Self-healing sealing coating concentrate, method for its production and use

Abstract

The application discloses a self-healing sealing coating concentrate liquid, which comprises a kind of complexing agent, a second complexing agent, a soluble cerium salt, a pH buffer, a wetting agent and deionized water.The application also discloses a preparation method and application thereof.The sealing coating obtained based on the self-healing sealing coating concentrate liquid has excellent compactness and excellent self-healing performance.Meanwhile, the preparation and application operation of the self-healing sealing coating concentrate liquid are simple, low in cost and environmentally friendly and pollution-free.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal surface treatment, in particular to a self-healing sealing coating concentrate, a preparation method and application thereof. BACKGROUND

[0002] Aluminum alloys are widely used in aerospace, chemical ships and automobile industries due to their low density, excellent mechanical properties and good processability. In practical applications, the surface of aluminum alloys is usually treated to improve their corrosion resistance and wear resistance, such as anodic oxidation, chemical plating, micro-arc oxidation and hard oxidation. Anodic oxidation is widely used to further improve the corrosion resistance, wear resistance and mechanical properties of aluminum alloys due to its advantages such as mature technology, low cost and strong decoration. Generally, the anodic oxidation film of aluminum alloy is composed of an inner barrier layer and an outer porous layer, and the composition of the anodic oxidation film structure determines that it must be sealed later. The quality of sealing treatment often determines the final performance and cost of aluminum alloy. The sealing techniques applied in the prior art mainly include high-pressure steam sealing, boiling water sealing, nickel salt sealing, cold nickel fluoride sealing and hexavalent chromium sealing. In actual use, the anodic oxidation film and sealing layer structure will be damaged under conditions such as bumping and impact, which will lead to discoloration and corrosion at the damaged site, which will seriously affect the performance and service life of aluminum alloy.

[0003] Therefore, it has become one of the hotspots in the field of aluminum alloy sealing technology to develop an aluminum alloy anodic oxidation film sealing technology that can self-heal under structural damage to prevent further corrosion of the aluminum alloy substrate and does not seriously affect the performance and service life of the aluminum alloy.

[0004] Chinese patent CN119877057A (publication date 2025.04.25) discloses an aluminum alloy surface and a treatment method thereof. The invention mainly includes four steps of surface cleaning, chemical pretreatment, pulse anodic oxidation and sealing treatment of aluminum alloy; the sealing self-healing effect mainly reflects the following aspects: Ce 3+ is released when the cerium complex is exposed to an oxidizing environment for a long time, and it migrates to the damaged area, finally forms an oxide deposit and actively repairs the damaged area, delaying corrosion; but its disadvantages mainly include: 1) ultrasonic assistance is required during the sealing stage, which not only increases the operation difficulty and production cost, but also has no practical operation feasibility in actual production activities; 2) it cannot ensure that the nano zinc oxide can effectively fill the micropores of the pulse anodic oxidation film, thereby realizing the dual sealing effect with Ce 3+ .

[0005] Chinese patent CN101275265A (publication date 2008.10.01) discloses a method of depositing cerium-containing compounds in the anodic oxide film of aluminum and its alloys. The invention mainly includes four steps of pretreatment of the surface of aluminum and its alloys, anodic oxidation, alternating current deposition of cerium-containing compounds and sealing treatment. The invention mainly adds the alternating current deposition of cerium-containing compounds process before the sealing process, and makes the oxide film have self-healing performance by increasing the content of Ce 3+ or Ce 4+ The invention has the advantages of simple process, convenient operation, low investment, and can be added with low-voltage alternating current power supply in the original oxidation process workshop; but the main disadvantages are: 1) using oxidizing agent to promote the transformation of Ce 3+ to Ce 4+ ; 2) using alternating current process in the cerium salt deposition process to increase the adhesion between the cerium salt and the base material oxide film, which will limit the scale and operability of actual production. SUMMARY

[0006] The purpose of the present application is to provide a self-healing sealing coating concentrate and its preparation method and application to solve the problems of the prior art.

