A plating method for a self-repairing anti-corrosion layer on a brass surface

Abstract

The present invention relates to the technical field of metal surface plating, and in particular to a method for plating a self-repairing anti-corrosion layer on a brass surface. The present invention addresses the problem of the contradiction between the repair performance and mechanical properties of existing self-repairing anti-corrosion layers. Powder aluminizing technology is combined with self-repairing microcapsule materials to construct a composite coating on the surface of a brass substrate that synergizes macroscopic corrosion protection and microscopic self-repair. The microcapsule adopts a composite double-layer structure of a ceramic shell and a bio-based polymer shell, and encapsulates a treated anti-corrosion self-repairing agent inside. It has excellent heat resistance and impact resistance, can adapt to powder aluminizing process conditions, and releases repair substances when the coating is damaged. This composite protective layer improves the corrosion resistance of brass while giving it the ability to self-heal damage, overcoming the defect that it is difficult to balance repair efficiency and mechanical properties in existing self-repairing coatings, and significantly improves the corrosion resistance life and adhesion of the coating.

Description

Technical Field

[0001] The invention relates to the technical field of metal surface plating, and in particular to a plating method for a self-repairing anti-corrosion layer on a brass surface. Background Art

[0002] Brass is widely used in electronics, power generation, and construction due to its excellent electrical and thermal conductivity and machinability. However, brass is susceptible to corrosion in atmospheric and chloride ion environments. Conventional protective measures include surface plating, anti-corrosion coatings, and the addition of corrosion inhibitors. Powder aluminizing is a surface modification technology that effectively improves the corrosion resistance of copper alloys. By diffusing aluminum into the surface of the copper substrate at high temperatures, an aluminum-rich intermetallic compound layer is formed, which improves the substrate's oxidation and corrosion resistance. Powder aluminizing brass at 600°C for 3 hours produces an aluminized layer approximately 50µm thick, significantly improving the corrosion resistance and surface hardness of the brass. However, traditional aluminized layers are hard intermetallic compound coatings. Once the surface is scratched or cracked, the corrosive medium will quickly erode the substrate through the defects. The aluminized layer itself lacks the ability to heal and repair, resulting in limited protective performance.

[0003] To endow anti-corrosion coatings with the ability to self-heal after damage, various self-healing coating technologies have emerged in recent years. One approach involves the introduction of microcapsules encapsulated with a repair agent. When the coating is mechanically damaged and cracks form, the microcapsules rupture under stress, releasing the repair agent, which automatically heals the cracks or passivates the metal surface, restoring the coating's protective properties. This microcapsule-based self-healing strategy is considered a cost-effective and intelligent protection approach and has been widely studied and applied in polymer anti-corrosion coatings. However, existing microcapsule self-healing anti-corrosion coatings primarily use organic polymer matrices as carriers, and the common problem is the difficulty in balancing repair and mechanical properties. On the one hand, improving the coating's self-healing efficiency often requires the addition of higher microcapsule concentrations or the use of a soft matrix, making the coating matrix relatively fragile. On the other hand, differences in polarity and interfacial compatibility between the microcapsules and the coating matrix result in a decrease in the coating's initial mechanical strength and adhesion after the addition of the microcapsules, making it more susceptible to mechanical damage. For example, the prior art CN108796489A discloses a chromium-free passivation agent suitable for nano-self-repairing multi-level dense copper and copper alloys and its preparation process. Through the screening and compounding of inorganic salts, organic corrosion inhibitors, nano-film-forming agents, etc., its nano-film-forming agent is a nano-capsule containing an organic corrosion inhibitor. Once the film layer is damaged, the internal organic corrosion inhibitor will fill the damaged area to achieve new protection, thereby achieving long-term antioxidant and anti-discoloration protection for copper or copper alloys. However, its nano-capsules are easily damaged and are not tightly combined with the protective structure, and the purpose of long-term protection cannot be achieved.

