A trivalent chromium passivating agent and a method for passivating a metal surface

Abstract

The application belongs to the technical field of material surface treatment, and discloses a trivalent chromium passivation agent and a metal surface passivation method.The trivalent chromium passivation agent comprises trivalent chromium salt, complexing agent, film-forming promoter and water; the complexing agent comprises sulfosalicylic acid and triethanolamine; and the film-forming promoter comprises lanthanum nitrate, cerium nitrate, fluoroborate, tin salt and cobalt salt.The trivalent chromium passivation agent does not contain hexavalent chromium, has good environmental protection, can form a blue passivation film on the metal surface, the passivation film has strong corrosion resistance, is intuitive, and has no corrosion spots after a 600h or more bare film neutral salt spray test, and the passivation film does not change color and keeps uniform color.

Description

Technical Field

[0001] This invention belongs to the field of material surface treatment technology, and specifically relates to a trivalent chromium passivating agent and a method for passivating metal surfaces. Background Technology

[0002] High-silicon die-cast aluminum alloys are highly reactive and react with acids and alkalis, making their surfaces susceptible to corrosion. Therefore, they typically require surface anti-corrosion treatment (passivation), which involves applying a chemical conversion film (passivation film). Traditional hexavalent chromium passivators can form a dense, corrosion-resistant chemical conversion film on the aluminum alloy surface. However, due to the high toxicity, carcinogenicity, and environmental impact of hexavalent chromium, it has been gradually phased out. Currently, chromium-free passivation technology is more popular. However, chromium-free passivation technology has two problems: firstly, the passivation film formed after passivation is colorless, making it difficult to visually determine whether a passivation film has formed on the aluminum alloy surface; secondly, the passivation film formed without chromium has significantly weaker corrosion resistance than that formed with hexavalent chromium passivators, with a significantly shorter salt spray corrosion resistance time, mostly not exceeding 100 hours.

[0003] Therefore, it is essential to develop products that do not contain hexavalent chromium but can improve the corrosion resistance of high-silicon die-cast aluminum alloys. Summary of the Invention

[0004] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention proposes a trivalent chromium passivating agent and a metal surface passivation method. The trivalent chromium passivating agent does not contain hexavalent chromium, has good environmental protection, and can form a highly corrosion-resistant, visually appealing blue passivation film on the metal surface. Moreover, after more than 600 hours of bare film neutral salt spray testing, no corrosion spots are found, the passivation film basically does not change color, and the color remains uniform.

[0005] A first aspect of the present invention provides a trivalent chromium passivating agent comprising a trivalent chromium salt, a complexing agent, a film-forming promoter, and water; wherein the complexing agent comprises sulfosalicylic acid and triethanolamine, and the film-forming promoter comprises lanthanum nitrate, cerium nitrate, fluoroborate, tin salt, and cobalt salt.

[0006] Specifically, the main components of the trivalent chromium passivating agent of this invention, lanthanum nitrate and cerium nitrate, have electrode potentials close to those of hexavalent chromium, and their passivation oxidation capabilities are also very close to those of hexavalent chromium. When high-valence lanthanum and cerium are reduced to low-valence states, they can rapidly adsorb oxygen from the air and then oxidize back to high-valence states. The passivation film formed in this way has performance very similar to that of the hexavalent chromium passivation film. The sulfonic acid group in sulfosalicylic acid can coordinate with trivalent chromium ions, promoting the formation of the trivalent chromium film and facilitating the deposition of the passivation film. Simultaneously, in conjunction with triethanolamine, the ammonium cation in triethanolamine and the sulfonic acid group in sulfosalicylic acid have an electrostatic interaction, both of which can coordinate with trivalent chromium ions. The coordination interaction between the two complexing agents produces a synergistic promoting effect, further facilitating the deposition of the passivation film. Furthermore, triethanolamine also has a pH-regulating effect, acting as a pH adjuster to maintain the pH within a suitable range. The passivation film's corrosion resistance is enhanced by combining several substances, including lanthanum nitrate, cerium nitrate, fluoroborate, tin salt, and cobalt salt.

