EDTA-2Na and cerium ions proceeds within the optimal pH range (usually alkaline), preventing premature hydrolysis and precipitation of cerium ions and ensuring the long-term stability of the electrolyte.

[0029] The cerium salt includes Ce(CH3CO2)3·xH2O (cerium (III) acetate hydrate), where x is the number of water molecules of crystallization.

[0030] The cerium salt used in this invention is cerium(III) acetate hydrate, rather than other cerium salts such as cerium sulfate or cerium nitrate. Sulfate (SO4) 2- Nitrate (NO3): This substance is corrosive and may damage the passivation film formed in the early stages of micro-arc oxidation, or introduce harmful impurities, affecting the dielectric properties and corrosion resistance of the coating. - Acetate (CH3COO) may decompose under high pressure, producing nitrogen oxide gas, which interferes with the discharge process and may even cause defects such as porosity and looseness in the coating. - Firstly, cerium acetate has good solubility and can provide stable Ce. 3+ Firstly, cerium acetate decomposes into CO2 and H2O during discharge, without introducing harmful anions, resulting in a pure system. Therefore, cerium acetate exhibits better solubility and coordination stability in the EDTA-2Na complex system. Compared to cerium sulfate or cerium nitrate, acetate, as a weak organic acid anion, has a stronger buffering capacity for electrolyte pH, which is beneficial for the stable control of the MAO discharge process.

[0031] More importantly, different types of cerium salts lead to different technical effects. Specifically, on the one hand, there is the adaptability of the process. Micro-arc oxidation (MAO) involves plasma discharge, and acetate, as a weak organic acid anion, can significantly suppress the "explosion point" phenomenon during the discharge process compared to strong acid anions, resulting in smaller film pore sizes, which is the basis for achieving 600Hz fine discharge. On the other hand, there is the purity of the sealing products. Acetate decomposes into volatile products at the instantaneous high temperature of MAO, avoiding the residue of strong acid anion ions in the film pores and preventing the induction of local acid corrosion, thereby ensuring that the film has a longer-lasting active protection (self-healing) function.

[0032] Cerium (Ce) is a green self-healing inhibitor. Under the localized high temperature of MAO, it reacts with phosphate ions to form chemically stable cerium phosphate (CePO4) precipitate, thereby precisely sealing micropores. Furthermore, Ce possesses self-healing capabilities by releasing Ce... 3+ , with OH - The combined corrosion product Ce(OH)3 can resist Cl. - Further erosion, the solubility of Cu, Fe, V hydroxides, precipitation pH range, synergistic film-forming ability with Al(OH)3 and Ce 3+ Completely different, it cannot achieve self-repair.

[0033] Furthermore, this invention uses cerium salts, rather than other metal salts such as calcium salts. This is because if calcium-containing compounds, such as calcium acetate, were used, hydroxyapatite (containing calcium) might be formed, which is primarily used for biocompatibility and is a passive coating. The cerium phosphate (CePO4) generated in this invention not only achieves physical sealing but, more importantly, endows the membrane with active protection (self-healing) functionality. When the membrane is damaged and exposed to the substrate, cerium ions diffuse with the solution and form Ce(OH)3 precipitate to cover the micro-corrosion area. This chemical self-healing capability is completely absent in calcium salt systems.

[0034] In this invention, a specific electrolyte system of "exogenous cerium-EDTA-2Na-phosphate" is constructed, which possesses unique complexation equilibrium. The complexation constant of cerium ions (rare earth) and EDTA-2Na is completely different from that of calcium ions. In the strongly alkaline environment of micro-arc oxidation, without precise proportioning (such as the concentration range of the electrolyte), cerium ions are prone to hydrolysis and precipitation, leading to electrolyte failure and inability to achieve in-situ sealing. This invention uses a cerium salt system combined with specific high-frequency and high-voltage parameters (425~475V, 500~700Hz). Its technical effect lies not only in the in-situ generated cerium phosphate sealing the micropores, but also in the active protection (self-repair) achieved after coating damage by utilizing the electrochemical properties of rare earth elements. This leap from 'passive barrier' to 'active protection' cannot be achieved by simple element substitution.

[0035] Furthermore, the electrolyte mixing method includes: adding phosphate, complexing agent, alkali and cerium salt to water in sequence and stirring to mix. Specifically, first, phosphate is added to water and stirred until no visible particles precipitate in the solution. Then, complexing agent, alkali and cerium salt are added in sequence and stirred thoroughly until the resulting solution is evenly dispersed, thus preparing the micro-arc oxidation electrolyte of the multi-component system.

