Copper color passivation solution for zinc alloy as well as preparation method and passivation method of copper color passivation solution

Abstract

The invention relates to the technical field of metal surface treatment, in particular to a copper color passivation solution for zinc alloy and a preparation method and a passivation method of the copper color passivation solution. The copper color passivation solution for the zinc alloy comprises the following raw material components: 50-65 g / L of potassium dichromate, 5-15 g / L of cobalt nitrate, 3-10 g / L of manganese sulfate, 5-15 g / L of a buffering agent, 2-6 mL / L of sulfuric acid and the balance of water. According to the copper color passivation solution for the zinc alloy and the preparation method and the passivation method of the copper color passivation solution, the technological process is simplified, the production cost is reduced, the binding force, the abrasion resistance, the corrosion resistance and the antibacterial activity of a passivation film are remarkably improved, and the copper color passivation solution has wide application prospects. The copper color passivation solution for the zinc alloy is adopted for conducting passivation treatment on the surface of the zinc alloy, a layer of passivation film is formed on the surface of a zinc alloy workpiece, the passivation film has wiredrawing textures and uniform copper color, the visual effect is better, and the decoration performance of a product is improved.

Description

Technical Field

[0001] This application relates to the technical field of metal surface treatment, and in particular to a copper-colored passivation solution for zinc alloys, its preparation method, and passivation method. Background Technology

[0002] Zinc alloy die castings are widely used in construction, automotive, and other fields due to their excellent mechanical properties and low cost. However, when traditionally used with bronze-colored aluminum alloy doors and windows, zinc alloy die castings are often colored using painting or electroplating with black nickel. These processes have many problems, such as poor adhesion, complex processes, high costs, and environmental pollution from waste emissions.

[0003] While some research exists on zinc alloy surface treatment, most focuses on the preparation of simple passivation films. Research on copper-colored passivation films with special textures and good antibacterial properties is still in its early stages. For example, existing technologies disclose a non-toxic passivation solution for continuous zinc plating and its alloy coatings. Its main components include trivalent chromium salts, cobalt salts, and cerium salts, which can form a non-toxic and odorless passivation film on the zinc plating surface, but it does not address the preparation of copper-colored passivation films. Existing technologies also disclose a trivalent chromium high-corrosion-resistant blue-white passivating agent for zinc plating layers. Through specific formulations and processes, it improves the corrosion resistance and self-healing ability of the passivation film, but similarly, it does not address the preparation of copper-colored passivation films.

[0004] Therefore, exploring a passivation solution that can prepare a copper-colored passivation film with special texture on the surface of zinc alloy, while having good adhesion, wear resistance, corrosion resistance, and antibacterial properties, is of great significance for improving the decorative and practical properties of zinc alloy workpieces. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this application provides a copper-colored passivation solution for zinc alloys, its preparation method, and passivation method. This solution forms a copper-colored passivation film with a brushed texture on the surface of the zinc alloy workpiece. The passivation film has good adhesion to the zinc alloy, giving the zinc alloy excellent wear resistance, corrosion resistance, and antibacterial properties. This not only simplifies the process and reduces costs but also provides excellent decorative effects.

[0006] In a first aspect, this application provides a copper-colored passivation solution for zinc alloys, employing the following technical solution: A copper-colored passivation solution for zinc alloys comprises the following raw material components: potassium dichromate 50-65 g / L, cobalt nitrate 5-15 g / L, manganese sulfate 3-10 g / L, buffer 5-15 g / L, and sulfuric acid 2-6 mL / L, with the balance being water.

[0007] Preferably, the pH of the passivation solution is 1-1.5.

[0008] Preferably, the buffer includes at least one of boric acid and anhydrous citric acid.

[0009] By adopting the above technical solution, this application provides a copper-colored passivation solution for zinc alloys, based on a special passivation solution formulation. Potassium dichromate, as a strong oxidizing agent, can oxidize the zinc on the surface of the zinc alloy to generate zinc ions (Zn). 2+ and trivalent chromium ions Cr 3+ This redox reaction not only promotes the formation of the passivation film, but also generates a dense oxide film on the zinc alloy surface, providing a foundation for subsequent passivation film growth.