[0007] This invention, by employing the aforementioned technical solution, rationally combines trivalent chromium salts, sulfosalicylic acid, triethanolamine, lanthanum nitrate, cerium nitrate, fluoroborate, tin salts, and cobalt salts. This combination achieves both high passivation and oxidation capabilities while enhancing metal ion chelation ability. Consequently, the trivalent chromium passivating agent of this invention can form a highly corrosion-resistant, blue passivation film on the metal surface. The film exhibits uniform color and shows no corrosion spots after more than 600 hours of neutral salt spray testing on a bare film. The passivation film remains essentially unchanged in color, maintaining a uniform appearance. The stability and durability of the passivation film are essentially equivalent to those of hexavalent chromium passivating films. Furthermore, this trivalent chromium passivating agent does not contain hexavalent chromium, making it environmentally friendly. In addition, the bath solution prepared using this trivalent chromium passivating agent maintains the main compounds at a high valence state during long-term production use, resulting in good bath solution stability. This avoids the need for frequent analysis and timely adjustments of the chromium content in other valence states during production.

[0008] According to some embodiments of the present invention, the product comprises, by weight, 10-20 parts of trivalent chromium salt, 1-8 parts of sulfosalicylic acid, 2-12 parts of triethanolamine, 1-10 parts of lanthanum nitrate, 1-10 parts of cerium nitrate, 10-30 parts of fluoroborate, 5-15 parts of tin salt, 5-15 parts of cobalt salt, and 10-30 parts of water.

[0009] According to some embodiments of the present invention, the trivalent chromium salt includes at least one of chromium acetate, chromium nitrate, chromium sulfate, and chromium chloride.

[0010] According to some embodiments of the present invention, the fluoroborate includes potassium fluoroborate and / or sodium fluoroborate.

[0011] According to some embodiments of the present invention, the tin salt includes at least one of tin sulfate, stannous sulfate, stannous chloride, and tin chloride.

[0012] According to some embodiments of the present invention, the cobalt salt includes at least one of cobalt acetate, cobalt chlorate, cobalt nitrate, and cobalt sulfate.

[0013] A second aspect of the present invention provides a method for preparing the trivalent chromium passivating agent described herein, comprising the following steps:

[0014] The components are mixed and stirred evenly to obtain the trivalent chromium passivating agent.

[0015] A third aspect of the present invention provides the application of the trivalent chromium passivating agent described herein in corrosion protection of metal surfaces.

[0016] According to some embodiments of the present invention, the metal is a high-silicon die-cast aluminum alloy, wherein the silicon content in the high-silicon die-cast aluminum alloy is 10-30 wt%.

[0017] A fourth aspect of the present invention provides a method for passivating a metal surface, comprising the following steps:

[0018] The metal is passivated by immersing it in the trivalent chromium passivating agent described in this invention.

[0019] According to some embodiments of the present invention, before the passivation is performed, the metal is further subjected to degreasing and water washing steps.

[0020] According to some embodiments of the present invention, the specific process of degreasing is as follows: the metal is immersed in a sodium hydroxide solution of 10-30 g / L at a temperature of 20-42°C for 5-8 minutes, and the pH of the solution is 8.5-9.5.

[0021] According to some embodiments of the present invention, the number of water washes is 1-3 times, and the time of each water wash is 30-90 seconds.

[0022] According to some embodiments of the present invention, the passivation temperature is 20-40°C; and / or the passivation time is 1-5 min; and / or the passivation pH value is 3.5-4.0.

[0023] According to some embodiments of the present invention, after the passivation is performed, the steps of washing and drying the metal are further included.

[0024] According to some embodiments of the present invention, the drying temperature is 80-100°C and the drying time is 10-30 min.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] Compared with traditional hexavalent chromium passivating agents, the trivalent chromium passivating agent of this invention does not contain hexavalent chromium, is more environmentally friendly, and makes wastewater treatment relatively simpler. This is because wastewater treated with hexavalent chromium passivating agents must first be reduced to trivalent chromium with a reducing agent before further treatment. Therefore, using the trivalent chromium passivating agent of this invention can save a lot of time and cost.

[0027] Compared to treatment with chromium-free passivating agents, the passivation film formed by the trivalent chromium passivating agent of this invention is a visually obvious blue film, while the passivation film formed by the chromium-free passivating agent is colorless, making it difficult to determine whether a passivation film is present and resulting in poor visibility. Customers will tend to prefer products with a visually obvious passivation film. At the same time, the passivation film formed by the trivalent chromium passivating agent of this invention shows no corrosion spots after more than 600 hours of bare film neutral salt spray testing, and the passivation film basically does not change color, maintaining a uniform color. Its resistance to neutral salt spray corrosion is significantly better than that of the passivation film formed by the chromium-free passivating agent. Attached Figure Description

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] Figure 1 These are photos of the product before and after testing in Example 1;

[0030] Figure 2 The images show the products from control group 1 before and after testing.

