Electroplating process of multi-element metal anti-corrosion coating

Abstract

The invention relates to the technical field of electroplating, and particularly discloses an electroplating process of a multi-element metal anti-corrosion coating, which comprises the following steps: S1, carrying out surface roughening, oil removal and acid pickling activation on a base material to obtain a pretreated base material; s2, electroplating the surface of the pretreated base material to form an Al-Zn-Mo-nano silicon carbide-fluorinated graphene composite bottom layer; s3, forming a polyethyleneimine-nano silicon dioxide composite film on the surface of the composite bottom layer through electrophoretic coating; s4, electroplating is conducted on the surface of the composite film through pulse-direct current coupling electroplating, so that a Ni-Mo-P-B gradient functional layer is formed; and S5, electroplating the surface of the gradient functional layer to form a surface layer of Ni-W-P-nano zinc oxide. The multi-element metal anti-corrosion coating prepared by the invention is compounded with a nano material by virtue of multiple processes, and has high-strength combination, long-acting corrosion resistance and self-repairing capability.

Description

Technical Field

[0001] The present application relates to the technical field of electroplating, and more specifically, to an electroplating process for a multi-element metal anti-corrosion coating. Background Art

[0002] Oilfield surface pipelines are a core component of the oil and gas transportation system, and their safe and stable operation is directly related to the development benefits and ecological safety of the oil and gas fields. However, these pipelines are mostly made of carbon steel and are exposed to complex media containing water, CO2, H2S, microorganisms, and chloride ions for long periods of time, making corrosion a particularly prominent problem. Among them, CO2 corrosion is the most common and destructive form of failure in oilfield surface pipelines. Especially in environments containing water, chloride ions, and gaseous CO2, the carbon steel surface is prone to localized corrosion and pitting, which can lead to pipeline perforation or other failures in severe cases.

[0003] To address these challenges, electroplating metal anti-corrosion coatings has become a key approach to improving pipeline corrosion resistance. This technology uses electrolysis to deposit one or more layers of metal / alloy coatings on the surface of a carbon steel substrate, creating a dual mechanism of physical barrier and electrochemical protection, significantly extending pipeline service life.

[0004] The patent application document with publication number CN113416990 discloses a process for preparing metal-coated anti-corrosion pipes, which includes the following preparation steps: S1. Surface treatment: first, the surface of the pipe is degreased and derusted, and then treated with a zinc-manganese medium-temperature phosphating solution; S2. Bottom layer electroplating: nickel-cobalt electroplating is performed on the inner and outer surfaces of the treated pipe to form a bottom layer nickel-cobalt alloy coating; S3. Electrophoretic coating: acrylic paint is electrophoretically coated on the outer wall of the bottom layer nickel-cobalt alloy coating; S4. Winding conductive wire: winding the conductive wire on the outer wall of the pipe, wherein both ends of the conductive wire extend to the outside of the pipe; S5. Middle layer electroplating: middle layer nickel-cobalt electroplating is performed on the outer wall of the pipe to form a middle layer nickel-cobalt alloy coating; S6. Coating treatment: a layer of hydrophobic isolation substance is coated on the outer wall of the pipe, and the hydrophobic isolation substance is used to improve the hydrophobicity of the pipe; S7. Insulation treatment: a layer of insulation layer is coated on the outer wall of the pipe.

[0005] In this technical solution, the nickel-cobalt alloy passivation film is mainly composed of NiO and CoO. In an environment containing chloride ions, it is easy to form stable complexes with the metal ions in the passivation film, causing the passivation film to continue to dissolve, destroying the electrochemical protection barrier that the pipe originally relied on; and the columnar crystals of the nickel-cobalt alloy coating have a columnar crystal structure. Chloride ions can penetrate the film layer through dual paths of lattice diffusion and grain boundary penetration. When chloride ions gather at the grain boundaries, a "chloride ion concentration cell" is formed, which in turn causes intergranular corrosion and weakens the corrosion resistance of the pipe. Summary of the Invention

[0006] In order to improve the anti-corrosion performance in complex media containing water, chloride ions and carbon dioxide, the present application provides an electroplating process for a multi-element metal anti-corrosion coating.

[0007] The present application provides an electroplating process for a multi-element metal anti-corrosion coating, which adopts the following technical solutions: The electroplating process of the multi-element metal anti-corrosion coating of the present application comprises the following steps: S1: roughening the surface of the substrate, degreasing it, and performing pickling and activation to obtain a pretreated substrate; S2: electroplating on the surface of the pretreated substrate to form a composite bottom layer of Al-Zn-Mo-nano silicon carbide-fluorinated graphene; S3: forming a polyethyleneimine-nano-silica composite film on the surface of the composite base layer by electrophoretic coating; S4: electroplating a Ni-Mo-PB gradient functional layer on the surface of the composite film by pulse-DC coupled electroplating; S5: Electroplating a Ni-WP-nano zinc oxide surface layer is performed on the surface of the gradient functional layer.