[0004] In summary, while existing microcapsule-based self-healing coatings for brass can automatically repair damaged areas, the coatings' mechanical properties and long-term reliability are somewhat compromised. Combining macroscopic corrosion resistance with microscopic self-healing capabilities to enhance the corrosion resistance of the brass surface while ensuring the coating's mechanical strength and adhesion remains a pressing technical challenge. Summary of the Invention

[0005] The present invention aims to overcome the drawbacks of existing self-repairing anti-corrosion coatings, where repair and mechanical properties are mutually constrained, by providing a method for plating a self-repairing anti-corrosion coating on a brass surface. This method, by constructing a synergistic protection system combining macroscopic corrosion protection with microscopic self-repair, enables the brass surface anti-corrosion coating to not only improve corrosion resistance but also possess an automatic damage repair function, thereby significantly extending the service life of brass products in corrosive environments. Furthermore, by formulating the microcapsule material system so that it can participate in the aluminizing process without being destroyed, the microcapsules and the aluminizing layer are tightly bonded, achieving long-term protection.

[0006] The specific technical solutions are as follows:

[0007] A method for plating a self-repairing anti-corrosion layer on a brass surface comprises the following steps:

[0008] S1: Bio-based polymer materials and inorganic ceramic materials are coated with the repair agent to prepare composite structure microcapsules A;

[0009] S2: Aluminum powder, an inert carrier, a halide activator, and an organic binder are uniformly mixed, and a certain proportion of composite structure microcapsules A are added to prepare an aluminizing agent B;

[0010] S3: burying the surface pretreated brass substrate in aluminizing agent B and heating and keeping it warm to form a composite self-repairing anti-corrosion layer;

[0011] S4: After S3 completes the plating of the composite self-repairing anti-corrosion layer, it is cooled and purged with compressed air. Then, unreacted aluminum powder is recovered by vibration screening. Then, it is pickled for 30 seconds with 5% citric acid. Finally, it is rinsed with deionized water and dried to complete the plating.

[0012] Furthermore, the composite structure microcapsule A described in S1 is a double-layer shell structure, the inner shell is made of the bio-based polymer material, and the outer shell is made of the inorganic ceramic material.

[0013] Furthermore, the bio-based polymer material includes chitosan and gelatin added with glutaraldehyde, the inorganic ceramic material is silicon dioxide, and the repair agent includes benzotriazole, epoxy resin monomer, and linseed oil.

[0014] Furthermore, the benzotriazole needs to be loaded on MgAl-LDH by intercalation; the epoxy resin monomer needs to be added with a nano-montmorillonite polymerization inhibitor; and the linseed oil needs to be added with a nano-silica aerogel.

[0015] Furthermore, the mass proportions of the aluminum powder, inert carrier, halide activator and organic binder described in S2 are: the aluminum powder accounts for 55% to 65%, the inert carrier accounts for 30% to 40%, the halide activator accounts for 3% to 8%, and the organic binder accounts for 0.5%; the composite structure microcapsules A added in a certain proportion are added at a mass ratio of 5% of the aluminizing agent B.

[0016] Furthermore, the inert carrier includes alumina powder and diatomaceous earth, the halide activator includes NH4Cl and NH4F, and the organic binder is polyvinyl alcohol.

[0017] Furthermore, the surface pretreatment described in S3 includes alkaline degreasing, pickling activation and sandblasting.

[0018] Furthermore, the heating and heat preservation described in S3 is heating to 550° C. and keeping warm for 3 hours.

[0019] Furthermore, the cooling process described in S4 includes first slowly cooling from 550° C. to 300° C. in the furnace, and then rapidly cooling to room temperature by introducing air.

[0020] Furthermore, the process is firstly carried out by slowly cooling from 550° C. to 300° C. in the furnace, with a cooling rate of 2-5° C. / min.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The present invention achieves long-term protection for the substrate by constructing an aluminized intermetallic compound layer on the brass surface, providing excellent corrosion and wear resistance. At the same time, the introduction of microcapsules gives the coating the ability to self-repair when damaged. When microcracks or scratches occur in the aluminized layer, the active substances released by the microcapsules can quickly passivate the metal or heal the cracks, significantly reducing the rate of corrosion damage expansion. As a result, the coating prepared by the present invention exhibits a more lasting protective effect in severe corrosive environments.

[0023] (2) The aluminized layer of the present invention is formed by diffusion and is metallurgically bonded to the brass substrate, and its adhesion is far superior to that of organic coatings. At the same time, the hardness and strength of the aluminized layer are high, and it can effectively resist mechanical wear. Although the composite coating contains microcapsules, due to the small size of the microcapsules and the fact that they are plated together with the aluminizing process, they have little effect on the continuity of the aluminized layer substrate and will not significantly reduce the structural strength of the coating.

