Alkaline nickel-free and fluorine-free sealant and sealing process for aluminum alloy anodized film

Abstract

The present invention discloses an alkaline nickel-free and fluorine-free sealing agent for anodized aluminum alloy films, comprising a sealing agent and a pH regulator; the sealing agent composition and the amount of each component are calculated by volume mass as follows: sodium stannate: 3-20 g / L; organic acid: 3-12 g / L; surfactant: 0.2-2 g / L; the remainder is distilled water. The present invention also discloses the above-mentioned alkaline nickel-free and fluorine-free sealing process for anodized aluminum alloys, and the process steps are as follows: preparing a sealing agent; performing a sealing treatment on the anodized aluminum alloy, and washing it with water twice and drying it or drying it after the treatment. After the anodized aluminum alloy is sealed by this process, a layer of transparent SnO2 sealing film can be obtained on the anodized surface of the aluminum alloy, which does not affect the appearance of the anodized or dyed layer, and significantly improves the surface corrosion resistance. The anodized aluminum alloy sealing agent of the present invention is nickel-free and fluorine-free, alkaline and environmentally friendly, simple to operate, low in cost, and easy to realize industrialization.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material surface treatment, and in particular relates to an alkaline nickel-free and fluorine-free sealing agent and a sealing process for an aluminum alloy anodized film. Background Art

[0002] Aluminum alloys are widely used in building profiles, aerospace, rail transportation, electronic 3C and other fields due to their excellent electrical conductivity, thermal conductivity and high specific strength. However, the standard electrode potential of aluminum is relatively negative (-1.663V) and its chemical properties are relatively active. Although it can form a protective oxide film under natural conditions, its corrosion resistance is limited. In practical applications, necessary surface treatment is usually required to improve the corrosion resistance of aluminum alloys, among which anodizing is one of the most widely used surface treatment technologies.

[0003] The main component of aluminum alloy anodized film is aluminum oxide, which is divided into two layers in microstructure. The outer layer is a porous layer with a porous structure, and the bottom layer is a continuous dense film layer, which makes the aluminum alloy anodized film have good corrosion resistance and the porous layer is convenient for surface coloring. Therefore, anodizing process is widely used in aluminum alloy surface treatment. However, due to the limited thickness of the dense film layer, the anodized film usually needs to be sealed.

[0004] There are many traditional sealing processes for anodized films, some of which are based on the expansion of hydration reaction products, such as hot water sealing and water vapor sealing; some are based on organic shielding, and are sealed by grease, wax, resin, paint, etc. For example, patent CN200810108699.8 applies for protection of a sealing method for anodized films of light metal materials. This technology coats the surface of the anodized film with paint, and completes the sealing of the anodized film through thermal curing or UV curing, which can achieve the same effect as nickel acetate sealing on the surface.

[0005] Most of them use salt hydrolysis sealing. Currently, the most widely used in the field is nickel-containing salt sealing. For example, patent CN111188071B applies for protection of a high-performance sealing process for aluminum alloy anodizing. The sealing agent of this process is a composite of nickel sulfate and other salts, and then appropriate additives are added to achieve a good sealing effect.

[0006] Some other technologies achieve the purpose of improving corrosion resistance by generating fluoride sealing. For example, patent CN110129855B applies for protection of a surface treatment method for aluminum alloy corrosion protection. First, it is treated with a solution composed of cerium nitrate, potassium fluorozirconate or potassium fluorotitanate, sodium hexametaphosphate, manganese dihydrogen phosphate, etc., and then soaked in hexadecanoic acid ethanol solution for 1 to 2 hours, and finally the sealing treatment is completed to obtain a surface with good corrosion resistance. For example, CN104342736 A applies for protection of a nickel-free room temperature sealing process and sealing agent for aluminum alloy oxide film, which contains at least one compound A of a water-soluble titanium compound or a water-soluble zirconium compound (the water-soluble titanium compound or the water-soluble zirconium compound is its sulfate, fluoride, or organic salt), an organic compound B with multiple functional groups as a stabilizer, a promoter (the promoter is a fluoride) and a pH buffer, and finally completes the sealing at a sealing speed of 0.5-3.0um / min, a temperature of 15-35°C and a pH value of 3.5-6.5, thereby obtaining good corrosion resistance.

