A plating aid liquid for hot galvanizing process, and a preparation method and application thereof

Abstract

This application relates to the field of hot-dip galvanizing corrosion protection, specifically disclosing a flux for hot-dip galvanizing processes, its preparation method, and its application. The flux for hot-dip galvanizing processes, by weight, comprises the following components: 80-100 parts zinc chloride; 140-160 parts ammonium chloride; 40-45 parts metal oxide nanoparticles; 15-18 parts responsive EDTA microcapsules; 7.5-9 parts polyvinyl butyral fiber; and 1500 parts water. The metal oxide nanoparticles include cerium oxide nanoparticles and / or zirconium oxide nanoparticles. The responsive EDTA microcapsules are prepared from EDTA, chitosan, and N-isopropylacrylamide. The flux of this application improves zinc layer adhesion, reduces surface defects, and reduces workpiece corrosion. It also actively reduces the amount of FeCl3 in the system, inhibiting its embedding in the zinc layer and forming pits, thereby significantly reducing coating defects.

Description

Technical Field

[0001] This application relates to the technical field of hot-dip galvanizing corrosion protection, and in particular to a flux for hot-dip galvanizing process, its preparation method and application. Background Technology

[0002] Steel components are primarily composed of reactive iron, which reacts with moisture and oxygen in a normal atmospheric environment to form rust. The corrosion rate accelerates significantly when the relative humidity exceeds 60%. Corrosion not only affects appearance but also weakens the strength and stability of the steel, increasing the risk of structural failure. Corrosion protection measures for steel components include coating, hot-dip galvanizing, and spraying. Hot-dip galvanizing forms a zinc-iron alloy layer on the surface of the steel component and combines electrochemical protection with physical barrier mechanisms, thus gaining widespread application.

[0003] To enhance the corrosion resistance of hot-dip galvanizing, fluxing is typically applied before hot-dip galvanizing. Common fluxing solutions used in hot-dip galvanizing include ammonium chloride and zinc chloride. Ammonium chloride rapidly decomposes at high temperatures to generate NH3 and HCl gases, purifying the interface between the workpiece and the molten zinc. Zinc chloride reacts with scum in the molten zinc, reducing incomplete galvanizing. The combined use of both cleans the workpiece, removing iron oxide and ferrous oxide from its surface and depositing a salt film to prevent rust, isolate the workpiece from air, reduce the surface tension of the molten zinc, and accelerate the wetting and alloying reaction between the iron workpiece and the molten zinc. Therefore, as a crucial step in the pretreatment process for hot-dip galvanizing, the performance of the flux directly affects the adhesion, uniformity, and corrosion resistance of the zinc layer.

[0004] However, zinc chloride and ammonium chloride also have certain drawbacks. Firstly, the zinc layer adhesion is insufficient; traditional fluxing solutions have limited activation effects on steel surfaces, easily leading to weak bonding between the zinc layer and the workpiece, resulting in peeling and flaking during use. Secondly, there are many galvanizing defects; the fluxing solution has poor stability, easily causing precipitation or excessively rapid evaporation, leading to defects such as pitting, incomplete plating, and runs in the zinc layer. Finally, they are highly corrosive; high concentrations of chloride ions easily corrode equipment, and the wastewater discharge pollutes the environment. Therefore, providing a fluxing solution with excellent comprehensive performance for hot-dip galvanizing is crucial for the hot-dip galvanizing process. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides a flux for hot-dip galvanizing processes, its preparation method, and its application.

[0006] In a first aspect, this application provides a flux for hot-dip galvanizing, comprising the following components by weight: 80-100 parts zinc chloride; 140-160 parts ammonium chloride; 40-45 parts metal oxide nanoparticles; 15-18 parts responsive EDTA microcapsules; 7.5-9 parts polyvinyl butyral fiber; and 1500 parts water. The metal oxide nanoparticles include cerium oxide nanoparticles and / or zirconium oxide nanoparticles. The responsive EDTA microcapsules are prepared from EDTA, chitosan, and N-isopropylacrylamide.

[0007] By adopting the above technical solution, this application uses zinc chloride and ammonium chloride as the main fluxing materials, and adjusts the concentration of zinc chloride to 53-67 g / L and the concentration of ammonium chloride to 93-107 g / L, which is about 40% lower than the prior art. The chloride ion concentration is greatly reduced, which reduces the corrosion of the workpiece.

[0008] Preferably, the metal oxide nanoparticles include cerium oxide nanoparticles and zirconium oxide nanoparticles.

[0009] Preferably, the weight ratio of the cerium oxide nanoparticles to the zirconium oxide nanoparticles is 7:(1-2).

[0010] This application incorporates metal oxide nanoparticles composed of cerium oxide nanoparticles and / or zirconium oxide nanoparticles. Both cerium oxide and zirconium oxide nanoparticles can refine grains and reduce microcracks. Furthermore, their surfaces readily adsorb water molecules to form hydroxyl groups, which further dehydrate at high temperatures to form carboxyl groups. These carboxyl groups form stable coordination bonds with the workpiece surface, enhancing the adhesion of the coating and reducing defects. Additionally, the oxygen storage capacity of cerium oxide nanoparticles can regulate the oxidizing properties of the flux, reduce zinc bath oxidation, and inhibit zinc dross formation. Zirconia nanoparticles exhibit higher chemical stability and can significantly reduce the number of coating cracks.

