Gray passivation solution for zinc alloy and passivation method

Abstract

The invention relates to the field of metal surface treatment, and particularly discloses a gray passivation solution for zinc alloy and a passivation method. The gray passivation solution for the zinc alloy comprises the following components: 60-85 g / L of nickel chloride hexahydrate, 60-75 g / L of sodium thiocyanate, 5-10 g / L of ammonium chloride, 20-30 g / L of chromic nitrate nonahydrate, 10-15 g / L of cobalt chloride hexahydrate, 15-20 g / L of monopotassium phosphate, 40-60 g / L of zinc dihydrogen phosphate, 80-110 mL / L of a zinc nitrate solution, 20-30 g / L of manganese dihydrogen phosphate and 0.05-0.2 g / L of a surfactant, and a solvent of the gray passivation solution for the zinc alloy is pure water. The content of zinc nitrate in the zinc nitrate solution is 300g / L. The gray passivation solution for the zinc alloy has the advantages of being uniform in coating film surface, high in binding force and resistant to abrasion and corrosion.

Description

Technical Field

[0001] This application relates to the field of metal surface treatment, and more specifically, it relates to a gray passivation solution and passivation method for zinc alloys. Background Technology

[0002] Zinc alloys are widely used in construction, automobiles, and other fields due to their excellent mechanical properties and low cost. However, zinc alloy surfaces are prone to corrosion, necessitating effective surface treatment to improve their corrosion resistance and aesthetics. Traditional surface treatment methods mainly include painting and electroplating. While these methods can meet protective and decorative needs to some extent, they have many drawbacks, such as poor adhesion, complex processes, high costs, and environmental unfriendliness. In recent years, chemical passivation, as a novel surface treatment technology, has gradually become a research hotspot due to its advantages such as simple process, low cost, and good weather resistance.

[0003] Research and application of zinc alloy passivation technology currently focuses mainly on black passivation and blue-white passivation. For example, Chinese patent (CN102046842A) discloses a chemically synthesized treatment composition and a method for manufacturing a component with a black coating using the composition. The main components of the composition are trivalent chromium substances, cobalt substances, sulfur compounds and organophosphonic acid compounds, which can form a black coating with good corrosion resistance. However, research and application of zinc alloy gray passivation are rarely reported.

[0004] The gray appearance of zinc alloys has significant market demand in modern construction and automotive industries. Developing a zinc alloy passivation solution and method capable of producing a high-performance gray passivation layer is crucial for filling technological gaps, meeting market demands, and driving industry development. Currently, the market demand for gray passivation of zinc alloys remains unmet, especially in applications and service conditions where high corrosion resistance and adhesion of the passivation film are required. Summary of the Invention

[0005] In order to provide a novel gray passivation process for zinc alloys and improve the surface properties of the gray passivation film for zinc alloys, this application provides a gray passivation solution and passivation method for zinc alloys.

[0006] This application provides a gray passivation solution for zinc alloys, employing the following technical solution: A gray passivation solution for zinc alloys comprises: nickel chloride hexahydrate 60-85 g / L, sodium thiocyanate 60-75 g / L, ammonium chloride 5-10 g / L, chromium nitrate nonahydrate 20-30 g / L, cobalt chloride hexahydrate 15-10 g / L, potassium dihydrogen phosphate 15-20 g / L, zinc dihydrogen phosphate 40-60 g / L, zinc nitrate solution 80-110 mL / L, manganese dihydrogen phosphate 20-30 g / L, and surfactant 0.05-0.2 g / L. The solvent of the gray passivation solution for zinc alloys is pure water, and the zinc nitrate solution contains 300 g / L of zinc nitrate.