[0007] The present application adopts the following technical solutions:

[0008] A self-healing sealing coating concentrate, the self-healing sealing coating concentrate comprises a type of complexing agent, a type of complexing agent, a soluble cerium salt, a pH buffer, a wetting agent and deionized water;

[0009] The first type of complexing agent includes one or more of propionic acid and its salts, lactic acid and its salts, glycine and its salts, malic acid and its salts, tartaric acid and its salts, acetic acid and its salts;

[0010] The second type of complexing agent includes one or both of asparagine and glutamine;

[0011] The soluble cerium salt is one or more of cerium chloride, cerium triiodide, cerium carbonate, cerium acetate and cerium phosphate;

[0012] The pH buffer is one or more of ammonium oxalate, phosphate buffer and ammonium phthalate;

[0013] The wetting agent is one or more of phosphate betaine type, sulfobetaine type and carboxyl betaine type;

[0014] The mass ratio of the first type of complexing agent, the second type of complexing agent, the soluble cerium salt, the pH buffer and the wetting agent is 10-25:20-30:25-55:15-20:3-10, and the balance is deionized water.

[0015] The preparation method of the above-mentioned self-healing sealing coating concentrate comprises the following steps:

[0016] (1) According to the formula, weigh each component, and dissolve each component into a transparent solution with deionized water;

[0017] (2) Mix the first type of complexing agent solution with the soluble cerium salt solution and continuously stir until homogeneous to obtain a mixed solution;

[0018] (3) Add the pH buffer solution and the wetting agent solution to the mixed solution obtained in step (2) under stirring and continuously stir until the mixed solution is homogeneous, and adjust the pH of the mixed solution to 7.5-9.0 using ammonia water;

[0019] (4) Add the second type of complexing agent solution to the mixed solution obtained in step (3) under stirring and continuously stir until the mixed solution is homogeneous, and adjust the pH of the mixed solution to 7.5-9.0 using ammonia water.

[0020] Application of the above self-healing sealing coating concentrate in sealing of anodic oxide film of an aluminum alloy.

[0021] Further, in use, the following steps are included:

[0022] (1) Surface pretreatment:

[0023] a) Oil and alkali removal: Place the aluminum alloy substrate in the oil and alkali removal solution to remove oil and alkali, and then take it out and wash with water;

[0024] b) Stain removal: Place the aluminum alloy substrate after oil and alkali removal in the stain removal solution to remove stains, and then take it out and wash with water;

[0025] (2) Anodizing: Place the aluminum alloy substrate after surface pretreatment in the anodizing solution to anodize, and then take it out and wash with water;

[0026] (3) Dyeing: Place the aluminum alloy substrate after anodizing in the dyeing solution to dye, and then take it out and wash with water;

[0027] (4) Sealing: Place the aluminum alloy substrate after dyeing in the sealing solution to seal, and then take it out, wash with water, and dry; wherein the sealing solution comprises 80-120 ml / l of the self-healing sealing coating concentrate, and the balance is deionized water; during work, adjust the pH of the sealing solution to 7.5-9.0 using ammonia water; the working temperature of the sealing solution is 25-50°C, and the working time is 15-30 min.

[0028] Further, in step (1), the oil-removing alkaline etching solution comprises 40-55 g / l NaOH, 30-35 g / l Na2CO3, 18-30 g / l NaHCO3, 25-35 g / l NaH2PO4, 3-8 g / l Tween-60, 25-35 g / l Na2SiO3, and the rest is deionized water; during operation, the pH of the oil-removing alkaline etching solution is adjusted to 8.0-9.5 by using a 200 g / l-250 g / l NaOH solution; the working temperature of the oil-removing alkaline etching solution is 55-60 ℃, and the working time is 5-10 min.

[0029] Further, in step (1), the stain-removing solution comprises 65-80 ml / l 98 wt% H2SO4 and 5-12 ml / l 40 w / v% HF, and the rest is deionized water; the working temperature of the stain-removing solution is 25-35 ℃, and the working time is 60-90 s.

[0030] Further, in step (2), the anodic oxidation solution comprises 30-45 ml / l 98 wt% H2SO4 and 35-50 g / l tartaric acid, and the rest is deionized water; the working temperature of the anodic oxidation solution is 10-55 ℃, the direct current power source is 15-30 V, and the working time is 60-90 min.

[0031] Further, the anodic oxidation film obtained by anodic oxidation has a thickness of 20-35 μm.

[0032] Further, in step (3), the dyeing solution comprises 1-25 g / l color powder (the specific color can be purchased according to the corresponding requirements), and the rest is deionized water; the working temperature of the dyeing solution is 35-50 ℃, and the working time is 10-30 min.

[0033] Further, in step (4), the blow-drying is performed by using a high-pressure air gun, and the pressure of the high-pressure air gun is 1.0-2.5 MPa.