[0031] Figure 3 The images show the actual products of control group 2 before and after testing. Detailed Implementation

[0032] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments can be obtained from conventional commercial sources or by existing technical methods. Unless otherwise specified, the testing or experimental methods are conventional methods in the art. Room temperature in the embodiments of the present invention refers to 25°C.

[0033] Example 1

[0034] A trivalent chromium passivating agent, comprising the following components in parts by weight:

[0035] The ingredients are: 15 parts chromium acetate, 6 parts sulfosalicylic acid, 9 parts triethanolamine, 5 parts lanthanum nitrate, 5 parts cerium nitrate, 20 parts potassium fluoroborate, 10 parts stannous sulfate, 10 parts cobalt acetate, and 20 parts water.

[0036] The above-mentioned trivalent chromium passivating agent is prepared by mixing the components and stirring evenly.

[0037] A method for passivating the surface of high-silicon die-cast aluminum alloy includes the following steps:

[0038] S1. Pretreatment: Immerse the high-silicon die-cast aluminum alloy in a 20g / L sodium hydroxide solution (pH 9.0) at room temperature for 5 minutes. Then remove the high-silicon die-cast aluminum alloy, wash it twice with water at room temperature for 1 minute each time, and let it air dry for later use.

[0039] S2. Preparation of passivation bath solution: Mix the above trivalent chromium passivating agent with water to obtain a passivation bath solution, wherein the passivation bath solution contains 15wt% trivalent chromium passivating agent and the pH of the passivation bath solution is 3.8.

[0040] S3, passivation treatment: Immerse the pretreated high-silicon die-cast aluminum alloy in the passivation bath of S2 for 3 minutes at room temperature.

[0041] S4. Washing and drying: Wash the passivated high-silicon die-cast aluminum alloy with water at room temperature for 1 minute, and then dry it at 100℃ for 15 minutes.

[0042] Example 2

[0043] A trivalent chromium passivating agent, comprising the following components in parts by weight:

[0044] 15 parts chromium acetate, 5 parts sulfosalicylic acid, 10 parts triethanolamine, 5 parts lanthanum nitrate, 5 parts cerium nitrate, 20 parts potassium fluoroborate, 10 parts tin sulfate, 10 parts cobalt sulfate, and 20 parts water.

[0045] The above-mentioned trivalent chromium passivating agent is prepared by mixing the components and stirring evenly.

[0046] A method for passivating the surface of high-silicon die-cast aluminum alloy includes the following steps:

[0047] S1. Pretreatment: Immerse the high-silicon die-cast aluminum alloy in a 20g / L sodium hydroxide solution (pH 9.1) at room temperature for 5 minutes. Then remove the high-silicon die-cast aluminum alloy, wash it twice with water at room temperature for 1 minute each time, and air dry it for later use.

[0048] S2. Preparation of passivation bath solution: Mix the above trivalent chromium passivating agent with water to obtain a passivation bath solution, wherein the passivation bath solution contains 15wt% trivalent chromium passivating agent and the pH of the passivation bath solution is 3.7.

[0049] S3, passivation treatment: Immerse the pretreated high-silicon die-cast aluminum alloy in the passivation bath of S2 for 3 minutes at room temperature.

[0050] S4. Washing and drying: Wash the passivated high-silicon die-cast aluminum alloy with water at room temperature for 1 minute, and then dry it at 100℃ for 15 minutes.

[0051] Example 3

[0052] A trivalent chromium passivating agent, comprising the following components in parts by weight:

[0053] The ingredients are: 15 parts chromium acetate, 7 parts sulfosalicylic acid, 8 parts triethanolamine, 5 parts lanthanum nitrate, 5 parts cerium nitrate, 20 parts potassium fluoroborate, 10 parts tin chloride, 10 parts cobalt nitrate, and 20 parts water.

[0054] The above-mentioned trivalent chromium passivating agent is prepared by mixing the components and stirring evenly.

[0055] A method for passivating the surface of high-silicon die-cast aluminum alloy includes the following steps:

[0056] S1. Pretreatment: Immerse the high-silicon die-cast aluminum alloy in a 20g / L sodium hydroxide solution (pH 8.9) at room temperature for 5 minutes. Then remove the high-silicon die-cast aluminum alloy, wash it twice with water at room temperature for 1 minute each time, and air dry it for later use.