[0008] In this scheme, a rough and clean interface suitable for electroplating is formed on the surface of the substrate by pre-treating the substrate. The composite bottom layer is based on Al-Zn-Mo alloy. Zn forms a micro-battery at the damaged part of the passivation film through a lower electrode potential, dissolving preferentially to provide cathodic protection, while Al forms a barrier protection through the passivation film, and the two form a synergistic mechanism. MoO4 2- After being partially reduced to an intermediate state, some molybdate is generated, which repairs the micropores of the passivation film, making it more stable and dense, improving the resistance of the passivation film to chloride ion corrosion and its repassivation ability, and inhibiting the initiation of pitting corrosion. Nano-silicon carbide and fluorinated graphene are evenly dispersed in the coating to form a composite physical barrier; in the electrophoretic coating composite film, the amino group in the polyethyleneimine bonds with the hydroxyl group on the surface of the composite bottom passivation film to improve the interface bonding strength, and the nano-silicon dioxide fills the pores to improve the density; pulse-DC coupled electroplating regulates the composition and structure of the coating: a high-phosphorus amorphous layer is formed in the initial pulse stage, and a nickel-rich crystalline layer is generated in the terminal DC stage, achieving a gradient structure with a decreasing phosphorus content from the inside to the outside, thereby achieving a gradient change in the molybdenum and phosphorus content from the inside to the outside, forming a gradient functional layer; tungsten in the Ni-WP alloy in the surface layer is oxidized to form a dense WO3 passivation film as the outermost physical barrier, directly physically blocking the corrosive medium, and nano-ZnO dissolves into Zn in the acidic micro-region. 2+, migrating to the cathode region (pH>10) through electrochemical driving forces, where it forms a precipitate, sealing some microcracks. (This self-healing mechanism relies on the high-pH cathode region created by oxygen reduction reactions in the corrosion microenvironment and is suitable for oxygen-containing electrolyte environments.) In this solution, a multi-layer passivation film / protective layer (surface WO3, gradient Ni / Mo / P oxide, and underlying Al2O3) and a sacrificial anode (Zn) together form a multi-layer physical and electrochemical protective barrier, significantly improving overall corrosion resistance.

[0009] Preferably, in step S1, the specific method for roughening the surface of the substrate is: spraying oxalic acid with a concentration of 55-65 g / L and ferric nitrate with a concentration of 90-110 g / L in sequence, with a spraying time of 20-35 min.

[0010] Preferably, in step S1, the specific method of oil removal is: spraying a mixed solution A with a concentration of 12-15 g / L sodium lauryl sulfate, a concentration of 8-10 g / L sodium metasilicate, and a concentration of 2-4 g / L sodium hydroxide for 8-10 minutes.

[0011] Preferably, in step S1, the specific method of the pickling activation is: spraying a mixed solution B with a concentration of 12-15 g / L of malic acid and 8-10 g / L of tartaric acid for 6-8 minutes.

[0012] In this scheme, oxalic acid-ferric nitrate etching forms an uneven microscopic interface, which, in conjunction with the directional arrangement of the polar groups of the silicate transition layer, provides a dual binding basis of mechanical intercalation and chemical adsorption for the subsequent coating. When a weak acid activation solution composed of malic acid and tartaric acid is subsequently used for treatment, the organic acid gently dissolves the residual oxide film on the surface and simultaneously binds to the Fe 2+ The chelation effect continuously maintains the active state of the substrate surface, and finally forms a clean interface with appropriate roughness and rich chemical active sites, laying a solid foundation for the uniform deposition of high-quality anti-corrosion coatings.

[0013] Preferably, in step S2, the plating solution A of the composite bottom layer includes Al2(SO4)3·18H2O 70~90g / L, ZnSO4·7H2O 80~100g / L, Na2MoO4·2H2O 25~35g / L, sodium gluconate 30~40g / L, nano-silicon carbide 4~6g / L, fluorinated graphene 0.3~0.6g / L, and cetyltrimethylammonium bromide 0.5~1g / L.

[0014] Preferably, in step S2, the electroplating temperature is 50-55°C, and the current density is 5-5.2A / dm 2 , the electroplating time is 20~25min.

[0015] In this scheme, Al-Zn-Mo alloy is used as the matrix, and zinc is used as a sacrificial anode to preferentially corrode, compensating for the risk of aluminum passivation film rupture and forming electrochemical protection; aluminum is oxidized to form a dense Al2O3 passivation film, and molybdenum ions promote the stability of the passivation film to inhibit pitting corrosion; sodium molybdate forms a stable complex with sodium gluconate to avoid precipitation and stabilize the electroplating process; nano-silicon carbide and fluorinated graphene are evenly dispersed in the coating to form a composite barrier, which not only blocks the penetration of water molecules through fluorinated graphene, but also uses nano-silicon carbide to improve wear resistance, jointly blocking the invasion of corrosive media.

[0016] Preferably, in step S3, the electrophoretic coating electrophoretic liquid includes 5-7 g / L polyethyleneimine, 2-3 g / L nano-silicon dioxide, 50-65 mL / L ethylene glycol butyl ether, 5-7 g / L hydroxyethyl cellulose, and 1.2-1.5 g / L triethylamine.

[0017] Preferably, in step S3, the electrophoretic coating temperature is 30-35°C, and the current density is 1-1.1 A / dm 2 , the electrophoretic coating time is 10~12min.

[0018] In this scheme, under weakly alkaline conditions, polyethyleneimine forms high-density coordination bonds with the underlying metal, significantly enhancing the bonding strength; nano-silica fills the pores, effectively blocking the penetration of corrosive media.

[0019] Preferably, in step S4, the plating solution B of the gradient functional layer includes NiSO4·6H2O 130~160g / L, Na2MoO4·7H2O 15~25g / L, NaH2PO2·H2O 45~65g / L, boric acid 30~50g / L, NaBH4 0.5~1g / L, and succinic acid 20~35g / L.

[0020] Preferably, in step S4, the pulse-DC coupled electroplating is divided into an initial stage and a termination stage. In the initial stage, the pulse duty cycle is 30% to 40%, the electroplating temperature is 45 to 50°C, and the current density is 3 to 3.3 A / dm 2 , the electroplating time is 30~35min; in the termination stage, the electroplating temperature is 60~65℃, the current density is 5~5.3A / dm 2 , the electroplating time is 15~18min.

[0021] In this scheme, pulse-DC coupled electroplating is used: the initial low duty cycle pulse reduces hydrogen evolution, forming a low-phosphorus, highly crystallized nickel-rich layer to improve toughness; the DC high current in the termination stage promotes the co-deposition of P and Mo, forming an amorphous / nanocrystalline composite structure, so that the Mo and P content changes gradiently from the inside to the outside, enhancing the interlayer bonding strength; the introduction of boron reduces the risk of hydrogen embrittlement of the coating, buffers the problem of interfacial stress cracking, and at the same time optimizes the transition of mechanical properties of the coating from the bottom layer to the surface layer, reducing interlayer stress concentration.