[0036] In some embodiments of this implementation, the aluminum alloy includes commercially available 5083 aluminum alloy.

[0037] Furthermore, aluminum alloys require surface pretreatment before use. This pretreatment includes rough grinding, polishing, ultrasonic treatment, water washing, and drying. Specifically: First, the aluminum alloy is rough ground using polishing paste mixed with anhydrous ethanol. Then, it undergoes ultrasonic treatment in anhydrous ethanol, followed by rinsing with deionized water and drying. Preferably, the surface pretreatment of commercial 5083 aluminum alloy involves: sequentially rough grinding the commercial 5083 aluminum alloy with 200#, 400#, 800#, 1200#, and 1500# metallographic sandpaper to remove surface oxides and oil. Polishing is then performed using W1.5 polishing paste, followed by ultrasonic treatment at 40kHz for 5-20 minutes in anhydrous ethanol, and finally rinsing with deionized water and drying.

[0038] It should be noted that the micro-arc oxidation process utilizes the instantaneous high temperature (10) in a micro-area generated by high-voltage breakdown. 3 -10 4 K) and high pressure. This high temperature is what drives Ce. 3+ With PO4 3- The thermodynamic and kinetic necessary conditions for the "in-situ reaction" to generate molten CePO4 within the discharge channel. High pressure "forces" the molten Al2O3 and CePO4 mixture into and "backfills" the discharge channel, achieving a sealed orifice.

[0039] This invention employs a micro-arc oxidation (MAO) process, rather than other processes such as constant current deposition. Firstly, there is a difference in energy levels: constant current deposition is a low-temperature, low-energy electrochemical process; while this invention utilizes micro-arc oxidation (MAO), which generates localized, instantaneous high temperatures (thousands of degrees Celsius) and high pressures through plasma discharge. Secondly, the reaction pathways differ: in MAO, the electrolyte components (cerium salts, phosphates) not only deposit but also undergo in-situ chemical reactions within the discharge channel, generating thermodynamically stable new phases (such as cerium phosphate). This in-situ phase transformation under high-temperature excitation is impossible to achieve with constant current deposition. Therefore, this invention achieves a "two-in-one" integration of film growth and pore sealing. The sealing material is generated in-situ from within the film layer, chemically bonded to or deeply embedded in the ceramic substrate, resulting in a much stronger bond than traditional deposition layers. Experimental data demonstrates that this invention improves the corrosion resistance of 5083 aluminum alloy by nearly five orders of magnitude, a leap forward that is difficult to achieve with conventional deposition processes. Furthermore, this invention emphasizes active protection while achieving one-step in-situ pore sealing.

[0040] Therefore, different processing techniques lead to different technical effects: on the one hand, there is a qualitative change in functional properties. Constant current deposition can usually only seal surface openings, providing only static physical shielding. In this invention, however, the plasma discharge generated by MAO can directly transport the reactants to the bottom of the discharge channel deep within the film, achieving full-depth sealing. Through micro-arc oxidation, cerium is anchored in the ceramic phase as a specific phase (cerium phosphate). Experiments have shown that when the film is damaged, this system exhibits significant active protection (self-repair) capabilities, inducing the formation of a new protective layer at the scratches. This dynamic protection effect is completely absent in constant current deposition. On the other hand, there is a difference in bonding strength. Low-temperature electrodeposition often results in physical accumulation or thin film coverage, with weak bonding between the sealant and the substrate. This invention utilizes the instantaneous high temperature generated by plasma discharge to achieve lattice-level high-temperature in-situ composite of the sealant and the ceramic film. MAO grows in situ, and the sealant and film are an integrated structure, with its peel resistance and film density (corrosion resistance improved by 5 orders of magnitude) far exceeding that of conventional deposition processes. Therefore, the 600Hz frequency and 425~475V voltage selected in this invention are to ensure that cerium ions can accurately enter the discharge channel to participate in the thermochemical reaction. If a low-energy process is used, this in-situ phase transformation cannot be induced, and thus it is impossible to obtain a film layer with both "in-situ sealing" and "self-healing" functions.

[0041] In some embodiments of this implementation, the parameters of the micro-arc oxidation process are: voltage of 400-500V, frequency of 400-800Hz, duty cycle of 10-35%, electrolyte temperature of 20-25℃, and micro-arc oxidation time of 5-15min. Throughout the process, a mechanical stirrer is used to continuously and gently stir the electrolyte to ensure uniform temperature and component transport. Finally, a micro-arc oxidation ceramic film layer with both in-situ sealing and active protection functions is obtained on the aluminum alloy surface. The film is then rinsed with deionized water and allowed to air dry naturally.