[0057] S2. Preparation of passivation bath solution: Mix the above trivalent chromium passivating agent with water to obtain a passivation bath solution, wherein the passivation bath solution contains 15wt% trivalent chromium passivating agent and the pH of the passivation bath solution is 3.6.

[0058] S3, passivation treatment: Immerse the pretreated high-silicon die-cast aluminum alloy in the passivation bath of S2 for 3 minutes at room temperature.

[0059] S4. Washing and drying: Wash the passivated high-silicon die-cast aluminum alloy with water at room temperature for 1 minute, and then dry it at 100℃ for 15 minutes.

[0060] Comparative Example 1 (The difference from Example 1 is that tartaric acid was used instead of triethanolamine)

[0061] A trivalent chromium passivating agent, comprising the following components in parts by weight:

[0062] The ingredients are: 15 parts chromium acetate, 6 parts sulfosalicylic acid, 9 parts tartaric acid, 5 parts lanthanum nitrate, 5 parts cerium nitrate, 20 parts potassium fluoroborate, 10 parts stannous sulfate, 10 parts cobalt acetate, and 20 parts water.

[0063] The above-mentioned trivalent chromium passivating agent is prepared by mixing the components and stirring evenly.

[0064] A method for passivating the surface of high-silicon die-cast aluminum alloy includes the following steps:

[0065] S1. Pretreatment: Immerse the high-silicon die-cast aluminum alloy in a 20g / L sodium hydroxide solution (pH 9.0) at room temperature for 5 minutes. Then remove the high-silicon die-cast aluminum alloy, wash it twice with water at room temperature for 1 minute each time, and let it air dry for later use.

[0066] S2. Preparation of passivation bath solution: Mix the above trivalent chromium passivating agent with water to obtain a passivation bath solution, wherein the passivation bath solution contains 15wt% trivalent chromium passivating agent and the pH of the passivation bath solution is 3.8.

[0067] S3, passivation treatment: Immerse the pretreated high-silicon die-cast aluminum alloy in the passivation bath of S2 for 3 minutes at room temperature.

[0068] S4. Washing and drying: Wash the passivated high-silicon die-cast aluminum alloy with water at room temperature for 1 minute, and then dry it at 100℃ for 15 minutes.

[0069] Comparative Example 2 (the difference from Example 1 is that no tin salt was added)

[0070] A trivalent chromium passivating agent, comprising the following components in parts by weight:

[0071] The ingredients are: 15 parts chromium acetate, 6 parts sulfosalicylic acid, 9 parts triethanolamine, 5 parts lanthanum nitrate, 5 parts cerium nitrate, 20 parts potassium fluoroborate, 20 parts cobalt acetate, and 20 parts water.

[0072] The above-mentioned trivalent chromium passivating agent is prepared by mixing the components and stirring evenly.

[0073] A method for passivating the surface of high-silicon die-cast aluminum alloy includes the following steps:

[0074] S1. Pretreatment: Immerse the high-silicon die-cast aluminum alloy in a 20g / L sodium hydroxide solution (pH 9.0) at room temperature for 5 minutes. Then remove the high-silicon die-cast aluminum alloy, wash it twice with water at room temperature for 1 minute each time, and let it air dry for later use.

[0075] S2. Preparation of passivation bath solution: Mix the above trivalent chromium passivating agent with water to obtain a passivation bath solution, wherein the passivation bath solution contains 15wt% trivalent chromium passivating agent and the pH of the passivation bath solution is 3.8.

[0076] S3, passivation treatment: Immerse the pretreated high-silicon die-cast aluminum alloy in the passivation bath of S2 for 3 minutes at room temperature.

[0077] S4. Washing and drying: Wash the passivated high-silicon die-cast aluminum alloy with water at room temperature for 1 minute, and then dry it at 100℃ for 15 minutes.

[0078] Product corrosion resistance test

[0079] The high-silicon die-cast aluminum alloys of Examples 1-3 and Comparative Examples 1-2, after surface passivation treatment, were subjected to neutral salt spray corrosion resistance tests. The test conditions were as follows: salt spray chamber temperature 35±2℃, saturated air chamber temperature 47±1℃, salt water pH 6.8, and compressed air pressure 1 kg / cm².2 The sodium chloride concentration was 50 g / L, and the spray rate was 1.8 mL / h. Simultaneously, tests were conducted on high-silicon die-cast aluminum alloys treated with either a hexavalent chromium passivator (control group 1) or a chromium-free passivator (control group 2). The hexavalent chromium passivator consisted of 15% hydrofluoric acid, 65% chromium trioxide, 5% sodium citrate, and the balance being water. The chromium-free passivator consisted of 10% fluorozirconic acid, 10% fluorotitanic acid, 10% fluorosilicic acid, 15% potassium fluorozirconate, 3% polyacrylic acid, 2% citric acid, and the balance being water.

