Die-casting aluminum alloy passivator and use method thereof

Abstract

The invention relates to the technical field of metal surface treatment, in particular to a die-casting aluminum alloy passivator and a using method thereof.The die-casting aluminum alloy passivator comprises a chelating agent, a corrosion inhibitor, an accelerant, a film-forming agent, silica sol, a pH regulator and water. The die-casting aluminum alloy passivating agent provided by the invention can form a colorless and compact chemical passivation film on the surface of a die-casting aluminum alloy, so that the die-casting aluminum alloy has excellent corrosion resistance, does not contain harmful substances such as strong acid, strong alkali, nitrate, cyanide and the like, is pollution-free to the environment and human bodies, and has excellent corrosion resistance according to a standard GB / T10125-1997 Artificial Atmosphere Corrosion Test-Salt Spray Test. And the neutral salt spray test can reach more than 400 hours, and meanwhile, the preparation process is simple, low in cost and suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of metal surface treatment, and particularly relates to a passivating agent for die-cast aluminum alloy and a method for using the same. Background Art

[0002] Die-cast aluminum alloy products are increasingly widely used in daily life, industrial and agricultural production. Since die-cast aluminum alloy is relatively active, if these aluminum products are directly placed in the air, especially during the export shipping process, they are easily oxidized in humid air. Therefore, the surface treatment of aluminum products is particularly important. Coating a chemical passivation layer on the surface of aluminum and its alloys opens up a new direction for anti-corrosion and anti-oxidation problems.

[0003] Currently, the treatment agents for die-cast aluminum surfaces on the market are basically conversion film treatment agents composed of trivalent chromium, hexavalent chromium or rare earth modification combined with strong oxidants. Among them, the treatment agents containing trivalent chromium and hexavalent chromium can form a good passivation film on the aluminum alloy surface, but due to the serious harm of trivalent chromium and hexavalent chromium to the environment and human health, there are obvious environmental pollution problems; although the use of rare earth modification has improved the environmental pollution to some extent, the problem still cannot be completely solved, and it often leads to a decline in various performance indicators of the passivation film, unable to meet the actual application requirements, such as color change on the surface of die-cast aluminum, ash hanging, and a decrease in the bonding ability after painting; the corrosion resistance decreases or fails to meet the standard, especially the salt spray test time is generally relatively short, and basically does not exceed 72 hours of salt spray test.

[0004] In view of the above problems in the prior art, some solutions have been proposed, such as: Patent CN117987820A discloses a passivating agent for die-cast aluminum and aluminum alloy conversion film and a preparation method thereof, including γ-aminopropyltriethoxysilane, cyclopentadienyldibutoxychlorotitanium, sodium laureth carboxylate, zirconium isooctanoate, aluminum coupling agent AL-M, and water. Patent CN106048580A discloses a passivation film treatment agent for die-cast aluminum alloy, including inorganic acid, zirconate, vanadate, manganate, calcium salt, and surfactant. The passivation films formed by the above two types of passivating agents on the die-cast aluminum surface have improved some technologies, but there are still problems such as color change, decreased painting bonding ability, and insufficient corrosion resistance. In particular, the salt spray test time is generally short, and the performance of the passivation film still needs to be further improved.

[0005] In summary, developing a pollution-free and excellent-performance passivating agent is an urgent problem to be solved at present. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a passivating agent for die-cast aluminum alloy and its usage method. The passivating agent for die-cast aluminum alloy provided by the present invention can form a colorless and dense chemical passivation film on the surface of die-cast aluminum alloy, endowing it with excellent corrosion resistance. Moreover, it does not contain harmful substances such as strong acids, strong alkalis, nitrates, and cyanides, causing no pollution to the environment and human body. At the same time, the preparation process is simple and the cost is low, making it suitable for industrial production.

[0007] It is achieved through the following technical solutions:

[0008] On the one hand, the present invention provides a passivating agent for die-cast aluminum alloy, comprising: a chelating agent, a corrosion inhibitor, a promoter, a film-forming agent, silica sol, a pH regulator, and water.

[0009] Further, the chelating agent is at least one of tartaric acid, glutamic acid, and EDTA-2NA. The chelating agent has a chelating effect on metal ions. Through chelation by the chelating agent, excessive metal ions can be avoided from inhibiting the formation rate and quality of the passivation film.

[0010] Further, in the passivating agent, the proportion of the chelating agent is 2-5%, preferably 2%, 3%, 4%, 5%.

[0011] Further, the corrosion inhibitor is at least one of siloxanone, sodium citrate, sodium dodecylbenzenesulfonate, and fatty alcohol polyoxyethylene phosphate. The corrosion inhibitor can control the die-cast aluminum alloy that has undergone pretreatment from being corroded during the passivation reaction process.

