Self-sealing, self-healing aluminum alloy corrosion-resistant coating and method of making same

Abstract

The application belongs to the technical field of metal material surface treatment, and provides a self-sealing and self-healing aluminum alloy corrosion-resistant coating and a preparation method thereof. The aluminum alloy is subjected to micro-arc oxidation treatment in a phosphate electrolyte containing cerium ions to prepare a self-sealing and self-healing micro-arc oxidation coating on the surface of the aluminum alloy, thereby solving the technical problems of poor sealing effect and complex process of the aluminum alloy micro-arc oxidation coating in the prior art, and achieving the beneficial effects of providing long-term active corrosion protection for the aluminum alloy and simplifying the process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal material surface treatment, and particularly relates to a self-sealing and self-healing aluminum alloy corrosion-resistant coating and a preparation method thereof. BACKGROUND

[0002] Aluminum alloy has a wide range of applications in the fields of aerospace, marine equipment, automobiles and 3C electronic components due to its low density, high strength and easy processing. However, aluminum alloy components are prone to corrosion when directly serving in actual environmental media, which limits their application. At present, a micro-arc oxidation coating is usually prepared on the surface of the aluminum alloy to improve the corrosion resistance of the aluminum alloy. However, the growth behavior of the micro-arc oxidation coating leads to a large number of pores on the surface, and the corrosion medium is easy to penetrate the coating to reach the substrate along the pores during long-term use, and cause local corrosion. Therefore, it is crucial to treat the weak pores on the surface of the micro-arc oxidation coating to improve the corrosion resistance.

[0003] In the prior art, a secondary sealing technology can effectively alleviate or prevent the penetration of the corrosion medium along the pores, and thus improve the corrosion resistance of the micro-arc oxidation coating. Among them, organic sealing is to completely cover the pores by coating organic matter on the surface of the micro-arc oxidation coating, but the organic matter and the inorganic coating are only physically combined, which is easy to cause the coating to fall off, and the organic matter is easy to age and fail during long-term service. Nano-particle sealing is to realize the aggregation and plugging of nano-particles at the pore position by growing the coating of the aluminum alloy in the micro-arc oxidation electrolyte containing nano-particles, but the nano-particles are easy to aggregate and precipitate in the electrolyte, resulting in poor sealing effect, and usually an additional particle surface charge modification is required, which is complex.

[0004] The present application provides a self-sealing and self-healing micro-arc oxidation coating on the surface of the aluminum alloy by micro-arc oxidation treatment of the aluminum alloy in a phosphate electrolyte containing cerium ions. The preparation method provided by the present application is simple in process, and the prepared coating has the technical effects of corrosion resistance, self-sealing and self-healing, solving the technical problems of poor sealing effect and complex process of the aluminum alloy micro-arc oxidation coating in the prior art. SUMMARY

[0005] The present application provides a self-sealing and self-healing aluminum alloy corrosion-resistant coating and a preparation method thereof, to solve the technical problems of easy corrosion of the aluminum alloy, poor sealing effect of the micro-arc oxidation coating and complex process in the prior art.

[0006] In one aspect, the present application provides a preparation method of a self-sealing and self-healing aluminum alloy corrosion-resistant coating, which comprises the following steps: taking an aluminum alloy as a substrate, and placing the aluminum alloy substrate into an electrolyte for micro-arc oxidation treatment; the electrolyte comprises phosphate, sodium hydroxide, disodium ethylenediaminetetraacetate and soluble cerium salt.

[0007] According to the present invention, a method for preparing a self-sealing, self-healing corrosion-resistant coating for aluminum alloys is provided, wherein the concentration of the phosphate is 3~20 g·L. -1 The concentration of sodium hydroxide is 1~10 g·L. -1 The concentration of disodium ethylenediaminetetraacetate is 2~10 g·L. -1 The concentration of soluble cerium salts is 1~20 g·L. -1 .

[0008] According to the present invention, a method for preparing a self-sealing, self-healing corrosion-resistant coating for aluminum alloys is provided, wherein the phosphate includes at least one of sodium hexametaphosphate, sodium pyrophosphate, sodium dihydrogen phosphate, and sodium tripolyphosphate.

