Chromium-free black passivation solution for zinc alloy and passivation method

Abstract

The invention discloses a chromium-free black passivation solution for a zinc alloy. The chromium-free black passivation solution comprises the following components in percentage by mass: 5-10% of nickel ammonium sulfate, 2-6% of sodium thiocyanate, 0.2-1% of ammonium chloride, 0.02-0.1% of a surfactant, 0.1-0.5% of other additives and the balance of water. The invention further discloses a zinc alloy passivation treatment method. Compared with the prior art, a uniform matte black film layer can be obtained and has certain decorativeness, good binding force and good corrosion resistance after the neutral salt mist time is 60 h, the service life of zinc alloy is effectively prolonged, and the problem of environmental pollution is effectively avoided through a chromium-free formula.

Description

Technical Field

[0001] The invention belongs to the technical field of metal surface treatment, and in particular relates to a chromium-free black passivation solution for zinc alloy and a passivation method. Background Art

[0002] As an efficient means of metal surface coloring, zinc alloy passivation technology has been widely used in industrial production due to its simplicity of process steps and relatively low cost. However, the traditional hexavalent chromium passivation process, although relatively mature in technology, faces severe environmental challenges due to the high toxicity of hexavalent chromium, especially due to the strict restrictions of relevant regulations such as the European Union, and its application prospects are increasingly limited. On the other hand, as an alternative, trivalent chromium passivation technology reduces the toxicity risk to a certain extent, but in actual application, over time, the trivalent chromium passivation film tends to transform into hexavalent chromium, which not only affects the stability and durability of the passivation layer, but also may reintroduce toxicity problems, thereby limiting its long-term application effect. In view of this, the development of a chromium-free passivating agent that can effectively avoid the environmental and health risks brought by hexavalent chromium and ensure the stability and performance of the passivation film is of great significance to the innovation and progress of zinc alloy surface treatment technology. At present, there are few reports on relevant examples of chromium-free passivation technology for zinc alloys.

[0003] Chinese patent (CN200710146228.1) discloses a chromium-free passivation treatment solution for zinc alloy die castings, the main components of which are water-soluble yttrium salt, metavanadate, organic acid and oxidant, etc. The appearance of the obtained passivation film is blue, and corrosion occurs after 8 hours of salt spray.

[0004] A Chinese patent (CN 107090576A) discloses a chromium-free passivation solution for zinc alloys, the main components of which are sodium molybdate, titanium sulfate, hydrogen peroxide, etc. The acid salt spray time of the obtained passivation film is 16 hours. The color of the passivation film is not described, so the decorative effect cannot be evaluated. In addition, hydrogen peroxide is used in the formula, which is easy to decompose, so in actual use, it may affect the stability of the passivation effect.

[0005] In order to overcome the problems of poor environmental protection, low decorative properties and general corrosion resistance of the above passivation technologies, the present invention provides a chromium-free black passivation solution for zinc alloy and a passivation method. Summary of the invention

[0006] The purpose of the present invention is to provide a chromium-free black passivation liquid and a passivation method for zinc alloy, which have good passivation effect, can obtain a uniform matte black passivation film, have certain decorative properties, have good bonding strength between the film layer and the substrate, have good corrosion resistance, effectively extend the service life of the zinc alloy, and the chromium-free formula effectively avoids environmental pollution problems.

[0007] To this end, on the one hand, the present invention provides a chromium-free black passivation solution for zinc alloy, comprising the following components, calculated by mass percentage:

[0008] Ammonium nickel sulfate 5-10%, sodium thiocyanate 2-6%, ammonium chloride 0.2-1%, surfactant 0.02-0.1%, other additives 0.1-0.5% and the balance water.

[0009] As a further description of the above technical solution:

[0010] The surfactant is at least one of sodium dodecyl sulfate, sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, hexadecyltrimethylammonium chloride or ethylenediaminetetraacetic acid.

[0011] As a further description of the above technical solution:

[0012] The other additives are at least one of quick-dissolving sodium silicate, sodium metasilicate or fumed silica.