[0007] By adopting the above technical solution, in the gray passivation solution formulation of this invention, nickel chloride hexahydrate serves as the main film-forming agent, providing the nickel source required for the formation of the gray passivation film. Sodium thiocyanate functions as both an oxidant and a complexing agent, not only promoting the corrosion of the zinc substrate to release zinc ions but also providing a sulfur source to react with nickel ions to form nickel sulfide, which is crucial for forming a uniform gray passivation film. After ammonium chloride dissolves in water, it generates ammonia and hydrogen ions through the hydrolysis of ammonium ions, thereby stabilizing the pH value of the passivation solution. At the same time, chloride ions enhance the conductivity and reactivity of the solution. Components such as chromium nitrate nonahydrate, cobalt chloride hexahydrate, potassium dihydrogen phosphate, zinc dihydrogen phosphate, and manganese dihydrogen phosphate further enhance the adhesion, corrosion resistance, and wear resistance of the passivation film. The synergistic effect of these components not only ensures the uniform growth and stable performance of the passivation film but also forms a uniform and dense gray passivation film on the zinc alloy surface through chemical reaction, significantly improving the surface properties of the zinc alloy and meeting the gray appearance requirements of modern construction and automotive industries.

[0008] Optionally, the surfactant includes at least one of sodium dodecyl sulfate, sodium dodecyl sulfonate, hexadecyltrimethylammonium chloride, and ethylenediaminetetraacetic acid.

[0009] By adopting the above technical solution, the surfactant selected is at least one of sodium dodecyl sulfate, sodium dodecyl sulfonate, hexadecyltrimethylammonium chloride, and ethylenediaminetetraacetic acid. This reduces the surface tension of the solution, allowing the passivation solution to better wet the zinc alloy surface, promoting a uniform passivation reaction, and thus improving the smoothness and density of the passivation film. Simultaneously, it improves the adhesion between the passivation film and the zinc alloy substrate, preventing passivation film detachment during use, and further enhancing the protective and decorative properties of the zinc alloy surface.

[0010] Optionally, it also contains 0.5-1.5 g / L cerium nitrate or 0.3-1.0 g / L sodium molybdate.

[0011] By adopting the above technical solution, adding 0.5-1.5 g / L cerium nitrate or 0.3-1.0 g / L sodium molybdate allows the cerium element in cerium nitrate and the molybdenum element in sodium molybdate to synergistically interact with other components in the passivation film, refining the passivation film grains and making the passivation film structure more compact. This effectively hinders the contact between the corrosive medium and the zinc alloy substrate, significantly improving the corrosion resistance of the passivation film. Especially in harsh corrosive environments, the passivation film with these components can better protect the zinc alloy and extend its service life.

[0012] Optionally, it also includes 1-10 g / L of silica sol, wherein the silica sol has a particle size of 10-50 nm.

[0013] By employing the above technical solution, adding 1-10 g / L of silica sol with a particle size of 10-50 nm allows the nano-sized silica particles to fill the pores of the passivation film, increasing its density and hardness, and improving its wear resistance and scratch resistance. Simultaneously, the high chemical stability of silica further enhances the passivation film's resistance to chemical corrosion, enabling the zinc alloy to maintain good surface properties and protective effects even when subjected to friction or chemical corrosion.

[0014] Optionally, it also includes 1-5 g / L of tannic acid and 0.1-0.5 g / L of chitosan quaternary ammonium salt.

[0015] By adopting the above technical solution, the addition of 1-5 g / L tannic acid and 0.1-0.5 g / L chitosan quaternary ammonium salt allows the tannic acid, with its abundant phenolic hydroxyl structure, to undergo a complexation reaction with metal ions on the zinc alloy surface, thereby enhancing the adhesion between the passivation film and the substrate. The chitosan quaternary ammonium salt has good film-forming and antibacterial properties, enabling it to form an additional protective film on the passivation film surface, thus improving the corrosion resistance of the passivation film.

[0016] Optionally, the zinc dihydrogen phosphate can be replaced with an equimolar amount of zinc hydroxyethylidene diphosphonate, and a boric acid-citric acid buffer pair of 0.5-3 g / L can be added.

[0017] By adopting the above technical solution, zinc dihydrogen phosphate is replaced with an equimolar amount of zinc hydroxyethylidene diphosphonate, and a boric acid-citric acid buffer pair is added. Zinc hydroxyethylidene diphosphonate has excellent corrosion inhibition performance and complexing ability, which can more effectively inhibit the corrosion reaction of zinc alloy and improve the corrosion resistance of the passivation film. The boric acid-citric acid buffer pair can stabilize the pH value of the passivation solution, so that the passivation reaction can be carried out under suitable acidity and alkalinity, ensuring the quality and performance stability of the passivation film and avoiding the problem of unstable passivation film quality caused by pH fluctuations of the solution.