[0009] According to the present invention, a method for preparing a self-sealing, self-healing corrosion-resistant coating for aluminum alloys is provided, wherein the soluble cerium salt includes at least one of cerium nitrate, cerium acetate, and cerium carbonate.

[0010] According to the present invention, a method for preparing a self-sealing, self-healing corrosion-resistant aluminum alloy coating is provided, wherein the aluminum alloy substrate is any one of 2-series aluminum alloy, 5-series aluminum alloy, 6-series aluminum alloy, and 7-series aluminum alloy.

[0011] According to the present invention, a method for preparing a self-sealing, self-healing corrosion-resistant aluminum alloy coating is provided, wherein the micro-arc oxidation treatment is performed using an AC power supply in constant current mode, with the aluminum alloy substrate as the anode and the stainless steel electrolytic cell as the cathode.

[0012] According to the present invention, a method for preparing a self-sealing, self-healing corrosion-resistant coating for aluminum alloy is provided, wherein the AC power supply has a power of 10~100kW and a current density of 2~10A·dm. -2 The frequency is 200~1000Hz, the duty cycle is 10~30%, and the discharge time is 5~20 minutes; the temperature of the electrolyte during the micro-arc oxidation process is 35~45℃.

[0013] According to the present invention, a method for preparing a self-sealing, self-healing corrosion-resistant aluminum alloy coating is provided. The preparation method further includes pretreatment of the aluminum alloy substrate, wherein the pretreatment is, in sequence, surface polishing and cleaning.

[0014] According to the present invention, a method for preparing a self-sealing, self-healing corrosion-resistant aluminum alloy coating is provided, wherein the cleaning is performed under ultrasonic conditions for 5 to 15 minutes; the cleaning is performed sequentially using deionized water and anhydrous ethanol.

[0015] On the other hand, the present invention provides a self-sealing, self-healing corrosion-resistant coating for aluminum alloys.

[0016] The self-sealing and self-healing corrosion-resistant coating of an aluminum alloy and a preparation method thereof are provided, a self-sealing and self-healing micro-arc oxidation coating is prepared on the surface of the aluminum alloy by subjecting the aluminum alloy to micro-arc oxidation treatment in a phosphate electrolyte containing cerium ions, the technical problems of poor sealing effect and complex process of the micro-arc oxidation coating of the aluminum alloy in the prior art are solved, and the beneficial effects of providing long-term active corrosion protection for the aluminum alloy and simplifying the process are achieved. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the present application or prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0018] Figure 1 is a self-healing principle diagram of the self-sealing and self-healing corrosion-resistant coating of an aluminum alloy provided by the embodiments of the present application;

[0019] Figure 2 is a discharge curve diagram of the embodiments 1-3 and the comparative example 1 in the preparation of the coating;

[0020] Figure 3 is a SEM diagram of the coating prepared by the embodiments 1-3 and the comparative example 1 of the present application;

[0021] Figure 4 is a LCSM diagram of the coating prepared by the embodiments 1-3 and the comparative example 1 of the present application;

[0022] Figure 5 is a Tafel curve diagram of the embodiments 1-3, the comparative example 1 and the 2A12 aluminum alloy in the present application in the electrochemical test in a 3.5wt.% NaCl solution;

[0023] Figure 6 is an EDS area scan diagram of the inside of the scratch of the coating prepared by the embodiments 2 and the comparative example 1 of the present application;

[0024] Figure 7 is an EDS line scan diagram of the inside of the scratch of the coating prepared by the embodiments 2 and the comparative example 1 of the present application. DETAILED DESCRIPTION

[0025] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described clearly and completely below in conjunction with the drawings in the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0026] The present application provides a preparation method of a self-pore-closing and self-healing aluminum alloy corrosion-resistant coating, which comprises the following steps: taking an aluminum alloy as a substrate, and placing the aluminum alloy substrate into an electrolyte for micro-arc oxidation treatment; the electrolyte comprises a phosphate, sodium hydroxide, disodium ethylenediaminetetraacetate and a soluble cerium salt.