[0042] Preferably, the micro-arc oxidation is performed in a constant voltage mode. The parameters of the micro-arc oxidation process are: voltage of 425~475V, frequency of 500~700Hz, duty cycle of 15~25%, electrolyte temperature of 20~25℃, and micro-arc oxidation time of 8~12min.

[0043] Micro-arc oxidation is an extremely high-energy physicochemical process. The precise coupling of voltage (425~475V) and frequency (500~700Hz) is crucial for inducing specific chemical reactions. Different voltages lead to variations in breakdown energy levels. In this invention, the voltage cannot be too low; if it does not exceed 350V, cerium ions in the electrolyte will struggle to acquire sufficient excitation energy to penetrate deep into the discharge channel for reaction. This invention, using a high voltage of 425~475V, ensures that the plasma discharge effectively breaks down the nascent film, allowing cerium ions and phosphate ions to undergo a high-temperature in-situ reaction within the micropores. Furthermore, different frequencies allow for control over the sealing quality. For example, in the comparative example, a coarse spark at 200Hz leads to large, penetrating pores in the film; while at 600Hz, high-frequency micro-energy discharge is achieved. This "refined" discharge is the physical prerequisite for achieving "in-situ sealing" without compromising the film's density.

[0044] Specifically, the reasons for selecting 600Hz in this invention include the following: ① Refined discharge control: When the frequency is increased from 200Hz to 600Hz (the preferred range of this invention is 500~700Hz), the number of discharges per unit time increases, but the energy released by a single pulse is more fine and uniform. This avoids the formation of large pores and is conducive to the densification of the membrane structure. ② In-situ reaction kinetics: High-frequency discharge creates a more frequent local instantaneous high-temperature environment, which is more conducive to the efficient chemical reaction between cerium ions and phosphate ions in the electrolyte inside the micropores. This "high-frequency micro-area reaction" allows the generated cerium phosphate to be backfilled and solidified more uniformly in the pores, thereby achieving more perfect in-situ chemical sealing. ③ Membrane quality balance: 200Hz often leads to increased membrane stress and more cracks due to excessively rapid heat accumulation; while 600Hz can achieve the best balance between film formation rate and membrane quality, ensuring that the membrane has sufficient thickness and excellent sealing and active protection functions.

[0045] As a preferred embodiment, the present invention provides a method for preparing a coating that combines in-situ sealing and active protection functions, comprising the following steps: S1: Material pretreatment: Pretreatment of the surface of aluminum alloy (such as commercial 5083 aluminum alloy).

[0046] S2: Preparation of micro-arc oxidation electrolyte: Na4P2O7, C 10 H 14 N₂O₈·2H₂O, NaOH, and Ce(CH₃CO₂)₃·xH₂O were sequentially added to deionized water, wherein the concentration of Na₄P₂O₇ was 5~25 g / L; the concentration of C... 10 H 14The concentration of N2O8·2H2O is 2~8 g / L; the concentration of NaOH is 0.25~2.0 g / L; and the concentration of Ce(CH3CO2)3·xH2O is 1~20 g / L.

[0047] S3: A coating that combines in-situ sealing and active protection functions. The pretreated aluminum alloy (such as commercial 5083 aluminum alloy) is placed in the stainless steel electrolytic cell of the micro-arc oxidation equipment. The aluminum alloy (such as commercial 5083 aluminum alloy) serves as the anode, and the stainless steel electrolytic cell serves as the cathode. The micro-arc oxidation electrolyte prepared in step S2 is added to the stainless steel electrolytic cell. The aluminum alloy (such as commercial 5083 aluminum alloy) is subjected to micro-arc oxidation treatment using a micro-arc oxidation power supply. The micro-arc oxidation treatment process parameters are: voltage: 400~500V, frequency: 400~800Hz, duty cycle: 10~35%, electrolyte temperature: 20~25℃, and micro-arc oxidation treatment time: 5~15min. Throughout the treatment process, the mechanical stirrer is turned on to continuously and gently stir the electrolyte to ensure uniform temperature and component transfer. Finally, a micro-arc oxidation ceramic film layer with both in-situ sealing and active protection functions is obtained on the surface of the commercial 5083 aluminum alloy. The film is then rinsed with deionized water and allowed to air dry naturally.