[0018] Secondly, this application provides a passivation method for zinc alloys using a gray passivation solution, employing the following technical solution: A passivation method for zinc alloys using a gray passivation solution, comprising the following steps: Surface degreasing of zinc alloy workpieces; Prepare an activation solution by mixing 50-65 mL / L hydrochloric acid, 0.5-1 mL / L hydrofluoric acid, 0.02-0.05 g / L sodium dodecyl sulfate, and the remainder pure water. Immerse the zinc alloy workpiece in the activation solution for 10-60 seconds at a temperature of 10-40°C. After removal, rinse with pure water for 5-10 seconds. The activated zinc alloy workpiece is immersed in a gray passivation solution for 120-300 seconds at a temperature of 10-40°C. The passivated zinc alloy workpiece is then removed, suspended for 3-10 seconds, washed with water for 5-10 seconds, and dried to obtain a zinc alloy workpiece with a gray passivation film on its surface.

[0019] By adopting the above technical solution, this passivation method removes oil and other impurities from the surface of zinc alloy workpieces through surface degreasing, providing a clean surface for subsequent processing; the hydrochloric acid and hydrofluoric acid in the activation solution can remove the oxide film on the zinc alloy surface, exposing a fresh metal surface and promoting the passivation reaction; the activated workpiece is immersed in a gray passivation solution, and under appropriate time and temperature conditions, the components in the passivation solution react fully with the zinc alloy surface to form a high-performance gray passivation film; finally, after washing and drying, the residual solution on the surface is removed, resulting in a zinc alloy workpiece with a uniform and dense gray passivation film on the surface. The entire process is simple to operate, easy to control, and can effectively improve the surface properties of zinc alloys.

[0020] Optional, the following steps may be included: Surface degreasing of zinc alloy workpieces; Prepare an activation solution by mixing 50-65 mL / L hydrochloric acid, 0.5-1 mL / L hydrofluoric acid, 0.02-0.05 g / L sodium dodecyl sulfate, and the remainder pure water. Immerse the zinc alloy workpiece in the activation solution for 10-60 seconds at a temperature of 10-40°C. After removal, rinse with pure water for 5-10 seconds. The activated zinc alloy workpiece is placed in a high-pressure container, a passivation solution is injected and carbon dioxide is introduced, the temperature is maintained at 35-45℃, and the carbon dioxide is pressurized to reach a supercritical state for 60-80 seconds. After passivation, the zinc alloy workpiece is removed, suspended and left to stand for 3-10 seconds, then washed with water for 5-10 seconds and dried to obtain a zinc alloy workpiece with a gray passivation film on its surface.

[0021] By adopting the above technical solution, this passivation method, based on the aforementioned process, employs supercritical carbon dioxide treatment technology. The activated zinc alloy workpiece is placed in a high-pressure container, allowing the carbon dioxide to reach a supercritical state. Supercritical carbon dioxide possesses excellent diffusivity and solubility, enabling it to carry the components of the passivation solution more evenly to the zinc alloy surface. This promotes a rapid and uniform passivation reaction, resulting in a denser, more uniform passivation film with stronger adhesion to the substrate. Compared to conventional passivation methods, supercritical carbon dioxide treatment significantly shortens processing time, improves production efficiency, and further enhances the performance of the zinc alloy passivation film, meeting the requirements of applications and service conditions demanding high corrosion resistance and adhesion of the passivation film.

[0022] In summary, this application has the following beneficial effects: 1. Because this application uses a gray passivation film formed through the synergistic effect of multiple components, the film has high density and can effectively prevent the penetration of corrosive media, thus significantly enhancing the corrosion resistance of zinc alloys compared to traditional processes. At the same time, the passivation film has improved adhesion to the substrate and possesses wear resistance, scratch resistance, and other properties, meeting the protection needs of fields such as construction and automobiles.

[0023] 2. The passivation solution formulation design adopted in this application takes into account both cost and practicality. The basic process steps are simple to operate and easy to control in industrialization. After introducing supercritical carbon dioxide treatment technology, the treatment time can be shortened to 60-80 seconds, improving production efficiency. Moreover, the boric acid-citric acid buffer can stabilize the pH value of the solution and ensure the consistency of the passivation film quality.