[0027] In the present application, the concentration of the phosphate is 3-20 g·L -1 , preferably 11-18 g·L -1 , and further preferably 14-16 g·L -1 ; the concentration of the sodium hydroxide is 1-10 g·L -1 , preferably 2-8 g·L -1 , and further preferably 4-6 g·L -1 ; the concentration of the disodium ethylenediaminetetraacetate is 2-10 g·L -1 , preferably 3-8 g·L -1 , and further preferably 4-6 g·L -1 ; and the concentration of the soluble cerium salt is 1-20 g·L -1 , preferably 5-18 g·L -1 , and further preferably 8-15 g·L -1 .

[0028] In the present application, the phosphate comprises at least one of sodium hexametaphosphate, sodium pyrophosphate, sodium dihydrogen phosphate and sodium tripolyphosphate, preferably sodium hexametaphosphate or sodium dihydrogen phosphate, and further preferably sodium hexametaphosphate.

[0029] In the present application, the soluble cerium salt comprises at least one of cerium nitrate, cerium acetate and cerium carbonate, preferably cerium nitrate or cerium acetate, and further preferably cerium acetate.

[0030] In the present application, the aluminum alloy substrate is any one of 2-series aluminum alloy, 5-series aluminum alloy, 6-series aluminum alloy and 7-series aluminum alloy, preferably 2-series aluminum alloy, and further preferably 2A12 aluminum alloy.

[0031] In the present application, the micro-arc oxidation treatment is operated in a constant current mode by using an alternating current power supply, the aluminum alloy substrate is used as an anode, and a stainless steel electrolytic cell is used as a cathode.

[0032] In the present application, the power of the alternating current power supply is 10-100 kW, preferably 12-50 kW, further preferably 15-20 kW; the current density is 2-10 A·dm -2 , preferably 3-8 A·dm -2 , further preferably 4-6 A·dm -2 ; the frequency is 200-1000 Hz, preferably 300-700 Hz, further preferably 400-600 Hz; the duty cycle is 10-30%, preferably 12-20%, further preferably 14-16%; the discharge time is 5-20 minutes, preferably 8-18 minutes, further preferably 10-15 minutes; the temperature of the electrolyte during the micro-arc oxidation process is 35-45℃.

[0033] In the present application, the preparation method further comprises pretreating the aluminum alloy substrate, and the pretreatment comprises surface polishing treatment and cleaning in sequence.

[0034] In the present application, the cleaning is performed under ultrasonic conditions, and the ultrasonic time is 5-15 minutes, preferably 8-12 minutes, further preferably 10 minutes; the cleaning is performed by using deionized water and anhydrous ethanol in sequence.

[0035] The present application also provides a self-pore-sealing and self-healing aluminum alloy corrosion-resistant coating.

[0036] The technical solutions provided by the present application will be described in detail below in conjunction with examples, but they should not be understood as limiting the scope of protection of the present application.

[0037] Example 1

[0038] A 2A12 aluminum alloy was cut into a sample with a size of 50 mm×25 mm×1 mm, the surface of the aluminum alloy sample was polished by 2000 mesh sandpaper, and then ultrasonic cleaning was performed by using deionized water and anhydrous ethanol in sequence for 10 minutes to obtain an aluminum alloy substrate. Sodium hexametaphosphate, sodium hydroxide, disodium ethylenediaminetetraacetate and cerous acetate were added to the deionized water in sequence to prepare an electrolyte with a concentration of sodium hexametaphosphate of 15 g·L -1 , a concentration of sodium hydroxide of 5 g·L -1 , a concentration of disodium ethylenediaminetetraacetate of 5 g·L -1 , and a concentration of cerous acetate of 5 g·L -1 . A 15 kW alternating current power supply micro-arc oxidation device was used to perform micro-arc oxidation on the surface of the aluminum alloy substrate in a constant current mode. Among them, the aluminum alloy substrate was used as an anode, and a stainless steel electrolytic cell was used as a cathode, and the current density was controlled to be 5 A·dm -2With a frequency of 500Hz, a duty cycle of 15%, and a discharge time of 10 minutes, a self-sealing and self-healing corrosion-resistant aluminum alloy coating was obtained. During the micro-arc oxidation process, circulating water was used to ensure the electrolyte temperature remained between 35 and 45°C to prevent the coating from being ablated due to excessively high arc temperatures.