[0007] In addition, there are some methods of sealing with acidic sealants. For example, patent CN112760692B applies for protection of an aluminum alloy anodizing sealing liquid and a sealing method thereof. The sealing liquid is obtained by adding nano-silica sol, polyurethane and surfactant to interact with each other, and mixing them under ultrasonic action, and making the pH reach 4.5-6.8. Finally, the aluminum alloy is placed in a sealing liquid at 65°C-70°C for 35s-45s, which helps to improve the corrosion resistance of the aluminum alloy.

[0008] Although the nickel salt used in the above patent has an excellent sealing effect and the fluorine-containing process can also obtain good corrosion resistance, current environmental regulations have begun to clearly restrict the use of nickel-containing and fluorine-containing processes. Therefore, it is urgent to develop an alkaline nickel-free, fluorine-free and environmentally friendly anodizing sealing process. Summary of the invention

[0009] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide an alkaline nickel-free and fluorine-free sealant for aluminum alloy anodized films, aiming to solve the damage to the environment caused by the nickel-containing or fluorine-containing sealants widely used in the field, and to seal the aluminum alloy anodized films with an alkaline stannate system, so that the corrosion resistance of the sealed surface is significantly improved.

[0010] To achieve the above object, the technical solution of the present invention is as follows:

[0011] An alkaline nickel-free and fluorine-free sealant for anodized films of aluminum alloys comprises a sealant and a pH regulator; the sealant composition and the amount of each component are calculated by volume mass as follows: sodium stannate: 3-20 g / L; organic acid: 3-12 g / L; surfactant: 0.2-2 g / L; the remainder is distilled water; the pH regulator composition and the amount of each component are calculated by volume mass as follows: organic acid; 12 g / L NaOH solution; the organic acid in the sealant is the same as the organic acid in the pH regulator.

[0012] Preferably, the organic acid is one or more of acetic acid, citric acid, propionic acid, malic acid, succinic acid, succinic acid, adipic acid, ascorbic acid, aspartic acid, salicylic acid, maleic acid, glycine, lactic acid, glutamic acid, polyacrylic acid, tannic acid, and tryptophan.

[0013] Preferably, the surfactant is one or more of alkyl glucoside, tea saponin, cocamidopropyl betaine, monoalkyl phosphate, alkyl glucamide, polyepoxysuccinic acid, polymaleic acid citrate, alcohol ether carboxylate, and α-sulfo fatty acid methyl ester salt.

[0014] Another object of the present invention is to provide a nickel-free and fluorine-free sealing process for aluminum alloy anodized film, which can take into account the environmental protection of each link of production, application and emission, while considering the process cost and operability; wherein, the process comprises:

[0015] 1. Pre-treatment of aluminum alloy degreasing and pickling, the specific processing steps are as follows:

[0016] (1) Alkaline washing and degreasing: Place the aluminum alloy product in a solution containing 10g / L NaOH, 2 CO 3 8g / L, Na 3 PO 4 In 12g / L alkaline washing solution, perform alkaline washing at room temperature for 1-3 minutes;

[0017] (2) Wash twice with running tap water and once with deionized water;

[0018] (3) Pickling: The aluminum alloy product is placed in a concentrated H 2 SO 4 100g / L, H 3 PO 4 20ml / L, HF6ml / L, OP-10 0.3g / L pickling solution, pickling at room temperature for 1-3 minutes;

[0019] (4) Wash twice with running tap water and once with deionized water;

[0020] 2. Aluminum alloy anodizing treatment: The pre-treated aluminum alloy is immersed in an anodizing tank for anodizing treatment; the anodizing tank liquid composition is H 2 SO 4 160g / L-180g / L, treatment temperature 19±1℃, DC anodization 35-40min, current density 1.5A / dm 2 ;

[0021] 3. Sealing treatment of anodized film: the aluminum alloy after anodizing treatment is immediately immersed in the sealant for sealing treatment; the sealant is adjusted to pH = 9-11 with the pH adjuster, and then heated to 40-60°C. After the anodized workpiece is cleaned, it is directly immersed in the sealant for sealing treatment. The sealing time is 15-30 minutes. After the sealing treatment is completed, it is washed with water twice and blown or dried.