[0024] (3) The present invention utilizes a microcapsule design with a ceramic / bio-based composite wall shell, combined with special treatment of the repair agent, to enable the microcapsules to withstand the high-temperature aluminizing process while also exhibiting effective release characteristics under room-temperature service conditions. Consequently, the microcapsules maintain excellent performance during both coating manufacturing and use, and are less susceptible to premature failure. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of a plating method for a self-repairing anti-corrosion layer on a brass surface according to the present invention;

[0026] Figure 2 This is a comparison chart of the standard neutral salt spray test results in Experimental Example 1 of the present invention;

[0027] Figure 3 This is a comparison chart of the scratch salt spray test results in Experimental Example 1 of the present invention. DETAILED DESCRIPTION

[0028] The following examples further illustrate and describe the technical solutions of the present invention. It is particularly noted that each specific embodiment is intended to be a concretization and explanation of the technical solutions and should not be construed as limiting the scope of protection of the present invention. Persons of ordinary skill in the art are entitled to modify the technical solutions of these embodiments and to substitute equivalent features for some or all of the technical features. Such modifications or substitutions do not alter the essence of the corresponding technical solutions and do not deviate from the scope of the technical solutions described in the present invention.

[0029] The present invention proposes a plating method for a self-repairing anti-corrosion layer on a brass surface. Figure 1 The figure shows a flow chart of a plating method for a self-repairing anti-corrosion layer on a brass surface according to the present invention. The detailed preparation steps are as follows:

[0030] 1. Preparation of self-repairing microcapsules

[0031] Self-healing microcapsules utilize a double-shell structure, with an inner layer composed of a bio-based polymer and an outer layer composed of an inorganic ceramic. The inner polymer is preferably selected from natural polymers such as chitosan or gelatin. A primary capsule shell is formed around a core material containing the healing agent via emulsion polymerization or interfacial polymerization. Subsequently, a thin inorganic silica shell is deposited on the capsule surface via sol-gel in situ deposition, resulting in a microcapsule with a "ceramic shell + bio-based shell" composite structure. The core material of these microcapsules is a corrosion-resistant self-healing agent, preferably a corrosion inhibitor such as benzotriazole (BTA), epoxy resin monomer, or linseed oil. One or more of these can be selected based on the application. These corrosion inhibitors require treatment, preferably benzotriazole intercalated onto MgAl-LDH, nano-montmorillonite polymerization inhibitor added to epoxy resin monomer, or nano-silica aerogel added to linseed oil. This treatment prevents excessive loss of the corrosion inhibitor during the aluminization process.

[0032] This double-shell design gives the microcapsules both the toughness of a mechanical shell and the heat resistance of an inorganic shell, allowing them to maintain structural stability during the subsequent high-temperature aluminization process without leakage or thermal decomposition. The inner bio-based polymer layer provides excellent toughness and interfacial compatibility, while the outer inorganic ceramic layer imparts high hardness, heat resistance (>500°C), and chemical stability, forming a composite shell. While traditional polymer microcapsules readily decompose above 300°C, the ceramic shell layer can be controlled in thickness through a sol-gel method, maintaining structural integrity during the subsequent high-temperature aluminization process and preventing premature leakage of the core material. Furthermore, the bio-based polymer raw materials chitosan and gelatin are biodegradable and low in toxicity.

[0033] The chitosan used above needs to be modified by acetylation and glutaraldehyde is added to improve hydrophobicity and temperature resistance. The amino groups on its molecular chain can chelate metal ions and enhance adhesion to the brass substrate; the gelatin material needs to be cross-linked with glutaraldehyde to improve mechanical strength and temperature resistance, and its thermal response characteristics can promote the release of the repair agent when locally heated; it is preferred to use natural plant colloid gum arabic, which can be compounded with chitosan to form an interpenetrating network and improve the density of the capsule wall.

[0034] 2. Prepare powder aluminizing agent

[0035] According to a conventional powder aluminizing formula, aluminum powder, an inert carrier, and a halide activator are uniformly mixed. Aluminum powder with a purity of ≥99% and a particle size of 50-100µm is preferred. Alumina powder or diatomaceous earth is used as the inert carrier to prevent sintering and agglomeration of the aluminum powder. The halide activator, selected from NH₄Cl or NH₄F, generates active aluminum halides upon heating to promote the diffusion of aluminum atoms. In the present invention, the prepared self-healing microcapsules are added to the aluminizing powder mixture in a specific proportion, preferably 5% of the total weight of the aluminizing agent. The microcapsules are uniformly dispersed throughout the powder by gentle stirring or drum mixing. A small amount of polyvinyl alcohol (PVA), an organic binder, is preferably added to the powder blend to enhance the microcapsule's adhesion to the brass workpiece surface. This binder decomposes and volatilizes upon subsequent heating, without interfering with the aluminizing reaction.