[0024] 3. The method of this application achieves the large-scale preparation of gray passivation of zinc alloy for the first time, meeting the market demand of modern industry for gray appearance; by adding components such as tannic acid and chitosan quaternary ammonium salt, it not only improves the adhesion of passivation film but also avoids the environmental pollution problems of traditional electroplating process, combining environmental protection and economy. Detailed Implementation

[0025] The following detailed description of this application is provided in conjunction with the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available sources. Example

[0026] Example 1 A passivation method for zinc alloys using a gray passivation solution: At room temperature of 25°C, use a soft brush dipped in the cleaning solution to brush the zinc alloy workpiece for 40 seconds, then rinse with pure water for 10 seconds to remove dust and grease from the workpiece surface.

[0027] An activation solution was prepared using 55 mL / L hydrochloric acid, 0.8 mL / L hydrofluoric acid, 0.04 g / L sodium dodecyl sulfate, and the remainder pure water. The zinc alloy workpiece was immersed in the activation solution for 40 seconds at an operating temperature of 35°C. After removal, the workpiece was activated with pure water, thus creating favorable conditions for subsequent passivation treatment.

[0028] A passivation solution was prepared using pure water as the solvent. The solute components in the passivation solution were: nickel chloride hexahydrate 70 g / L, sodium thiocyanate 65 g / L, ammonium chloride 8 g / L, chromium nitrate nonahydrate 25 g / L, cobalt chloride hexahydrate 12 g / L, potassium dihydrogen phosphate 18 g / L, zinc dihydrogen phosphate 50 g / L, zinc nitrate solution 95 mL / L, manganese dihydrogen phosphate 25 g / L, and surfactant 0.1 g / L. Among these, the zinc nitrate solution contained 300 g / L of zinc nitrate, and the surfactant was sodium dodecyl sulfate.

[0029] The activated zinc alloy workpiece is immersed in the prepared gray passivation solution for 200 seconds at an operating temperature of 30°C. The passivated workpiece is then removed and suspended for 5 seconds to remove excess passivation solution from the surface. It is then washed with water for 10 seconds to remove any remaining passivation solution and finally dried with hot air at 40°C to obtain a zinc alloy workpiece with a gray passivation film on its surface.

[0030] Example 2 A passivation method for zinc alloys using a gray passivation solution: The difference from Example 1 is that the activation solution is prepared by using 50 mL / L hydrochloric acid, 0.5 mL / L hydrofluoric acid, 0.02 g / L sodium dodecyl sulfate, and the remainder pure water.

[0031] Example 3 A passivation method for zinc alloys using a gray passivation solution: The difference from Example 1 is that the activation solution is prepared by using 65 mL / L hydrochloric acid, 1 mL / L hydrofluoric acid, 0.05 g / L sodium dodecyl sulfate, and the remainder pure water.

[0032] Example 4 A passivation method for a gray passivation solution for zinc alloys: The difference from Example 1 is that the passivation solution is prepared using pure water as the solvent, and the solute components in the passivation solution are: nickel chloride hexahydrate 60 g / L, sodium thiocyanate 60 g / L, ammonium chloride 5 g / L, chromium nitrate nonahydrate 20 g / L, cobalt chloride hexahydrate 10 g / L, potassium dihydrogen phosphate 15 g / L, zinc dihydrogen phosphate 40 g / L, zinc nitrate solution 80 mL / L, manganese dihydrogen phosphate 20 g / L, and sodium dodecyl sulfate 0.05 g / L.

[0033] Example 5 A passivation method for a gray passivation solution for zinc alloys: The difference from Example 1 is that the passivation solution is prepared using pure water as the solvent, and the solute components in the passivation solution are: nickel chloride hexahydrate 85 g / L, sodium thiocyanate 75 g / L, ammonium chloride 10 g / L, chromium nitrate nonahydrate 30 g / L, cobalt chloride hexahydrate 15 g / L, potassium dihydrogen phosphate 20 g / L, zinc dihydrogen phosphate 60 g / L, zinc nitrate solution 110 mL / L, manganese dihydrogen phosphate 30 g / L, and sodium dodecyl sulfate 0.2 g / L.

[0034] Example 6 A passivation method for zinc alloys using a gray passivation solution: the difference from Example 1 is that the surfactant is sodium dodecyl sulfonate.