[0022] Preferably, in step S5, the plating solution C used for the surface layer includes 190-220 g / L of NiSO4·6H2O, 20-30 g / L of Na2WO4, 55-75 g / L of NaH2PO2·H2O, 3-5 g / L of nano zinc oxide, 1-2 g / L of polyvinyl pyrrolidone, and 2-3 g / L of silane coupling agent KH550.

[0023] Preferably, in step S5, the electroplating temperature is 85-90°C, and the current density is 2.5-2.8 A / dm 2 , the plating time is 25~27min; In this scheme, tungsten in Ni-WP alloy is oxidized to form a dense WO3 passivation film, which physically blocks the penetration of chloride ions; nano zinc oxide dissolves Zn in chloride-containing medium. 2+ , reacts with chloride ions to form layered dihydroxy salts, which self-repair and seal microcracks; the silane coupling agent KH550 enhances the interfacial bonding between the surface layer and the functional layer, improves the density and wear resistance of the coating, and forms double protection. At the same time, the surface WO3 film and the underlying Al2O3 passivation film form a spatially separated double physical barrier, which cooperates with the Ni / Mo / P oxide protective layer and Zn sacrificial anode in the intermediate gradient layer to achieve multi-level protection.

[0024] Preferably, the substrate is a carbon steel substrate.

[0025] Preferably, in step S2, the nano-silicon carbide and fluorinated graphene undergo the following pretreatment steps before use: S11: adding nano-silicon carbide, fluorinated graphene and sodium perfluorooctane sulfonate to an alcohol solution and mixing uniformly, adding a double-bond silane coupling agent and mixing uniformly, adjusting the pH to 4.0-4.5, heating to 50-70° C., reacting for 3-5 hours, solid-liquid separation, washing, and drying to obtain a silanized composite material; S12: Under an inert atmosphere at -5~5℃, add trifluoroacetic acid and perchloric acid into the reactor, adjust the pH to 2.5~3, then add the silanization composite material and aniline monomer and mix evenly, slowly add the composite initiator, react for 9~11h, separate the solid and liquid, wash, and dry to obtain the product.

[0026] Preferably, the mass ratio of the total mass of the nano-silicon carbide and fluorinated graphene, sodium perfluorooctane sulfonate, silane coupling agent and aniline monomer is 100: (0.5-1): (6-9): (18-22).

[0027] Preferably, the aniline monomer is selected from at least one of 3,4-dimethylaniline and 2,3-dimethylaniline.

[0028] Preferably, the volume ratio of trifluoromethanesulfonic acid to acetic acid is (1.5-2.5):1.

[0029] In this scheme, the silanization reaction forms Si-O bonds, strengthening the interfacial bonding between the filler and the metal matrix. The polyaniline coating provides electrostatic repulsion and steric hindrance, ensuring stable dispersion of the nanofiller in the plating solution and preventing agglomeration. Its amino groups coordinate with metal ions, promoting heterogeneous nucleation of grains, refining grains, and improving the density of the coating. Furthermore, the aniline coating imparts electrical conductivity to the nano-silicon carbide and fluorinated graphene, reducing localized corrosion caused by uneven dispersion.

[0030] Preferably, the composite initiator comprises ammonium persulfate and copper sulfate, and the amount of the composite initiator used is 2% to 4% of the mass of the aniline monomer.

[0031] Preferably, the mass ratio of ammonium persulfate to copper sulfate is (5-7.5):1.

[0032] In this scheme, ammonium persulfate provides oxidative free radicals to initiate the polymerization of aniline monomers; the copper ions in copper sulfate catalyze the polymerization rate, preventing excessive reaction and resulting rapid polymerization. Together, these two dynamic regulatory mechanisms ensure uniform polyaniline coating on the nanomaterial surface, preventing aniline self-aggregation and precipitation while maintaining the integrity of the coating layer, laying the foundation for the dispersion and performance of the nanofiller in the subsequent coating.

[0033] In summary, this application has the following beneficial effects: In the electroplating process of the multi-metal anti-corrosion coating of the present application, the substrate is pretreated to construct a rough and clean interface to enhance the initial bonding strength of the coating; the composite bottom layer constructs a physical barrier through the synergistic effect of the multi-metal matrix and nanomaterials, effectively extending the penetration path of the corrosive medium; then, a polyethyleneimine-nanosilica composite film is formed on the surface of the composite bottom layer by electrophoretic coating, and the interlayer bonding strength is strengthened by the coordination bonding of the polymer chain and the nanoparticles, forming a dense transition film layer on the surface of the composite bottom layer; then, a Ni-Mo-PB gradient functional layer is constructed on the surface of the composite film by a pulse-DC coupling process, which significantly reduces the tendency of galvanic corrosion; finally, a Ni-WP-nano zinc oxide surface layer is formed by electroplating on the surface of the gradient functional layer, and a dynamic self-repair mechanism is introduced to generate layered hydroxides by the release of zinc ions and the reaction with the corrosive medium, thereby achieving active repair of the damaged area. DETAILED DESCRIPTION

[0034] The present application is further described in detail below with reference to the embodiments.

[0035] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application are all commercially available.

[0036] In the following examples, unless otherwise specified, the pH adjuster used was 10% by mass of ammonia water or citric acid.

[0037] The particle size distribution of nano-zinc oxide is 20~50nm; the particle size distribution of nano-silicon carbide is 10~20nm; the fluorinated graphene has a lamellar structure with a thickness of 5~20nm and a lateral size of 1~3μm; the particle size distribution of nano-silicon dioxide is 20~50nm; and the molecular weight distribution of polyethyleneimine is 5000~50000g / mol.