[0012] Further, in the passivating agent, the proportion of the corrosion inhibitor is 2-5%, preferably 2%, 3%, 4%, 5%.

[0013] Further, the promoter is at least one of maleic anhydride and polyacrylic acid. The promoter provides a reaction environment for promoting the formation of the passivation film.

[0014] Further, in the passivating agent, the proportion of the promoter is 3-10%, preferably 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%.

[0015] Further, the film-forming agent is at least one of 1-phenyl-5-mercapto-1,2,3,4-tetrazole, sodium molybdate, ethylene glycol, and glycerol. The film-forming agent is the main component for forming the passivation film and plays a role in forming the main framework of the passivation film.

[0016] Further, in the passivating agent, the proportion of the film-forming agent is 5-8%, preferably 5%, 6%, 7%, 8%.

[0017] Further, the pH regulator is triethanolamine. The pH regulator is used to adjust and stabilize the pH and control the passivation reaction process from being corroded.

[0018] Further, in the passivator, the pH regulator accounts for 3-7%, preferably 3%, 4%, 5%, 6%, 7%.

[0019] Further, the silica sol is nano-silica sol. The silica sol plays a role in filling the micropores of the passivation film.

[0020] Further, in the passivator, the silica sol accounts for 5-8%, preferably 5%, 6%, 7%, 8%.

[0021] Further, the die-cast aluminum alloy passivator, by weight percentage, includes: 2-5% of chelating agent, 2-5% of corrosion inhibitor, 3-10% of accelerator, 5-8% of film-forming agent, 5-8% of silica sol, 3-7% of pH regulator, and the balance is water.

[0022] On the other hand, the present invention provides a method for using a die-cast aluminum alloy passivator, including the following steps:

[0023] S1: Add the die-cast aluminum alloy passivator of the present invention into a passivation tank, mix and dissolve to obtain a passivator solution;

[0024] S2: Put the pre-treated die-cast aluminum alloy workpiece into the passivation tank in S1 for passivation treatment, air dry and bake dry to complete passivation.

[0025] Further, in S1, the concentration of the passivator solution is 10-15 wt%.

[0026] Further, the pre-treatment of the die-cast aluminum alloy can adopt a conventional pre-treatment method, for example, placing it in an acid solution, soaking at 25-40°C for 1-3 min, and rinsing.

[0027] Further, the passivation temperature is 40-60°C, preferably 40°C, 45°C, 50°C, 55°C, 60°C.

[0028] Further, the passivation time is 3-8 min, preferably 3 min, 4 min, 5 min, 6 min, 7 min, 8 min.

[0029] Further, after S2 is completed, when the passivation liquid in the tank decreases as the workpiece is taken away, directly add the passivator into the tank.

[0030] Further, the concentration of the added passivator solution is 10-15 wt%, preferably 10 wt%, 12 wt%, 14 wt%, 15 wt%.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] The passivator provided by the present invention has its components reasonably screened and is a highly efficient compound of a chelating agent, a corrosion inhibitor, a promoter, a film-forming agent, silica sol, a pH regulator and water; the corrosion inhibitor and the pH regulator control that the passivation reaction process is not corroded. The corrosion inhibitor can slow down the passivation reaction rate, making the formation process of the passivation film uniform and dense; the pH regulator can adjust the pH value of the passivation solution to keep it within the optimal film-forming range; the chelating agent can chelate with metal ions to form stable coordination compounds, thus avoiding excessive metal ions from inhibiting the formation rate and quality of the passivation film; the film-forming agent is the main component for the formation of the passivation film and plays the role of forming the main framework of the passivation film. It can form a chemical check with the surface of die-cast aluminum alloy to improve the adhesion of the passivation film; the promoter provides a reaction environment for promoting the formation of the passivation film; silica sol plays the role of filling the micropores of the passivation film and can enhance the density and wear resistance of the passivation film. The passivator provided by the present invention has its components cooperate synergistically, so that the passivator has good passivation effects, short passivation time, low use concentration, good corrosion resistance, and is very safe for humans and tank containers.

[0033] The passivator provided by the present invention has simple components and is easy to prepare, and is suitable for industrial production.

[0034] The passivator provided by the present invention does not contain harmful substances such as strong acids and alkalis, nitrates, cyanides, hexamethylenetetramine, halogens and flammable and explosive substances, and is non-polluting to the environment and humans, completely solving the environmental pollution problems existing in the existing passivators.

[0035] The passivator provided by the present invention can form a colorless and dense chemical passivation film on the surface of die-cast aluminum alloy, avoiding the defect that the existing passivator causes the surface discoloration of die-cast aluminum alloy.

[0036] The passivation film formed by the passivator of the present invention has excellent corrosion resistance. According to the method of the standard GB / T10125-1997 "Artificial Atmosphere Corrosion Test - Salt Spray Test", the neutral salt spray test can reach about 500 hours, which is much higher than the salt spray test time of the passivation film formed by the existing passivator (only 72 hours), greatly improving the corrosion resistance of die-cast aluminum alloy.