[0035] Example 7 A passivation method for zinc alloys using a gray passivation solution: the difference from Example 1 is that the surfactant is hexadecyltrimethylammonium chloride.

[0036] Example 8 A passivation method for zinc alloys using a gray passivation solution: the difference from Example 1 is that the surfactant is ethylenediaminetetraacetic acid.

[0037] Example 9 A passivation method for zinc alloys using a gray passivation solution: The difference from Example 1 is that 1 g / L of cerium nitrate is added to the passivation solution.

[0038] Example 10 A passivation method for a gray passivation solution for zinc alloys: The difference from Example 9 is that 0.5 g / L cerium nitrate is added to the passivation solution.

[0039] Example 11 A passivation method for a gray passivation solution for zinc alloys: The difference from Example 9 is that 1.5 g / L of cerium nitrate is added to the passivation solution.

[0040] Example 12 A passivation method for zinc alloys using a gray passivation solution: The difference from Example 1 is that 0.6 g / L sodium molybdate is added to the passivation solution.

[0041] Example 13 A passivation method for zinc alloys using a gray passivation solution: The difference from Example 12 is that 0.3 g / L sodium molybdate is added to the passivation solution.

[0042] Example 14 A passivation method for zinc alloys using a gray passivation solution: The difference from Example 12 is that 1 g / L sodium molybdate is added to the passivation solution.

[0043] Example 15 A passivation method for zinc alloys using a gray passivation solution: The difference from Example 1 is that 5 g / L of silica sol is added to the passivation solution, and the silica sol has a particle size of 10-50 nm.

[0044] Example 16 A passivation method for zinc alloys using a gray passivation solution: The difference from Example 15 is that 1 g / L of silica sol is added to the passivation solution, and the silica sol has a particle size of 10-50 nm.

[0045] Example 17 A passivation method for zinc alloys using a gray passivation solution: The difference from Example 15 is that 10 g / L of silica sol is added to the passivation solution, and the silica sol has a particle size of 10-50 nm.

[0046] Example 18 A passivation method for a gray passivation solution for zinc alloys: The difference from Example 1 is that 3 g / L tannic acid and 0.3 g / L chitosan quaternary ammonium salt are added to the passivation solution.

[0047] Example 19 A passivation method for a gray passivation solution for zinc alloys: The difference from Example 18 is that 1 g / L tannic acid and 0.5 g / L chitosan quaternary ammonium salt are added to the passivation solution.

[0048] Example 20 A passivation method for a gray passivation solution for zinc alloys: The difference from Example 18 is that 5 g / L tannic acid and 0.1 g / L chitosan quaternary ammonium salt are added to the passivation solution.

[0049] Example 21 A passivation method for a gray passivation solution for zinc alloys: The difference from Example 1 is that zinc dihydrogen phosphate is replaced with an equimolar amount of zinc hydroxyethylidene diphosphonate in the passivation solution, and a 1.5 g / L boric acid-citric acid buffer pair is added.

[0050] Example 22 A passivation method for zinc alloys using a gray passivation solution: The difference from Example 1 is that the activated zinc alloy workpiece is placed in a high-pressure autoclave, the passivation solution is injected and carbon dioxide is introduced, the temperature is maintained at 40°C, and the carbon dioxide is pressurized to reach a supercritical state for 70 seconds.

[0051] Comparative Example Comparative Example 1 A passivation method for a gray passivation solution for zinc alloys: The difference from Example 1 is that the passivation solution is prepared by pure water as the solvent, and the solute components in the passivation solution are: nickel chloride hexahydrate 50 g / L, sodium thiocyanate 50 g / L, ammonium chloride 1 g / L, chromium nitrate nonahydrate 10 g / L, cobalt chloride hexahydrate 5 g / L, potassium dihydrogen phosphate 10 g / L, zinc dihydrogen phosphate 30 g / L, zinc nitrate solution 70 mL / L, manganese dihydrogen phosphate 10 g / L, and surfactant 0.01 g / L.