[0010] In the passivation film formed with the participation of potassium dichromate, Cr is also present. 6+ and Cr 3+ Compounds, through the synergistic effect of the two, Cr 6+ Promotes densification and improves membrane density; at the same time, Cr 3+ It can resist chemical corrosion, giving the formed passivation film long-term stability.

[0011] Cobalt nitrate and manganese sulfate dissociate into Co in solution. 2+ and Mn 2+ These metal ions undergo a complexation reaction with boric acid and sulfuric acid in the passivation solution to form stable complexes. These complexes can be uniformly distributed on the zinc alloy surface, further enhancing the adhesion and corrosion resistance of the passivation film.

[0012] The addition of sulfuric acid not only provides an acidic environment but also ensures that the various components in the passivation solution can react fully by adjusting the pH value of the solution. Under acidic conditions, the metal ions and complexes in the passivation film can be rapidly deposited on the zinc alloy surface to form a uniform passivation film. During the deposition process, the complexes preferentially align along a certain direction. As the reaction proceeds, the passivation film gradually solidifies, thus forming a copper-colored surface with a brushed texture on a macroscopic scale.

[0013] Under the combined action of buffers (such as boric acid and anhydrous citric acid) and sulfuric acid in the solution, due to the combined effects of factors such as solution concentration gradient, surface tension and stress changes, and differences in deposit growth rate, these factors interact and cause a certain degree of growth and contraction on the film surface at the microscopic level. This results in fine wrinkles in the passivation film during its formation. This microstructure not only further enhances the visual effect of the passivation film's brushed texture but also increases its surface area, further improving its corrosion resistance and decorative properties.

[0014] The copper color of the passivation film mainly comes from the Co in the passivation solution. 2+ and Mn 2+The complexation reaction of ions and the special structure formed by the passivation film during curing are key factors. These metal ions are uniformly distributed within the passivation film, resulting in a uniform copper color. Within a certain time range, the copper color gradually deepens with prolonged passivation time. This is because the chemical reaction in the passivation solution continues, allowing more metal ions to participate in the reaction and deposit on the zinc alloy surface, thus forming a thicker and darker passivation film. Simultaneously, the dwell time also affects the color depth. A longer dwell time allows more reactants to deposit and react on the surface, further deepening the color. Therefore, by precisely controlling the passivation time and dwell time, the color depth of the copper passivation film can be adjusted to meet different decorative and functional requirements.

[0015] In addition, the cobalt oxide (Co3O4 or CoO) component generated in the passivation film significantly inhibits bacterial growth and reproduction, reduces bacterial adhesion, and improves the antibacterial properties of the zinc alloy surface through mechanisms such as interfering with bacterial cell membrane function, generating reactive oxygen species, inhibiting enzyme activity, and changing bacterial physiological state. This makes it suitable for fields with high hygiene requirements.

[0016] In summary, through the aforementioned chemical reactions and physical processes, the copper-colored passivation solution for zinc alloys described in this application can form a copper-colored passivation film with a brushed texture on the surface of the zinc alloy. This passivation film exhibits excellent adhesion to the zinc alloy, and not only improves the wear resistance, corrosion resistance, and antibacterial properties of the zinc alloy, but also provides good decorative properties. Furthermore, the method described in this application simplifies the process flow, reduces production costs, and has broad application prospects.

[0017] Secondly, this application provides a method for preparing a copper-colored passivation solution for zinc alloys, comprising the following technical solution: a method for preparing a copper-colored passivation solution for zinc alloys, wherein the preparation method comprises the following steps: Weigh out each ingredient according to the formula; Potassium dichromate, cobalt nitrate, manganese sulfate, buffer, sulfuric acid, and water are mixed and the pH is adjusted to 1-1.5 to obtain a passivation solution.