[0036] The mass percentage of each component is as follows:

[0037] Aluminum powder accounts for 55% to 65%, inert carriers account for 30% to 40%, halide activators account for 3% to 8%, microcapsule additives account for 5%, and organic binders account for 0.5%. When mixing the microcapsules, the double-shell microcapsules are mixed with the infiltrant and evenly dispersed using a double-cone vacuum mixer (20 rpm for 30 minutes) to prevent mechanical shear damage to the microcapsule structure. The organic binder can also be used as a temporary binder by spraying it onto the surface of the brass workpiece, then covering it with the microcapsule-mixed aluminized powder and pre-baking it at 80°C for 10 minutes for initial curing.

[0038] 3. Aluminum plating process

[0039] A brass substrate that has undergone surface pretreatment (cleaning, degreasing, and sandblasting) is embedded in the aforementioned aluminized powder mixture containing microcapsules. The workpiece and powder are placed in a heat-resistant, sealed container and heated to a predetermined temperature under an inert or slightly reducing atmosphere. The temperature is then maintained for a predetermined period to allow the aluminizing reaction to proceed. The preferred aluminizing temperature is 550°C for 3 hours. Under these conditions, the aluminum powder vaporizes under the action of a halide activator and infiltrates the brass surface, where it diffuses and reacts with the copper and zinc elements to form a Cu-Al intermetallic compound layer. Furthermore, the microcapsules dispersed within the powder, protected by an outer ceramic shell, withstand these temperatures without rupture, and the self-healing agent contained within them remains largely sealed. Some microcapsules are embedded in the surface and subsurface regions of the aluminized layer, achieving an integrated bond between the microcapsules and the layer. After the aluminizing and holding period is complete, the workpiece is cooled to room temperature, the workpiece is removed, and any residual powder on the surface is removed to produce a self-healing, anti-corrosion composite coating on the brass surface.

[0040] In the surface pretreatment of the brass substrate, an alkaline degreasing solution of 50 g / L NaOH and 30 g / L Na3PO4 was first used, and the substrate was placed in an ultrasonic bath at 65°C for 10 minutes, and then a 10% concentration of H2SO4 and Activation was achieved by pickling with 0.5 g / L thiourea for 30 seconds at room temperature, followed by rinsing with deionized water. During the sandblasting stage, 120-mesh white corundum sand was used, with an air pressure of 0.5 MPa and a blasting distance of 15 cm. This roughening achieved an activated surface with a roughness of 4.2 ± 0.3 μm, which increased the microcapsule attachment area by more than 30%.

[0041] During the aluminizing process, the brass workpiece is preferably hung vertically in the center of the aluminizing box and filled with aluminizing agent with a filling density of 1.8g / cm 3 It is preferred to introduce a mixture of argon and 5% hydrogen into the infiltration box to form a slightly reducing atmosphere and control the oxygen partial pressure to ≤10 -3 Pa.

[0042] After aluminizing, cooling is controlled by a gradient cooling process, first from 550°C to 300°C. This process is furnace cooling at a cooling rate of 2-5°C / min, avoiding excessive cooling to suppress thermal cracking in the aluminized layer. Then, cooling from 300°C to room temperature is carried out, mainly by rapid cooling with air to avoid the precipitation of the brittle CuAl2 phase. Surface cleaning after aluminizing includes removing residual powder by blowing with compressed air, then vibrating and screening to recover unreacted aluminum powder, and then a short pickling with 5% citric acid for 30 seconds to remove the oxide film. Finally, it is rinsed with deionized water and dried.

[0043] During the above-mentioned aluminum infiltration process, the holding temperature was controlled at 550°C. On the one hand, considering that the recrystallization temperature of brass is above 500°C, the aluminum diffusion coefficient is increased to 1.7×10 -13 m 2 / s, under this condition, excessive volatilization of zinc in copper can be avoided; aluminum forms Cu9Al4 (γ2 phase), CuAl (β phase), and α-Cu (Al, Zn) solid solutions at different depths from shallow to deep; on the other hand, at this temperature, the SiO2 shell of the capsule will undergo viscous flow densification, the porosity will drop rapidly, and the oxygen permeability will drop rapidly at the same time, forming a dense oxygen and heat insulation layer to protect the inner layer material; coupled with the protective treatment of the inner layer material, it can be ensured that the microcapsules are not destroyed during the aluminum infiltration process.