[0037] The passivator of the present invention has a fast passivation film formation speed on the surface of die-cast aluminum alloy and good bonding ability after painting, avoiding the defect that the existing passivator causes the decline of the painting bonding ability.

[0038] The conditions for forming a passivation film on the surface of die-cast aluminum alloy by the passivator of the present invention are mild. It only needs to be passivated at 40 - 60 °C, has low requirements for passivation equipment, is easy to prepare, is suitable for industrial production, and reduces production costs; the passivation temperature is low, the use concentration of the passivator is low, and no other treatments such as curing are required, and the operation is convenient. At the same time, it is very safe for humans and tank containers.

[0039] The passivation film formed by the present invention is colorless, has excellent corrosion resistance and painting bonding ability, does not cause environmental pollution, and is beneficial to subsequent processes. Detailed implementation manners

[0040] The above passivator will be further elaborated through specific implementation manners below.

[0041] Example 1

[0042] A new type of die-casting aluminum alloy passivator, by weight percentage: tartaric acid 3%, siloxanone 2%, sodium dodecylbenzenesulfonate 1%, polyacrylic acid 4%, 1-phenyl-5-mercaptotetrazole 4%, sodium molybdate 1%, ethylene glycol 2%, nano-silica sol 5%, triethanolamine 3%, water 75%.

[0043] Add each component to water and mix and dissolve them.

[0044] ① Place the workpiece to be passivated on the fixture, put it into the pretreatment tank, soak it at 30°C for 2 minutes, rinse it, then put it into the passivator tank and perform passivation treatment at 50°C for 5 minutes, and dry it by air drying or baking.

[0045] ② Place the workpiece to be passivated on the fixture, put it into the pretreatment tank, soak it at 35°C for 1 minute, rinse it, then put it into the passivator tank and perform passivation treatment at 55°C for 8 minutes, and dry it by air drying or baking.

[0046] Example 2

[0047] A new type of die-casting aluminum alloy passivator, by weight percentage: tartaric acid 3%, EDTA-2NA 1%, siloxanone 1%, sodium citrate 3%, maleic anhydride 5%, 1-phenyl-5-mercaptotetrazole 3%, glycerol 4%, nano-silica sol 6%, triethanolamine 3%, water 71%.

[0048] Add each component to water and mix and dissolve them.

[0049] ① Place the workpiece to be passivated on the fixture, put it into the pretreatment tank, soak it at 30°C for 2 minutes, rinse it, then put it into the passivator tank and perform passivation treatment at 50°C for 5 minutes, and dry it by air drying or baking.

[0050] ② Place the workpiece to be passivated on the fixture, put it into the pretreatment tank, soak it at 35°C for 1 minute, rinse it, then put it into the passivator tank and perform passivation treatment at 55°C for 8 minutes, and dry it by air drying or baking.

[0051] Example 3

[0052] A new type of passivating agent for die-cast aluminum alloy, by weight percentage: sodium citrate 1%, EDTA-2NA 3%, silicone ketone 2%, fatty alcohol polyoxyethylene phosphate 2%, maleic anhydride 3%, 1-phenyl-5-mercapto-tetrazole 5%, glycerol 3%, nano-silica sol 8%, triethanolamine 5%, water 68%.

[0053] Add each component to water and mix and dissolve them.

[0054] ① Place the workpiece to be passivated and the fixture on a rack, put them into the pretreatment tank, soak at 30°C for 2 minutes, rinse, then put them into the passivating agent tank for passivation treatment at 50°C for 5 minutes, and air-dry and bake dry.

[0055] ② Place the workpiece to be passivated and the fixture on a rack, put them into the pretreatment tank, soak at 35°C for 1 minute, rinse, then put them into the passivating agent tank for passivation treatment at 55°C for 8 minutes, and air-dry and bake dry.

[0056] Example 4

[0057] A new type of passivating agent for die-cast aluminum alloy, by weight percentage: glutamic acid 2%, sodium citrate 3%, sodium dodecylbenzenesulfonate 2%, silicone ketone 1%, fatty alcohol polyoxyethylene phosphate 2%, maleic anhydride 4%, 1-phenyl-5-mercapto-tetrazole 1%, ethylene glycol 3%, glycerol 3%, nano-silica sol 5%, triethanolamine 6%, water 68%.

[0058] Add each component to water and mix and dissolve them.

[0059] ① Place the workpiece to be passivated and the fixture on a rack, put them into the pretreatment tank, soak at 30°C for 2 minutes, rinse, then put them into the passivating agent tank for passivation treatment at 50°C for 5 minutes, and air-dry and bake dry.