[0011] Responsive EDTA microcapsules, prepared from EDTA, chitosan, and N-isopropylacrylamide, exhibit excellent pH responsiveness. They respond to pH changes when ammonium chloride decomposes to produce NH3 and HCl gases, or when residual Fe from acid washing is consumed. 2+ Oxidized to Fe3 in the flux solution + When a hydrolysis chain reaction is initiated, the pH of the system decreases. At this point, the wall material of the responsive EDTA microcapsules ruptures and releases the core material EDTA. The chelating ability of EDTA can inhibit Fe3+ at high temperatures. + Crystallization reduces the amount of FeCl3 in the system, inhibiting its embedding in the zinc layer and forming pits, thereby significantly reducing coating defects. Polyvinyl butyral fibers can form a mesh-like scaffold at certain temperatures, effectively blocking the volatilization of NH3 gas and maintaining a more stable content of effective components within the system. In general, the flux in this application has low concentrations of zinc chloride and ammonium chloride, resulting in a low chloride ion content. Therefore, the corrosion of the workpiece is naturally reduced. Furthermore, the metal oxide nanoparticles significantly enhance the adhesion of the coating, reduce the number of coating cracks, and inhibit defect formation. The polyvinyl butyral fiber helps maintain a more stable content of effective components within the system. Therefore, even if the concentrations of zinc chloride and ammonium chloride are reduced, the fluxing effect will not be affected; on the contrary, it will improve zinc layer adhesion, reduce surface defects, and decrease the degree of workpiece corrosion. More importantly, this application also incorporates responsive EDTA microcapsules. Once the pH of the system decreases, EDTA will gradually be released, reducing the amount of FeCl3 in the system and inhibiting its embedding in the zinc layer to form pits, thereby greatly reducing coating defects. Preferably, the responsive EDTA microcapsules are also grafted with polymethacrylic acid.

[0012] By adopting the above technical solution, this application also performs polymethacrylic acid grafting treatment on the responsive EDTA microcapsules, giving them the ability to respond to temperature, promoting the release of EDTA from both the increase of temperature and the decrease of pH, further reducing the amount of FeCl3 in the system, and making the coating defects closer to zero.

[0013] Preferably, the raw materials used also include 3-3.5 parts of polyurethane fiber.

[0014] By adopting the above technical solution, this application also adds polyurethane fiber to the system, which can achieve a good synergistic effect with polyvinyl butyral fiber. Polyurethane fiber provides a certain elasticity, while polyvinyl butyral fiber provides temperature sensitivity. When the two are combined, the temperature memory function of polyvinyl butyral fiber can be covered by the hard segment glass transition temperature part of polyurethane fiber, forming a dynamic support structure, further blocking the volatilization of NH3 gas, and maintaining a more stable content of effective components in the system.

[0015] Secondly, this application provides a method for preparing the flux solution for the above-mentioned hot-dip galvanizing process, comprising the following steps: S1. Preparation of responsive EDTA microcapsules: EDTA was added to a chitosan solution, and a condensing agent was added to start the reaction. Then, acetone was added to precipitate the product, which was washed, filtered, and dried to obtain EDTA microcapsules. The EDTA microcapsules and brominating agent were dispersed in an organic solvent and reacted under inert gas protection. Then, the EDTA microcapsules and the catalyst were dispersed together in an N-isopropylacrylamide solution and reacted under inert gas protection. The reaction was continued, filtered, washed, and dried to obtain responsive EDTA microcapsules. S2. Disperse metal oxide nanoparticles in water and sonicate for 30-60 min to form a dispersion; S3. Add zinc chloride, ammonium chloride, responsive EDTA microcapsules and polyvinyl butyral fiber to the dispersion in S2, and mix evenly to obtain a flux solution for hot-dip galvanizing process.

[0016] By adopting the above technical solution, a flux solution for hot-dip galvanizing can be prepared. This flux solution uses low concentrations of zinc chloride and ammonium chloride as the main fluxing raw materials, which can reduce the corrosion of the workpiece. The addition of metal oxide nanoparticles can enhance the adhesion of the coating, reduce cracks, and inhibit the formation of zinc dross. Responsive EDTA microcapsules can release EDTA when the pH of the system decreases, reducing coating defects. Polyvinyl butyral fiber can maintain the stability of the content of effective components in the system.

[0017] Preferably, in step S1, polymethacrylic acid is further added to enhance and modify the responsive EDTA microcapsules, specifically as follows: The responsive EDTA microcapsules and the catalyst were co-dispersed in a polymethacrylic acid solution, reacted under inert gas protection, filtered, washed, and dried to obtain the enhanced responsive EDTA microcapsules.

[0018] By adopting the above technical solution, this application performs polymethacrylic acid grafting treatment on responsive EDTA microcapsules to endow them with temperature responsiveness, promotes EDTA release from both temperature increase and pH decrease, further reduces the amount of FeCl3 in the system, and makes the coating defects closer to zero.

[0019] Preferably, the catalyst in S1 comprises cuprous bromide and copper bromide in a weight ratio of (20-25):(8-10).