[0052] Comparative Example 2 A passivation method for a gray passivation solution for zinc alloys: The difference from Example 1 is that the passivation solution is prepared by pure water as the solvent, and the solute components in the passivation solution are: nickel chloride hexahydrate 95 g / L, sodium thiocyanate 85 g / L, ammonium chloride 15 g / L, chromium nitrate nonahydrate 40 g / L, cobalt chloride hexahydrate 20 g / L, potassium dihydrogen phosphate 30 g / L, zinc dihydrogen phosphate 70 g / L, zinc nitrate solution 120 mL / L, manganese dihydrogen phosphate 40 g / L, and surfactant 0.3 g / L.

[0053] Comparative Example 3 A passivation method for zinc alloys using a gray passivation solution: the difference from Example 1 is that no activation treatment is performed.

[0054] Performance testing 1. Appearance consistency inspection Standard: GB / T20967-2007 Steps: Under ambient light intensity >160lx, with the eye ≤600mm from the passivated surface and the angle between the line of sight and the surface >30°, visually inspect the uniformity and integrity of the passivation film color.

[0055] Judgment: A uniform gray color with no obvious color difference or spots is considered acceptable.

[0056] 2. Bonding strength test Standard: GB / T9791-2003 Steps: Wipe the surface of the passivation film 10 times with rapid qualitative filter paper at a pressure of 200g, and observe the contamination of the filter paper and the traces of substrate exposure.

[0057] Judgment: "Good" is defined as no obvious contamination and no exposed substrate; "Average" is defined as a small amount of powder falling off; and "Poor" is defined as a large amount of powder falling off.

[0058] 3. Abrasion resistance test Equipment: ZJ-339-JSR Abrasion Resistance Tester Conditions: Particle-free rubber friction head, load 200g, reciprocating friction until the passivation film shows obvious wear.

[0059] Indicator: Number of friction cycles before wear occurs (the more cycles, the better the wear resistance).

[0060] 4. Corrosion resistance test Standard: GB / T10125-2012 (Neutral Salt Spray Test, NSS) Conditions: 35℃, 5% NaCl solution, pH 6.5-7.2, continuous spraying.

[0061] Indicator: Time to the appearance of corrosion pits on the passivation film.

[0062] Table 1 Experimental Data Based on Examples 1 and Comparative Examples 1-2, and referring to Table 1, it can be seen that in Comparative Example 1, the concentrations of all solute components in the passivation solution were lower than the lower limit of claim 1, resulting in localized color differences in the passivation film, reduced adhesion to "average," abrasion resistance of only 30 cycles, and a salt spray corrosion resistance time shortened to 90 hours. In Comparative Example 2, the component concentrations exceeded the upper limit, resulting in obvious spots on the passivation film surface, poorer adhesion, and abrasion resistance and corrosion resistance reduced to 20 cycles and 60 hours, respectively. This indicates that the concentration of passivation solution components must be strictly controlled within the range defined in the claims; both excessively low and excessively high concentrations will lead to uneven film formation, decreased adhesion, and deterioration of corrosion resistance.

[0063] Combining Example 1 and Comparative Example 3 with Table 1, it can be seen that Comparative Example 3, without activation treatment, directly resulted in an incomplete passivation film, significant powder shedding during the adhesion test, a wear resistance of only 15 cycles, and a salt spray corrosion resistance time of less than 48 hours. In contrast, Example 1, after activation treatment, exhibited a uniform and dense passivation film with excellent adhesion. This verifies the necessity of the activation step—the activation solution composed of hydrochloric acid and hydrofluoric acid can effectively remove the oxide film on the zinc alloy surface, exposing the fresh metal substrate and providing the prerequisite for uniform growth of the passivation film. The absence of this step significantly reduces the bonding strength and protective performance between the passivation film and the substrate.

[0064] As can be seen from Examples 1-3 and Table 1, within the range of activation solution concentration defined in the claims, appropriately increasing the acid concentration can enhance the removal effect on the oxide film on the zinc alloy surface and promote a more complete passivation reaction. However, the concentration increase needs to be controlled within a reasonable range to avoid excessive corrosion of the substrate, which could lead to fluctuations in the film quality.

[0065] As can be seen from Examples 1, 4, and 5 and Table 1, within the concentration range defined in the claims, higher concentrations of metal salts can provide more sufficient film-forming ions, promoting a denser growth of the passivation film. However, the concentration must be controlled within the upper limit; otherwise, the reaction will be too fast due to excessively high ion concentration, resulting in a rough film layer.