[0038] Pretreatment Preparation Examples 1~3 Pretreatment Preparation Example 1 The nano-silicon carbide and fluorinated graphene prepared in this pretreatment example were subjected to the following pretreatment steps before use: S11: 10 g of nano-silicon carbide, 0.75 g of fluorinated graphene, and 0.054 g of sodium perfluorooctane sulfonate were added to 50 mL of ethanol aqueous solution (the volume ratio of ethanol to deionized water was 1:1), transferred to an ultrasonic device, and ultrasonicated at a power of 90 W and a frequency of 40 kHz for 15 min. 0.645 g of vinyltriethoxysilane was added and ultrasonicated for 20 min. The pH was adjusted to 4.5 with 10% glacial acetic acid, and nitrogen was introduced for deoxygenation for 15 min. The temperature was raised to 50°C, and the reaction was stirred for 5 h. After the reaction was completed, the mixture was centrifuged, and the precipitate was washed 3 times with deionized water and once with ethanol. The mixture was placed in a vacuum drying oven and dried at 50°C to constant weight to obtain a silanized composite material. S12: At -5°C and under argon atmosphere, add 15 mL of trifluoroacetic acid and 10 mL of perchloric acid to the reactor, then slowly add deionized water to dilute to a pH of about 3, then add the silanized composite and 1.935 g of 3,4-dimethylaniline and stir until evenly dispersed, slowly add the initiator mixture dropwise, after the addition is complete, maintain -5°C, react for 11 hours, the reaction system is dark green and transparent, pour the reaction solution into 200 mL of ice water for precipitation, filter and wash until neutral, transfer to a vacuum drying oven, and dry at 50°C to constant weight to obtain the pretreated composite.

[0039] The initiator mixture is prepared by mixing 0.068 g of ammonium persulfate, 0.009 g of copper sulfate and 5 mL of deionized water.

[0040] Pretreatment Preparation Example 2 The nano-silicon carbide and fluorinated graphene prepared in this pretreatment example were subjected to the following pretreatment steps before use: S11: 10 g of nano-silicon carbide, 0.9 g of fluorinated graphene, and 0.109 g of sodium perfluorooctane sulfonate were added to 50 mL of ethanol aqueous solution (the volume ratio of ethanol to deionized water was 1:1), and ultrasonicated at a power of 90 W and a frequency of 40 kHz for 20 min. 0.981 g of vinyltriethoxysilane was added and ultrasonicated for 25 min. The pH was adjusted to 4.0 with 10% glacial acetic acid, and nitrogen was introduced for deoxygenation for 30 min. The temperature was raised to 70°C, and the reaction was stirred for 3 h. After the reaction was completed, the mixture was centrifuged, and the precipitate was washed 3 times with deionized water and once with ethanol. The mixture was placed in a vacuum drying oven and dried at 50°C to constant weight to obtain a silanized composite. S12: At 5°C and under argon atmosphere, add 20 mL of trifluoroacetic acid and 8 mL of perchloric acid to the reactor, then slowly add deionized water to dilute to a pH of about 2.5, then add the silanized composite material and 2.398 g of 2,3-dimethylaniline and stir until evenly dispersed, slowly add the initiator mixture dropwise, after the addition is complete, maintain 5°C, react for 9 hours, and the reaction system becomes dark green and transparent. Pour the reaction solution into 300 mL of ice water for precipitation, filter and wash until neutral, transfer to a vacuum drying oven, and dry at 50°C to constant weight to obtain the pretreated composite material.

[0041] The initiator mixture is prepared by mixing 0.042 g of ammonium persulfate, 0.006 g of copper sulfate and 5 mL of deionized water.

[0042] Pretreatment Preparation Example 3 The nano-silicon carbide and fluorinated graphene prepared in this pretreatment example were subjected to the following pretreatment steps before use: S11: 10 g of nano-silicon carbide, 1 g of fluorinated graphene, and 0.083 g of sodium perfluorooctane sulfonate were added to 50 mL of ethanol aqueous solution (the volume ratio of ethanol to deionized water was 1:1), and ultrasonicated at a power of 90 W and a frequency of 40 kHz for 20 min. 0.825 g of vinyltriethoxysilane was added and ultrasonicated for 25 min. The pH was adjusted to 4.3 with 10% glacial acetic acid, and nitrogen was introduced for deoxygenation for 25 min. The temperature was raised to 60°C, and the reaction was stirred for 4 h. After the reaction was completed, the mixture was centrifuged, and the precipitate was washed 3 times with deionized water and once with ethanol. The mixture was placed in a vacuum drying oven and dried at 50°C to constant weight to obtain a silanized composite material. S12: At 0°C and under argon atmosphere, add 16 mL of trifluoroacetic acid and 8 mL of perchloric acid to the reactor, then slowly add deionized water to dilute to a pH of about 2.7, then add the silanized composite and 2.2 g of 3,4-dimethylaniline and stir until evenly dispersed, slowly add the initiator mixture dropwise, after the addition is complete, maintain 0°C and react for 10 hours. The reaction system is dark green and transparent, pour the reaction solution into 300 mL of ice water for precipitation, filter and wash until neutral, transfer to a vacuum drying oven, and dry at 50°C to constant weight to obtain the pretreated composite.

[0043] The initiator mixture is prepared by mixing 0.055 g of ammonium persulfate, 0.011 g of copper sulfate and 5 mL of deionized water.