[0013] On the other hand, the present invention also provides a method for zinc alloy passivation treatment, comprising the following steps:

[0014] 1) dissolving ammonium nickel sulfate in 50% volume of pure water, adding sodium thiocyanate while stirring, and after the sodium thiocyanate is completely dissolved, adding ammonium chloride and stirring until the sodium thiocyanate is completely dissolved to obtain solution A;

[0015] 2) Dissolve the surfactant in 5% volume of pure water and stir until fully dissolved to obtain solution B;

[0016] 3) dissolving the additive in 5% volume of pure water, stirring to fully disperse it, and obtaining liquid C;

[0017] 4) Transfer liquid B and liquid C to liquid A respectively during stirring, add the remaining water and stir, and ultrasonicate for 15 minutes to obtain a passivation solution; wherein the mass ratio of the ammonium nickel sulfate, sodium thiocyanate, ammonium chloride, surfactant and other additives is (5-10%): (2-6%): (0.2-1%): (0.02-0.1%): (0.1-0.5%);

[0018] 5) immersing the zinc alloy workpiece in the passivation solution to perform a passivation operation to form a passivation film on the surface of the zinc alloy workpiece, wherein the zinc alloy workpiece and the passivation film together constitute a zinc alloy passivation semi-finished product;

[0019] 6) Drying the zinc alloy passivation semi-finished product with hot air to obtain a zinc alloy passivation finished product.

[0020] As a further description of the above technical solution:

[0021] The passivation operation temperature in step 5) is 10-40° C., and the operation time of the passivation operation is 1-10 min.

[0022] As a further description of the above technical solution:

[0023] Before the zinc alloy workpiece is immersed in the passivation solution, the zinc alloy workpiece is immersed in an activating agent for activation.

[0024] As a further description of the above technical solution:

[0025] The activator includes the following components in mass percentage (20-50%): (0.5-2%): (0.04-1%). Specifically, before the zinc alloy workpiece is immersed in the passivating agent, hydrochloric acid, hydrofluoric acid and sodium dodecyl sulfate are stirred to mix the components evenly to obtain the activator, and the zinc alloy workpiece is immersed in the activator to perform the activation operation.

[0026] As a further description of the above technical solution:

[0027] Before immersing the zinc alloy workpiece in the activator, the surface of the zinc alloy workpiece is scrubbed with a decontamination liquid to perform a degreasing operation.

[0028] As a further description of the above technical solution:

[0029] Before degreasing the zinc alloy workpiece, the surface of the zinc alloy workpiece is polished with 600-grit sandpaper until the texture is uniform and the oxide scale is removed. At the same time, the uniform polishing texture is conducive to the uniform formation of the passivation film.

[0030] As a further description of the above technical solution:

[0031] The degreasing operation temperature is 10-40°C, and the degreasing operation time is 1-5 minutes; or the activation operation temperature is 10-35°C, and the activation operation time is 0.5-2 minutes; the zinc alloy workpiece needs to be rinsed with pure water for 5-10 seconds before activation, passivation and hot air drying.

[0032] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0033] In the present invention, ammonium nickel sulfate is used as a film-forming agent to provide a nickel source and a sulfur source for generating black nickel sulfide / nickel oxide, and sodium thiocyanate can be used as an oxidant and a complexing agent at the same time to promote the corrosion of the zinc matrix, release thiocyanate and metal ion complexation, stabilize the passivation solution, and provide a nickel source for generating nickel sulfide, which is an important factor for generating a black film layer. At the same time, since ammonium chloride is soluble in water, ammonium ions are hydrolyzed to generate ammonia water and hydrogen ions, so ammonium chloride can stabilize the pH of the passivation solution, and the surfactant in the passivation solution can reduce the surface tension, increase the wetting effect of the passivation solution, and be conducive to the uniform generation of the passivation film, providing the necessary conditions for the thickness and color uniformity of the film layer. Further, in the process of matrix dissolution and film layer deposition, the silicon oxide particles provided by the additive are dispersed and deposited in the pores of the film layer, and due to the characteristics of silicon oxide and the leveling effect on the microscopic surface of the film layer, the corrosion resistance and wear resistance of the passivation film are greatly improved, and this filling effect can cause a matte effect, so a uniform and dense matte black passivation film with good corrosion resistance can be obtained. Currently, there are very few examples of chrome-free black passivation. The chrome-free black passivation solution and passivation method for zinc alloy disclosed in the present invention are environmentally friendly, highly decorative, and easy to use, providing a new idea for chrome-free black passivation of zinc alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a photo of the zinc alloy chromium-free black passivation film prepared in Example 1. DETAILED DESCRIPTION