[0039] Example 2

[0040] 2A12 aluminum alloy samples were cut into 50mm × 25mm × 1mm pieces. The surfaces of the aluminum alloy samples were polished using 2000-grit sandpaper, and then ultrasonically cleaned for 10 minutes each with deionized water and anhydrous ethanol to obtain the aluminum alloy matrix. Sodium hexametaphosphate, sodium hydroxide, disodium ethylenediaminetetraacetate, and cerium acetate were added sequentially to the deionized water to prepare a sodium hexametaphosphate solution with a concentration of 15 g·L⁻¹. -1 The concentration of sodium hydroxide is 5 g·L⁻¹ -1 The concentration of disodium ethylenediaminetetraacetate is 5 g·L⁻¹. -1 The concentration of cerium acetate is 10 g·L⁻¹ -1 The electrolyte was used. A 15kW AC power supply micro-arc oxidation device was employed to perform micro-arc oxidation on the surface of the aluminum alloy substrate in constant current mode. The aluminum alloy substrate served as the anode, and the stainless steel electrolytic cell served as the cathode, with the current density controlled at 5 A·dm³. -2 With a frequency of 500Hz, a duty cycle of 15%, and a discharge time of 10 minutes, a self-sealing and self-healing corrosion-resistant aluminum alloy coating was obtained. During the micro-arc oxidation process, circulating water was used to ensure the electrolyte temperature remained between 35 and 45°C to prevent the coating from being ablated due to excessively high arc temperatures.

[0041] Example 3

[0042] 2A12 aluminum alloy samples were cut into 50mm × 25mm × 1mm pieces. The surfaces of the aluminum alloy samples were polished using 2000-grit sandpaper, and then ultrasonically cleaned for 10 minutes each with deionized water and anhydrous ethanol to obtain the aluminum alloy matrix. Sodium hexametaphosphate, sodium hydroxide, disodium ethylenediaminetetraacetate, and cerium acetate were added sequentially to the deionized water to prepare a sodium hexametaphosphate solution with a concentration of 15 g·L⁻¹. -1 The concentration of sodium hydroxide is 5 g·L⁻¹ -1 The concentration of disodium ethylenediaminetetraacetate is 5 g·L⁻¹. -1 The concentration of cerium acetate is 15 g·L⁻¹ -1 The electrolyte was used. A 15kW AC power supply micro-arc oxidation device was employed to perform micro-arc oxidation on the surface of the aluminum alloy substrate in constant current mode. The aluminum alloy substrate served as the anode, and the stainless steel electrolytic cell served as the cathode, with the current density controlled at 5 A·dm³. -2, the frequency is 500Hz, the duty cycle is 15%, the discharge time is 10 minutes, and the self-sealing and self-healing aluminum alloy corrosion-resistant coating is obtained.

[0043] Comparative Example 1

[0044] 2A12 aluminum alloy is cut into a sample with a size of 50mm*25mm*1mm, the surface of the aluminum alloy sample is polished by 2000 mesh sandpaper, and then the aluminum alloy sample is ultrasonically cleaned with deionized water and anhydrous ethanol for 10 minutes in sequence to obtain an aluminum alloy substrate. Sodium hexametaphosphate, sodium hydroxide, disodium ethylenediaminetetraacetate and cerium acetate are sequentially added to the deionized water to prepare an electrolyte with a concentration of sodium hexametaphosphate of 15g / L -1 , a concentration of sodium hydroxide of 5g / L -1 , and a concentration of disodium ethylenediaminetetraacetate of 5g / L -1 . A 15kW AC power micro-arc oxidation device is used to perform micro-arc oxidation on the surface of the aluminum alloy substrate in a constant current mode. The aluminum alloy substrate is used as an anode, and a stainless steel electrolytic cell is used as a cathode. The current density is controlled to be 5A / dm -2 , the frequency is 500Hz, the duty cycle is 15%, and the discharge time is 10 minutes, and a micro-arc oxidation coating is obtained. Circulating water is used to ensure that the temperature of the electrolyte is 35-45℃ during the micro-arc oxidation process, so as to prevent the ablation of the coating caused by the excessively high arc temperature.