[0044] Through the above steps, the composite coating obtained on the surface of the brass substrate of the present invention consists of two parts: one is an aluminized alloy layer densely attached to the substrate, the main phase of which is a Cu-Al intermetallic phase, providing an overall corrosion-resistant barrier and high-hardness support; the other is self-repairing microcapsules dispersed in the infiltration layer. When the coating is locally damaged by stress or corrosive media erosion and defects appear, the microcapsules at the corresponding positions will rupture and release the internal anti-corrosion agent, forming a protective film on the metal surface and healing the cracks in the coating, thereby preventing further corrosion expansion; the synergistic effect of this macro-anti-corrosion and micro-self-repair can better form long-term anti-corrosion protection.

[0045] Example 1, a method for plating a self-repairing anti-corrosion layer on a brass surface, as follows:

[0046] S1: 5g of benzotriazole loaded with corrosion inhibitor intercalated onto MgAl-LDH was used as the core material. 10g of gelatin and 10g of gum arabic were added to 500mL of deionized water, stirred, and heated to 50°C to dissolve the solution, forming a composite bio-based wall material solution. Benzotriazole solid was dispersed in the above solution, and the pH was adjusted to 4.0. 2mL of glutaraldehyde crosslinker was added dropwise with stirring, and the reaction was maintained for 2 hours to form gelatin-gum arabic microcapsules that initially encapsulated the benzotriazole. The microcapsules were then coated with ceramic shells via a sol-gel method. 5mL of tetraethyl orthosilicate (TEOS) and 2mL of ammonia catalyst were added to the microcapsule suspension, and the suspension was hydrolyzed at room temperature for 4 hours with stirring to generate an in situ SiO2 inorganic shell layer on the microcapsule surface. The product was collected, centrifuged, washed, and vacuum-dried to obtain a self-healing microcapsule powder with a gelatin / gum arabic and silica composite shell.

[0047] S2: Prepare an aluminizing mixture by taking 57 g of aluminum powder, 33 g of aluminum oxide powder, 4.5 g of ammonium chloride, and 0.5 g of polyvinyl alcohol, and then adding 5 g of the microcapsule powder prepared in S1. Mix them using a double-cone vacuum mixer to evenly distribute the microcapsules in the aluminizing mixture.

[0048] S3: The surface of a brass (H65 copper alloy) sample with a size of 50mm×50mm×5mm was degreased, activated and sandblasted, and then a layer of diluted organic binder, a 2% by mass aqueous solution of polyvinyl alcohol, was sprayed on it. After spraying, it was dried in the shade to make the surface slightly sticky to facilitate powder adhesion. The sample was hung vertically in the center of the infiltration box and filled with an aluminum infiltration mixture around it. The infiltration box was then placed in a heating furnace, and a mixed atmosphere of argon and 5% hydrogen was introduced into the infiltration box. The temperature was raised to 550℃, and after keeping warm for 3 hours, a composite self-repairing anti-corrosion layer was formed on the surface of the sample.

[0049] S4: After aluminizing and plating, the sample is first slowly cooled from 550°C to 300°C in the furnace, and then rapidly cooled to room temperature by introducing air. The cooled coated sample is first purged with compressed air, then vibrated and sieved to recover unreacted aluminum powder, and then pickled with 5% citric acid for 30 seconds. Finally, it is rinsed with deionized water and dried to complete the plating.

[0050] Example 2, with reference to the preparation method of Example 1, except that:

[0051] S1: Take epoxy resin monomer added with nano-montmorillonite as the core material.

[0052] S2: Prepare an aluminizing mixture by taking 52 g of aluminum powder, 38 g of aluminum oxide powder, 4.5 g of ammonium fluoride, and 0.5 g of polyvinyl alcohol.

[0053] The other steps are the same.

