Chemical oxidation treatment liquid for aluminum and aluminum alloys and method thereof

Abstract

The application discloses a chemical oxidation treatment solution for aluminum and aluminum alloy and a method thereof, wherein the treatment solution is configured into an aqueous solution according to the following proportions: fluorozirconate, hexafluorozirconic acid, phosphate, rare earth salt, 2-amino benzoic acid, benzotriazole and sodium vanadate, and the pH value of the solution is between 3.5 and 4.3. The chemical oxidation treatment solution has simple components, does not contain elements such as chromium which affect the environment, has low process control requirements, is prepared into a chemical oxidation solution which is used under normal temperature conditions, has a simple process, has high adhesion to an organic paint film, and is suitable for surface treatment of aluminum and aluminum alloy parts in various shapes.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aluminum alloy surface treatment, and relates to an easy-to-operate environment-friendly chemical oxidation treatment solution for aluminum and aluminum alloy and a chemical oxidation method thereof. BACKGROUND

[0002] Aluminum and aluminum alloy are widely used in the field of aviation due to their light weight, strong plasticity, high strength and other characteristics, such as aircraft wing upper panel, bulkhead, skin and other parts. However, aluminum alloy has poor corrosion resistance due to its active chemical properties, so a primer layer is usually prepared on the surface of the parts before engineering application, and an organic paint layer is coated. The primer layer is generally prepared by chemical oxidation, anodic oxidation and micro-arc oxidation, among which the chemical oxidation process is the simplest, has the lowest cost, has low requirements for the shape of the parts, and can form a protective oxide film without the aid of an external power supply, which has a significant effect on improving the corrosion resistance of the aluminum alloy surface and the adhesion of the organic paint layer, and is one of the main methods for the pretreatment of aluminum alloy before coating.

[0003] Currently, the chemical oxidation used in China mainly places the parts in a chromate chemical oxidation treatment solution containing 3-10 g / L CrO3, and forms a chromium-containing oxide film with a thickness of 0.5-3 μm on the surface of the aluminum alloy through chemical reaction, which has a certain self-repairing ability and better corrosion resistance than other chemical oxidation films, and is widely used in various chemical oxidation treatment processes. CrO3 and other hexavalent chromium ions increase the risk of human carcinogenesis, and the process requires high protection for personnel and strict treatment of waste liquid, which brings great inconvenience to production. With the improvement of people's green environmental protection consciousness and the gradual improvement of environmental control requirements, there is an urgent need for a low-toxicity / non-toxic, environmentally friendly chemical oxidation treatment solution to replace the existing chromate chemical oxidation treatment solution.

[0004] Environment-friendly aluminum alloy chemical oxidation treatment solutions are divided into trivalent chromium systems and chromium-free systems, and the chromium-free system does not contain chromium ions, which is more in line with the requirements of green environmental protection, and the waste liquid treatment is also simpler. Currently, the aluminum alloy oxide film formed by chromium-free chemical oxidation treatment has poor performance stability and cannot meet the 168 h neutral salt spray resistance, so it cannot meet the requirements of the aviation field. At the same time, the surface treatment process requires that the temperature of the treatment solution be maintained at a high temperature range, generally in the range of 50-80℃, so that a good conversion film can be formed on the surface of the aluminum alloy, which easily leads to serious volatilization of the solution, and the maintenance of the treatment solution and the stability of the coating are extremely prominent, which leads to the delay of the engineering application of chromium-free environment-friendly aluminum alloy chemical oxidation in the aviation field. SUMMARY

[0005] The purpose of the present application is:

[0006] To solve the problems of high temperature of chromium-free chemical oxidation treatment tank solution, poor corrosion resistance of the film layer and the like, an easy-to-operate and environmentally friendly chromium-free chemical oxidation treatment solution is provided.

[0007] The technical problem of the present application is:

[0008] Currently, the performance stability of the aluminum alloy oxidation film layer of the chromium-free chemical oxidation treatment is poor, and cannot meet the 168h neutral salt spray resistance performance, thus cannot meet the use requirements in the aviation field. Meanwhile, the treatment solution temperature needs to be kept in a high temperature range, generally in the range of 50-80 DEG C, so as to form a good conversion film on the surface of the aluminum alloy, which is easy to cause serious volatilization of the solution, and the maintenance of the treatment solution and the stability of the coating are extremely prominent, leading to that the engineering application of the chromium-free and environmentally friendly aluminum alloy chemical oxidation cannot be applied in the aviation field.