[0045] The self-sealing and self-healing aluminum alloy corrosion-resistant coating and the preparation method thereof will be described below. Figures 1-7

[0046] Figure 1 It is a self-healing principle diagram of the self-sealing and self-healing aluminum alloy corrosion-resistant coating provided by the embodiment of the present application.

[0047] As shown in Figure 1 , Comparative Example 1 is not doped with Ce, and Cl - in the corrosion medium is difficult to corrode the Al2O3 coating body, but can easily penetrate the coating along the pores on the surface and inside of the coating to reach the substrate interface, and then cause the anodic dissolution corrosion of the aluminum alloy substrate at the interface.

[0048] Anode: Al→Al 3+ +3e - ;

[0049] Cathode: O2+2H2O+4e - →4OH - .

[0050] Al 3+ and OH - ​The corrosion product Al(OH)3will be quickly produced and deposited on the corroded surface. Meanwhile, the corrosion product Al(OH)3is not stable and will be further dissolved by Cl - in the corrosion medium to form loose corrosion product Al(OH) 3-n Cl n (n = 1, 2, 3), reaction formula:

[0051] Al 3+ + 3OH - → Al(OH)3.

[0052] Al(OH)3+ nCl - → Al(OH) 3-n Cl n + nOH - , n = 1, 2, 3.

[0053] The loose corrosion product does not have a protective effect, so the local corrosion site becomes a local weak point, and with the immersion corrosion process, it accelerates the formation of local pitting and eventually causes the failure of the micro-arc oxidation coating.

[0054] For the Ce-doped micro-arc oxidation coatings of Examples 1-3, the in-situ grown cerium phosphate and aluminum oxide form a mixed melt that fills the pores inside the surface, forming a self-sealing effect, which effectively hinders the penetration of the corrosion medium along the pores to the coating / substrate interface. The cerium phosphate grown inside the coating is mainly in the form of nanocrystals wrapped in amorphous and uniformly distributed throughout the aluminum oxide coating. During the long-term corrosion process, it is inevitable that the corrosion medium will locally penetrate to the coating / substrate interface and undergo the above reaction, and the corrosion product Al(OH)3will be further dissolved by Cl - to form a corrosion micro-zone, while the cerium phosphate in the nearby coating is easily dissolved in the process to release Ce 3+ ions, and the low Ksp corrosion product Ce(OH)3is generated at a faster rate, reaction formula: Ce 3+ + 3OH - → Ce(OH)3.

[0055] Generally, the loose Al(OH)3single corrosion product cannot effectively prevent the further diffusion corrosion of Cl - , which will further lead to the longitudinal development of local pitting. However, the deposition of Ksp Ce(OH)3enhances the compactness of Al(OH)3, forming an Al(OH)3 / Ce(OH)3mixed corrosion product layer, which effectively prevents the further diffusion corrosion of Cl -The self-sealing and self-healing corrosion-resistant coating for aluminum alloys provided by this invention exhibits self-healing properties, effectively slowing down coating failure caused by localized corrosion and significantly improving the long-term corrosion protection performance of the aluminum alloy substrate.

[0056] Figure 2 These are discharge curves of Examples 1-3 and Comparative Example 1 during the preparation of micro-arc oxidation coatings.