[0018] Thirdly, this application provides a method for passivating the surface of a zinc alloy using a copper-colored passivation solution, employing the following technical solution: A method for passivating the surface of a zinc alloy using a copper-colored passivation solution, comprising the following steps: Degreasing treatment: Degreasing treatment is performed on the surface of zinc alloy workpieces; Activation treatment: The zinc alloy workpiece is immersed in an activation solution for activation; Passivation film formation: The activated zinc alloy workpiece is immersed in a copper-colored passivation solution for passivation, and a copper-colored conversion film is formed on the surface of the zinc alloy workpiece; Post-treatment: The passivated zinc alloy workpiece is left to stand in the air, then rinsed and dried to obtain a copper-colored passivation film with a brushed texture on the surface of the zinc alloy workpiece.

[0019] Preferably, the activation reaction temperature of the zinc alloy workpiece is 10-40℃, and the reaction time is 10-60 seconds.

[0020] Preferably, after activating the zinc alloy workpiece, it is rinsed with water for 5-10 seconds.

[0021] Preferably, the activation solution comprises the following raw material components: 50-65 mL / L hydrochloric acid, 0.5-1 mL / L hydrofluoric acid, and 0.02-0.05 g / L sodium dodecyl sulfate, with the balance being water.

[0022] Preferably, the passivation reaction temperature for the zinc alloy workpiece is 10-40℃, and the reaction time is 30-420 seconds.

[0023] Preferably, the passivated zinc alloy workpiece is left to stand in the air for 30-300 seconds.

[0024] In one specific implementation scheme, a method for passivating the surface of a zinc alloy using a copper-colored passivation solution is provided, the passivation method comprising the following steps: (1) Degreasing treatment: Use a soft brush and detergent to mechanically brush the surface of the zinc alloy workpiece for 30-60 seconds, then rinse with pure water for 5-10 seconds. (2) Activation treatment: Immerse the zinc alloy workpiece in the activation solution and treat it at 10-40℃ for 10-60 seconds. After treatment, rinse it with pure water for 5-10 seconds. This step effectively removes the oxide layer on the surface of the zinc alloy workpiece and enhances the activity of the substrate. (3) Passivation film formation: The activated zinc alloy workpiece is immersed in copper-colored passivation solution and reacted at 10-40℃ for 30-420 seconds to form a uniform copper-colored conversion film on the surface. (4) Color control: After passivation, the zinc alloy workpiece is left to stand in the air for 30-300 seconds to achieve color control of the film layer; (5) Post-treatment: After rinsing the zinc alloy workpiece with pure water for 5-10 seconds, dry it with hot air to obtain a copper-colored passivation film with a brushed texture on the surface of the zinc alloy workpiece.

[0025] In summary, this application includes at least one of the following beneficial technical effects: This application discloses a copper-colored passivation liquid for zinc alloys, its preparation method and passivation method. Through chemical passivation treatment, a copper-colored passivation film is formed in one step, which simplifies the process and reduces production costs. The zinc alloy surface is passivated by using a copper-colored passivation solution for zinc alloys according to this application, forming a passivation film on the surface of the zinc alloy workpiece. The passivation film has a brushed texture and a uniform copper color, resulting in a better visual effect and enhancing the decorative properties of the product. This application achieves the preparation of a brushed texture and copper-colored passivation film through specific formulation and process conditions, filling a gap in this field; The passivation film prepared by the method of this application has good adhesion, wear resistance, corrosion resistance, and antibacterial properties, as well as good decorative properties, and has broad application prospects. The cobalt oxide in the passivation film of this application inhibits bacterial growth and reduces bacterial adhesion through multiple mechanisms, exhibiting excellent antibacterial properties and making it suitable for fields with high hygiene requirements. Attached Figure Description

[0026] Figure 1 Image of the passivation film sample prepared in Example 1; Figure 2 Image of the passivation film sample prepared in Example 2; Figure 3 This is a diagram of the passivation film sample prepared in Example 3. Detailed Implementation

[0027] The technical solutions of this application are further illustrated by specific embodiments below. These specific embodiments do not represent a limitation on the scope of protection of this application. Any non-essential modifications and adjustments made by others based on the concept of this application still fall within the scope of protection of this application.