[0009] The technical solution of the present application is:

[0010] To solve the above technical problems, the present application provides an easy-to-operate and environmentally friendly chemical oxidation treatment solution for aluminum and aluminum alloy. The present application considers the corrosion mechanism of the aluminum alloy, and under the combined action of 2-aminobenzoic acid, benzotriazole and sodium vanadate, the areas with large potential difference in the aluminum alloy are buffered, the uniformity of the film layer is improved, and the internal stress of the film layer is reduced. The main mechanism is that the complex is preferentially formed in the low potential area, and is adsorbed on the surface to form a conversion film, such as copper-rich second phase particles. Under the combined modification of the rare earth salt and benzotriazole, even if the treatment solution is at room temperature (25-40 DEG C), the conversion film on the surface of the treated aluminum alloy still has high compactness. In addition, the phosphate will promote the formation of AlPO4 and ZrPO4 on the surface during the film forming process, promote the formation of AlPO4·ZrPO4·Al2O3 conversion film, and further improve the compactness of the film layer and the corrosion resistance of the film layer.

[0011] The treatment solution is configured into an aqueous solution in the following proportions: fluorozirconate 20-30 g / L, hexafluorotitanic acid 2-8 g / L, phosphate 0.1-2 g / L, rare earth salt 2-5 g / L, 2-aminobenzoic acid 0.02-0.5 g / L, benzotriazole 0.02-0.5 g / L, vanadate 0.5-5 g / L, and the pH value of the treatment solution is between 3.0 and 4.5.

[0012] Preferably, the fluorozirconate is one or more of potassium fluorozirconate, magnesium fluorozirconate.

[0013] Preferably, the rare earth salt is cerium sulfate, cerium nitrate, cerium naphthenate, lanthanum chloride, lanthanum nitrate or a mixture thereof.

[0014] Preferably, the phosphate is one or a mixture of sodium phosphate and sodium hexametaphosphate.

[0015] In order to realize the balance of the surface film layer dissolution and film forming process of the aluminum alloy in the treatment liquid, promote the stable growth of the film layer, the solution temperature range of the chemical oxidation treatment liquid is regulated to be 25-40℃, and the pH of the treatment liquid is between 3.0-4.5 according to the following configuration:

[0016] The advantages and beneficial effects of the present application are:

[0017] The formula of the present application does not contain hexavalent chromium, trivalent chromium and other chromium ions, has little harmful influence on human body and environment, the use temperature of the treatment liquid is in a large range of 25-40℃, the process condition is mild, the film forming process is stable and controllable, the film can be uniformly formed on the surface of the aluminum alloy, the internal stress is low, and the bonding force with the substrate is firm. No subsequent sealing and other process treatment are needed. The components of the present application are all common chemical reagents, the raw material procurement is simple and convenient, and the cost is low. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0019] Figure 1 The appearance diagram of the surface conversion film of the 2024-T3 aluminum alloy of an embodiment of the present application;

[0020] Figure 2 The appearance diagram of the film layer of the 2024-T3 aluminum alloy chemical oxidation test piece after neutral salt spray corrosion for 168h of an embodiment of the present application;

[0021] Figure 3 The appearance diagram of the surface conversion film of the 7075-T7451 aluminum alloy of an embodiment of the present application;

[0022] Figure 4 The appearance diagram of the film layer of the 7075-T7451 aluminum alloy chemical oxidation test piece after neutral salt spray corrosion for 168h of an embodiment of the present application. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the protection scope of the present application.

[0024] It should be noted that the features of the embodiments and the features in the embodiments can be combined with each other without conflict, and each embodiment can be mutually referred to and quoted. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0025] Embodiment 1

[0026] An easy-to-operate environmentally friendly chemical oxidation treatment solution for aluminum and aluminum alloy is configured into an aqueous solution in the following proportions: sodium fluorozirconate 22 g / L, hexafluorotitanic acid 2 g / L, phosphate 0.5 g / L, cerium sulfate 3 g / L, 2-aminobenzoic acid 0.2 g / L, benzotriazole 0.3 g / L, sodium vanadate 2 g / L, the pH value of the treatment solution is 4.0, and the temperature of the treatment solution is 25°C.