[0048] Furthermore, in step S1, the commercial 5083 aluminum alloy is first rough ground, polished with W1.5 polishing paste and anhydrous ethanol, then ultrasonically treated with anhydrous ethanol at 40KHz for 10~15min, and then the aluminum alloy surface is rinsed with deionized water and dried for later use.

[0049] A second typical embodiment of the present invention provides a coating that combines in-situ sealing and active protection functions, which is prepared by the above-described preparation method.

[0050] The coating is a micro-arc oxidation ceramic film that combines in-situ sealing and active protection functions. The coating contains cerium phosphate synthesized in-situ using a micro-arc oxidation process. Specifically, within the high-temperature, high-pressure region of the micro-arc discharge, cerium ions react with phosphate ions to form cerium phosphate and other products, which are then condensed along with the molten oxide and backfilled into the pores, forming a strong bond with the substrate oxide, thereby achieving in-situ sealing of the pores.

[0051] A third embodiment of the present invention provides a micro-arc oxidation system, using an aluminum alloy as the anode and a stainless steel electrolytic cell as the cathode, wherein the anode, cathode and electrolyte constitute an electrochemical reaction system; wherein the electrolyte is the electrolyte described above.

[0052] The fourth embodiment of the present invention provides the application of the coating with both in-situ sealing and active protection functions prepared by the above preparation method, or the coating with both in-situ sealing and active protection functions, in corrosion resistance in the fields of shipbuilding and marine engineering.

[0053] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0054] Example 1: S1: Material Pretreatment Commercial 5083 aluminum alloy surface pretreatment: The commercial 5083 aluminum alloy was coarsely ground with 200#, 400#, 800#, 1200# and 1500# metallographic sandpaper in sequence to remove surface oxides and oil stains. Polishing was performed with W1.5 polishing paste and anhydrous ethanol. Then, ultrasonic treatment was performed in anhydrous ethanol at 40KHz for 10 minutes. Finally, the aluminum alloy surface was rinsed with deionized water and dried for later use.

[0055] S2: Preparation of micro-arc oxidation electrolyte First, add Na4P2O7 to deionized water and stir until no visible precipitate remains in the solution. Then, add C sequentially. 10 H 14 The micro-arc oxidation electrolyte for the multi-component system was prepared by mixing N₂O₈·2H₂O, NaOH, and Ce(CH₃CO₂)₃·xH₂O, and stirring thoroughly until the resulting solution was uniformly dispersed. The concentration of Na₄P₂O₇ was 15 g / L; the concentration of C... 10 H 14 The concentration of N2O8·2H2O is 5.84 g / L; the concentration of NaOH is 1 g / L; and the concentration of Ce(CH3CO2)3·xH2O is 5 g / L.

[0056] S3: Preparation of micro-arc oxidation ceramic films with both in-situ sealing and active protection functions The pretreated commercial 5083 aluminum alloy was placed in the stainless steel electrolytic cell of the micro-arc oxidation equipment, with the commercial 5083 aluminum alloy as the anode and the stainless steel electrolytic cell as the cathode. The micro-arc oxidation electrolyte prepared in step S2 was added to the stainless steel electrolytic cell. The commercial 5083 aluminum alloy was subjected to micro-arc oxidation treatment in constant voltage mode using a micro-arc oxidation power supply. The micro-arc oxidation treatment process parameters were: voltage: 450V, frequency: 600Hz, duty cycle: 20%, electrolyte temperature: 20~25℃, and micro-arc oxidation treatment time: 10min. The electrolyte was continuously mechanically stirred throughout the oxidation process. Finally, a micro-arc oxidation ceramic film layer with both in-situ sealing and active protection functions was obtained on the surface of the commercial 5083 aluminum alloy. The film was rinsed with deionized water and allowed to air dry naturally.

[0057] Example 2: S1: Material Pretreatment Commercial 5083 aluminum alloy surface pretreatment: The commercial 5083 aluminum alloy was coarsely ground with 200#, 400#, 800#, 1200# and 1500# metallographic sandpaper in sequence to remove surface oxides and oil stains. Polishing was performed with W1.5 polishing paste and anhydrous ethanol. Then, ultrasonic treatment was performed in anhydrous ethanol at 40KHz for 10 minutes. Finally, the aluminum alloy surface was rinsed with deionized water and dried for later use.