[0020] By employing the above technical solution, this application controls the weight ratio of the two components. The interface between CuBr2 and CuBr forms synergistic active sites, improving overall catalytic efficiency. This optimizes the catalyst's microstructure, inhibits the migration and aggregation of active sites, and CuBr2 acts as a structural stabilizer, preventing the sintering of CuBr particles and thus maintaining the long-term stability of the catalyst. The heterojunction interface between the two components forms an electron redistribution region. This change in electronic structure optimizes the adsorption energy of reaction intermediates. The combined use of both effectively promotes the reaction between responsive EDTA microcapsules and polymethyl methacrylate, allowing polymethyl methacrylate to be better grafted onto the responsive EDTA microcapsules, enhancing its temperature response capability, further reducing the amount of FeCl3 in the system, and minimizing coating defects. Preferably, in step S3, polyurethane fiber and dispersion, zinc chloride, ammonium chloride, responsive EDTA microcapsules and polyvinyl butyral fiber are also added.

[0021] By adopting the above technical solution, polyurethane fiber is added to the flux solution for hot-dip galvanizing and blended with other raw materials. The polyurethane fiber and polyvinyl butyral fiber are synergistically combined. The polyurethane fiber provides elasticity, and the polyvinyl butyral fiber provides temperature sensitivity. The combination of the two allows the temperature memory function of the polyvinyl butyral fiber to be covered by the glass transition portion of the hard segment of the polyurethane fiber, forming a dynamic support structure. This further blocks the volatilization of NH3 gas and maintains a more stable content of effective components in the system.

[0022] Thirdly, this application provides a hot-dip galvanizing process, including the following steps: I. Alkali washing and degreasing; II. Pickling to remove rust; III. Flushing: Immerse the workpiece obtained in II in the fluxing solution for the hot-dip galvanizing process and perform fluxing at a temperature of 80-90°C for 30-40 seconds; IV. Hot-dip galvanizing; V. Cooling and drying.

[0023] By adopting the above technical solutions, alkaline degreasing and acid pickling can remove oil and rust from the workpiece surface; using a flux containing a specific ratio of zinc chloride, ammonium chloride, metal oxide nanoparticles, responsive EDTA microcapsules, polyvinyl butyral fiber, and water for fluxing can reduce chloride ion concentration and mitigate corrosion of the workpiece; metal oxide nanoparticles enhance coating adhesion and reduce cracks and defects; responsive EDTA microcapsules reduce pitting defects in the coating; and polyvinyl butyral fiber maintains the stability of the effective component content of the system; subsequent hot-dip galvanizing, cooling, and drying complete the hot-dip galvanizing process, improving zinc layer adhesion, reducing surface defects, and reducing the degree of corrosion of the workpiece.

[0024] In summary, this application has the following beneficial technical effects: This application reduces the concentrations of zinc chloride and ammonium chloride, thereby decreasing the chloride ion content and mitigating corrosion of the workpiece. Metal oxide nanoparticles refine grains, reduce microcracks, enhance coating adhesion, and reduce defects. Cerium oxide nanoparticles regulate the oxidizing properties of the flux and inhibit zinc dross formation, while zirconium oxide nanoparticles reduce the number of coating cracks. The responsive EDTA microcapsules exhibit pH-responsiveness, releasing EDTA when the system pH decreases, thus inhibiting Fe2+ corrosion at high temperatures. 3+ Crystallization reduces coating defects; polyvinyl butyral fibers can form a mesh-like support at a certain temperature, blocking the volatilization of NH3 gas and maintaining the stability of the effective component content in the system; responsive EDTA microcapsules grafted with polymethyl methacrylate have temperature-responsive capabilities, further reducing the amount of FeCl3 in the system and reducing coating defects; and by utilizing the synergistic combination of polyurethane fibers and polyvinyl butyral fibers, a dynamic support structure is formed, further blocking the volatilization of NH3 gas and maintaining the stability of the effective component content in the system. In the fluxing solution of this application, the concentrations of zinc chloride and ammonium chloride are low, and the chloride ion content is small. Therefore, the corrosion of the workpiece is naturally reduced. Furthermore, the metal oxide nanoparticles can significantly enhance the adhesion of the coating, reduce the number of coating cracks, and inhibit the formation of defects. Polyvinyl butyral fiber can maintain a more stable content of effective components in the system. Therefore, even if the concentrations of zinc chloride and ammonium chloride are reduced, the fluxing effect will not be affected. On the contrary, the adhesion of the zinc layer is improved, surface defects are reduced, and the degree of corrosion of the workpiece is reduced. More importantly, this application also adds responsive EDTA microcapsules. Once the pH in the system decreases, EDTA will be gradually released and the amount of FeCl3 in the system will be reduced, inhibiting its embedding in the zinc layer to form pits, thereby greatly reducing coating defects. In the hot-dip galvanizing process of this application, alkaline washing and degreasing, and acid pickling and rust removal can remove oil and rust from the workpiece surface; using a flux containing a specific ratio of zinc chloride, ammonium chloride, metal oxide nanoparticles, responsive EDTA microcapsules, polyvinyl butyral fiber and water for fluxing can reduce chloride ion concentration and mitigate corrosion of the workpiece; metal oxide nanoparticles enhance coating adhesion and reduce cracks and defects; responsive EDTA microcapsules reduce pitting defects in the coating; and polyvinyl butyral fiber maintains the stability of the effective component content of the system; subsequent hot-dip galvanizing, cooling and drying complete the hot-dip galvanizing process, improving zinc layer adhesion, reducing surface defects and reducing the degree of corrosion of the workpiece. Detailed Implementation