[0027] Before chemical oxidation using the present treatment solution, the 2024-T3 aluminum alloy is treated as follows: a water-based cleaning agent is used to remove oil from the aluminum alloy parts, an alkaline cleaning solution is used to clean the aluminum alloy, a 30% nitric acid solution is used to remove the loose oxide film on the surface of the aluminum alloy parts, and after cold water cleaning, the aluminum alloy parts are immersed in the chemical oxidation treatment solution of the present application for 5 minutes. After treatment, the parts are rinsed with cold water and dried with hot air to obtain a uniform colorless, smooth and uniform film.

[0028] Figure 1 The appearance of the conversion film on the surface of the 2024-T3 aluminum alloy of an embodiment of the present application is shown in FIG. 2. Figure 1 As shown, the thickness of the conversion film is about 1.5 μm. The surface film is uniform and dense, and the conversion film on the pit part formed by pickling treatment is complete.

[0029] The appearance of the film layer on the 2024-T3 aluminum alloy chemical oxidation test piece after neutral salt spray corrosion for 168 h is shown in FIG. 2. Figure 2 As shown, according to the GB / T 10125 standard, there are no obvious corrosion points on the surface after 168 h of neutral salt spray corrosion.

[0030] Embodiment 2

[0031] An easy-to-operate environmentally friendly chemical oxidation treatment solution for aluminum and aluminum alloy is configured into an aqueous solution in the following proportions: potassium fluorozirconate 25 g / L, hexafluorotitanic acid 8 g / L, sodium phosphate 1 g / L, cerium chloride 4 g / L, 2-aminobenzoic acid 0.5 g / L, benzotriazole 0.5 g / L, vanadate 2 g / L, the pH value of the treatment solution is 3.5, and the temperature of the treatment solution is 33°C.

[0032] Before chemical oxidation using the present treatment solution, the 7075-T7451 aluminum alloy is treated as follows: the aluminum alloy parts are degreased using a water-based cleaner, the aluminum alloy is etched using an alkaline cleaning solution, and then the loose oxide film on the surface of the aluminum alloy parts is removed using a 30% nitric acid solution. After cold water cleaning, the aluminum alloy parts are immersed in the chemical oxidation treatment solution of the present application for 12 minutes. After treatment, the parts are rinsed with cold water and then dried with hot air to obtain a uniform, colorless, smooth and uniform film.

[0033] Figure 3 is a surface conversion film appearance diagram of 7075-T7451 aluminum alloy. As shown in Figure 3 , the thickness of the conversion film is about 1.6 μm. The surface film is uniform and dense, and the conversion film on the etching pit part is complete.

[0034] Figure 4 is a film layer appearance diagram of 7075-T7451 aluminum alloy chemical oxidation test piece after neutral salt spray corrosion for 168 h. As shown in Figure 4 , according to GB / T 10125 standard, there is no obvious corrosion point on the surface after 168 h of neutral salt spray environment corrosion.

[0035] In some embodiments, when the treatment solution deviates from the predetermined pH value between 3.0 and 4.5, it is adjusted by nitric acid (HNO3) and sodium hydroxide (NaOH).

[0036] In some embodiments, a chemical oxidation method for aluminum and aluminum alloy, using the above-mentioned chemical oxidation treatment solution for aluminum and aluminum alloy, the method comprises the following steps:

[0037] S1, removing the natural oxide film on the surface of the aluminum or aluminum alloy test piece;

[0038] S2, immersing the aluminum or aluminum alloy test piece with the natural oxide film removed in the chemical oxidation treatment solution for aluminum and aluminum alloy at a temperature in the range of 25-40°C for 3-12 min, so that the phosphate will promote the formation of AlPO4, ZrPO4 on the surface during film formation, promote the formation of AlPO4•ZrPO4•Al2O3 conversion film, and further improve the film layer density and corrosion resistance;

[0039] S3, removing the aluminum or aluminum alloy test piece and using deionized water to remove the residual treatment solution.

[0040] In some embodiments, step S1 comprises:

[0041] removing the natural oxide film on the surface of the aluminum or aluminum alloy test piece by mechanical method; or,

[0042] Before the chemical oxidation using the treatment solution, the 2024-T3 aluminum alloy is treated as follows: the aluminum alloy parts are degreased using a water-based cleaner, the aluminum alloy parts are etched using an alkaline cleaning solution, and the loose oxide film on the surface of the aluminum alloy parts is removed using a 30% nitric acid solution.