[0044] Example 1 The electroplating process of the multi-element metal anti-corrosion coating of this embodiment includes the following steps: S1: At 20°C, spray oxalic acid with a concentration of 55g / L onto the surface of the carbon steel substrate at a spraying pressure of 0.5MPa, circulate spraying and keep in a wet state for 10min, rinse with clean water for 3min, then circulate spray ferric nitrate with a concentration of 90g / L and keep in a wet state for 10min, rinse with clean water for 3min, then spray a mixed solution A with a concentration of 12g / L sodium lauryl sulfate, a concentration of 8g / L sodium metasilicate and a concentration of 2g / L sodium hydroxide onto the surface of the carbon steel substrate at a spraying pressure of 0.3MPa and continue spraying for 8min, rinse with clean water for 3min, then spray a mixed solution B with a concentration of 12g / L malic acid and 8g / L tartaric acid onto the surface of the carbon steel substrate at a spraying pressure of 0.2MPa, circulate spraying and keep in a wet state for 6min, then rinse with clean water, and dry with hot air circulation at 45°C±5°C for 15min to obtain a pretreated substrate; S2: Electroplating treatment is performed on the surface of the pretreated substrate to form a composite bottom layer of Al-Zn-Mo-nano-silicon carbide-fluorinated graphene. The electroplating solution includes: Al2(SO4)3·18H2O 70g / L, ZnSO4·7H2O 80g / L, Na2MoO4·2H2O 25g / L, sodium gluconate 30g / L, nano-silicon carbide 4g / L, fluorinated graphene 0.3g / L, hexadecyltrimethylammonium bromide 0.5g / L, the pH of the electroplating solution is 4.5, and the current density is 5A / dm 2 , temperature 50℃, electroplating time 25min; S3: Electrophoretic coating is performed on the surface of the composite bottom layer to form a polyethyleneimine-nanosilica composite film. The electrophoretic solution includes: polyethyleneimine 5g / L, nanosilica 2g / L, ethylene glycol butyl ether 50mL / L, hydroxyethyl cellulose 5g / L, triethylamine 1.2g / L, the pH of the electrophoretic solution is 8.3, the temperature is 30℃, and the current density is 1.0A / dm2 , electrophoresis time 12 min; S4: performing pulse-DC coupled electroplating treatment on the surface of the composite film to form a Ni-Mo-PB gradient functional layer; The electroplating solution includes: NiSO4·6H2O 130g / L, Na2MoO4·7H2O 15g / L, NaH2PO2·H2O 45g / L, boric acid 30g / L, NaBH4 0.5g / L, succinic acid 20g / L, pH 4.5, and the pulse-DC coupled electroplating is divided into an initial stage and a termination stage. In the initial stage, the pulse duty cycle is 30%, the frequency is 100Hz, the temperature is 45°C, and the current density is 3A / dm 2 , electroplating time 35min; the termination stage: DC mode, temperature 60℃, current density 5A / dm 2 , electroplating time 18min; S5: Electroplating is performed on the surface of the gradient functional layer to form a Ni-WP-nano zinc oxide surface layer; the electroplating solution includes 190 g / L NiSO4·6H2O, 20 g / L Na2WO4, 55 g / L NaH2PO2·H2O, 3 g / L nano zinc oxide, 1 g / L polyvinyl pyrrolidone, and 2 g / L silane coupling agent KH550; the pH of the electroplating solution is 4.8, the temperature is 85°C, and the current density is 2.5 A / dm 2 , electroplating time 27min.

[0045] Example 2 The electroplating process of the multi-element metal anti-corrosion coating of this embodiment includes the following steps: S1: At 20°C, oxalic acid with a concentration of 65g / L was sprayed onto the surface of the carbon steel substrate at a spraying pressure of 0.5MPa, and the mixture was circulated and sprayed to maintain a wet state for 15min. After rinsing with clean water for 3min, ferric nitrate with a concentration of 110g / L was circulated and sprayed to maintain a wet state for 10min. After rinsing with clean water for 3min, a mixed solution A with a concentration of 15g / L sodium lauryl sulfate, a concentration of 10g / L sodium metasilicate and a concentration of 4g / L sodium hydroxide was sprayed onto the surface of the carbon steel substrate at a spraying pressure of 0.3MPa for 10min. After rinsing with clean water for 3min, a mixed solution B with a concentration of 15g / L malic acid and 10g / L tartaric acid was sprayed onto the surface of the carbon steel substrate at a spraying pressure of 0.2MPa, and the mixture was circulated and sprayed to maintain a wet state for 8min. After rinsing with clean water, the substrate was dried with hot air circulation at 45°C±5°C for 20min to obtain a pretreated substrate. S2: Electroplating treatment is performed on the surface of the pretreated substrate to form a composite bottom layer of Al-Zn-Mo-nano-silicon carbide-fluorinated graphene. The electroplating solution includes: Al2(SO4)3·18H2O 90g / L, ZnSO4·7H2O 100g / L, Na2MoO4·2H2O 35g / L, sodium gluconate 40g / L, nano-silicon carbide 6g / L, fluorinated graphene 0.6g / L, hexadecyltrimethylammonium bromide 0.75g / L, the pH of the electroplating solution is 4.5, and the current density is 5.2A / dm 2 , temperature 50℃, electroplating time 20min; S3: Electrophoretic coating is performed on the surface of the composite bottom layer to form a polyethyleneimine-nanosilica composite film. The electrophoretic solution includes: polyethyleneimine 7g / L, nanosilica 3g / L, ethylene glycol butyl ether 65mL / L, hydroxyethyl cellulose 7g / L, triethylamine 1.5g / L, the pH of the electrophoretic solution is 8.3, the temperature is 35℃, and the current density is 1.1A / dm 2 , electrophoresis time 10 min; S4: performing pulse-DC coupled electroplating treatment on the surface of the composite film to form a Ni-Mo-PB gradient functional layer; Electroplating solution B includes: NiSO4·6H2O 160g / L, Na2MoO4·7H2O 25g / L, NaH2PO2·H2O 65g / L, boric acid 50g / L, NaBH41g / L, succinic acid 35g / L, pH 4.5. The pulse-DC coupled electroplating is divided into an initial stage and a termination stage. In the initial stage, the pulse duty cycle is 40%, the frequency is 100Hz, the temperature is 50°C, and the current density is 3.2A / dm 2 , electroplating time 30min; the termination stage: DC mode, temperature 65℃, current density 5.3A / dm 2 , electroplating time 15min; S5: Electroplating treatment is performed on the surface of the gradient functional layer to form a surface layer of Ni-WP-nano zinc oxide; the electroplating solution C includes NiSO4·6H2O 220g / L, Na2WO4 30g / L, NaH2PO2·H2O 75g / L, nano zinc oxide 5g / L, polyvinyl pyrrolidone 2g / L, and silane coupling agent KH550 3g / L; the pH of the electroplating solution is 4.8, the temperature is 90°C, and the current density is 2.8A / dm 2 , electroplating time 25min.