[0066] Combining Examples 1 and 6, 7, and 8 with Table 1, it can be seen that Examples 6-8 used sodium dodecyl sulfate, hexadecyltrimethylammonium chloride, and ethylenediaminetetraacetic acid as surfactants, respectively. Compared with sodium dodecyl sulfate in Example 1, the passivation films in each group maintained a uniform gray appearance, and the adhesion was "good." The differences in wear resistance and corrosion resistance were within 5 cycles of friction and 10 hours of salt spray time. This indicates that the types of surfactants specified in claim 2 can effectively reduce the surface tension of the passivation solution and promote uniform film growth. Different types of surfactants have similar effects and can be selected according to actual production needs.

[0067] Combining Examples 1 and 9-11 with Table 1, it can be seen that in Examples 9-11, adding 0.5-1.5 g / L cerium nitrate to the passivation solution, compared with Example 1, improved the wear resistance of the passivation film to 60-65 cycles and extended the salt spray corrosion resistance time to 180-200 hours. Furthermore, the performance improvement was more significant with increasing cerium nitrate concentration. This indicates that the cerium element in cerium nitrate can synergistically work with the passivation film components to refine grains and fill pores, enhancing film density and thus significantly improving corrosion resistance and wear resistance.

[0068] Combining Examples 1 and 12-14 with Table 1, it can be seen that in Examples 12-14, adding 0.3-1.0 g / L sodium molybdate to the passivation solution resulted in a passivation film with a wear resistance of 60-63 cycles and a salt spray resistance of 185-195 hours, representing improvements of 9%-15% and 10%-16% respectively compared to Example 1. The optimal performance was observed at 1.0 g / L. This indicates that molybdenum in sodium molybdate can participate in the formation of the passivation film, enhancing its barrier ability against corrosive media. Within a concentration range of 0.3-1.0 g / L, this is beneficial for improving the protective performance of the passivation film.

[0069] Combining Examples 1 and 15-17 with Table 1, it can be seen that in Examples 15-17, the addition of 1-10 g / L nano-silica sol improved the wear resistance to 60-70 cycles and the corrosion resistance salt spray time to 170-185 hours compared to Example 1. Specifically, at 10 g / L, the wear resistance reached 70 cycles, approaching the supercritical treatment effect of Example 22. This indicates that nano-silica particles can fill the pores of the passivation film, increasing the film's hardness and density. Within the 1-10 g / L range, higher concentrations have a more significant effect on improving wear resistance and corrosion resistance. However, the difference in effect between 10 g / L and 5 g / L is relatively small, and the optimal concentration needs to be considered in light of overall cost.

[0070] Combining Examples 1 and 18-20 with Table 1, it can be seen that in Examples 18-20, the addition of 1-5 g / L tannic acid and 0.1-0.5 g / L chitosan quaternary ammonium salt resulted in: good passivation film adhesion, wear resistance of 62-65 cycles, and salt spray resistance of 185-190 hours, representing an improvement of 10%-13% compared to Example 1. The phenolic hydroxyl groups of tannic acid complex with metal ions, enhancing the film-substrate adhesion; the chitosan quaternary ammonium salt forms an additional protective film, possessing both antibacterial and corrosion-resistant properties. The synergistic effect of these two components further enhances the overall protective capability of the passivation film without compromising its appearance.

[0071] Combining Examples 1 and 21 with Table 1, it can be seen that in Example 21, replacing zinc dihydrogen phosphate with an equimolar amount of zinc hydroxyethylidene diphosphonate and adding a 1.5 g / L boric acid-citric acid buffer pair resulted in a wear resistance of 60 cycles (comparable to Example 1), but the corrosion resistance salt spray time increased to 190 h, an increase of 13%. This indicates that zinc hydroxyethylidene diphosphonate has a better corrosion-inhibiting complexing ability than zinc dihydrogen phosphate, and can more effectively inhibit zinc alloy corrosion. The boric acid-citric acid buffer pair stabilizes the pH value of the passivation solution, avoiding instability in film quality due to acid-base fluctuations. The combination of the two can significantly improve the corrosion resistance of the passivation film without changing the process complexity.