[0028] All raw materials involved in this application are commercially available products. The following detailed description of this application is provided in conjunction with examples and comparative examples.

[0029] Example 1: A method for preparing a brushed textured copper-colored passivation film on a zinc alloy surface includes the following steps: (1) preparing a passivation solution: Take 55 g / L potassium dichromate, 8 g / L cobalt nitrate, 5 g / L manganese sulfate, 10 g / L boric acid, and 4 mL / L sulfuric acid, dissolve them in pure water and adjust the pH to 1.2 to obtain a passivation solution; (2) Prepare the activation solution; Take 55 mL / L hydrochloric acid, 0.8 mL / L hydrofluoric acid, and 0.03 g / L sodium dodecyl sulfate, dissolve them in pure water to obtain an activation solution; (3) Degreasing treatment: The surface of the zinc alloy workpiece is mechanically brushed for 45 seconds with a soft brush and detergent, and then rinsed with pure water for 8 seconds to remove dust and grease from the workpiece surface. (4) Activation treatment: The zinc alloy workpiece is immersed in the activation solution and treated at 25°C for 30 seconds, then rinsed with pure water for 8 seconds. (5) Passivation film formation: The activated workpiece is immersed in the passivation solution and treated at 25°C for 180 seconds. (6) Post-processing: After passivating, the zinc alloy workpiece is left to stand in air for 35 seconds, then rinsed with pure water for 8 seconds and dried with hot air. This forms a copper-colored passivation film with a brushed texture on the surface of the zinc alloy workpiece. The passivation film is like... Figure 1 As shown.

[0030] Example 2: A method for preparing a brushed textured copper-colored passivation film on a zinc alloy surface includes the following steps: (1) Preparation of passivation solution: Take 60 g / L potassium dichromate, 12 g / L cobalt nitrate, 8 g / L manganese sulfate, 12 g / L boric acid, and 5 mL / L sulfuric acid, dissolve them in pure water, and adjust the pH to 1.3. (2) Prepare the activation solution; Take 60 mL / L hydrochloric acid, 0.9 mL / L hydrofluoric acid, and 0.04 g / L sodium dodecyl sulfate, dissolve them in pure water to obtain an activation solution; (3) Degreasing treatment: The surface of the zinc alloy workpiece is mechanically brushed for 50 seconds with a soft brush and detergent, and then rinsed with pure water for 10 seconds to remove dust and grease from the workpiece surface. (4) Activation treatment: Immerse the zinc alloy workpiece in the activation solution, treat it at 30°C for 45 seconds, and rinse it with pure water for 10 seconds. (5) Passivation film formation: The activated workpiece is immersed in the passivation solution and treated at 30°C for 300 seconds. (6) Post-processing: After the passivated zinc alloy workpiece is left to stand in air for 40 seconds, it is rinsed with pure water for 10 seconds and dried with hot air. This forms a copper-colored passivation film with a brushed texture on the surface of the zinc alloy workpiece. The passivation film is like... Figure 2 As shown.

[0031] Example 3: A method for preparing a brushed textured copper-colored passivation film on a zinc alloy surface includes the following steps: (1) preparing a passivation solution: Take 50 g / L potassium dichromate, 5 g / L cobalt nitrate, 3 g / L manganese sulfate, 10 g / L boric acid, and 2 mL / L sulfuric acid, dissolve them in pure water and adjust the pH to 1.0 to obtain a passivation solution; (2) Prepare the activation solution; Dissolve 50 mL / L hydrochloric acid, 0.5 mL / L hydrofluoric acid, and 0.02 g / L sodium dodecyl sulfate in pure water to obtain an activation solution. (3) Degreasing treatment: The surface of the zinc alloy workpiece is mechanically brushed for 30 seconds with a soft brush and detergent, and then rinsed with pure water for 5 seconds to remove dust and grease from the workpiece surface. (4) Activation treatment: Immerse the zinc alloy workpiece in the activation solution, treat it at 10°C for 10 seconds, and rinse it with pure water for 5 seconds. (5) Passivation film formation: The activated workpiece is immersed in the passivation solution and treated at 10°C for 420 seconds. (6) Post-processing: After passivating, the zinc alloy workpiece is left to stand in air for 50 seconds, then rinsed with pure water for 5 seconds and dried with hot air. This forms a copper-colored passivation film with a brushed texture on the surface of the zinc alloy workpiece. The passivation film is as follows: Figure 3 As shown.