[0054] Example 3, with reference to the preparation method of Example 1, except that:

[0055] S1: Take 10g of linseed oil added with nano-silica aerogel as the core material, replace the inner bio-based wall material with chitosan, dissolve 1g of chitosan in 100ml of 2% acetic acid aqueous solution, add 0.5g of emulsifier Span-80, and add 1ml of glutaraldehyde crosslinker dropwise while stirring. React at room temperature for 3 hours to obtain chitosan shell-coated oil-core microcapsules.

[0056] S2: Prepare an aluminizing mixture by taking 61 g of aluminum powder, 29 g of diatomaceous earth, 4.5 g of ammonium chloride, and 0.5 g of polyvinyl alcohol.

[0057] The other steps are the same.

[0058] Comparative Example 1, referring to the preparation method of Example 1, but only performing powder aluminizing treatment without adding microcapsules, the aluminizing mixture contains 55g of aluminum powder, 40g of aluminum oxide powder, 4.5g of ammonium fluoride, and 0.5g of polyvinyl alcohol.

[0059] Comparative Example 2 refers to the preparation method of Example 1, but uses conventional in-situ polymerization method to prepare microcapsules with a single-layer urea-formaldehyde resin shell instead.

[0060] In comparative example 3, a conventional organic self-repairing anti-corrosion coating was used as a comparative sample. A commercially available epoxy zinc-rich primer coated H65 brass sample was selected as a comparison. 10 wt% of the microcapsules prepared in Example 1 were added to the formula. The sample was cured at room temperature for 7 days before use in the test.

[0061] In Experimental Example 1, the plated workpieces of Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to a standard neutral salt spray test (NSS) and a scratch salt spray test. The standard neutral salt spray test (NSS) refers to the method of ISO 9227:2022 neutral salt spray test (NSS), and the specific settings are as follows:

[0062] (1) Sample preparation: The sample is cleaned with acetone or ethanol to remove surface contaminants, dried, and placed vertically in a salt spray chamber at an angle of 15° to 30° to the vertical.

[0063] (2) Test conditions: solution, 5% NaCl concentration; temperature, 35 ± 2°C; spray mode, continuous spray, sedimentation volume 1-2 mL / (h·80 cm²); time, 1000 h.

[0064] (3) Result evaluation: Visually inspect the coating surface for red rust or blistering.

[0065] The scratch salt spray test setting conditions are basically the same as the neutral salt spray test (NSS), except that a sharp blade is used to create a 0.5mm wide scratch on the coating surface, the duration is reduced to 240 hours, and the result is evaluated by observing the spread of corrosion products at the scratch. The experimental results are shown in Table 1 and Appendix Figure 2 and attached Figure 3 shown.

[0066] Table 1 Comparison of experimental results of Experimental Example 1

[0067]

[0068] From the results in the accompanying drawings and tables, it can be seen that the technical solution of the embodiment can better play an anti-corrosion function, and after damage occurs, the microcapsules can be used to repair the damaged area to prevent further spread of corrosion; Comparative Example 1 does not add microcapsules, and cannot repair the damaged area in time. Even if the complete coating can provide better protection, when damage occurs, the overall function of the protective layer can be quickly destroyed from the damaged area; Although Comparative Example 2 adopts a combination of aluminization and microcapsules, the structure and material of its microcapsules cannot be preserved intact under the high temperature during the aluminization process. On the contrary, due to ablation, many defects are left in the aluminized layer, resulting in the original protective performance being affected; Comparative Example 3 adopts a combination of traditional coating protective layer and microcapsules, and the protection time is short. Although there is microcapsule repair, it cannot form a coordinated effect with the coating.

[0069] In Experimental Example 2, the workpieces coated with Examples 1-3 and Comparative Examples 1-3 were subjected to surface mechanical property testing, including adhesion testing, coating hardness testing, and mechanical friction testing. Adhesion testing was performed according to ASTM D3359, "Standard Test Method for Adhesion by Tape Method." A 10×10 grid was scratched onto the coating surface, extending deep into the brass substrate, using a 1mm-edge cutter. The coating was then rapidly peeled off at a 60° angle using adhesive tape. The coating was then graded based on the area of ​​detachment, with grades ranging from 0 to 5 representing increasing detachment area.

[0070] The hardness test of the diffusion layer refers to the standard ASTM E384-2022 "Standard for Testing Microhardness of Materials". The measurement is performed using a Vickers hardness tester with the load set to HV0.1 and the dwell time set to 10-15 seconds. The hardness value is calculated by taking the average diagonal length of the 5-point indentation.