[0034] The present application has the following advantages:

[0035] 1. The closed coating obtained based on the self-healing closed coating concentrate of the present application not only has excellent compactness, but also has excellent self-healing performance. Meanwhile, the preparation and application operation of the self-healing closed coating concentrate of the present application are simple, low in cost, and environmentally friendly and pollution-free.

[0036] 2. The closed coating obtained based on the self-healing closed coating concentrate of the present application avoids special process flows such as repeated closed process flows and electrolytic process flows, and realizes the purpose of strong binding force with the anodic oxidation film by using a type of complexing agent (one end of the type of complexing agent is complexed with cerium salt ions, and the other end forms a metal bond with the anodic oxidation film, thereby ensuring the strong binding force of the closed coating with the anodic oxidation film).

[0037] 3. When the self-healing sealing coating concentrate of the present invention is applied, it is used in conjunction with tartaric acid in the anodic oxidation solution (mainly used to control the pore size of the porous layer of the anodic oxide film) to ensure Ce 3+ Successfully entering and forming oxides or hydroxides for filling (ensuring the porous layer pore size of the anodic oxide film is adjustable, i.e., ensuring that Ce has already combined with a type of complexing agent). 3+ It can penetrate into porous layers.

[0038] 4. When the self-healing sealing coating concentrate of the present invention is applied, Ce2O3 and Ce(OH)3 are first generated in the porous layer of the anodic oxide film to fill the porous layer. Secondly, as the reaction proceeds, the sealing solution also generates a sealing coating on the surface of the anodic oxide film (avoiding the use of oxidants such as hydrogen peroxide, through the electron-withdrawing effect of the amide groups of the second type of complexing agent, so that Ce2O3 and Ce(OH)3 are formed). 3+ The electron cloud in Ce is biased towards the amide group, promoting Ce 3+ To Ce 4+ The transformation utilizes the characteristic that Ce(OH)4 has a lower solubility than Ce(OH)3 to form a sealed coating on the surface of the anodic oxide film, thereby achieving dual protection for the aluminum alloy substrate.

[0039] 5. The sealing coating obtained from the self-healing sealing coating concentrate of the present invention exhibits excellent self-healing properties in an alkaline environment. That is, even if the structure of the sealing coating is damaged, it can spontaneously repair itself within a short period of time without external action, providing effective protection for improving the corrosion resistance of aluminum alloy anodic oxide films. The self-healing principle of the sealing coating of the present invention is as follows:

[0040] 2Ce(OH)3→Ce2O3+3H2O (1)

[0041] 4Ce 3+ +O2+12OH - +2H2O→4Ce(OH)4 (2)

[0042] Ce(OH)4 → CeO2 + 2H2O (3)

[0043] When the aluminum alloy substrate is scratched and punctured, the Ce(OH)3 inside is exposed and reacts (1) to release trivalent cerium ions (Ce). 3+ The trivalent cerium ion (Ce) 3+ It will further react with hydroxide ions to generate Ce(OH)4, of which a portion of Ce(OH)4 will then be converted into CeO2. Therefore, the new sealing coating composed of Ce(OH)4 and CeO2 will once again seal the exposed aluminum alloy substrate, i.e., self-healing sealing effect. Detailed Implementation

[0044] The present invention will be further explained below with reference to the embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0045] The ammonia water mentioned below refers to industrial ammonia water, which is an aqueous solution containing 25wt% to 28wt% ammonia.

[0046] The corrosion resistance of the components in the following embodiments was tested according to the neutral salt spray test (NSS) and copper accelerated acetic acid salt spray test (CASS) in GB / T12967.3-2022 "Test Methods for Anodized Films and Organic Polymer Films of Aluminum and Aluminum Alloys Part 3: Salt Spray Test"; the sealing quality was tested according to the sodium phosphate molybdate method in GB / T 8753.1-2017 "Evaluation Method for Sealing Quality of Anodized Films of Aluminum and Aluminum Alloys Part 1: Acid Immersion Weight Loss Method"; and the uniform corrosion full immersion test method for metallic materials in the laboratory was performed according to JB / T 7901-2023, i.e., a scratch was made on the anodized aluminum alloy after the self-healing sealing coating was applied with a utility knife, and the scratch reached the aluminum alloy substrate (i.e., through the anodized film), and then the component was immersed in different pH solutions (using 250g / L). The scratches were treated with NaOH solution to adjust the pH, and then immersed in 3.5 wt% NaCl solution for different time periods (12h, 24h, 48h, 72h, 96h, and 120h) to check whether the scratches were automatically repaired and whether the parts were corroded. The 3.5 wt% NaCl solution was changed daily, and the pH needed to be readjusted and confirmed. The pH values ​​of the 3.5 wt% NaCl solution corresponding to Examples 1, 2, and 3 were 8.5, 7.5, and 9.0, respectively.