[0025] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0026] Example 1.1 A method for preparing a flux solution for hot-dip galvanizing, comprising the following steps: S1. Preparation of responsive EDTA microcapsules: Chitosan with a degree of deacetylation >85% was dissolved in a mixture of 1wt% acetic acid and methanol (volume ratio 1:1), stirred until completely dissolved to form a 5wt% chitosan solution. Then, EDTA was added at a chitosan to EDTA mass ratio of 1:10, and stirred until homogeneous. A condensing agent, 1-ethyl-3-(3-dimethylpropylamino)carbodiimide, at 120% of the molar amount of EDTA, was added dropwise. The reaction was carried out at 45℃ and pH=5.5 for 20 h. Acetone was then added to precipitate the product. After filtration, the product was washed once each with methanol, propanol, and diethyl ether to remove unreacted products. Finally, the product was vacuum dried at 50℃ to obtain EDTA microcapsules. 100g of EDTA microcapsules were mixed with 145.6g of triethylamine and 12.85L of dichloromethane, stirred in an ice-water bath at 4℃, and then 186g of [unspecified substance] was added under nitrogen protection. 2-Bromoisobutyryl bromide was reacted for 4 hours, and the microcapsules were repeatedly washed with ethanol and dried at 50°C. Then, the entire capsule was immersed in 9 L of 1 wt% N-N-isopropylacrylamide solution (the solvent was methanol and deionized water in a volume ratio of 2:7). 13.3 g of catalyst (2.5 g cuprous bromide, 0.8 g copper bromide and 10 g pentamethyldiethylenetriamine) was also added. The reaction was carried out under nitrogen protection for 100 min. The reaction was terminated by purging oxygen. The microcapsules were repeatedly washed with DMF and ethanol to remove residual unreacted components and dried at 50°C to obtain responsive EDTA microcapsules. S2. Disperse 40g of metal oxide nanoparticles (cerium oxide nanoparticles) in 1.5L of water and sonicate for 60min to form a dispersion. S3. Add 80g zinc chloride, 160g ammonium chloride, 18g responsive EDTA microcapsules obtained in S1 and 7.5g polyvinyl butyral fiber to the dispersion obtained in S2, mix evenly to obtain a flux solution for hot-dip galvanizing process.

[0027] Example 1.2 A method for preparing a flux solution for hot-dip galvanizing, comprising the following steps: S1. Preparation of responsive EDTA microcapsules: Chitosan with a degree of deacetylation >85% was dissolved in a mixture of 1wt% acetic acid and methanol (volume ratio 1:1), stirred until completely dissolved to form a 5wt% chitosan solution. Then, EDTA was added at a chitosan to EDTA mass ratio of 1:10, and stirred until homogeneous. A condensing agent, 1-ethyl-3-(3-dimethylpropylamino)carbodiimide, at 120% of the molar amount of EDTA, was added dropwise. The reaction was carried out at 45℃ and pH=5.5 for 20 h. Acetone was then added to precipitate the product. After filtration, the product was washed once each with methanol, propanol, and diethyl ether to remove unreacted products. Finally, the product was vacuum dried at 50℃ to obtain EDTA microcapsules. 100g of EDTA microcapsules were mixed with 145.6g of triethylamine and 12.85L of dichloromethane, stirred in an ice-water bath at 4℃, and then 186g of [unspecified substance] was added under nitrogen protection. 2-Bromoisobutyryl bromide was reacted for 4 hours, and the microcapsules were repeatedly washed with ethanol and dried at 50°C. Then, the entire capsule was immersed in 9 L of 1 wt% N-N-isopropylacrylamide solution (the solvent was methanol and deionized water in a volume ratio of 2:7). 13.3 g of catalyst (2.5 g cuprous bromide, 0.8 g copper bromide and 10 g pentamethyldiethylenetriamine) was also added. The reaction was carried out under nitrogen protection for 100 min. The reaction was terminated by purging oxygen. The microcapsules were repeatedly washed with DMF and ethanol to remove residual unreacted components and dried at 50°C to obtain responsive EDTA microcapsules. S2. Disperse 45g of metal oxide nanoparticles (cerium oxide nanoparticles) in 1.5L of water and sonicate for 30min to form a dispersion. S3. Add 100g zinc chloride, 140g ammonium chloride, 15g responsive EDTA microcapsules obtained in S1 and 9g polyvinyl butyral fiber to the dispersion obtained in S2, mix evenly to obtain a flux solution for hot-dip galvanizing process.

[0028] Example 2.1 A method for preparing a flux solution for hot-dip galvanizing is different from that in Example 1.1 in that, in S2, the metal oxide nanoparticles are zirconium oxide nanoparticles, while the rest are the same as in Example 1.1.

[0029] Example 2.2 A method for preparing a flux solution for hot-dip galvanizing is different from that in Example 1.1 in that, in S2, the metal oxide nanoparticles are composed of 35g of cerium oxide nanoparticles and 5g of zirconium oxide nanoparticles, while the rest are the same as in Example 1.1.