[0058] S2: Preparation of micro-arc oxidation electrolyte First, add Na4P2O7 to deionized water and stir until no visible precipitate remains in the solution. Then, add C sequentially. 10 H 14 The micro-arc oxidation electrolyte for the multi-component system was prepared by mixing N₂O₈·2H₂O, NaOH, and Ce(CH₃CO₂)₃·xH₂O, and stirring thoroughly until the resulting solution was uniformly dispersed. The concentration of Na₄P₂O₇ was 15 g / L; the concentration of C... 10 H 14 The concentration of N2O8·2H2O is 5.84 g / L; the concentration of NaOH is 1 g / L; and the concentration of Ce(CH3CO2)3·xH2O is 10 g / L.

[0059] S3: Preparation of micro-arc oxidation ceramic films with both in-situ sealing and active protection functions The pretreated commercial 5083 aluminum alloy was placed in the stainless steel electrolytic cell of the micro-arc oxidation equipment, with the commercial 5083 aluminum alloy as the anode and the stainless steel electrolytic cell as the cathode. The micro-arc oxidation electrolyte prepared in step S2 was added to the stainless steel electrolytic cell. The commercial 5083 aluminum alloy was subjected to micro-arc oxidation treatment in constant voltage mode using a micro-arc oxidation power supply. The micro-arc oxidation treatment process parameters were: voltage: 450V, frequency: 600Hz, duty cycle: 20%, electrolyte temperature: 20~25℃, and micro-arc oxidation treatment time: 10min. The electrolyte was continuously mechanically stirred throughout the oxidation process. Finally, a micro-arc oxidation ceramic film layer with both in-situ sealing and active protection functions was obtained on the surface of the commercial 5083 aluminum alloy. The film was rinsed with deionized water and allowed to air dry naturally.

[0060] Example 3: S1: Material Pretreatment Commercial 5083 aluminum alloy surface pretreatment: The commercial 5083 aluminum alloy was coarsely ground with 200#, 400#, 800#, 1200# and 1500# metallographic sandpaper in sequence to remove surface oxides and oil stains. Polishing was performed with W1.5 polishing paste and anhydrous ethanol. Then, ultrasonic treatment was performed in anhydrous ethanol at 40KHz for 10 minutes. Finally, the aluminum alloy surface was rinsed with deionized water and dried for later use.

[0061] S2: Preparation of micro-arc oxidation electrolyte First, add Na4P2O7 to deionized water and stir until no visible precipitate remains in the solution. Then, add C sequentially. 10 H 14 The micro-arc oxidation electrolyte for the multi-component system was prepared by mixing N₂O₈·2H₂O, NaOH, and Ce(CH₃CO₂)₃·xH₂O, and stirring thoroughly until the resulting solution was uniformly dispersed. The concentration of Na₄P₂O₇ was 15 g / L; the concentration of C... 10 H 14 The concentration of N2O8·2H2O is 5.84 g / L; the concentration of NaOH is 1 g / L; and the concentration of Ce(CH3CO2)3·xH2O is 15 g / L.

[0062] S3: Preparation of micro-arc oxidation ceramic films with both in-situ sealing and active protection functions The pretreated commercial 5083 aluminum alloy was placed in the stainless steel electrolytic cell of the micro-arc oxidation equipment, with the commercial 5083 aluminum alloy as the anode and the stainless steel electrolytic cell as the cathode. The micro-arc oxidation electrolyte prepared in step S2 was added to the stainless steel electrolytic cell. The commercial 5083 aluminum alloy was subjected to micro-arc oxidation treatment in constant voltage mode using a micro-arc oxidation power supply. The micro-arc oxidation treatment process parameters were: voltage: 450V, frequency: 600Hz, duty cycle: 20%, electrolyte temperature: 20~25℃, and micro-arc oxidation treatment time: 10min. The electrolyte was continuously mechanically stirred throughout the oxidation process. Finally, a micro-arc oxidation ceramic film layer with both in-situ sealing and active protection functions was obtained on the surface of the commercial 5083 aluminum alloy. The film was rinsed with deionized water and allowed to air dry naturally.

[0063] Comparative Example 1: S1: Material Pretreatment Commercial 5083 aluminum alloy surface pretreatment: The commercial 5083 aluminum alloy was coarsely ground with 200#, 400#, 800#, 1200# and 1500# metallographic sandpaper in sequence to remove surface oxides and oil stains. Polishing was performed with W1.5 polishing paste and anhydrous ethanol. Then, ultrasonic treatment was performed in anhydrous ethanol at 40KHz for 10 minutes. Finally, the aluminum alloy surface was rinsed with deionized water and dried for later use.