[0047] The degreasing and alkaline etching solutions in each embodiment include 45 g / L NaOH, 32 g / L Na2CO3, 25 g / L NaHCO3, 30 g / L NaH2PO4, 5 g / L Tween-60, and 30 g / L Na2SiO3, with the balance being deionized water; the stain removal solution includes 70 ml / L 98 wt% H2SO4 and 8 ml / L 40 w / v% HF, with the balance being deionized water; the anodizing solution includes 40 ml / L 98 wt% H2SO4 and 45 g / L tartaric acid, with the balance being deionized water.

[0048] Example 1

[0049] The self-healing sealing coating concentrate in this embodiment includes 18 g / L propionic acid, 25 g / L asparagine, 40 g / L cerium trichloride, 18 g / L ammonium oxalate, and 6 g / L sulfobetaine-12, with the remainder being deionized water.

[0050] The preparation procedure of the self-healing sealing coating concentrate is as follows: each component is weighed according to the above formula, and each component is dissolved into a transparent solution with deionized water; first, the propionic acid solution and the cerium trichloride solution are mixed and continuously stirred until homogeneous, then the ammonium oxalate solution, the sulfobetaine-12 solution are added under stirring and continuously stirred until homogeneous, and the pH of the mixed solution is adjusted to 8.0 using ammonia water; finally, the aspartic acid solution is added under stirring and continuously stirred until homogeneous, and the pH of the mixed solution is adjusted to 8.0 again using ammonia water, ready for use.

[0051] (1) Oil and alkali removal: the aluminum alloy substrate is placed in an oil and alkali removal solution at 60°C and pH 8.5 (pH adjusted by 250 g / l NaOH solution) for 5 min for oil and alkali removal, then taken out and washed with water, ready for use;

[0052] (2) Stain removal: the aluminum alloy substrate after oil and alkali removal is placed in a stain removal solution at 35°C for 60 s for stain removal, then taken out and washed with water, ready for use;

[0053] (3) Anodizing: the aluminum alloy substrate after stain removal is placed in an anodizing solution at 45°C for 85 min, and at the same time, a voltage of 15V is applied to it using a direct current power supply, for anodizing, then taken out and washed with water, ready for use; wherein the obtained anodizing film thickness is 26 μm;

[0054] (4) Dyeing: the aluminum alloy substrate after anodizing is placed in a solution of 8 g / l color powder (Hangzhou Heyun Technology Co., Ltd. ODM DYE ORANGE (OR214)) at 45°C for 30 min for dyeing, then taken out and washed with water, ready for use;

[0055] (5) Sealing: the aluminum alloy substrate after dyeing is placed in a sealing solution at 50°C, containing 100 ml / l self-healing sealing coating concentrate, pH 8.0 (pH adjusted by ammonia water) for 25 min for sealing, then taken out and washed with water, and then dried using a high-pressure air gun (1.5 MPa).

[0056] Example 2

[0057] The self-healing sealing coating concentrate in this example includes 25 g / l glycine, 30 g / l glutamine, 55 g / l cerium acetate, 20 g / l ammonium phthalate and 10 g / l dodecyl dimethyl betaine, and the balance is deionized water.

[0058] The preparation procedure of the self-healing sealing coating concentrate is as follows: each component is weighed according to the above formula, and each component is dissolved into a transparent solution with deionized water; first, the glycine solution and the cerium acetate solution are mixed and continuously stirred until homogeneous, then the ammonium phthalate solution and the dodecyl dimethyl betaine solution are added under stirring and continuously stirred until homogeneous, and the pH of the mixed solution is adjusted to 9.0 using ammonia water; finally, the glutamine solution is added under stirring and continuously stirred until homogeneous, and the pH of the mixed solution is adjusted to 9.0 again using ammonia water, ready for use.