[0057] like Figure 2 As shown, the discharge curve can be divided into three stages: the first stage is the surface passivation stage (0~60s), the second stage is the passivation layer breakdown discharge stage (60~300s), and the third stage is the rapid and stable growth stage of the micro-arc oxidation coating (300~600s). In the initial 0~60s, the aluminum alloy in the phosphate-containing electrolyte undergoes a matrix oxidation reaction under the influence of current to form a dense Al2O3 passivation layer, resulting in a very rapid voltage rise. Furthermore, the voltage increase rate accelerates with increasing Ce salt content, as more Ce salt reduces the free path of ion movement in the solution, decreasing the conductivity of the phosphate electrolyte and thus leading to a higher passivation voltage. When the voltage continues to rise to the breakdown voltage of the Al2O3 passivation layer, the large amount of charge accumulated on the surface begins to be released, similar to the discharge stage of a capacitor, entering the passivation layer breakdown discharge stage (60~300s). The sample surface voltage gradually increases, and the higher the Ce salt content, the greater the voltage increase, consistent with the evolution pattern of the initial passivation stage. During this stage, as the voltage increases, the insulating passivation layer on the sample surface grows slowly. The resulting electric arc breaks down the Al2O3 passivation layer, forming a discharge channel. The molten aluminum substrate is ejected and comes into contact with the electrolyte, undergoing a chemical or plasma reaction, thereby generating aluminum oxide and aluminum metal salts. Simultaneously, the high temperature within the discharge channel promotes the reaction of Ce ions and PO4 ions in the electrolyte. 3- The reaction produces Ce phosphate, which melts inside the pores. After 300 seconds, the micro-arc oxidation coating enters a rapid and stable growth stage, during which the discharge voltage of the coating gradually increases, and the arc discharge process becomes more intense. The higher the Ce salt content, the greater the coating resistance, and the more significant the voltage increase. As the discharge process begins and ends repeatedly, the coating gradually grows and eventually forms a complex mixed phase. After 600 seconds, the arc on the coating surface becomes enormous due to the high voltage, and localized continuous breakdown arcs cause coating ablation. Therefore, the micro-arc oxidation discharge process is terminated to obtain the final micro-arc oxidation coating.

[0058] Figure 3 These are SEM images of the coatings prepared in Examples 1-3 and Comparative Example 1 of the present invention.

[0059] like Figure 3 As shown, Figure 3(a) is Comparative Example 1, Figure 3 (b) is Example 1, Figure 3 (c) is Example 2, Figure 3 (d) is Example 3. It can be seen that the micro-arc oxidation coating surfaces of Examples 1-3 and Comparative Example 1 all exhibit typical porous structures. The edges of the pores are all similar to the shape of craters, which is because the discharge behavior and the process of volcanic eruption are very similar, and the molten material will accumulate at the pore opening. However, obviously, the pores of the coating doped with different contents of Ce salt are very different, and the pore distribution and pore size are obviously different. The pore distribution of Comparative Example 1 is dense, and the pore size is small, except for some large pores greater than 5 μm, there are also many dense nanoscale pores nearby. This is because the undoped micro-arc oxidation coating growth voltage is small, and the main phase of the coating is only Al2O3, and the difficulty of coating breakdown is small under the same voltage, so the arc density increases, and therefore small size arc discharge phenomenon will occur. In contrast, it can be observed from Examples 1-3 that the pores on the surface of the micro-arc oxidation coating formed by doping Ce salt are obviously different, the number of pores is less, and the pore size is obviously increased. From Example 1 to Example 3, the concentration of Ce salt gradually increases, the number of pores gradually decreases, and the pore size gradually increases. On the one hand, the Ce salt changes the physical properties of the electrolyte, and the growth voltage of the coating is obviously increased. On the other hand, the phase of the formed coating changes, and in addition to the main phase Al2O3, there are also more metal salts. This leads to a change in the difficulty of coating breakdown to form a discharge channel. It is worth noting that there are a large number of fillers inside the pores on the surface of the coating doped with Ce salt, which almost realizes internal sealing along the pore wall. The larger the pore, the more obvious the filler, which is different from the added or self-generated nanoparticles reported in many literatures, and it is the first time to realize self-sealing micro-arc oxidation coating by one step. This is mainly due to the backfilling of exogenous Ce phosphate generated during the discharge process in the coating, which forms a metallurgical bond with the generated oxide and grows inside the pore, thereby effectively sealing the pore.