[0046] Example 3 The electroplating process of the multi-element metal anti-corrosion coating of this embodiment includes the following steps: S1: At 25°C, oxalic acid with a concentration of 60 g / L was sprayed onto the surface of the carbon steel substrate at a spraying pressure of 0.5 MPa, and the mixture was circulated and sprayed to maintain a wet state for 20 minutes. After rinsing with clean water for 3 minutes, ferric nitrate with a concentration of 100 g / L was circulated and sprayed to maintain a wet state for 15 minutes. After rinsing with clean water for 3 minutes, a mixed solution A with a concentration of 13 g / L sodium lauryl sulfate, a concentration of 9 g / L sodium metasilicate and a concentration of 3 g / L sodium hydroxide was sprayed onto the surface of the carbon steel substrate at a spraying pressure of 0.4 MPa and continued to spray for 9 minutes. After rinsing with clean water for 3 minutes, a mixed solution B with a concentration of 13 g / L malic acid and 9 g / L tartaric acid was sprayed onto the surface of the carbon steel substrate at a spraying pressure of 0.3 MPa, circulated and sprayed to maintain a wet state for 7 minutes. After rinsing with clean water, the substrate was dried with hot air circulation at 45°C±5°C for 20 minutes to obtain a pretreated substrate. S2: Electroplating treatment is performed on the surface of the pretreated substrate to form a composite bottom layer of Al-Zn-Mo-nano-silicon carbide-fluorinated graphene. The electroplating solution includes: Al2(SO4)3·18H2O 80g / L, ZnSO4·7H2O 90g / L, Na2MoO4·2H2O 30g / L, sodium gluconate 35g / L, nano-silicon carbide 5g / L, fluorinated graphene 0.5g / L, and hexadecyltrimethylammonium bromide 1g / L. The pH of the electroplating solution is 4.5, the temperature is 55°C, and the current density is 5.1A / dm 2 , electroplating time 22min; S3: Electrophoretic coating is performed on the surface of the composite bottom layer to form a polyethyleneimine-nanosilica composite film. The electrophoretic solution includes: polyethyleneimine 6g / L, nanosilica 2.5g / L, ethylene glycol butyl ether 60mL / L, hydroxyethyl cellulose 6g / L, triethylamine 1.3g / L, the pH of the electrophoretic solution is 8.3, the temperature is 35℃, and the current density is 1.1A / dm 2 , electrophoresis time 11 min; S4: performing pulse-DC coupled electroplating treatment on the surface of the composite film to form a Ni-Mo-PB gradient functional layer; Electroplating solution B includes: NiSO4·6H2O 140g / L, Na2MoO4·7H2O 20g / L, NaH2PO2·H2O 50g / L, boric acid 40g / L, NaBH4 0.75g / L, succinic acid 28g / L, pH 4.5. The pulse-DC coupled electroplating is divided into an initial stage and a termination stage. In the initial stage, the pulse duty cycle is 35%, the frequency is 100Hz, the temperature is 50°C, and the current density is 3.1A / dm 2 , electroplating time 32min; the termination stage: DC mode, temperature 65℃, current density 5.1A / dm 2 , electroplating time 16min; S5: Electroplating treatment is performed on the surface of the gradient functional layer to form a surface layer of Ni-WP-nano zinc oxide; the electroplating solution C includes NiSO4·6H2O 210g / L, Na2WO4 22g / L, NaH2PO2·H2O 65g / L, nano zinc oxide 4g / L, polyvinyl pyrrolidone 1.5g / L, and silane coupling agent KH550 2.5g / L; the pH of the electroplating solution is 4.8, the temperature is 85°C, and the current density is 2.6A / dm 2 , electroplating time 26min.

[0047] Example 4 The difference between this embodiment and embodiment 3 is that: In step S2, the pretreatment compound from the pretreatment preparation example 1 is used to replace the nano-silicon carbide and fluorinated graphene, that is: S2: Electroplating treatment is performed on the surface of the pretreated substrate to form a composite bottom layer of Al-Zn-Mo-nanosilicon carbide-fluorinated graphene. The electroplating solution includes: Al2(SO4)3·18H2O 80g / L, ZnSO4·7H2O 90g / L, Na2MoO4·2H2O 30g / L, sodium gluconate 35g / L, pretreatment compound 5.5g / L, hexadecyltrimethylammonium bromide 1g / L, the electroplating solution pH is 4.5, the temperature is 55°C, and the current density is 5.1A / dm 2 , electroplating time 22min; Other details are the same as in Example 3.

[0048] Example 5 The difference between this embodiment and embodiment 4 is that: In step S2, the pre-treated composite is obtained from the pre-treatment preparation example 2.

[0049] Other details are the same as in Example 4.

[0050] Example 6 The difference between this embodiment and embodiment 5 is that: In step S2, the pre-treated composite is obtained from the pre-treatment preparation example 3.

[0051] Other details are the same as in Example 5.