[0035] The specific embodiments of the present invention are further described below. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0036] Embodiment 1:

[0037] A chromium-free black passivation solution for zinc alloys comprises the following components, calculated by mass percentage: 6% ammonium nickel sulfate, 3% sodium thiocyanate, 0.2% ammonium chloride, 0.02% sodium dodecyl sulfate, 0.5% sodium metasilicate and the remainder water.

[0038] Ammonium nickel sulfate was dissolved in 50% pure water, sodium thiocyanate was added and stirred to dissolve, and then ammonium chloride was added and stirred to dissolve to obtain liquid A. Sodium dodecyl sulfate was dissolved in 5% pure water to obtain liquid B, and sodium metasilicate was dissolved in 5% pure water to obtain liquid C. During the stirring process, liquid B and liquid C were added to liquid A respectively, and the passivation solution was obtained by stirring / ultrasonication for 15 minutes after adding the excess water.

[0039] Passivation process:

[0040] (1) Grinding: Use 600-grit sandpaper to grind the surface of the zinc alloy workpiece until the texture is uniform;

[0041] (2) Degreasing: For the surface of zinc alloy workpiece, use 30℃ degreasing liquid and soft brush to scrub for 5 minutes;

[0042] (3) Cleaning: Rinse the surface of the zinc alloy workpiece with pure water at room temperature for 5 seconds;

[0043] (4) Activation: Weigh or measure hydrochloric acid, hydrofluoric acid, and sodium dodecyl sulfate in a mass ratio of 25:2:1, stir to mix the components evenly, and obtain an activator. Vertically suspend the zinc alloy workpiece and immerse it in the activation solution. The immersion time is 30 seconds, and the temperature of the activation solution is 15°C.

[0044] (5) Cleaning: Rinse the surface of the zinc alloy workpiece with pure water at room temperature for 5 seconds;

[0045] (6) Passivation: The zinc alloy workpiece is suspended vertically and immersed in the passivation solution for 5 min at a temperature of 40°C.

[0046] (7) Cleaning: Rinse the surface of the zinc alloy workpiece with pure water at room temperature for 10 seconds;

[0047] (8) Drying: Use hot air to dry the residual moisture on the working surface of the zinc alloy to obtain a uniform matte black passivation film.

[0048] The black passivation sample prepared in this embodiment is photographed. Figure 1 As shown, the passivation film is uniform matte black and the film layer is complete.

[0049] Embodiment 2:

[0050] A chromium-free black passivation solution for zinc alloys comprises the following components, measured by mass percentage: 10% ammonium nickel sulfate, 2% sodium thiocyanate, 0.6% ammonium chloride, 0.07% sodium dodecylbenzene sulfonate, 0.1% fumed silicon dioxide and the remainder water.

[0051] Ammonium nickel sulfate was dissolved in 50% pure water, sodium thiocyanate was added and stirred to dissolve, and then ammonium chloride was added and stirred to dissolve to obtain liquid A. Sodium dodecylbenzene sulfonate was dissolved in 5% pure water to obtain liquid B, and fumed silica was dissolved in 5% pure water to obtain liquid C. During the stirring process, liquid B and liquid C were added to liquid A respectively, and the remaining amount of water was added and stirred / ultrasonicated for 15 minutes to obtain the passivation solution.

[0052] Passivation process:

[0053] (1) Grinding: Use 600-grit sandpaper to grind the surface of the zinc alloy workpiece until the texture is uniform;

[0054] (2) Degreasing: For the surface of zinc alloy workpiece, use 20℃ degreasing liquid and soft brush to scrub for 2 minutes;

[0055] (3) Cleaning: Rinse the surface of the zinc alloy workpiece with pure water at room temperature for 7 seconds;

[0056] (4) Activation: Weigh or measure hydrochloric acid, hydrofluoric acid, and sodium dodecyl sulfate in a mass ratio of 50:1:0.07, stir to mix the components evenly, and obtain an activator. Vertically hang the zinc alloy workpiece and immerse it in the activation solution. The immersion time is 1 min, and the temperature of the activation solution is 10°C.