[0022] Beneficial effects of the present invention:

[0023] 1. The processing temperature of the process of the present invention is 40-60°C, which is not high and is conducive to energy saving.

[0024] 2. The sealing layer obtained by the present invention is colorless and transparent, does not change the appearance of the workpiece, is conducive to the sealing treatment of the anodized film after dyeing, and maintains the original color tone.

[0025] 3. The sealant of the present invention does not contain Ni, F and other harmful ions, and is a safe and environmentally friendly sealing treatment process.

[0026] 4. The process described in the present invention is an alkaline process, and no acid mist or corrosive gas is generated during the working process, which has little corrosion to equipment and low harm to human body.

[0027] 5. The sealing process of the present invention can obtain a surface with excellent corrosion resistance. The sealing layer is mainly composed of Sn compounds, mainly SnO 2 (containing some incompletely dehydrated β-stannic acid), different from other sealing layers, SnO 2 The sealing layer is transparent, conductive, and has good wettability with solder, which can provide good weldability for subsequent welding.

[0028] 6. The sealing agent of the present invention has simple composition, simple operation, low cost and is easy to industrialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the process flow chart of the alkaline nickel-free and fluorine-free sealing process for aluminum alloy anodizing;

[0030] Figure 2 These are the Tafel polarization curves of the closed surface and the unclosed surface in 3.5wt.% NaCl solution. DETAILED DESCRIPTION

[0031] The present invention provides an alkaline nickel-free and fluorine-free sealant and sealing process for aluminum alloy anodized film. In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be emphasized that the specific implementation process uses 6063 aluminum alloy sheet, which does not mean that the present invention is only applicable to 6063 aluminum alloy, nor does it mean that the present invention is only applicable to sheet. The implementation process does not dye the anodized film, but directly seals it, but this process is also applicable to the process of dyeing and then sealing. It should be understood that the selected substrate material, morphology, and whether it is dyed in the specific embodiments described here are only used to explain the present invention, and are not used to limit the present invention.

[0032] The composition and dosage of each component of the sealing agent of the present invention are as follows: sodium stannate: 3-20 g / L; organic acid: 3-12 g / L; surfactant: 0.2-2 g / L; and the balance is distilled water.

[0033] According to the composition of the above-mentioned sealing agent and the dosage range of each component, the specific preferred dosage is as follows:

[0034] Sodium stannate: 3-20 g / L, preferably 6-15 g / L;

[0035] Organic acid: 3-12 g / L, preferably 5-9 g / L;

[0036] Surfactant: 0.2-2 g / L, preferably 0.6-1.2 g / L;

[0037] Example 1

[0038] like Figure 1 As shown, the nickel-free and fluorine-free environmentally friendly sealing process of the present invention comprises the following steps:

[0039] 1. Pre-treatment of aluminum alloy degreasing and pickling, the specific processing steps are as follows:

[0040] (1) Alkaline washing and degreasing: Place the aluminum alloy product in a solution containing 10g / L NaOH, 2 CO 3 8g / L, Na 3 PO 4 In 12g / L alkaline washing solution, perform alkaline washing at room temperature for 1-3 minutes.

[0041] (2) Wash twice with running tap water and once with deionized water.

[0042] (3) Pickling: The aluminum alloy product is placed in a concentrated H 2 SO 4 100g / L, H 3PO 4 Pickling is carried out at room temperature for 1-3 minutes in a pickling solution of 20ml / L, HF6ml / L, and OP-10 0.3g / L.

[0043] (4) Wash twice with running tap water and once with deionized water.

[0044] 2. Aluminum alloy anodizing treatment: The pre-treated aluminum alloy is immersed in an anodizing tank for anodizing treatment. The composition of the anodizing tank liquid is H 2 SO 4 160g / L-180g / L, treatment temperature 19±1℃, DC anodization 35-40min, current density 1.5A / dm 2 .