[0052] Comparative Example 1 The electroplating process of the multi-element metal anti-corrosion coating of this comparative example includes the following steps: S1: At 20°C, spray oxalic acid with a concentration of 55g / L onto the surface of the carbon steel substrate at a spraying pressure of 0.5MPa, circulate spraying and keep in a wet state for 10min, rinse with clean water for 3min, then circulate spray ferric nitrate with a concentration of 90g / L and keep in a wet state for 10min, rinse with clean water for 3min, then spray a mixed solution A with a concentration of 12g / L sodium lauryl sulfate, a concentration of 8g / L sodium metasilicate and a concentration of 2g / L sodium hydroxide onto the surface of the carbon steel substrate at a spraying pressure of 0.3MPa and continue spraying for 8min, rinse with clean water for 3min, then spray a mixed solution B with a concentration of 12g / L malic acid and 8g / L tartaric acid onto the surface of the carbon steel substrate at a spraying pressure of 0.2MPa, circulate spraying and keep in a wet state for 6min, then rinse with clean water, and dry with hot air circulation at 45°C±5°C for 15min to obtain a pretreated substrate; S2: Electroplating treatment is performed on the surface of the pretreated substrate to form a composite bottom layer of Al-Zn-Mo-nano-silicon carbide-fluorinated graphene. The electroplating solution includes: Al2(SO4)3·18H2O 70g / L, ZnSO4·7H2O 80g / L, Na2MoO4·2H2O 25g / L, sodium gluconate 30g / L, nano-silicon carbide 4g / L, fluorinated graphene 0.3g / L, hexadecyltrimethylammonium bromide 0.5g / L, the pH of the electroplating solution is 4.5, and the current density is 5A / dm 2 , temperature 50℃, electroplating time 25min; S3: Pulse-DC coupled electroplating is performed on the surface of the composite bottom layer to form a Ni-Mo-PB gradient functional layer; the electroplating solution includes: NiSO4·6H2O 130g / L, Na2MoO4·7H2O 15g / L, NaH2PO2·H2O 45g / L, boric acid 30g / L, NaBH4 0.5g / L, succinic acid 20g / L, pH 4.5, and the pulse-DC coupled electroplating is divided into an initial stage and a termination stage. The initial stage: a pulse duty cycle of 30%, a frequency of 100Hz, a temperature of 45°C, and a current density of 3A / dm 2 , electroplating time 35min; the termination stage: DC mode, temperature 60℃, current density 5A / dm 2 , electroplating time 18min; S4: Electroplating treatment is performed on the surface of the gradient functional layer to form a surface layer of Ni-WP-nano zinc oxide; the electroplating solution includes NiSO4·6H2O 190g / L, Na2WO4 20g / L, NaH2PO2·H2O 55g / L, nano zinc oxide 3g / L, polyvinyl pyrrolidone 1g / L, and silane coupling agent KH550 2g / L; the pH of the electroplating solution is 4.8, the temperature is 85°C, and the current density is 2.5A / dm 2, electroplating time 27min.

[0053] Comparative Example 2 The difference between this comparative example and Example 1 is: S4: Electroplating treatment is performed on the surface of the composite bottom layer to form a Ni-Mo-PB gradient functional layer; the electroplating solution includes: NiSO4·6H2O 130g / L, Na2MoO4·7H2O 15g / L, NaH2PO2·H2O 45g / L, boric acid 30g / L, NaBH4 0.5g / L, succinic acid 20g / L, pH 4.5, temperature 60°C, current density 5A / dm 2 , electroplating time 18min.

[0054] Other details are the same as in Example 1.

[0055] Comparative Example 3 The difference between this comparative example and Example 1 is: S5: Electroplating treatment is performed on the surface of the gradient functional layer to form a surface layer of Ni-WP-nano zinc oxide; the electroplating solution includes NiSO4·6H2O 190g / L, Na2WO4 20g / L, NaH2PO2·H2O 55g / L, polyvinyl pyrrolidone 1g / L, and silane coupling agent KH550 2g / L; the pH of the electroplating solution is 4.8, the temperature is 85°C, and the current density is 2.5A / dm 2 , electroplating time 27min.

[0056] Other details are the same as in Example 1.

[0057] Performance testing The carbon steel substrates prepared in Examples 1-6 and Comparative Examples 1-3 were cut, the edges were epoxy-sealed, and adhesion strength testing was performed according to GB / T5270-2005; autoclave simulation corrosion rate testing was performed according to NACE-TM0172-2001; and scratch self-repair testing was performed according to ASTM D7087-05. Detailed data are shown in Table 1.

[0058] Preparation of the corrosive medium: mass fraction of 1.65% sodium chloride and 0.12% sodium bicarbonate, carbon dioxide pressurized to 0.5 MPa (saturated dissolution at 25°C, measured pH of 4.2).

[0059] Scratch preparation: A nano-scratch tester was used to prepare scratches with a length of 10 mm, a width of 30 ± 2 μm, and a depth reaching the substrate. The scratched specimen was then immersed in a 1.65% sodium chloride solution at room temperature of 25°C ± 2°C and exposed to air (dissolved oxygen concentration of approximately 8 mg / L). The width change was recorded, and the repair rate after 72 h was calculated.

[0060] Table 1 Performance test data of carbon steel substrates prepared in Examples 1 to 6 and Comparative Examples 1 to 3

[0061] Comprehensive analysis of the performance test data in Table 1 shows that: In Examples 1 to 3, by gradually optimizing the concentrations of each component and the process parameters, the adhesion strength of the coating showed an increasing trend, the corrosion rate continued to decrease, the repair rate increased simultaneously, and the appearance remained smooth. This shows that the adjustment of the concentrations of each component and the process parameters has optimized the substrate coating adhesion, corrosion resistance, and self-repair ability to a certain extent. Based on Example 3, Examples 4 to 6 pretreated the nano-silicon carbide and fluorinated graphene used in the composite bottom layer by silanization and aniline coating, strengthening the interface bonding between the nano-silicon carbide and fluorinated graphene and the metal matrix, further improving the adhesion strength, significantly reducing the corrosion rate, but the improvement in the repair rate slowed down. This shows that the pretreatment process improves the density and interface bonding of the coating substrate, but the repair rate is more directly affected by the self-repair mechanism of the surface nano-zinc oxide.