[0057] (5) Cleaning: Rinse the surface of the zinc alloy workpiece with pure water at room temperature for 5 seconds;

[0058] (6) Passivation: The zinc alloy workpiece is suspended vertically and immersed in the passivation solution for 2 min at a temperature of 30 °C.

[0059] (7) Cleaning: Rinse the surface of the zinc alloy workpiece with pure water at room temperature for 8 seconds;

[0060] (8) Drying: Use hot air to dry the residual moisture on the working surface of the zinc alloy to obtain a uniform matte black passivation film.

[0061] After the black passivation sample prepared in this embodiment was left to age naturally for 24 hours, a salt spray test was performed. According to the salt spray test of artificial atmosphere corrosion test in GB / T 10125-2012, white rust appeared when the neutral salt spray time reached 60 hours.

[0062] Embodiment 3:

[0063] A chromium-free black passivation solution for zinc alloy comprises the following components, calculated by mass percentage: 8% ammonium nickel sulfate, 5% sodium thiocyanate, 0.5% ammonium chloride, 0.04% hexadecyltrimethylammonium chloride, 0.3% sodium metasilicate and the remainder water.

[0064] Ammonium nickel sulfate was dissolved in 50% pure water, sodium thiocyanate was added and stirred to dissolve, and then ammonium chloride was added and stirred to dissolve to obtain liquid A. Hexadecyltrimethylammonium chloride was dissolved in 5% pure water to obtain liquid B, and sodium metasilicate was dissolved in 5% pure water to obtain liquid C. During the stirring process, liquid B and liquid C were added to liquid A respectively, and the passivation solution was obtained after stirring / ultrasonication for 15 minutes after adding the excess water.

[0065] Passivation process:

[0066] (1) Grinding: Use 600-grit sandpaper to grind the surface of the zinc alloy workpiece until the texture is uniform;

[0067] (2) Degreasing: For the surface of zinc alloy workpiece, use 40℃ degreasing liquid and soft brush to scrub for 4 minutes;

[0068] (3) Cleaning: Rinse the surface of the zinc alloy workpiece with pure water at room temperature for 7 seconds;

[0069] (4) Activation: Weigh or measure hydrochloric acid, hydrofluoric acid, and sodium dodecyl sulfate in a mass ratio of 25:1.2:0.05, stir to mix the components evenly, and obtain an activator. Vertically suspend the zinc alloy workpiece and immerse it in the activation solution. The immersion time is 1 min, and the temperature of the activation solution is 35°C.

[0070] (5) Cleaning: Rinse the surface of the zinc alloy workpiece with pure water at room temperature for 7 seconds;

[0071] (6) Passivation: The zinc alloy workpiece is suspended vertically and immersed in the passivation solution (passivation solution) for 7 min at a temperature of 20 °C.

[0072] (7) Cleaning: Rinse the surface of the zinc alloy workpiece with pure water at room temperature for 5 seconds;

[0073] (8) Drying: Use hot air to dry the residual moisture on the working surface of the zinc alloy to obtain a uniform matte black passivation film.

[0074] Therefore, the beneficial effects of the present invention are:

[0075] In the present invention, ammonium nickel sulfate is used as a film-forming agent to provide a nickel source and a sulfur source for generating black nickel sulfide / nickel oxide, and sodium thiocyanate can be used as an oxidant and a complexing agent at the same time to promote the corrosion of the zinc matrix, release thiocyanate and metal ion complexation, stabilize the passivation solution, and provide a nickel source for generating nickel sulfide, which is an important factor for generating a black film layer. At the same time, since ammonium chloride is soluble in water, ammonium ions are hydrolyzed to generate ammonia water and hydrogen ions, so ammonium chloride can stabilize the pH of the passivation solution, and the surfactant in the passivation solution can reduce the surface tension, increase the wetting effect of the passivation solution, and be conducive to the uniform generation of the passivation film, providing the necessary conditions for the thickness and color uniformity of the film layer. Further, in the process of matrix dissolution and film layer deposition, the silicon oxide particles provided by the additive are dispersed and deposited in the pores of the film layer, and due to the characteristics of silicon oxide and the leveling effect on the microscopic surface of the film layer, the corrosion resistance and wear resistance of the passivation film are greatly improved, and this filling effect can cause a matte effect, so a uniform and dense matte black passivation film with good corrosion resistance can be obtained. Currently, there are very few examples of chrome-free black passivation. The chrome-free black passivation solution and passivation method for zinc alloy disclosed in the present invention are environmentally friendly, highly decorative, and easy to use, providing a new idea for chrome-free black passivation of zinc alloy.