[0064] S2: Preparation of micro-arc oxidation electrolyte First, add Na4P2O7 to deionized water and stir until no visible precipitate remains in the solution. Then, add C sequentially. 10 H 14 N₂O₈·2H₂O and NaOH were added and stirred thoroughly until the resulting solution was uniformly dispersed to prepare the micro-arc oxidation electrolyte for the multi-component system. The concentration of Na₄P₂O₇ was 15 g / L; the concentration of C... 10 H 14 The concentration of N2O8·2H2O is 5.84 g / L; the concentration of NaOH is 1 g / L.

[0065] S3: Preparation of micro-arc oxidation ceramic film The pretreated commercial 5083 aluminum alloy was placed in the stainless steel electrolytic cell of the micro-arc oxidation equipment, with the commercial 5083 aluminum alloy as the anode and the stainless steel electrolytic cell as the cathode. The micro-arc oxidation electrolyte prepared in step S2 was added to the stainless steel electrolytic cell. The commercial 5083 aluminum alloy was subjected to micro-arc oxidation treatment in constant voltage mode using a micro-arc oxidation power supply. The micro-arc oxidation treatment process parameters were: voltage: 450V, frequency: 600Hz, duty cycle: 20%, electrolyte temperature: 20~25℃, and micro-arc oxidation treatment time: 10min. The electrolyte was continuously mechanically stirred throughout the oxidation process. Finally, a typical porous micro-arc oxidation ceramic film was obtained on the surface of the commercial 5083 aluminum alloy. The film was rinsed with deionized water and allowed to air dry naturally.

[0066] Comparative Example 2 Compared to Comparative Example 1, the electrolyte composition was the same, both being 5.84 g / LC. 10 H 14 The formula is N₂O₈·2H₂O, 15 g / L Na₄P₂O₇, 1 g / L NaOH, voltage 450 V, duty cycle 20%, time 10 min, with the only difference being the frequency, which is 200 Hz. All other steps are the same.

[0067] Experimental results show that at a lower frequency of 200Hz, the single pulse discharge time is relatively long, resulting in excessively intense and coarse discharge sparks. The prepared ceramic film has a porous surface with obvious large discharge pores and microcracks, exhibiting poor performance and making it difficult to obtain visualized data.

[0068] The following is combined Figure 1 ~ Figure 6 This invention describes a method for preparing a commercially available 5083 aluminum alloy micro-arc oxidation ceramic film that combines in-situ sealing and active protection functions.

[0069] like Figure 1As shown, the micro-arc oxidation device used in this invention uses a stainless steel electrolytic cell as the cathode and commercial 5083 aluminum alloy as the anode. This invention uses ice as a cooling medium to control the temperature of the electrolyte, preventing excessively high electrolyte temperatures from leading to poor micro-arc oxidation. Furthermore, a mechanical stirrer is used during the micro-arc oxidation process to agitate the electrolyte, ensuring uniform electrolyte composition and temperature distribution. This method is economical, effective, and highly repeatable.

[0070] like Figure 2 As shown, X-ray diffraction (XRD) phase analysis of the ceramic films obtained in Examples 1 to 3 and Comparative Example 1 clearly reveals their compositional differences. The film of Comparative Example 1 mainly comprises an aluminum matrix, γ-Al₂O₃, α-Al₂O₃, and a small amount of aluminum phosphate (AlPO₄), with the alumina phase being dominant. In contrast, the film of Example 1, based on the above phases, exhibits clear characteristic diffraction peaks of cerium phosphate (CePO₄). With the increase of cerium salt content in the electrolyte, the intensity of the cerium phosphate diffraction peaks in the films of Examples 2 and 3 significantly increases. This result directly confirms that, under the process conditions set in this invention, cerium phosphate can be synthesized in situ during micro-arc oxidation and successfully incorporated into the ceramic film.