[0059] (1) Oil and alkali removal: the aluminum alloy substrate is placed in an oil and alkali removal solution at 60°C and pH 8.5 (pH adjusted by 250 g / l NaOH solution) for 8 min for oil and alkali removal, then taken out and washed with water, ready for use;

[0060] (2) Stain removal: the aluminum alloy substrate after oil and alkali removal is placed in a stain removal solution at 35°C for 80 s for stain removal, then taken out and washed with water, ready for use;

[0061] (3) Anodizing: the aluminum alloy substrate after stain removal is placed in an anodizing solution at 45°C for 90 min, and at the same time, a voltage of 18V is applied to it using a direct current power supply, for anodizing, then taken out and washed with water, ready for use; wherein the obtained anodizing film thickness is 30 μm;

[0062] (4) Dyeing: the aluminum alloy substrate after anodizing is placed in a solution of 10 g / l color powder (Hangzhou Heyun Technology Co., Ltd. ODM DYE BROWN (BN615)) at 50°C for 15 min for dyeing, then taken out and washed with water, ready for use;

[0063] (5) Sealing: the aluminum alloy substrate after dyeing is placed in a sealing solution at 45°C, with 80 ml / l self-healing sealing coating concentrate and pH 9.0 (pH adjusted by ammonia water) for 30 min for sealing, then taken out and washed with water, and then dried using a high-pressure air gun (1.5 MPa).

[0064] Example 3

[0065] The self-healing sealing coating concentrate in this example includes 10 g / l tartaric acid, 15 g / l glutamine, 15 g / l asparagine, 30 g / l cerium carbonate, 20 g / l ammonium phthalate and 5 g / l tetradecyl hydroxypropyl phosphate betaine, and the balance is deionized water.

[0066] The preparation procedure of the self-healing sealing coating concentrate is as follows: each component is weighed according to the above formula, and each component is dissolved into a transparent solution with deionized water; first, the tartaric acid solution and the cerium carbonate solution are mixed and continuously stirred until homogeneous, then the ammonium phthalate solution and the tetradecyl hydroxypropyl phosphatidylcholine solution are added under stirring and continuously stirred until homogeneous, and the pH of the mixed solution is adjusted to 7.5 using ammonia water; finally, the glutamine solution and the asparagine solution are added under stirring and continuously stirred until homogeneous, and the pH of the mixed solution is adjusted to 7.5 using ammonia water again, and is ready for use.

[0067] (1) Oil and alkali removal: the aluminum alloy substrate is placed in an oil and alkali removal solution at 60°C and pH 9.0 (pH is adjusted by 250 g / l NaOH solution) for 5 min for oil and alkali removal, then taken out and washed with water, and is ready for use;

[0068] (2) Stain removal: the aluminum alloy substrate after oil and alkali removal is placed in a stain removal solution at 30°C for 70 s for stain removal, then taken out and washed with water, and is ready for use;

[0069] (3) Anodizing: the aluminum alloy substrate after stain removal is placed in an anodizing solution at 55°C for 80 min, and a voltage of 22V is applied to it at the same time using a direct current power supply for anodizing, then taken out and washed with water, and is ready for use; wherein the thickness of the anodizing film obtained is 24 μm;

[0070] (4) Dyeing: the aluminum alloy substrate after anodizing is placed in a solution containing 5 g / l color powder (Hangzhou Heyun Technology Co., Ltd. ODM DYE YELLOW (YW3105)) at 50°C for 20 min for dyeing, then taken out and washed with water, and is ready for use;

[0071] (5) Sealing: the aluminum alloy substrate after dyeing is placed in a sealing solution at 45°C containing 120 ml / l self-healing sealing coating concentrate and pH 7.5 (pH is adjusted by ammonia water) for 30 min for sealing, then taken out and washed with water, and is ready for use using a high-pressure air gun (1.5 MPa).

[0072] The products obtained in each example are subjected to performance testing, and the test results are shown in the following table:

[0073] neutral salt spray test (NSS) copper-accelerated acetic acid salt spray test (CASS) acid immersion corrosion weight loss method - sodium molybdate-phosphoric acid method self-healing performance Example 1 10 scale 10 scale 0 mg / dm 2 ]] scratch was initially healed at 12 h, completely healed at 72 h, and no corrosion phenomenon Example 2 10 scale 10 scale 0 mg / dm 2 ]] scratch was initially healed at 12 h, completely healed at 24 h, and no corrosion phenomenon Example 3 10 scale 10 scale 0 mg / dm 2 ]] scratch was completely healed at 12 h, and no corrosion phenomenon