[0030] Example 2.3 A method for preparing a flux solution for hot-dip galvanizing is different from that in Example 1.1, in S2, the metal oxide nanoparticles are composed of 31.1g of cerium oxide nanoparticles and 3.9g of zirconium oxide nanoparticles, while the rest are the same as in Example 1.1.

[0031] Example 2.4 A method for preparing a flux solution for hot-dip galvanizing process differs from Example 1.1 in that, in S2, the metal oxide nanoparticles consist of 25g of cerium oxide nanoparticles and 15g of zirconium oxide nanoparticles, while the rest are the same as in Example 1.1.

[0032] Example 2.5 A method for preparing a flux solution for hot-dip galvanizing process differs from Example 1.1 in that, in S2, the metal oxide nanoparticles consist of 33g of cerium oxide nanoparticles and 2g of zirconium oxide nanoparticles, while the rest are the same as in Example 1.1.

[0033] Example 3 A method for preparing a flux for hot-dip galvanizing processes differs from Example 1.1 in that, in step S1, polymethyl methacrylate is added to enhance and modify the responsive EDTA microcapsules. Specifically, 100g of the responsive EDTA microcapsules are immersed in 9L of a 1wt% polymethyl methacrylate solution (the solvent is methanol and deionized water in a volume ratio of 2:7), and 13.3g of catalyst (2.5g of cuprous bromide, 0.8g of copper bromide, and 10g of pentamethyldiethylenetriamine) is added. The mixture is reacted for 100min under nitrogen protection and at 60°C. The reaction is terminated by introducing oxygen, and the microcapsules are repeatedly washed with DMF and ethanol to remove residual unreacted components. The mixture is then dried at 50°C to obtain the enhanced responsive EDTA microcapsules. In step S3, 80g of zinc chloride, 160g of ammonium chloride, and 18g of... are added to the dispersion obtained in step S2. The enhanced responsive EDTA microcapsules obtained from S1 and 7.5g of polyvinyl butyral fiber were mixed evenly to obtain a flux solution for hot-dip galvanizing.

[0034] Example 4.1 A method for preparing a flux for hot-dip galvanizing is different from Example 3 in that the catalyst used in preparing responsive EDTA microcapsules and enhanced responsive EDTA microcapsules consists of 2.2g cuprous bromide, 1.1g copper bromide and 10g pentamethyldiethylenetriamine, while the rest is the same as in Example 3.

[0035] Example 4.2 A method for preparing a flux for hot-dip galvanizing is different from Example 3 in that the catalyst used in preparing responsive EDTA microcapsules and enhanced responsive EDTA microcapsules is composed of 3.3g cuprous bromide and 10g pentamethyldiethylenetriamine, while the rest is the same as in Example 3.

[0036] Example 4.3 A method for preparing a flux for hot-dip galvanizing is different from Example 3 in that the catalyst used in preparing responsive EDTA microcapsules and enhanced responsive EDTA microcapsules is composed of 3.3g copper bromide and 10g pentamethyldiethylenetriamine, while the rest is the same as in Example 3.

[0037] Example 4.4 A method for preparing a flux for hot-dip galvanizing is different from Example 3 in that the catalyst used in preparing responsive EDTA microcapsules and enhanced responsive EDTA microcapsules is composed of 2g cuprous bromide, 1.3g copper bromide and 10g pentamethyldiethylenetriamine, while the rest is the same as in Example 3.

[0038] Example 4.5 A method for preparing a flux for hot-dip galvanizing is different from Example 3 in that the catalyst used in preparing responsive EDTA microcapsules and enhanced responsive EDTA microcapsules is composed of 2.8g cuprous bromide, 0.5g copper bromide and 10g pentamethyldiethylenetriamine, while the rest is the same as in Example 3.

[0039] Example 5.1 A method for preparing a flux solution for hot-dip galvanizing process differs from Example 1.1 in that 2g of polyurethane fiber is added in step S3, while the rest is the same as in Example 1.1.

[0040] Example 5.2 A method for preparing a flux solution for hot-dip galvanizing is different from that in Example 1.1 in that 3g of polyurethane fiber is added in step S3, while the rest is the same as in Example 1.1.

[0041] Example 5.3 A method for preparing a flux solution for hot-dip galvanizing process differs from Example 1.1 in that 3.5g of polyurethane fiber is added in step S3, while the rest is the same as in Example 1.1.

[0042] Example 5.4 A method for preparing a flux solution for hot-dip galvanizing is different from that in Example 1.1 in that 5g of polyurethane fiber is added in step S3, while the rest is the same as in Example 1.1.

[0043] Comparative Example 1.1 The difference from Example 1.1 is that S2 is removed. The specific operation in S3 is as follows: 80g of zinc chloride, 160g of ammonium chloride, 18g of the responsive EDTA microcapsules obtained in S1 and 7.5g of polyvinyl butyral fiber are mixed and dispersed in 1.5L of water. After mixing evenly, a flux solution for hot-dip galvanizing process is obtained. The rest is the same as in Example 1.1.

[0044] Comparative Example 1.2 The difference from Example 1.1 is that the specific operation in S3 is as follows: 80g of zinc chloride, 160g of ammonium chloride and 18g of responsive EDTA microcapsules obtained in S1 are added to the dispersion obtained in S2, and after being mixed evenly, a flux solution for hot-dip galvanizing process is obtained. The rest is the same as in Example 1.1.