[0071] like Figure 3 As shown, Figure 3 (a) Figure 3 (b) Figure 3 (c) Figure 3 Images (d) in the table are SEM images of Comparative Example 1, Example 1, Example 2, and Example 3, respectively, showing significant changes in surface morphology. Figure 3 As shown in (a) of Comparative Example 1, the film exhibits a typical micro-arc oxidation porous structure, with numerous "crater"-like discharge pores and microcracks. The pores are small in size but densely distributed. This structure originates from the eruption and rapid quenching of molten oxides during discharge. The high discharge density and low breakdown voltage together result in a dense network of micropores and cracks, which become the main channels for the penetration of corrosive media. In stark contrast, as shown in (a), the film layer of Comparative Example 1 exhibits a typical micro-arc oxidation porous structure, with numerous "crater"-like discharge pores and microcracks visible. The pores are small in size but densely distributed. This structure originates from the eruption and rapid quenching of molten oxides during discharge. The high discharge density and low breakdown voltage together lead to a dense network of micropores and cracks, which become the main channels for the penetration of corrosive media. Figure 3 (b) Figure 3 (c) and Figure 3As shown in (d), the morphology of the films in Examples 1 to 3 underwent fundamental changes. First, the size of the surface pores increased, but their distribution became significantly sparser. This is because the introduction of cerium salts altered the conductivity of the electrolyte and the dielectric properties of the film, leading to an increase in breakdown voltage. Discharge points tended to concentrate at local weak points, thus forming fewer but larger discharge channels. More importantly, a large amount of filling material could be clearly observed inside these pores, achieving in-situ sealing of the pores. This is mainly attributed to the products such as cerium phosphate generated by the reaction of cerium ions and phosphate ions in the high-temperature and high-pressure region of micro-arc discharge, which condensed along with the molten oxide and backfilled into the pores, forming a strong bond with the matrix oxide. Among them, the film surface of Example 2 was the most uniform and smooth, with the fewest visible pores and cracks, showing the best in-situ sealing effect.

[0072] like Figure 4 As shown, after micro-arc oxidation treatment, the corrosion current density of commercial 5083 aluminum alloy decreased from 1.43 × 10⁻⁶. -5 A·cm -2 The values ​​were reduced to 4.87 × 10⁻⁶ in Comparative Example 1. -9 A·cm -2 Example 1: 2.57 × 10 -9 A·cm -2 Example 2: 7.59 × 10 -10 A·cm -2 And 8.93×10 in Example 3 -10 A·cm -2 The corrosion resistance decreased by nearly five orders of magnitude. This demonstrates that the micro-arc oxidation film designed in this invention significantly improves the corrosion resistance of commercial 5083 aluminum alloy substrates. The in-situ sealed micro-arc oxidation ceramic film prepared in Example 2 exhibits the best corrosion resistance. This indicates that the micro-arc oxidation ceramic film effectively seals the pores of the commercial 5083 aluminum alloy, effectively preventing the erosion of the substrate by the solution medium and greatly improving the corrosion resistance of the commercial 5083 aluminum alloy surface.

[0073] like Figure 5 As shown, the surface of the film prepared in Comparative Example 1 was artificially scratched, and then immersed in a 3.5 wt% NaCl solution for 120 hours to observe the corrosion at the interface. Figure 5 (a) and Figure 5 (b) shows the initial morphology of Comparative Example 1 after scratching. The scratch width is approximately 40 μm, exhibiting a typical plough furrow shape. Coating debris (such as...) is present at the scratch edges and inside the scratch. Figure 5 (As indicated by the orange arrow in the middle), and the aluminum alloy substrate has been exposed to the environment. Figure 5 (c) and Figure 5(d) shows the corrosion morphology of Comparative Example 1 after immersion for 120 hours. It can be seen that severe localized corrosion occurred around and inside the scratch, with localized peeling of the substrate and a large amount of corrosion products accumulating. Figure 5 (As indicated by the red arrow).

[0074] like Figure 6 As shown, EDS line scan and area scan analysis ( Figure 6 (c) and Figure 6 (d) indicates that the corrosion products are mainly Al and O, and should primarily consist of Al(OH)3 micro / nano particles. These results demonstrate that once the coating in Comparative Example 1 is damaged, its barrier function fails, failing to provide effective protection for the substrate. Instead, localized corrosion accelerates the substrate's degradation process.

[0075] like Figure 7 As shown, in Example 2 of the present invention, artificial scratches were applied, and then the sample was immersed in a 3.5 wt% NaCl solution for 120 hours to observe the corrosion at the interface. Figure 7 (a) and Figure 7 (b) in Example 2 shows the initial morphology after scratching, where the orange arrows indicate coating debris left by the scratching process. Figure 7 (c) and Figure 7 Image (d) shows the corrosion morphology of Example 2 after immersion for 120 hours. No significant changes were observed in the area inside and around the artificial scratches after immersion, and no severe localized corrosion was observed. Only a small number of micro / nano-sized corrosion product particles were observed on the exposed metal substrate surface, such as... Figure 7 As shown in (d) in the figure.