[0076] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A chromium-free black passivation solution for zinc alloy, characterized in that: The invention comprises the following components in percentage by mass: 5-10% of ammonium nickel sulfate, 2-6% of sodium thiocyanate, 0.2-1% of ammonium chloride, 0.02-0.1% of surfactant, 0.1-0.5% of other additives and the balance of water.

2. The chromium-free black passivation solution for zinc alloy according to claim 1, characterized in that: The surfactant is at least one of sodium dodecyl sulfate, sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, hexadecyltrimethylammonium chloride or ethylenediaminetetraacetic acid.

3. The chromium-free black passivation solution for zinc alloy according to claim 1, characterized in that: The other additives are at least one of quick-dissolving sodium silicate, sodium metasilicate or fumed silica.

4. A method for passivation treatment of zinc alloy, characterized in that: The following steps are involved: 1) dissolving ammonium nickel sulfate in 50% volume of pure water, adding sodium thiocyanate while stirring, and after the sodium thiocyanate is completely dissolved, adding ammonium chloride and stirring until the sodium thiocyanate is completely dissolved to obtain solution A; 2) Dissolve the surfactant in 5% volume of pure water and stir until fully dissolved to obtain solution B; 3) dissolving the additive in 5% volume of pure water, stirring to fully disperse it, and obtaining liquid C; 4) Transfer liquid B and liquid C to liquid A respectively during stirring, add the remaining water and stir, and ultrasonicate for 15 minutes to obtain a passivation solution; wherein the mass ratio of the ammonium nickel sulfate, sodium thiocyanate, ammonium chloride, surfactant and other additives is (5-10%): (2-6%): (0.2-1%): (0.02-0.1%): (0.1-0.5%); 5) immersing the zinc alloy workpiece in the passivation solution to perform a passivation operation to form a passivation film on the surface of the zinc alloy workpiece, wherein the zinc alloy workpiece and the passivation film together constitute a zinc alloy passivation semi-finished product; 6) Drying the zinc alloy passivation semi-finished product with hot air to obtain a zinc alloy passivation finished product.

5. A zinc alloy passivation treatment method according to claim 4, characterized in that: The passivation operation temperature in step 5) is 10-40° C., and the operation time of the passivation operation is 1-10 min.

6. A zinc alloy passivation treatment method according to claim 4, characterized in that: Before the zinc alloy workpiece is immersed in the passivation solution, the zinc alloy workpiece is immersed in an activating agent for activation.

7. A zinc alloy passivation treatment method according to claim 6, characterized in that: The activator includes the following components in mass percentage (20-50%): (0.5-2%): (0.04-1%).

8. A zinc alloy passivation treatment method according to claim 6, characterized in that: Before immersing the zinc alloy workpiece in the activator, the surface of the zinc alloy workpiece is scrubbed with a decontamination liquid to perform a degreasing operation.

9. A zinc alloy passivation treatment method according to claim 8, characterized in that: Before degreasing the zinc alloy workpiece, the surface of the zinc alloy workpiece was polished with 600-grit sandpaper until the texture was uniform and the oxide scale was removed.

10. A zinc alloy passivation treatment method according to claim 8, characterized in that: The degreasing operation temperature is 10-40°C, and the degreasing operation time is 1-5 minutes; or the activation operation temperature is 10-35°C, and the activation operation time is 0.5-2 minutes; the zinc alloy workpiece needs to be rinsed with pure water for 5-10 seconds before activation, passivation and hot air drying.

Images