[0060] ② Place the workpiece to be passivated and the fixture on a rack, put them into the pretreatment tank, soak at 35°C for 1 minute, rinse, then put them into the passivating agent tank for passivation treatment at 55°C for 8 minutes, and air-dry and bake dry.

[0061] Example 5

[0062] A new type of passivating agent for die-cast aluminum alloy, by weight percentage: sodium citrate 4%, tartaric acid 1%, sodium dodecylbenzenesulfonate 2%, fatty alcohol polyoxyethylene phosphate 3%, maleic anhydride 4%, 1-phenyl-5-mercapto-tetrazole 5%, glycerol 3%, nano-silica sol 8%, triethanolamine 5%, water 65%.

[0063] Add each component to water and mix and dissolve them.

[0064] ①Put the workpiece and fixture to be passivated aside and place them in the pretreatment tank, soak them at 30℃ for 2min, rinse them, then put them in the passivation tank at 50℃ for passivation treatment for 5min, and dry them in the air.

[0065] ②Put the workpiece and fixture to be passivated aside and place them in the pretreatment tank, soak them at 35℃ for 1min, rinse them, then put them in the passivation tank at 55℃ for passivation treatment for 8min, and dry them in the air.

[0066] Comparative Example 1

[0067] The difference from Example 3 is that there is no film-forming agent.

[0068] Comparative Example 2

[0069] The difference from Example 3 is that there is no chelating agent.

[0070] Comparative Example 3

[0071] The difference from Example 3 is that there is no corrosion inhibitor.

[0072] Comparative Example 4

[0073] The difference from Example 3 is that no silica sol is included.

[0074] Effect verification test 1

[0075] The neutral salt spray corrosion test was carried out on the passivated die-cast aluminum alloy products. The test method was based on the standard GB / T10125-1997 "Artificial atmosphere corrosion test-salt spray test" method. The temperature was 35°C, the salt water contained 5% sodium chloride, the pH value was 6.8, and the fog drop was 1.5mL / (h·cm 2 ), the results are shown in Table 1:

[0076] Table 1 Comparison of die-cast aluminum alloy workpiece morphology and salt spray test time after passivation

[0077]

[0078]

[0079] Conclusion: The passivation film formed by the die-cast aluminum alloy of the present invention is basically a natural color passivation film, which has no effect on the subsequent process. The passivation film generally has a long salt spray resistance test time, and the passivation film is uniform and dense.

[0080] Although some exemplary embodiments of the present invention have been shown above, it will be appreciated by those skilled in the art that changes may be made to the exemplary embodiments without departing from the principles or spirit of the present invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A die-casting aluminum alloy passivator, characterized in that: include: Chelating agent, corrosion inhibitor, accelerator, film former, silica sol, pH adjuster and water.

2. The die-casting aluminum alloy passivator according to claim 1, characterized in that: The chelating agent is at least one of tartaric acid, glutamic acid and EDTA-2NA.

3. The die-cast aluminum alloy passivator according to claim 1, characterized in that: The corrosion inhibitor is at least one of siloxane ketone, sodium citrate, sodium dodecylbenzene sulfonate and fatty alcohol polyoxyethylene phosphate.

4. The die-cast aluminum alloy passivator according to claim 1, characterized in that: The accelerator is at least one of maleic anhydride and polyacrylic acid.

5. The die-cast aluminum alloy passivator according to claim 1, characterized in that: The film-forming agent is at least one of 1-phenyl-5-mercaptotetrazole, sodium molybdate, ethylene glycol and glycerol.

6. The die-cast aluminum alloy passivator according to claim 1, characterized in that: The pH regulator is triethanolamine; and the silica sol is nano silica sol.

7. The die-cast aluminum alloy passivator according to claim 1, characterized in that: The die-cast aluminum alloy passivator comprises, by weight percentage, 2-5% of a chelating agent, 2-5% of a corrosion inhibitor, 3-10% of an accelerator, 5-8% of a film-forming agent, 5-8% of a silica sol, 3-7% of a pH regulator, and the balance being water.

8. A method for using the die-casting aluminum alloy passivator according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1: adding the die-cast aluminum alloy passivator according to any one of claims 1 to 7 into a passivation tank, mixing and dissolving, and preparing a passivator solution; S2: Place the pre-treated die-cast aluminum alloy workpiece into the S1 passivation tank for passivation treatment, dry it in the air, and complete the passivation.

9. The method of use according to claim 8, characterized in that: In S1, the concentration of the passivating agent solution is 10~15wt%; The passivation temperature is 40-60° C., and the passivation time is 3-8 min.

10. The method of use according to claim 8, characterized in that: After S2 is completed, when the passivation liquid in the tank is reduced as the workpiece is taken away, the passivation agent is directly added to the tank, and the concentration of the added passivation agent solution is 10-15wt%.

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