[0060] Figure 4 is the LCSM image of the coating prepared in Examples 1-3 and Comparative Example 1 of the present application.

[0061] As Figure 4 shown, Figure 4 (a) is Comparative Example 1, Figure 4 (b) is Example 1, Figure 4 (c) is Example 2, Figure 4 (d) is Example 3. The coating surfaces prepared in Examples 1-3 and Comparative Example 1 of the present application all have an uneven structure of molten material protrusions, and the content of Ce salt has no significant effect on the roughness of the micro-arc oxidation coating.

[0062] Figure 5 These are Tafel curves of electrochemical tests conducted on Examples 1-3, Comparative Example 1, and 2A12 aluminum alloy in a 3.5wt.% NaCl solution.

[0063] like Figure 5 As shown, after micro-arc oxidation treatment, the corrosion potential of the 2A12 aluminum alloy coating increased from -1.322V to -1.238V in Comparative Example 1. With the addition of Ce salt, the corrosion potential gradually increased, with -1.063V in Example 1, -0.788V in Example 2, and -0.802V in Example 3. Correspondingly, the corrosion current density increased from 2.649 × 10⁻⁶ V / V. -6 A·cm -2 The values ​​were reduced to 9.546 × 10⁻⁶ in Comparative Example 1. -9 A·cm -2 Example 1: 2.381 × 10 -9 A·cm -2 Example 2: 2.694 × 10 -10 A·cm -2 And 3.415×10 of Example 3 -10 A·cm -2 The maximum decrease was nearly four orders of magnitude. This shows that with the doping of Ce salt, the corrosion resistance of the micro-arc oxidation coating on the aluminum alloy substrate gradually improves. The self-sealing, self-healing aluminum alloy corrosion-resistant coating prepared in Example 2 exhibits the best corrosion resistance, indicating that the self-sealing of the molten material at weak pores effectively hinders the corrosion penetration of the salt solution into the coating. Furthermore, the polarization resistance of the sample typically reflects its corrosion rate; the higher the resistance, the lower the corrosion rate. Polarization resistance R p The Stern-Gear equation can be used to calculate:

[0064] .

[0065] in, ꞵ a and ꞵ c These are the two slopes near the extreme points of the Tafel curve. It can be seen that, compared to the 2A12 aluminum alloy substrate, the polarization resistance of the self-sealing, self-healing aluminum alloy corrosion-resistant coatings prepared in Examples 2 and 3 is increased by four orders of magnitude, indicating that the Ce salt-doped coating has better corrosion resistance.

[0066] Figure 6 These are EDS surface scan images of the interior of the coating scratches prepared in Example 2 and Comparative Example 1 of the present invention;

[0067] Figure 7EDS line scan of the inside of the scratch of the coating prepared in Example 2 and Comparative Example 1.