[0045] Comparative Example 1.3 The difference from Example 1.1 is that S1 is removed. The specific operation in S3 is as follows: 80g of zinc chloride, 160g of ammonium chloride and 7.5g of polyvinyl butyral fiber are added to the dispersion obtained in S2 and mixed evenly to obtain the flux solution for hot-dip galvanizing process. The rest is the same as in Example 1.1.

[0046] Comparative Example 2 S1. Preparation of EDTA microcapsules: Chitosan with a degree of deacetylation >85% was dissolved in a mixture of 1wt% acetic acid and methanol (volume ratio 1:1) and stirred until completely dissolved to form a 5wt% chitosan solution. Then, EDTA was added at a chitosan to EDTA mass ratio of 1:10 and stirred until homogeneous. 1-Ethyl-3-(3-dimethylpropylamino)carbodiimide, a condensing agent, was added dropwise at 120% of the molar amount of EDTA. The reaction was carried out at 45℃ and pH=5.5 for 20h. Acetone was then added to precipitate the product. After filtration, the product was washed once each with methanol, propanol and diethyl ether to remove unreacted products. Finally, the product was vacuum dried at 50℃ to obtain EDTA microcapsules. S2. Disperse 40g of metal oxide nanoparticles (cerium oxide nanoparticles) in 1.5L of water and sonicate for 60min to form a dispersion. S3. Add 80g zinc chloride, 160g ammonium chloride, 18g EDTA microcapsules obtained in S1 and 7.5g polyvinyl butyral fiber to the dispersion obtained in S2, mix well to obtain a flux solution for hot-dip galvanizing process.

[0047] Application Example 1 A hot-dip galvanizing process includes the following steps: I. Alkaline washing and degreasing: Immerse the workpiece in a 10wt% sodium hydroxide solution and soak it at 60℃ for 5 minutes, then wash it with water to remove residual oil stains adhering to the surface of the workpiece. II. Pickling and Rust Removal: The pickling solution is a 15wt% hydrochloric acid solution with 3.5g / L hexamethylenetetramine added to prevent over-pickling of the sample. The workpiece obtained in step I is immersed in the pickling solution at room temperature for 30 minutes. After pickling, it is washed with water to remove residual iron salts adhering to the iron substrate surface. III. Flushing: Immerse the workpiece obtained in II in the flux solution for hot-dip galvanizing prepared in Example 1.1 and flux at 90°C for 30 seconds; IV. Hot-dip galvanizing; The workpiece obtained in III is immersed in a zinc bath (0.005% Al, 0.03wt% Ni, balance Zn) at a temperature of 440℃ for 60s. V. Cooling and drying: Remove the workpiece from the zinc bath, cool it with water, and dry it to obtain a galvanized workpiece.

[0048] Application Example 2 A hot-dip galvanizing process includes the following steps: I. Alkaline washing and degreasing: Immerse the workpiece in a 10wt% sodium hydroxide solution and soak it at 60℃ for 5 minutes, then wash it with water to remove residual oil stains adhering to the surface of the workpiece. II. Pickling and Rust Removal: The pickling solution is a 15wt% hydrochloric acid solution with 3.5g / L hexamethylenetetramine added to prevent over-pickling of the sample. The workpiece obtained in step I is immersed in the pickling solution at room temperature for 30 minutes. After pickling, it is washed with water to remove residual iron salts adhering to the iron substrate surface. III. Flushing: Immerse the workpiece obtained in II in the flux solution for hot-dip galvanizing prepared in Example 1.2 and flux at 80°C for 40 seconds; IV. Hot-dip galvanizing; The workpiece obtained in III is immersed in a zinc bath (0.005% Al, 0.03wt% Ni, balance Zn) at a temperature of 440℃ for 60s. V. Cooling and drying: Remove the workpiece from the zinc bath, cool it with water, and dry it to obtain a galvanized workpiece.

[0049] Application Example 3-21 A hot-dip galvanizing process differs from Application Example 1 in that the flux used in the hot-dip galvanizing process prepared in Example 1.1 is replaced with the flux used in the hot-dip galvanizing process prepared in Examples 2.1-5.4 and Comparative Examples 1.1-2, respectively; otherwise, it is the same as Application Example 1.

[0050] Application Example 22 A hot-dip galvanizing process, which differs from Application Example 1 in that the temperature in III is 50°C, while the rest is the same as in Application Example 1.

[0051] Performance testing 1. Corrosion resistance: A neutral salt spray test was conducted according to GB / 6458-86. After 300 hours, the rust formation on the coating of the galvanized workpiece was observed, and the area ratio of the rusted area was recorded. 2. Adhesion Test: A cross-cut test was conducted according to GB / T 31586.2-2015. A single-edged cutting tool was used to make a penetrating "X-shaped cut," each cut approximately 40mm long. The intersection angle between two cuts should be 30°-45°. Approximately 75mm of pressure-sensitive adhesive tape was applied to the cut and removed within 5 minutes. The adhesion was then graded according to the following criteria: Level 0 – No peeling or separation; Level 1 – Minor peeling or separation along the cutting line or intersection; Level 2 – There are jagged edges along either side of the cutting line, with a width not exceeding 1.5 mm; Level 3 – There is jagged flaking along most of the cutting lines, with the flaking width on any one side reaching up to 3.0 mm; Level 4 – Most of the “X-shaped cut” area under the tape has come loose; Level 5 – Detachment occurs outside the “X-shaped cut” area; 3. Zinc layer quality inspection: Check the zinc layer surface for any unplated areas. If any are found, record the unplated area (cm²). 2 / m 2 ).