[0062] In contrast, in Comparative Example 1, after the electrophoretic coating layer is missing, the interlayer bonding force is greatly reduced, and the corrosive medium is more likely to penetrate the coating, causing pitting. In Comparative Example 2, the gradient functional layer cannot be formed by single DC electroplating, which reduces the corrosion resistance and causes micro-pitting. In Comparative Example 3, after the lack of nano zinc oxide, on the one hand, the filling effect of nanoparticles on the pores of the coating is lost, and the density is reduced. On the other hand, the lack of Zn 2+ The self-repair response mechanism reduces the repair rate and rust is visible at the scratches.

[0063] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. An electroplating process for a multi-element metal anti-corrosion coating, characterized in that: The steps include: S1: roughening the surface of the substrate, degreasing it, and performing pickling and activation to obtain a pretreated substrate; S2: forming a composite bottom layer of Al-Zn-Mo-nano silicon carbide-fluorinated graphene by electroplating on the surface of the pretreated substrate; S3: forming a polyethyleneimine-nano-silica composite film on the surface of the composite base layer by electrophoretic coating; S4: electroplating a Ni-Mo-PB gradient functional layer on the surface of the composite film by pulse-DC coupled electroplating; S5: Electroplating a Ni-WP-nano zinc oxide surface layer is performed on the surface of the gradient functional layer.

2. The electroplating process for the multi-element metal anti-corrosion coating according to claim 1, characterized in that: In step S1, the specific method for roughening the surface of the substrate is: In step S1, the specific method for roughening the surface of the substrate is: spraying oxalic acid with a concentration of 55~65g / L and ferric nitrate with a concentration of 90~110g / L in sequence, and the spraying time is 20~35min.

3. The electroplating process for the multi-element metal anti-corrosion coating according to claim 1, characterized in that: In step S1, the specific method of oil removal is: spraying a mixed solution B with a concentration of 12-15 g / L sodium lauryl sulfate, a concentration of 8-10 g / L sodium metasilicate, and a concentration of 2-4 g / L sodium hydroxide for 8-10 minutes.

4. The electroplating process for the multi-element metal anti-corrosion coating according to claim 1, characterized in that: In step S2, the plating solution A of the composite bottom layer includes Al2(SO4)3·18H2O 70~90g / L, ZnSO4·7H2O 80~100g / L, Na2MoO4·2H2O 25~35g / L, sodium gluconate 30~40g / L, nano-silicon carbide 4~6g / L, fluorinated graphene 0.3~0.6g / L, and cetyltrimethylammonium bromide 0.5~1g / L.

5. The electroplating process for the multi-element metal anti-corrosion coating according to claim 1, characterized in that: In step S3, the electrophoretic coating electrophoretic liquid includes 5-7 g / L polyethyleneimine, 2-3 g / L nano-silicon dioxide, 50-65 mL / L ethylene glycol butyl ether, 5-7 g / L hydroxyethyl cellulose, and 1.2-1.5 g / L triethylamine.

6. The electroplating process for the multi-element metal anti-corrosion coating according to claim 1, characterized in that: In step S4, the plating solution B of the gradient functional layer includes 130-160 g / L of NiSO4·6H2O, 15-25 g / L of Na2MoO4·7H2O, 45-65 g / L of NaH2PO2·H2O, 30-50 g / L of boric acid, 0.5-1 g / L of NaBH4, and 20-35 g / L of succinic acid.

7. The electroplating process for the multi-element metal anti-corrosion coating according to claim 1, characterized in that: In step S4, the pulse-DC coupled electroplating is divided into an initial stage and a termination stage. In the initial stage, the pulse duty cycle is 30% to 40%, the electroplating temperature is 45 to 50°C, and the current density is 3 to 3.3 A / dm 2 , the electroplating time is 30~35min; in the termination stage, the electroplating temperature is 60~65℃, the current density is 5~5.3A / dm 2 , the electroplating time is 15~18min.

8. The electroplating process for the multi-element metal anti-corrosion coating according to claim 1, characterized in that: In step S5, the plating solution C used for the surface layer includes 190-220 g / L of NiSO4·6H2O, 20-30 g / L of Na2WO4, 55-75 g / L of NaH2PO2·H2O, 3-5 g / L of nano zinc oxide, 1-2 g / L of polyvinyl pyrrolidone, and 2-3 g / L of silane coupling agent KH550.

9. The electroplating process for the multi-element metal anti-corrosion coating according to claim 1, characterized in that: In step S2, the nano-silicon carbide and fluorinated graphene undergo the following pretreatment steps before use: S11: adding nano-silicon carbide, fluorinated graphene and sodium perfluorooctane sulfonate to an alcohol solution and mixing uniformly, adding a double-bond silane coupling agent and mixing uniformly, adjusting the pH to 4.0-4.5, heating to 50-70° C., reacting for 3-5 hours, solid-liquid separation, washing, and drying to obtain a silanized composite material; S12: Under an inert atmosphere at -5~5℃, add trifluoroacetic acid and perchloric acid into the reactor, adjust the pH to 2.5~3, then add the silanization composite material and aniline monomer and mix evenly, slowly add the composite initiator, react for 9~11h, separate the solid and liquid, wash, and dry to obtain the product.

10. The electroplating process for the multi-element metal anti-corrosion coating according to claim 9, characterized in that: The mass ratio of the total mass of the nano-silicon carbide and the fluorinated graphene, sodium perfluorooctane sulfonate, the silane coupling agent and the aniline monomer is 100:(0.5-1):(6-9):(18-22).

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