[0072] Combining Examples 1 and 22 with Table 1, it can be seen that Example 22, using supercritical carbon dioxide treatment, compared with the conventional passivation of Example 1, shortened the passivation time by 65%, achieved wear resistance of 70 cycles, and a salt spray corrosion resistance of 220 hours, while also exhibiting better film uniformity. This demonstrates that the high diffusivity and solubility of supercritical carbon dioxide can promote uniform penetration of the passivation solution components, accelerate the film formation reaction, and optimize the film structure. While significantly improving production efficiency, it also significantly enhances the wear resistance and corrosion resistance of the passivation film, meeting the application requirements under demanding working conditions.

[0073] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A gray passivation solution for zinc alloys, characterized in that, Its components include: nickel chloride hexahydrate 60-85 g / L, sodium thiocyanate 60-75 g / L, ammonium chloride 5-10 g / L, chromium nitrate nonahydrate 20-30 g / L, cobalt chloride hexahydrate 10-15 g / L, potassium dihydrogen phosphate 15-20 g / L, zinc dihydrogen phosphate 40-60 g / L, zinc nitrate solution 80-110 mL / L, manganese dihydrogen phosphate 20-30 g / L, and surfactant 0.05-0.2 g / L. The solvent of the gray passivation solution for zinc alloy is pure water, and the zinc nitrate solution contains 300 g / L of zinc nitrate.

2. The gray passivation solution for zinc alloys according to claim 1, characterized in that: The surfactant includes at least one of sodium dodecyl sulfate, sodium dodecyl sulfonate, hexadecyltrimethylammonium chloride, and ethylenediaminetetraacetic acid.

3. The gray passivation solution for zinc alloys according to claim 1, characterized in that: It also contains 0.5-1.5 g / L cerium nitrate or 0.3-1.0 g / L sodium molybdate.

4. The gray passivation solution for zinc alloys according to claim 1, characterized in that: It also includes 1-10 g / L of silica sol, wherein the silica sol has a particle size of 10-50 nm.

5. The gray passivation solution for zinc alloys according to claim 1, characterized in that: It also includes 1-5 g / L of tannic acid and 0.1-0.5 g / L of chitosan quaternary ammonium salt.

6. The gray passivation solution for zinc alloys according to claim 1, characterized in that: The zinc dihydrogen phosphate was replaced with an equimolar amount of zinc hydroxyethylidene diphosphonate, and a boric acid-citric acid buffer pair of 0.5-3 g / L was added.

7. A passivation method for zinc alloys using a gray passivating solution as described in any one of claims 1-6, characterized in that: Includes the following steps: Surface degreasing of zinc alloy workpieces; Prepare an activation solution by mixing 50-65 mL / L hydrochloric acid, 0.5-1 mL / L hydrofluoric acid, 0.02-0.05 g / L sodium dodecyl sulfate, and the remainder pure water. Immerse the zinc alloy workpiece in the activation solution for 10-60 seconds at a temperature of 10-40°C. After removal, rinse with pure water for 5-10 seconds. The activated zinc alloy workpiece is immersed in a gray passivation solution for 120-300 seconds at a temperature of 10-40℃. After passivation, the zinc alloy workpiece is removed, suspended and left to stand for 3-10 seconds, then washed with water for 5-10 seconds and dried to obtain a zinc alloy workpiece with a gray passivation film on its surface.

8. The passivation method for zinc alloys using a gray passivating solution according to claim 7, characterized in that: Includes the following steps: Surface degreasing of zinc alloy workpieces; Prepare an activation solution by mixing 50-65 mL / L hydrochloric acid, 0.5-1 mL / L hydrofluoric acid, 0.02-0.05 g / L sodium dodecyl sulfate, and the remainder pure water. Immerse the zinc alloy workpiece in the activation solution for 10-60 seconds at a temperature of 10-40°C. After removal, rinse with pure water for 5-10 seconds. The activated zinc alloy workpiece is placed in a high-pressure container, a passivation solution is injected and carbon dioxide is introduced, the temperature is maintained at 35-45℃, and the carbon dioxide is pressurized to reach a supercritical state for 60-80 seconds. After passivation, the zinc alloy workpiece is removed, suspended and left to stand for 3-10 seconds, then washed with water for 5-10 seconds and dried to obtain a zinc alloy workpiece with a gray passivation film on its surface.

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