[0043] The above examples are only for easier understanding of the present application, and the present application is not limited to the above-mentioned methods. The engineering technicians can make corresponding changes according to the above, and any use of the above steps is a deformation of the environmental protection type chemical oxidation treatment solution for aluminum and aluminum alloy of the present application, and should be considered to fall within the protection scope of the present application.

[0044] The present patent is obtained on the basis of a large amount of formula and process research data, and the typical chemical oxidation treatment solution is prepared according to the following table:

[0045] Table 1: Typical chemical oxidation treatment solution formula

[0046]

[0047] It should be noted that the above process operations can be combined to different degrees. In order to be simple, the implementation modes of various combinations are not described again, and the order of the above operation steps can be flexibly adjusted or the above steps can be flexibly combined by the person skilled in the art according to the actual needs.

[0048] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of various equivalent modifications or replacements within the technical range disclosed by the present application, and these modifications or replacements should be covered within the protection scope of the present application.

Claims

1. A chemical oxidation treatment solution for aluminum and aluminum alloys, characterized in that, The treatment solution was prepared as an aqueous solution according to the following proportions: Fluorozironate 20~30 g / L, hexafluorozirconic acid 2~8 g / L, phosphate 0.1~2 g / L, rare earth salt 2~5 g / L, 2-aminobenzoic acid 0.02~0.5 g / L, benzotriazole 0.02~0.5 g / L, sodium vanadate 0.5~5 g / L.

2. The chemical oxidation treatment solution for aluminum and aluminum alloys as described in claim 1, characterized in that, in: The pH value of the prepared aqueous treatment solution is between 3.0 and 4.5; the temperature range of the aqueous solution is controlled between 25 and 40℃.

3. The chemical oxidation treatment solution for aluminum and aluminum alloys as described in claim 1, characterized in that, in: The fluorozirconate is potassium fluorozirconate or magnesium fluorozirconate.

4. The chemical oxidation treatment solution for aluminum and aluminum alloys as described in claim 1, characterized in that, in: The rare earth salt is cerium sulfate, cerium nitrate, cerium naphthenate, lanthanum chloride, lanthanum nitrate, or a mixture thereof.

5. The chemical oxidation treatment solution for aluminum and aluminum alloys as described in claim 1, characterized in that, in: The phosphate is any one or a mixture of two of sodium phosphate and sodium hexametaphosphate.

6. The chemical oxidation treatment solution for aluminum and aluminum alloys as described in claim 1, characterized in that, in: 2-Aminobenzoic acid is 0.05~0.5 g / L, benzotriazole is 0.02~0.5 g / L, and sodium vanadate is 0.5~5 g / L.

7. The chemical oxidation treatment solution for aluminum and aluminum alloys as described in claim 1, characterized in that, in: When the treatment solution deviates from the predetermined pH range of 3.0 to 4.5, it is adjusted with nitric acid and sodium hydroxide.

8. A method for the chemical oxidation of aluminum and aluminum alloys, characterized in that, The method of oxidizing aluminum and aluminum alloys using a chemical oxidation treatment solution as described in any one of claims 1-7 includes the following steps: S1, remove the natural oxide film from the surface of the aluminum or aluminum alloy specimen; S2, the aluminum or aluminum alloy specimens after removing the natural oxide film are immersed in a chemical oxidation treatment solution for aluminum and aluminum alloys at a temperature range of 25~40℃ for 3~12 minutes. This allows the phosphate to promote the formation of AlPO4 and ZrPO4 on the surface during the film formation process, and promotes the formation of AlPO4•ZrPO4•Al2O3 conversion film, further improving the film density and corrosion resistance. S3, remove aluminum or aluminum alloy for testing, and use deionized water spray to remove residual treatment liquid.

9. The method as described in claim 8, characterized in that, Step S1 includes: The natural oxide film on the surface of aluminum or aluminum alloy specimens is removed using mechanical methods; or, Before chemical oxidation using this treatment solution, the 2024-T3 aluminum alloy is treated as follows: the aluminum alloy parts are degreased with a water-based cleaning agent, and after being corroded with an alkaline cleaning solution, the loose oxide film on the surface of the aluminum alloy parts is removed with a 30% nitric acid solution.

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