[0052] Table 1 Data Record Table Group % of rusted areas Adhesion rating <![CDATA[Unplated area (cm 2 / m 2 )]]> Application Example 1 5.3 1 No plating defects Application Example 2 5.5 1 No plating defects Application Example 3 7.6 2 0.43 Application Example 4 4.6 0 No plating defects Application Example 5 4.5 0 No plating defects Application Example 6 5.4 1 No plating defects Application Example 7 5.5 1 No plating defects Application Example 8 3.9 1 No plating defects Application Example 9 3.9 0 No plating defects Application Example 10 4.2 1 0.29 Application Example 11 4.8 1 0.32 Application Example 12 4.0 1 0.25 Application Example 13 4.1 1 0.27 Application Example 14 5.0 0 No plating defects Application Example 15 4.3 0 No plating defects Application Example 16 4.2 0 No plating defects Application Example 17 4.8 0 No plating defects Application Example 18 8.9 3 1.32 Application Example 19 7.3 2 0.98 Application Example 20 9.8 1 0.19 Application Example 21 8.3 2 0.14 Application Example 22 8.7 2 0.20 Data Analysis: As shown in Table 1, the rust area ratio of the galvanized workpieces obtained from Application Examples 1-2 was 5.3-5.5%, with an adhesion grade of 1 and no missed plating. This indicates that the concentrations of zinc chloride and ammonium chloride in the flux of this application are low, and the chloride ion content is small, thus naturally reducing the corrosion of the workpiece. Furthermore, the metal oxide nanoparticles can significantly enhance the adhesion of the coating, reduce the number of coating cracks, and inhibit defect formation. Polyvinyl butyral fiber can maintain a more stable content of effective components in the system. Therefore, even if the concentrations of zinc chloride and ammonium chloride are reduced, the fluxing effect will not be affected. On the contrary, it will improve the adhesion of the zinc layer, reduce surface defects, and reduce the degree of corrosion of the workpiece. More importantly, this application also adds responsive EDTA microcapsules. Once the pH in the system decreases, EDTA will be gradually released and reduce the amount of FeCl3 in the system, inhibiting its embedding in the zinc layer to form pits, thereby greatly reducing coating defects.

[0053] In Application Examples 3-7, the composition of the metal oxide nanoparticles was adjusted. The results showed that the galvanized workpieces in Application Examples 4-5 had a lower rust removal area ratio and an adhesion grade of 0. It can be seen that by using a certain weight ratio of cerium oxide nanoparticles and zirconium oxide nanoparticles, the present application can fully enhance the adhesion of the coating, reduce defects, reduce zinc bath oxidation, inhibit zinc dross formation, and significantly reduce the number of coating cracks.

[0054] In Application Example 8, the responsive EDTA microcapsules were grafted with polymethacrylic acid. The results showed that the rust area ratio was reduced to 3.9%. It can be seen that the modification treatment of this application endows the responsive EDTA microcapsules with temperature response capability, promotes the release of EDTA from both the temperature increase and pH decrease aspects, further reduces the amount of FeCl3 in the system, and makes the coating defects closer to zero.

[0055] In Application Examples 9-13, the catalyst composition was adjusted in this application. The results showed that the rust-prone area of ​​the galvanized workpiece in Application Example 9 was lower, the adhesion grade was 0, and there was no uncoated surface. It can be seen that the interface between CuBr2 and CuBr forms synergistic active sites, which improves the overall catalytic efficiency, optimizes the microstructure of the catalyst, and inhibits the migration and aggregation of active sites. CuBr2 can act as a structural stabilizer to prevent the sintering of CuBr particles, thereby maintaining the long-term stability of the catalyst. The heterojunction interface between the two forms an electron redistribution region. This change in electronic structure can optimize the adsorption energy of the reaction intermediate. The combined use of the two can effectively promote the reaction between the responsive EDTA microcapsules and polymethyl methacrylate, allowing polymethyl methacrylate to be better grafted onto the responsive EDTA microcapsules, enhancing its temperature response capability, further reducing the amount of FeCl3 in the system, and reducing coating defects.

[0056] In application examples 14-17, polyurethane fibers were also added to the system. The results showed that the rust area of ​​the galvanized workpiece was significantly reduced, the adhesion level reached level 0, and there was no uncoated area on the workpiece surface. It can be seen that polyurethane fibers and polyvinyl butyral fibers can play a synergistic role. Polyurethane fibers provide elasticity, while polyvinyl butyral fibers provide temperature sensitivity. The combination of the two allows the temperature memory function of polyvinyl butyral fibers to be partially covered by the glass transition temperature of the hard segment of polyurethane fibers, forming a dynamic support structure. This further blocks the volatilization of NH3 gas and maintains a more stable content of effective components in the system.