[0032] Example 4: A method for preparing a brushed textured copper-colored passivation film on a zinc alloy surface, comprising the following steps: (1) Preparation of passivation solution: Take 55 g / L potassium dichromate, 8 g / L cobalt nitrate, 5 g / L manganese sulfate, 5 g / L boric acid, and 4 mL / L sulfuric acid, dissolve them in pure water and adjust the pH to 1.4 to obtain a passivation solution; (2) Prepare the activation solution; Take 60 mL / L hydrochloric acid, 0.7 mL / L hydrofluoric acid, and 0.04 g / L sodium dodecyl sulfate, dissolve them in pure water to obtain an activation solution; (3) Degreasing treatment: The surface of the zinc alloy workpiece is mechanically brushed for 50 seconds with a soft brush and detergent, and then rinsed with pure water for 7 seconds to remove dust and grease from the workpiece surface. (4) Activation treatment: Immerse the zinc alloy workpiece in the activation solution, treat it at 30°C for 35 seconds, and rinse it with pure water for 7 seconds; (5) Passivation film formation: The activated workpiece is immersed in the passivation solution and treated at 35°C for 100 seconds. (6) Post-processing: After the passivated zinc alloy workpiece is left to stand in the air for 60 seconds, it is rinsed with pure water for 8 seconds and dried with hot air to form a copper-colored passivation film with a brushed texture on the surface of the zinc alloy workpiece.

[0033] Example 5: A method for preparing a brushed textured copper-colored passivation film on a zinc alloy surface, comprising the following steps: (1) Preparation of passivation solution: Take 65 g / L potassium dichromate, 15 g / L cobalt nitrate, 10 g / L manganese sulfate, 15 g / L boric acid, and 6 mL / L sulfuric acid, dissolve them in pure water and adjust the pH to 1.5 to obtain a passivation solution; (2) Prepare the activation solution; Take 65 mL / L hydrochloric acid, 1 mL / L hydrofluoric acid, and 0.05 g / L sodium dodecyl sulfate, dissolve them in pure water to obtain an activation solution; (3) Degreasing treatment: The surface of the zinc alloy workpiece is mechanically brushed for 60 seconds with a soft brush and detergent, and then rinsed with pure water for 10 seconds to remove dust and grease from the workpiece surface. (4) Activation treatment: (5) Passivation film formation: Immerse the activated workpiece in the activation solution and treat it at 40°C for 60 seconds, then rinse it with pure water for 10 seconds; (6) Post-treatment: After the passivated zinc alloy workpiece is left to stand in the air for 70 seconds, it is rinsed with pure water for 10 seconds and dried with hot air to form a copper-colored passivation film with a brushed texture on the surface of the zinc alloy workpiece.

[0034] Example 6: The difference from Example 1 is that boric acid is replaced with anhydrous citric acid.

[0035] Comparative Example 1: The difference from Example 1 is that the amount of raw materials added to the passivation solution is different.

[0036] The passivation solution consists of: 49 g / L potassium dichromate, 4 g / L cobalt nitrate, 2 g / L manganese sulfate, 4 g / L boric acid, 1 mL / L sulfuric acid, and the remainder is water.

[0037] Comparative Example 2: The difference from Example 1 is that the amount of raw materials added to the passivation solution is different.

[0038] The passivation solution consists of: 66 g / L potassium dichromate, 16 g / L cobalt nitrate, 11 g / L manganese sulfate, 16 g / L boric acid, 7 mL / L sulfuric acid, and the remainder is water.