[0068] As shown in Figures 6-7 , where Figure 6 (a) is an EDS area scan of the inside of the scratch of the coating prepared in Comparative Example 1, Figure 6 (c) is an EDS area scan of the inside of the scratch of the coating prepared in Example 2, Figure 7 (a) is an EDS line scan of the inside of the scratch of the coating prepared in Comparative Example 1, Figure 7 (c) is an EDS line scan of the inside of the scratch of the coating prepared in Example 2. The coating of Comparative Example 1 and the coating of Example 2 were artificially scratched and immersed in a 3.5wt.% NaCl solution for 336h to observe the corrosion of the substrate / coating interface. The coating of Comparative Example 1 changed in morphology around and inside the scratch after immersion for 336h. As shown in Figure 6 (a) and Figure 7 (a), after the coating was scratched, severe local corrosion occurred around and inside the scratch, accompanied by a large amount of corrosion product accumulation, the corrosion product was in the form of micrometer / nanometer-sized particles, and the corrosion product was Al(OH)3. The above results show that once the coating is damaged, it cannot provide any protection for the substrate, and local corrosion can also accelerate the corrosion of the interface substrate. The coating of Example 2 was immersed for 336h under the same conditions, and it was found that there was almost no change inside and around the scratch, and no severe local corrosion occurred, showing good corrosion resistance. As shown in Figure 6 (c) and Figure 7 (c), upon magnification of the inside of the scratch, it can be seen that a thin layer of corrosion product and a small amount of micron-sized corrosion product flakes were attached to the flat metal surface inside. In addition to Al and O, P and Ce elements were also present on the aluminum alloy substrate. Among them, Al element was enriched at the edge of the scratch, P, O and Ce were locally enriched in the coating, and the morphology could be guessed to be scattered coating fragments. It is worth noting that the Ce element has a high content signal in the entire scratch area, indicating that it is uniformly distributed. The Ce element inside the scratch of the coating of Example 2 has a uniform distribution in addition to the particle enrichment in the entire scratch area. This can be attributed to the self-healing property of Ce 3+ When the coating is damaged, the Ce 3+ released from the coating at the interface enters the substrate interface with the solution and reacts with the local OH - produced by the corrosion of the Al substrate to form a hydroxide of Ce, which ultimately covers the local corrosion micro-area with Al(OH)3 and plays a corrosion protection role for the substrate. The immersion test results of the artificially scratched coating show that the self-sealing and self-healing aluminum alloy corrosion-resistant coating provided in the present application has a self-healing property and can provide effective active corrosion protection for the aluminum alloy substrate interface.

[0069] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the same; although the present application has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that the technical solutions recorded in the foregoing examples can still be modified, or some of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a self-sealing, self-healing corrosion-resistant coating for aluminum alloys, characterized in that, Using an aluminum alloy as the substrate, the aluminum alloy substrate is placed in an electrolyte for micro-arc oxidation treatment; the electrolyte includes phosphate, sodium hydroxide, disodium ethylenediaminetetraacetate and soluble cerium salt; The concentration of the phosphate is 3~20 g·L. -1 The concentration of sodium hydroxide is 1~10 g·L. -1 The concentration of disodium ethylenediaminetetraacetate is 2~10 g·L. -1 The concentration of soluble cerium salts is 1~20 g·L. -1 ; The micro-arc oxidation process is operated using an AC power supply in constant current mode; The AC power supply has a power of 10~100kW and a current density of 2~10A·dm. -2 The frequency is 200~1000Hz, the duty cycle is 10~30%, and the discharge time is 5~20 minutes; the temperature of the electrolyte during the micro-arc oxidation process is 35~45℃.

2. The method for preparing a self-sealing, self-healing corrosion-resistant aluminum alloy coating according to claim 1, characterized in that, The phosphate includes at least one of sodium hexametaphosphate, sodium pyrophosphate, sodium dihydrogen phosphate, and sodium tripolyphosphate.

3. The method for preparing a self-sealing, self-healing corrosion-resistant aluminum alloy coating according to claim 1, characterized in that, The soluble cerium salt includes at least one of cerium nitrate and cerium acetate.

4. The method for preparing a self-sealing, self-healing corrosion-resistant aluminum alloy coating according to claim 1, characterized in that, The aluminum alloy matrix is ​​any one of 2-series aluminum alloys, 5-series aluminum alloys, 6-series aluminum alloys, and 7-series aluminum alloys.

5. The method for preparing a self-sealing, self-healing corrosion-resistant aluminum alloy coating according to claim 1, characterized in that, The aluminum alloy substrate serves as the anode, and the stainless steel electrolytic cell serves as the cathode.

6. The method for preparing a self-sealing, self-healing corrosion-resistant aluminum alloy coating according to claim 1, characterized in that, The preparation method also includes pretreatment of the aluminum alloy substrate, which consists of surface polishing and cleaning.

7. The method for preparing a self-sealing, self-healing corrosion-resistant aluminum alloy coating according to claim 6, characterized in that, The cleaning is performed under ultrasonic conditions for 5 to 15 minutes; the cleaning is performed by sequentially using deionized water and anhydrous ethanol.

8. A self-sealing, self-healing corrosion-resistant aluminum alloy coating prepared by the preparation method according to any one of claims 1 to 7.

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