[0057] In Application Examples 18-20, this application removed metal oxide nanoparticles, polyvinyl butyral fibers, and responsive EDTA microcapsules, respectively. The results showed a significant decrease in the overall performance of the galvanized workpieces. This demonstrates that metal oxide nanoparticles can refine grains, reduce microcracks, and readily adsorb water molecules on their surface to form hydroxyl groups. These hydroxyl groups further dehydrate at high temperatures to form carboxyl groups. These carboxyl groups form stable coordination bonds with the workpiece surface, enhancing coating adhesion, reducing defects, decreasing zinc bath oxidation, inhibiting zinc dross formation, and reducing the number of coating cracks. The responsive EDTA microcapsules can inhibit Fe3+ at high temperatures. + Crystallization reduces the amount of FeCl3 in the system, inhibiting its embedding in the zinc layer and forming pits, thereby greatly reducing coating defects; polyvinyl butyral fiber can form a mesh-like support at a certain temperature, effectively blocking the volatilization of NH3 gas and maintaining a more stable content of effective components in the system.

[0058] In Application Example 21, this application replaced the responsive EDTA microcapsules with ordinary EDTA microcapsules. The results showed that the rust-forming area of ​​the galvanized workpiece was improved. This demonstrates that the responsive EDTA microcapsules can rupture and release the core material EDTA when the pH of the system decreases. The chelating ability of EDTA can inhibit Fe3+ at high temperatures. + Crystallization reduces the amount of FeCl3 in the system, inhibiting its embedding in the zinc layer and forming pits, thereby greatly reducing coating defects.

[0059] In Application Example 22, this application reduced the fluxing temperature, and the results showed that the overall performance of the galvanized workpiece dropped significantly. It can be seen that polyvinyl butyral fiber must be at a certain temperature to form a mesh-like support, effectively blocking the volatilization of NH3 gas and maintaining a more stable content of effective components in the system.

[0060] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A flux for hot-dip galvanizing, characterized in that, The raw materials used, by weight, include the following components: 80-100 parts zinc chloride; 140-160 parts of ammonium chloride; 40-45 parts of metal oxide nanoparticles; 15-18 parts of responsive EDTA microcapsules; 7.5-9 parts of polyvinyl butyral fiber; 1500 portions of water; The metal oxide nanoparticles include cerium oxide nanoparticles and / or zirconium oxide nanoparticles. The responsive EDTA microcapsules were prepared from EDTA, chitosan, and N-isopropylacrylamide.

2. The flux for hot-dip galvanizing process according to claim 1, characterized in that, The metal oxide nanoparticles include cerium oxide nanoparticles and zirconium oxide nanoparticles.

3. The flux for hot-dip galvanizing process according to claim 2, characterized in that, The weight ratio of the cerium oxide nanoparticles to the zirconium oxide nanoparticles is 7:(1-2).

4. The flux for hot-dip galvanizing process according to claim 1, characterized in that, The responsive EDTA microcapsules are also grafted with polymethacrylic acid.

5. The flux for hot-dip galvanizing according to claim 1, characterized in that, The raw materials used also include 3-3.5 parts of polyurethane fiber.

6. A method for preparing the flux solution for hot-dip galvanizing process according to claim 1, characterized in that, Includes the following steps: S1. Preparation of responsive EDTA microcapsules: EDTA was added to a chitosan solution, and a condensing agent was added to start the reaction. Then, acetone was added to precipitate the product, which was washed, filtered, and dried to obtain EDTA microcapsules. The EDTA microcapsules and brominating agent were dispersed in an organic solvent and reacted under inert gas protection. Then, the EDTA microcapsules and the catalyst were dispersed together in an N-isopropylacrylamide solution and reacted under inert gas protection. The reaction was continued, filtered, washed, and dried to obtain responsive EDTA microcapsules. S2. Disperse metal oxide nanoparticles in water and sonicate for 30-60 min to form a dispersion; S3. Add zinc chloride, ammonium chloride, responsive EDTA microcapsules and polyvinyl butyral fiber to the dispersion in S2, and mix evenly to obtain a flux solution for hot-dip galvanizing process.

7. The method for preparing the flux solution for hot-dip galvanizing process according to claim 6, characterized in that, In step S1, polymethacrylic acid is also added to enhance and modify the responsive EDTA microcapsules, specifically as follows: The responsive EDTA microcapsules and the catalyst were co-dispersed in a polymethacrylic acid solution, reacted under inert gas protection, filtered, washed, and dried to obtain the enhanced responsive EDTA microcapsules.

8. The method for preparing the flux solution for hot-dip galvanizing process according to claim 7, characterized in that, The catalyst in S1 comprises cuprous bromide and copper bromide in a weight ratio of (20-25):(8-10).

9. The method for preparing the flux solution for hot-dip galvanizing process according to claim 8, characterized in that, In step S3, polyurethane fiber and dispersion, zinc chloride, ammonium chloride, responsive EDTA microcapsules and polyvinyl butyral fiber are also added.

10. A hot-dip galvanizing process, characterized in that, Includes the following steps: I. Alkali washing and degreasing; II. Pickling to remove rust; III. Flushing: Immerse the workpiece obtained in II in the fluxing solution for hot-dip galvanizing process as described in claim 1, and perform fluxing at a temperature of 80-90°C for 30-40 seconds; IV. Hot-dip galvanizing; V. Cooling and drying.