[0071] The mechanical friction test was conducted with reference to the load design principles for friction tests in the standard GB / T 10119-2008, “Determination of the Dezincification Corrosion Resistance of Brass.” A linear reciprocating friction tester was used for the test, with a tungsten carbide ball as the counterwear component; a load of 5 N; a stroke of 10 mm; a frequency of 5 Hz; and a total number of cycles of 10,000. The wear rate was calculated as follows: wear rate = wear volume / (load × sliding distance).

[0072] Table 2 Comparison of experimental results of Experimental Example 2

[0073]

[0074] From the above results, it can be seen that the technical solution of the embodiment has better surface mechanical properties due to the aluminizing process, which can ensure long-term coverage protection; the numerical values ​​of Comparative Example 1 are basically the same as those of the embodiment, indicating that the microcapsules have little effect on the surface mechanical properties; although Comparative Example 2 adopts a combination of aluminizing and microcapsules, the structure and materials of its microcapsules cannot be preserved intact under the high temperature during the aluminizing process. On the contrary, due to burnout, many defects are left in the aluminizing layer, which affects the mechanical properties of the aluminizing layer to a certain extent; Comparative Example 3 adopts a combination of traditional soft protective layer and microcapsules, which has poor mechanical properties, and low long-term protection and ability to resist external impact.

Claims

1. A method for plating a self-repairing anti-corrosion layer on a brass surface, characterized in that: The following steps are involved: S1: A composite structure microcapsule A is prepared by coating a bio-based polymer material and an inorganic ceramic material with a repair agent, specifically by using emulsion polymerization or interfacial polymerization to form a primary capsule shell of a bio-based polymer material around a core material containing the repair agent, and then forming a thin shell of an inorganic ceramic material on the surface of the primary capsule shell by in-situ deposition of sol-gel; the bio-based polymer material includes chitosan and gelatin added with glutaraldehyde, the inorganic ceramic material is silica, and the repair agent includes benzotriazole, epoxy resin monomer, and linseed oil; the benzotriazole needs to be loaded on MgAl-LDH by intercalation; the epoxy resin monomer needs to be added with a nano-montmorillonite inhibitor; and the linseed oil needs to be added with nano-silica aerogel; S2: Aluminum powder, an inert carrier, a halide activator, and an organic binder are uniformly mixed, and a certain proportion of composite structure microcapsules A are added to prepare an aluminizing agent B; S3: burying the surface pretreated brass substrate in aluminizing agent B and heating and keeping it warm to form a composite self-repairing anti-corrosion layer; S4: After S3 completes the plating of the composite self-repairing anti-corrosion layer, it is cooled and purged with compressed air. Then, unreacted aluminum powder is recovered by vibration screening. Then, it is pickled for 30 seconds with 5% citric acid. Finally, it is rinsed with deionized water and dried to complete the plating.

2. A method for plating a self-repairing anti-corrosion layer on a brass surface according to claim 1, characterized in that: The mass proportions of the aluminum powder, inert carrier, halide activator and organic binder described in S2 are: the aluminum powder accounts for 55% to 65%, the inert carrier accounts for 30% to 40%, the halide activator accounts for 3% to 8%, and the organic binder accounts for 0.5%; the composite structure microcapsules A added in a certain proportion are added at a mass ratio of 5% of the aluminizing agent B.

3. A method for plating a self-repairing anti-corrosion layer on a brass surface according to claim 1 or 2, characterized in that: The inert carrier includes alumina powder and diatomaceous earth, the halide activator includes NH4Cl and NH4F, and the organic binder is polyvinyl alcohol.

4. A method for plating a self-repairing anti-corrosion layer on a brass surface according to claim 1, characterized in that: The surface pretreatment described in S3 includes alkaline degreasing, pickling activation and sandblasting.

5. A method for plating a self-repairing anti-corrosion layer on a brass surface according to claim 1, characterized in that: The heating and heat preservation described in S3 is heating to 550° C. and keeping the temperature for 3 hours.

6. A method for plating a self-repairing anti-corrosion layer on a brass surface according to claim 1, characterized in that: The cooling process described in S4 includes first slowly cooling from 550°C to 300°C in the furnace, and then rapidly cooling to room temperature by introducing air.

7. A method for plating a self-repairing anti-corrosion layer on a brass surface according to claim 6, characterized in that: The process is firstly to slowly cool from 550°C to 300°C in a furnace, with a cooling rate of 2-5°C / min.

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