[0045] 3. Sealing treatment of anodized film: After step (2) is completed, the anodized workpiece is immediately sealed after two water washes; the treatment temperature is 40°C and the time is 30 minutes. After the treatment is completed, the workpiece is immediately rinsed and blown or dried to complete the sealing treatment. The sealing agent used is composed of: sodium stannate 12g / L; acetic acid 1g / L; citric acid 4g / L; alkyl glycoside 0.2g / L; alkyl glucamide 0.3g / L. Use 10g / L citric acid solution and 12g / L NaOH solution to adjust pH to 10.5.

[0046] Example 2

[0047] 1. Pre-treatment of aluminum alloy degreasing and pickling, the specific processing steps are as follows:

[0048] (1) Alkaline washing and degreasing: Place the aluminum alloy product in a solution containing 10g / L NaOH, 2 CO 3 8g / L, Na 3 PO 4 In 12g / L alkaline washing solution, perform alkaline washing at room temperature for 1-3 minutes.

[0049] (2) Wash twice with running tap water and once with deionized water.

[0050] (3) Pickling: The aluminum alloy product is placed in a concentrated H 2 SO 4 100g / L, H 3 PO 4 Pickling is carried out at room temperature for 1-3 minutes in a pickling solution of 20ml / L, HF6ml / L, and OP-10 0.3g / L.

[0051] (4) Wash twice with running tap water and once with deionized water.

[0052] 2. Aluminum alloy anodizing treatment: The pre-treated aluminum alloy is immersed in an anodizing tank for anodizing treatment. The composition of the anodizing tank liquid is H 2 SO 4 160g / L-180g / L, treatment temperature 19±1℃, DC anodization 35-40min, current density 1.5A / dm 2 .

[0053] 3. Sealing treatment of anodized film: After step (2) is completed, the anodized workpiece is immediately sealed after two water washes; the treatment temperature is 45°C and the time is 24 minutes. After the treatment is completed, the workpiece is immediately rinsed and blown or dried to complete the sealing treatment. The sealing agent used is composed of: 15g / L sodium stannate; 5g / L malic acid; 2g / L tannic acid; 0.1g / L tea saponin; 0.5g / L cocamidopropyl betaine. Use 10g / L malic acid solution and 12g / L NaOH solution to adjust pH to 11.

[0054] Example 3

[0055] 1. Pre-treatment of aluminum alloy degreasing and pickling, the specific processing steps are as follows:

[0056] (1) Alkaline washing and degreasing: Place the aluminum alloy product in a solution containing 10g / L NaOH, 2 CO 3 8g / L, Na 3 PO 4 In 12g / L alkaline washing solution, perform alkaline washing at room temperature for 1-3 minutes.

[0057] (2) Wash twice with running tap water and once with deionized water.

[0058] (3) Pickling: The aluminum alloy product is placed in a concentrated H 2 SO 4 100g / L, H 3 PO 4 Pickling is carried out at room temperature for 1-3 minutes in a pickling solution of 20ml / L, HF6ml / L, and OP-10 0.3g / L.

[0059] (4) Wash twice with running tap water and once with deionized water.

[0060] 2. Aluminum alloy anodizing treatment: The pre-treated aluminum alloy is immersed in an anodizing tank for anodizing treatment. The composition of the anodizing tank liquid is H 2 SO 4 160g / L-180g / L, treatment temperature 19±1℃, DC anodization 35-40min, current density 1.5A / dm 2 .

[0061] 3. Sealing treatment of anodized film: After step (2) is completed, the anodized workpiece is immediately sealed after two water washes; the treatment temperature is 50°C and the time is 18 minutes. After the treatment is completed, the workpiece is immediately rinsed and blown or dried to complete the sealing treatment. The sealing agent used is composed of: 8g / L sodium stannate; 6g / L polyacrylic acid; 3g / L glycine; 0.5g / L monoalkyl phosphate; 0.3g / L polyepoxysuccinic acid. Use 10g / L polyacrylic acid solution and 12g / L NaOH solution to adjust pH to 10.