Claims

1. A self-healing, closed-coat, concentrate, characterized in that, The self-healing sealing coating concentrate solution comprises a kind of complexing agent, a second kind of complexing agent, soluble cerium salt, pH buffer, wetting agent and deionized water; The first kind of complexing agent comprises one or more of propionic acid and its salts, lactic acid and its salts, glycine and its salts, malic acid and its salts, tartaric acid and its salts, acetic acid and its salts; The second kind of complexing agent comprises one or both of asparagine and glutamine; The soluble cerium salt is one or more of cerium trichloride, cerium triiodide, cerium carbonate, cerium acetate and cerium phosphate; The pH buffer is one or more of ammonium oxalate, phosphate buffer and ammonium phthalate; The wetting agent is one or more of phosphoric acid betaine type, sulfobetaine type and carboxybetaine type; The mass ratio of the first kind of complexing agent, the second kind of complexing agent, the soluble cerium salt, the pH buffer and the wetting agent is 10-25:20-30:25-55:15-20:3-10, and the rest is deionized water.

2. A process for the preparation of a self-healing encapsulated coating concentrate as claimed in claim 1, characterized in that, The method comprises the following steps: (1) Each component is weighed according to the formula amount, and each component is dissolved into a transparent solution with an appropriate amount of deionized water; (2) The first kind of complexing agent solution is mixed with the soluble cerium salt solution and continuously stirred until homogeneous, to obtain a mixed solution; (3) The pH buffer solution and the wetting agent solution are added to the mixed solution obtained in step (2) under stirring and continuously stirred until the mixed solution is homogeneous, and the pH of the mixed solution is adjusted to 7.5-9.0 using ammonia; (4) The second kind of complexing agent solution is added to the mixed solution obtained in step (3) under stirring and continuously stirred until the mixed solution is homogeneous, and the pH of the mixed solution is adjusted to 7.5-9.0 using ammonia.

3. The self-healing sealing coating concentrate solution of claim 1 is used in sealing of an anodized film of an aluminum alloy.

4. Use according to claim 3, characterized in that, When used, the method comprises the following steps: (1) Surface pretreatment: a) Oil removal and alkali etching: the aluminum alloy substrate is placed in an oil removal and alkali etching solution for oil removal and alkali etching, and then taken out and washed with water; b) Stain removal: the aluminum alloy substrate after oil removal and alkali etching is placed in a stain removal solution for stain removal, and then taken out and washed with water; (2) Anodizing: the aluminum alloy substrate after surface pretreatment is placed in an anodizing solution for anodizing, and then taken out and washed with water; (3) Dyeing: the aluminum alloy substrate after anodizing is placed in a dyeing solution for dyeing, and then taken out and washed with water; (4) Sealing: the aluminum alloy substrate after dyeing is placed in a sealing solution for sealing, and then taken out, washed with water and dried; wherein the sealing solution comprises 80-120 ml / l of the self-healing sealing coating concentrate solution and the rest is deionized water; when used, the pH of the sealing solution is adjusted to 7.5-9.0 using ammonia; the working temperature of the sealing solution is 25-50°C, and the working time is 15-30 min.

5. Use according to claim 4, characterized in that, In step (1), the degreasing alkaline etching solution comprises 40-55 g / l NaOH, 30-35 g / l Na2CO3, 18-30 g / l NaHCO3, 25-35 g / l NaH2PO4, 3-8 g / l Tween-60, 25-35 g / l Na2SiO3, and the rest is deionized water; during operation, the pH of the degreasing alkaline etching solution is adjusted to 8.0-9.5 by using a 200 g / l-250 g / l NaOH solution; the working temperature of the degreasing alkaline etching solution is 55-60 °C, and the working time is 5-10 min.

6. Use according to claim 4, characterized in that, In step (1), the stain removal solution comprises 65-80 ml / l 98 wt% H2SO4, 5-12 ml / l 40 w / v% HF, and the rest is deionized water; the working temperature of the stain removal solution is 25-35 °C, and the working time is 60-90 s.

7. Use according to claim 4, characterized in that, In step (2), the anodizing solution comprises 30-45 ml / l 98 wt% H2SO4, 35-50 g / l tartaric acid, and the rest is deionized water; the working temperature of the anodizing solution is 10-55 °C, the direct current power is 15-30 V, and the working time is 60-90 min.

8. Use according to claim 7, characterized in that, The anodizing film obtained by anodizing has a thickness of 20-35 μm.

9. Use according to claim 4, characterized in that, In step (3), the dyeing solution comprises 1-25 g / l color powder, and the rest is deionized water; the working temperature of the dyeing solution is 35-50 °C, and the working time is 10-30 min.

10. Use according to claim 4, characterized in that, In step (4), the drying is performed by using a high-pressure air gun, and the pressure of the high-pressure air gun is 1.0-2.5 MPa.