[0080] The test results are shown in Table 1, and the physical images before and after the test are shown in the figure. Figure 1-3 As shown.

[0081] Table 1

[0082] Neutral salt spray test results Example 1 After 600 hours, no corrosion spots were found on the surface, and the morphology was basically the same as before the test. Example 2 After 600 hours, no corrosion spots were found on the surface, and the morphology was basically the same as before the test. Example 3 After 600 hours, no corrosion spots were found on the surface, and the morphology was basically the same as before the test. Comparative Example 1 Obvious corrosion spots appeared on the surface after 250 hours. Comparative Example 2 Obvious corrosion spots appeared on the surface after 300 hours. Control group 1 After 600 hours, no corrosion spots were found on the surface, and the morphology was basically the same as before the test. Control group 2 Obvious corrosion spots appeared on the surface after 80 hours.

[0083] Figure 1 These are actual photos of the product before and after testing in Example 1. Figure 1 (a) is a picture of the actual object before the test. Figure 1 (b) is a photograph of the actual product after 600 hours of testing. (From Table 1 and...) Figure 1 It can be seen that the product treated with the trivalent chromium passivating agent of this invention showed no corrosion spots after a bare film neutral salt spray test of more than 600 hours, and the passivation film remained basically unchanged in color, maintaining a uniform color. In contrast, the products treated with the trivalent chromium passivating agents of Comparative Examples 1 and 2 showed significantly weaker corrosion resistance than those of this invention.

[0084] Figure 2 These are images of the product in control group 1 before and after testing. Figure 2 (a) is a picture of the actual object before the test. Figure 2 (b) is a photograph of the actual product after 600 hours of testing. (From Table 1 and...) Figure 2 It can be seen that although control group 1 has good corrosion resistance, it contains hexavalent chromium, which is more harmful.

[0085] Figure 3 These are images of the control group 2 product before and after testing. Figure 3 (a) is a picture of the actual object before the test. Figure 3 (b) is a photograph of the actual product after 80 hours of testing. (From Table 1 and...) Figure 3 It is known that the corrosion resistance of the product treated with chromium-free passivating agent is significantly lower than that of the trivalent chromium passivating agent of the present invention, and the passivation film formed is colorless and cannot be directly observed.

[0086] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A trivalent chromium passivating agent, characterized in that, By weight, it includes 10-20 parts of trivalent chromium salt, 1-8 parts of sulfosalicylic acid, 2-12 parts of triethanolamine, 1-10 parts of lanthanum nitrate, 1-10 parts of cerium nitrate, 10-30 parts of fluoroborate, 5-15 parts of tin salt, 5-15 parts of cobalt salt, and 10-30 parts of water. The fluoroborate includes potassium fluoroborate and / or sodium fluoroborate; The tin salt includes at least one of tin sulfate, stannous sulfate, stannous chloride, and tin chloride.

2. The trivalent chromium passivating agent according to claim 1, characterized in that, The trivalent chromium salt includes at least one of chromium acetate, chromium nitrate, chromium sulfate, and chromium chloride.

3. The trivalent chromium passivating agent according to claim 1, characterized in that, The cobalt salt includes at least one of cobalt acetate, cobalt chlorate, cobalt nitrate, and cobalt sulfate.

4. The method for preparing the trivalent chromium passivating agent according to any one of claims 1-3, characterized in that, Includes the following steps: The components are mixed and stirred evenly to obtain the trivalent chromium passivating agent.

5. The application of the trivalent chromium passivating agent according to any one of claims 1-3 in corrosion protection of metal surfaces.

6. A method for passivating a metal surface, characterized in that, Includes the following steps: The metal is passivated by immersing it in the trivalent chromium passivating agent as described in any one of claims 1-3.

7. The metal surface passivation method according to claim 6, characterized in that, The passivation temperature is 20-40℃; and / or the passivation time is 1-5 min; and / or the passivation pH value is 3.5-4.0.

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