[0039] Comparative Example 3: The difference from Example 1 is that potassium dichromate is replaced with sodium dichromate.

[0040] Comparative Example 4: The difference from Example 1 is that cobalt nitrate is replaced with cobalt sulfate heptahydrate.

[0041] Comparative Example 5: The difference from Example 1 is that cobalt nitrate is replaced with cobalt chloride hexahydrate.

[0042] Comparative Example 6: The difference from Example 1 is that manganese sulfate is replaced with hydrated manganese chloride.

[0043] Comparative Example 7: The difference from Example 1 is that manganese sulfate is replaced with hydrated manganese nitrate.

[0044] Performance testing: The performance of the brushed copper-colored passivation film on the zinc alloy surface prepared using the processes described in the above embodiments and comparative examples was tested: Appearance: Refer to the direct visual inspection method in GB / T 20967-2007 standard. Under ambient light conditions of >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.

[0045] Adhesion: Referring to GB / T 9791-2003, the surface of the passivation film is wiped 10 times with a pressure of 200g using rapid qualitative filter paper. If there is no obvious staining on the white paper after wiping and no trace of exposed base metal, the adhesion of the passivation film is considered to be good. A little powder falling off is considered to have average adhesion, and a lot of obvious powder falling off is considered to have poor adhesion.

[0046] Wear resistance: The ZJ-339-JSR abrasion tester was used, with particle-free rubber as the friction head. A load of 200g was applied, and the zinc alloy sheet was fixed on the tester. The passivation film surface was subjected to friction test. One reciprocating motion was counted as one cycle. The number of friction cycles when wear occurred was detected.

[0047] Corrosion resistance: Neutral salt spray test (NSS test) was conducted according to GB / T 10125-2012 standard. The test was conducted at 35℃, with 5% NaCl solution and pH 6.5-7.2, and continuous spraying was performed to detect the time it took for corrosion spots to appear on the passivation film.

[0048] Antibacterial Properties: The antibacterial properties of the copper-colored passivation film on the surface of zinc alloy were tested according to ISO 22196-2011 standard. Samples were prepared in 50mm × 50mm sizes, with untreated zinc alloy used as a blank control. Staphylococcus aureus (ATCC 6538) and Escherichia coli (ATCC 25922) were selected as test strains, and the bacterial concentration was adjusted to 1.0 × 10⁻⁶. 5 ~5.0×10 5 CFU / mL. The experiment used the film coating method, in which 0.4 mL of bacterial solution was evenly coated on the sample surface, covered with a sterile polyethylene film, and incubated at 37℃ and 90% RH for 24 hours; after elution, the viable bacteria count was determined by plate counting method, and the inhibition rate was calculated.

[0049] Table 1 Performance Test Results As shown in Table 1, the passivation films prepared by the method of this application in Examples 1-6 not only significantly improve the adhesion, wear resistance and corrosion resistance of the passivation film, but also endow it with good antibacterial properties; the passivation solution forms a passivation film on the surface of the zinc alloy workpiece, and the passivation film has a brushed texture and uniform copper color, which has good decorative properties.

[0050] Based on the test results of Example 1, Comparative Example 1, and Comparative Example 2, it can be seen that by limiting the specific formula, the amount of each formula added, and the process conditions, this application has achieved the preparation of a copper-colored passivation film with a brushed texture, which significantly improves the adhesion, wear resistance, corrosion resistance, antibacterial properties, and decorative properties of the passivation film.

[0051] Based on the test results of Example 1 and Comparative Example 3, it can be seen that the test results of appearance, adhesion, wear resistance, corrosion resistance and antibacterial properties of Example 1 are all better than those of Comparative Example 3. This indicates that the added potassium dichromate and other raw materials have a synergistic effect, which not only promotes the formation of the passivation film, but also generates a dense oxide film on the zinc alloy surface, realizing the preparation of a copper-colored passivation film with a brushed texture. This significantly improves the adhesion, wear resistance, corrosion resistance, antibacterial properties and decorative properties of the passivation film.