[0062] Example 4

[0063] 1. Pre-treatment of aluminum alloy degreasing and pickling, the specific processing steps are as follows:

[0064] (1) Alkaline washing and degreasing: Place the aluminum alloy product in a solution containing 10g / L NaOH, 2 CO 3 8g / L, Na 3 PO 4 In 12g / L alkaline washing solution, perform alkaline washing at room temperature for 1-3 minutes.

[0065] (2) Wash twice with running tap water and once with deionized water.

[0066] (3) Pickling: The aluminum alloy product is placed in a concentrated H 2 SO 4 100g / L, H 3 PO 4 Pickling is carried out at room temperature for 1-3 minutes in a pickling solution of 20ml / L, HF6ml / L, and OP-10 0.3g / L.

[0067] (4) Wash twice with running tap water and once with deionized water.

[0068] 2. Aluminum alloy anodizing treatment: The pre-treated aluminum alloy is immersed in an anodizing tank for anodizing treatment. The composition of the anodizing tank liquid is H 2 SO 4 160g / L-180g / L, treatment temperature 19±1℃, DC anodization 35-40min, current density 1.5A / dm 2 .

[0069] 3. Sealing treatment of anodized film: After step (2) is completed, the anodized workpiece is immediately sealed after two water washes. The treatment temperature is 60°C and the time is 20 minutes. After the treatment is completed, the workpiece is immediately rinsed and blown or dried to complete the sealing treatment. The sealing agent used is composed of: 20g / L sodium stannate; 7g / L aspartic acid; 2g / L salicylic acid; 0.8g / L α-sulfo fatty acid methyl ester salt; 0.4g / L alkyl glucose amide. Use 8g / L aspartic acid solution and 12g / L NaOH solution to adjust pH to 10.7.

[0070] Example 5

[0071] 1. Pre-treatment of aluminum alloy degreasing and pickling, the specific processing steps are as follows:

[0072] (1) Alkaline washing and degreasing: Place the aluminum alloy product in a solution containing 10g / L NaOH, 2 CO 3 8g / L, Na 3 PO 4 In 12g / L alkaline washing solution, perform alkaline washing at room temperature for 1-3 minutes.

[0073] (2) Wash twice with running tap water and once with deionized water.

[0074] (3) Pickling: The aluminum alloy product is placed in a concentrated H 2 SO 4 100g / L, H 3 PO 4 Pickling is carried out at room temperature for 1-3 minutes in a pickling solution of 20ml / L, HF6ml / L, and OP-10 0.3g / L.

[0075] (4) Wash twice with running tap water and once with deionized water.

[0076] 2. Aluminum alloy anodizing treatment: The pre-treated aluminum alloy is immersed in an anodizing tank for anodizing treatment. The composition of the anodizing tank liquid is H 2 SO 4 160g / L-180g / L, treatment temperature 19±1℃, DC anodization 35-40min, current density 1.5A / dm 2 .

[0077] 3. Sealing treatment of anodized film: After step (2) is completed, the anodized workpiece is immediately sealed after two water washes; the treatment temperature is 55°C and the time is 16 minutes. After the treatment is completed, the workpiece is immediately rinsed and blown or dried to complete the sealing treatment. The sealing agent used is composed of: 18g / L sodium stannate; 4g / L propionic acid; 1.2g / L alcohol ether carboxylate. 8g / L propionic acid solution and 12g / L NaOH solution are used to adjust pH to 9.

[0078] The test pieces for electrochemical analysis described below are the test pieces prepared in Examples 1-4, and the corrosion resistance of the samples was analyzed by electrochemical methods. The test equipment used was a CHI-604e electrochemical workstation, which adopted a three-electrode system. The research electrode was the sample prepared in Examples 1-4, the auxiliary electrode was a 1cm×1cm platinum sheet, the reference electrode was a saturated calomel electrode, and the electrolyte solution was a 3.5wt.% (pH=6.8) NaCl solution. The voltage range of the test was ±300mV (relative to the open circuit voltage), and the scanning speed was 2mV / s. The test also compared the corrosion resistance of the unsealed anodized surface with that of the sealed sample, and the test results are as follows. Figure 2 The curve data fitting results are shown in Table 1 below:

[0079] Sample <![CDATA[E corr (V)]]> <![CDATA[i corr (μA·cm -2 )]]> <![CDATA[R p (kΩ·cm 2 )]]> Anodized surface -0.60 2.47 21.1 Example 1 -0.19 0.41 106.3 Example 2 -0.63 0.33 130.0 Example 3 -0.25 0.07 599.2 Example 4 -0.27 0.29 137.0

[0080] The test results show that the self-corrosion current density of the anodized surface in a 3.5wt.% NaCl solution is about 2.5μAcm -2 After the sealing treatment of this process, the self-corrosion current density is significantly reduced. The best value is the sample prepared in Example 3, and the icorr is 0.07μAcm -2 , down more than 30 times. It can be seen that the nickel-free and fluorine-free sealing technology significantly improves the corrosion resistance of the anodized surface of aluminum alloy.

[0081] The implementation methods of the present invention are not limited to the embodiments described, and any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention shall be equivalent replacement methods and shall be included in the protection scope of the present invention.

[0082] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

[0083] The above contents are only preferred embodiments of the present invention. For ordinary technicians in this field, according to the concept of the present invention, there will be changes in the specific implementation methods and application scopes. The content of this specification should not be understood as limiting the present invention.

Claims

1. Alkaline nickel-free and fluorine-free sealing liquid for aluminum alloy anodized film, characterized in that: Contains a sealing agent and a pH regulator; the composition of the sealing agent and the amount of each component are calculated by volume mass: Sodium stannate: 3-20g / L; Organic acid: 3-12g / L; Surfactant: 0.2-2g / L; The balance is distilled water; The pH regulator consists of: Organic acids; 12 g / L NaOH solution; the blocking agent is adjusted to pH=9-11 with the pH adjusting agent; The surfactant is one or more of alkyl glucoside, tea saponin, cocamidopropyl betaine, monoalkyl phosphate, alkyl glucamide, polyepoxysuccinic acid, polymaleic acid citrate, alcohol ether carboxylate, and α-sulfo fatty acid methyl ester salt; The organic acid in the sealing agent is the same as the organic acid in the pH regulator; the organic acid is one or more of acetic acid, citric acid, propionic acid, malic acid, succinic acid, adipic acid, ascorbic acid, aspartic acid, salicylic acid, maleic acid, glycine, lactic acid, glutamic acid, polyacrylic acid, tannic acid, and tryptophan.

2. A sealing process for an alkaline nickel-free and fluorine-free sealing liquid for anodized aluminum alloys as claimed in claim 1, characterized in that: The following technical steps are included:

1. Pre-treatment of aluminum alloy degreasing and pickling, the specific treatment steps are as follows: (1) Alkaline washing and degreasing: Place the aluminum alloy product in an alkaline washing solution containing 10g / L NaOH, 8g / L Na2CO3, and 12g / L Na3PO4, and wash at room temperature for 1-3 minutes; (2) Wash twice with running tap water and once with deionized water; (3) Pickling and polishing: Place the aluminum alloy product in a pickling solution containing concentrated H2SO4 100g / L, H3PO4 20ml / L, HF 6ml / L, OP-100.3 g / L, and pickle at room temperature for 1-3 minutes; (4) Wash twice with running tap water and once with deionized water; 2. Aluminum alloy anodizing treatment: immerse the pre-treated aluminum alloy in an anodizing tank for anodizing treatment; the anodizing tank liquid composition is H2SO4160g / L-180g / L, the treatment temperature is 19±1℃, DC anodizing is 35-40min, and the current density is 1.5A / dm 2 ; 3. Sealing treatment of anodized film: the sealing agent is adjusted to pH=9-11 with the pH adjusting agent to obtain a sealing solution, which is then heated to 40-60°C. After the anodized workpiece is cleaned, it is directly immersed in the sealing solution for sealing treatment. The sealing time is 15-30 min. After the sealing treatment is completed, it is washed with water twice and blown dry or dried.

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