[0076] like Figure 8 As shown, EDS surface scan analysis ( Figure 8 (b) indicates the presence of local enrichment regions of Ce, P, and O, combined with morphological observation and EDS line scan analysis ( Figure 8 (c) in the figure identifies the particles as coating fragments, as indicated by the orange arrow, which is different from... Figure 6 Corrosion products formed on the surface of Comparative Example 1. EDS surface scan analysis ( Figure 8 (b) further shows that, apart from coating fragments, Ce signals were detected throughout the scratched area, indicating a uniform distribution of Ce on the substrate surface. This phenomenon is attributed to Ce. 3+ Active protection mechanism: When the coating is damaged, Ce is released at the interface. 3+ As the solution diffuses to the exposed substrate surface, it reacts with OH- generated by the localized cathodic reaction. -The Ce(OH)3 precipitate, along with Al(OH)3, forms a physical barrier that covers the micro-corrosion zone, effectively inhibiting the spread of localized corrosion. These results demonstrate that Example 2 possesses active protection capabilities, providing active protection for the aluminum alloy substrate.

[0077] In summary, XRD and SEM analyses jointly revealed the in-situ formation of cerium phosphate and the effective filling of pores, which is the structural basis for the improved performance. Electrochemical data quantitatively verified that this structural evolution led to a leap in corrosion resistance. Immersion corrosion experiments after artificial scratching showed that Example 2 of the present invention has an active protection function, still providing protection for the 5083 substrate after the coating is damaged. It is worth noting that although Example 3 (15 g / L Ce) had the strongest cerium phosphate diffraction peak, its corrosion resistance did not exceed that of Example 2, indicating that there is an optimal range of cerium salt addition concentration. Excessive addition may affect the melt solidification behavior and stress state during the micro-arc oxidation process, thereby partially offsetting the positive effect of pore sealing. This finding highlights the importance of electrolyte composition optimization in the present invention.

[0078] In summary, this invention successfully achieved in-situ chemical sealing of micropores in the ceramic film layer of 5083 aluminum alloy during the micro-arc oxidation process, and prepared a ceramic coating with both in-situ sealing and active protection functions in one step. This effectively solved the bottleneck problem of traditional methods and provided a solution for expanding the practical application of commercial 5083 aluminum alloy.

[0079] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. 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 method for preparing a coating with both in-situ plugging and active protection functions, characterized in that, Includes the following steps: Using aluminum alloy as the anode and stainless steel electrolytic cell as the cathode, the anode, cathode and electrolyte constitute an electrochemical reaction system. A coating with both in-situ sealing and active protection functions is formed on the surface of aluminum alloy using micro-arc oxidation process. The electrolyte comprises phosphate, complexing agent, alkali, cerium salt and water; In the electrolyte, the concentration of phosphate is 5-25 g / L; the concentration of the complexing agent is 2-8 g / L; the concentration of the alkali is 0.25-1 g / L; and the concentration of the cerium salt is 10-20 g / L. The parameters of the micro-arc oxidation process are: voltage 425~475V, frequency 600Hz, duty cycle 10~35%, electrolyte temperature 20~25℃, and micro-arc oxidation time 5~15min. The phosphate is Na4P2O7, the complexing agent is EDTA-2Na, the base is NaOH, and the cerium salt is Ce(CH3CO2)3·xH2O; The aluminum alloy is 5083 aluminum alloy; Within the high-temperature, high-pressure region of micro-arc discharge, the products generated by the reaction of cerium ions and phosphate ions condense along with the molten oxide and backfill into the pores, forming a strong bond with the matrix oxide.

2. The production method according to claim 1, characterized by, Aluminum alloys require surface pretreatment before use; the surface pretreatment includes rough grinding, polishing, ultrasonication, water washing, and drying for later use.

3. The production method according to claim 1, characterized by, The electrolyte can be mixed by adding phosphate, complexing agent, alkali and cerium salt to water and stirring.

4. A coating with both in-situ plugging and active protection functions, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 3.

5. The coating of claim 4, wherein, The coating contains cerium phosphate synthesized in situ using a micro-arc oxidation process.

6. The application of a coating with both in-situ sealing and active protection functions prepared by the preparation method according to any one of claims 1 to 3, or the coating with both in-situ sealing and active protection functions according to claim 4 or 5, in corrosion resistance in the fields of shipbuilding and marine engineering.

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