[0052] Based on the test results of Example 1, Comparative Example 4, and Comparative Example 5, it can be seen that the test results of appearance, adhesion, wear resistance, corrosion resistance, and antibacterial properties of Example 1 are all better than those of Comparative Example 4 and Comparative Example 5. This indicates that the added cobalt nitrate and other raw materials work synergistically to achieve the preparation of a copper-colored passivation film with a brushed texture, which significantly improves the adhesion, wear resistance, corrosion resistance, antibacterial properties, and decorative properties of the passivation film.

[0053] Based on the test results of Example 1, Comparative Example 6, and Comparative Example 7, it can be seen that the test results of appearance, adhesion, wear resistance, corrosion resistance, and antibacterial properties of Example 1 are all better than those of Comparative Example 6 and Comparative Example 7. This indicates that the added manganese sulfate and other raw materials work synergistically to achieve the preparation of a copper-colored passivation film with a brushed texture, which significantly improves the adhesion, wear resistance, corrosion resistance, antibacterial properties, and decorative properties of the passivation film.

[0054] Example 7: To verify the effect of the passivation reaction time on the passivation film performance when zinc alloy workpieces are immersed in passivation solution for passivation, the reaction time of the passivation treatment in Example 1 was adjusted. Under the condition that other reaction conditions remain unchanged, the effect of different passivation treatment reaction times on the passivation film performance is shown in the table below.

[0055] Table 2. Effect of passivation time on passivation film performance As shown in the table above, the passivation time has a certain impact on the appearance, adhesion, wear resistance, corrosion resistance and antibacterial rate of the passivation film. When the passivation time is short, the reaction between the zinc alloy and the passivation solution is not fully carried out, which will lead to uneven distribution of film components, obvious color difference or spots, and a significant decrease in the adhesion, wear resistance, corrosion resistance and antibacterial rate of the passivation film.

[0056] When the passivation time is too long, the reaction time exceeds the critical value, and the film enters the aging stage, which triggers microcracks and extends to the zinc alloy substrate, causing the film to "micro-debond" from the zinc alloy substrate. This results in uneven distribution of film composition, obvious color difference or spots, and a significant decrease in the adhesion, wear resistance, corrosion resistance and antibacterial rate of the passivation film.

[0057] Therefore, when the passivation time is 30-420, the passivation film exhibits the best adhesion, wear resistance, corrosion resistance, and antibacterial rate. The passivation solution forms a passivation film on the surface of the zinc alloy workpiece. The passivation film has a brushed texture and a uniform copper color, and the color of the passivation film gradually deepens with the increase of the passivation time.

[0058] Example 8: To verify the effect of the settling time on the passivation film performance when the passivated zinc alloy workpiece is left to stand in air, the settling time in Example 1 was adjusted. The effect of different settling times on the passivation film performance is shown in the table below, with other reaction conditions remaining unchanged.

[0059] Table 3. Effect of settling time on passivation film performance As shown in the table above, the settling time has a certain impact on the appearance, adhesion, wear resistance, corrosion resistance and antibacterial rate of the passivation film. When the settling time is too short, the film layer cannot be cured and densified, which will lead to uneven distribution of film layer components, obvious color difference or spots, and a significant decrease in the adhesion, wear resistance, corrosion resistance and antibacterial rate of the passivation film.

[0060] When left to stand for a long time, the moisture in the film layer evaporates completely, and the film layer gradually dries, which causes the film layer to age. The film layer and the zinc alloy substrate "micro-detach" and the film layer performance deteriorates, which leads to uneven distribution of film layer components, obvious color difference or spots, and a significant decrease in the adhesion, wear resistance, corrosion resistance and antibacterial rate of the passivation film.

[0061] Therefore, when the settling time is 30-300 seconds, the bonding force between the passivation film and the zinc alloy is optimal, and the passivation film prepared has the best wear resistance, corrosion resistance and antibacterial effect. The passivation solution forms a passivation film on the surface of the zinc alloy workpiece. The passivation film has a brushed texture and a uniform copper color. And as the settling time increases, the color of the passivation film gradually deepens.

[0062] Example 8: To verify the effect of the pH value of the passivation solution on the performance of the passivation film, the pH value of the passivation solution in Example 1 was adjusted. Under the condition that other reaction conditions remained unchanged, the effect of the pH value of different passivation solutions on the performance of the passivation film is shown in the table below.

[0063] Table 4. Effect of pH value on passivation film performance As shown in the table above, the pH value has a certain impact on the uniformity of the copper-colored passivation film formed on the zinc alloy surface. When the pH is 1-1.5, it can balance the metal dissolution and complexation reaction, ensuring that the various components in the passivation solution can react fully, thereby promoting the formation of the passivation film and ultimately presenting a uniform copper color. If the pH deviates from this range, it will lead to uneven distribution of film components, obvious color difference or spots, and the adhesion, wear resistance, corrosion resistance and antibacterial rate of the passivation film will decrease significantly.

[0064] This application discloses a copper-colored passivation solution for zinc alloys, its preparation method, and passivation method. Through chemical passivation treatment, a copper-colored passivation film is formed in one step, simplifying the process and reducing production costs. By using the copper-colored passivation solution for zinc alloys of this application to passivate the surface of zinc alloys, a passivation film is formed on the surface of the zinc alloy workpiece. The passivation film has a brushed texture and a uniform copper color, resulting in a better visual effect and enhancing the decorative properties of the product.

Claims

1. A copper-colored passivation solution for zinc alloys, characterized in that: It includes the following raw material components: potassium dichromate 50-65 g / L, cobalt nitrate 5-15 g / L, manganese sulfate 3-10 g / L, buffer 5-15 g / L and sulfuric acid 2-6 mL / L, with the balance being water.

2. The copper-colored passivating solution for zinc alloys according to claim 1, characterized in that: The passivation solution has a pH of 1-1.

5.

3. The copper-colored passivation solution for zinc alloys according to claim 1, characterized in that: The buffer includes at least one of boric acid and anhydrous citric acid.

4. A method for preparing the copper-colored passivation solution for zinc alloys according to any one of claims 1-3, characterized in that: The preparation method steps are as follows: Weigh out each ingredient according to the formula; Potassium dichromate, cobalt nitrate, manganese sulfate, buffer, sulfuric acid, and water are mixed and the pH is adjusted to 1-1.5 to obtain a passivation solution.

5. A method for passivating the surface of a zinc alloy using the copper-colored passivating solution for zinc alloys as described in any one of claims 1-3, characterized in that, The passivation method involves the following steps: Degreasing treatment is performed on the surface of zinc alloy workpieces; The zinc alloy workpiece is activated by immersing it in an activation solution. The activated zinc alloy workpiece is immersed in a copper-colored passivation solution for passivation. After the passivated zinc alloy workpiece is left to stand in the air, it is rinsed and dried to obtain a copper-colored passivation film with a brushed texture on the surface of the zinc alloy workpiece.

6. The passivation method according to claim 5, characterized in that: The activation reaction temperature for the zinc alloy workpiece is 10-40℃, and the reaction time is 10-60 seconds.

7. The passivation method according to claim 5, characterized in that: After activating the zinc alloy workpiece, rinse it with water for 5-10 seconds.

8. The passivation method according to claim 5, characterized in that: The activation solution comprises the following raw material components: 50-65 mL / L hydrochloric acid, 0.5-1 mL / L hydrofluoric acid, and 0.02-0.05 g / L sodium dodecyl sulfate, with the balance being water.

9. The passivation method according to claim 5, characterized in that: The passivation reaction temperature for the zinc alloy workpiece is 10-40℃, and the reaction time is 30-420 seconds.

10. The passivation method according to claim 5, characterized in that: The passivated zinc alloy workpiece is left to stand in the air for 30-300 seconds.

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