A kind of aluminum alloy surface anticorrosion treatment method

Abstract

The invention relates to the technical field of corrosion protection, in particular to an aluminum alloy surface corrosion protection treatment method, which solves the problems that after a chelate of high-concentration phytic acid and metal ions damages a metal acid salt film layer, the oxidation resistance of the aluminum alloy becomes weak, and the organic acid film layer cannot become thicker due to the limitation of the organic acid concentration, etc. The invention comprises a passivation pretreatment, a passivation agent is used to passivate the surface of the aluminum alloy, and a phytic acid closed film is formed, the phytic acid is embedded to obtain slow-release particles, a closed liquid containing the slow-release particles is prepared, the surface of the passivation film is placed in the closed liquid for multi-stage ultrasonic treatment, the time interval of the single-stage ultrasonic treatment is 4-6 minutes, and finally a maleic acid resin film is coated, a coating containing maleic acid alkyd resin is coated on the surface of the phytic acid closed film, and high-temperature curing is performed to complete the corrosion protection treatment of the aluminum alloy; after the aluminum alloy is treated by the invention, its corrosion resistance is greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of corrosion protection, and in particular to a method for treating the surface of an aluminum alloy against corrosion. Background Art

[0002] Under normal conditions, aluminum alloy reacts with oxygen in the air to form an extremely dense oxide film, which has extremely low resistance to acids and alkalis. Therefore, in order to address the problem of poor corrosion resistance of aluminum alloys in acidic and alkaline environments and environments with high humidity, technical means such as electrophoretic coating films and chemical precipitation films have been developed. Electrophoretic coating is relatively complex and the control factors are difficult to grasp, so the yield rate is low. Most companies use chemical precipitation for anti-corrosion treatment, among which chromate, titanate and rare earth acid conversion films have appeared one after another, followed by organic acid chemical conversion treatments.

[0003] Among them, the use of phytic acid to treat the surface of aluminum alloy is relatively excellent. It not only does not pollute the environment, but also has a good effect on isolating oxygen. It also achieves electronic isolation that metal acid salts cannot do, and has high corrosion resistance under extreme salt spray tests. For example, in the aluminum alloy surface passivation solution and treatment method thereof disclosed in Chinese Patent Publication No. CN103834939A, phytic acid, sodium fluoride and nitric acid are used to directly passivate the surface of the aluminum alloy, and finally form a comprehensive anti-corrosion film layer. However, due to the insufficient amount of organic acids such as phytic acid, the chelating effect is not good, and it is difficult to form a completely continuous organic film layer; therefore, a metal salt oxide film layer is first prepared on the surface of the aluminum alloy, and then an organic acid film layer is prepared on the surface of the oxide film layer, thereby forming a relatively continuous film layer. The most novel technical means to achieve double blocking of oxygen and electrons is to be used.

[0004] However, when the above-mentioned double-layer membrane method was actually operated, it was found that the phytic acid concentration in the organic layer membrane could not exceed a certain value. If the concentration of phytic acid was too high, the number of phosphate groups per unit volume in the liquid would increase, thereby causing the pH to rise. The higher the pH, the stronger the chelating ability between phytic acid and metal atoms. In a high-concentration phytic acid solution, the rate at which phytic acid chelates metals is too fast, which has a great destructive effect on the metal acid salt film layer, forming irregular corrosion sites, causing the metal acid salt film layer to be discontinuous and incomplete, reducing the corrosion resistance of the aluminum alloy, and the thickness of the organic acid film layer cannot be further thickened to improve the corrosion resistance. Summary of the invention

[0005] In order to solve the problems that the chelation rate of phytic acid and metal ions is too fast when the phytic acid concentration is too high, causing the metal acid salt film layer to lose metal ions, the oxidation resistance of the film layer becomes weaker after the film layer is damaged, and the organic acid film layer cannot be thickened due to the limitation of the organic acid concentration, the present application provides an aluminum alloy surface anti-corrosion treatment method, and the technical solution adopted by the application includes the following treatment steps:

[0006] S1, passivation pretreatment, after grinding, alkali washing and deoxidation of the aluminum alloy surface, passivation of the aluminum alloy surface using a passivation agent to form a passivation film;

[0007] S2, formation of phytic acid blocking film, embedding treatment of phytic acid to obtain slow-release particles, preparing blocking solution containing slow-release particles, wherein the pH of the blocking solution is 2.5-3.0, placing the surface of the passivation film in the blocking solution for multi-stage ultrasonic treatment, the ultrasonic power is 120w-200w, the treatment temperature is 50-60°C, the single stage ultrasonic treatment of the multi-stage ultrasonic treatment is 1-2min, and the interval time of the single stage ultrasonic treatment is 4-6min;

[0008] S3, coating of maleic acid resin film, coating a coating containing maleic acid alkyd resin on the surface of phytic acid sealing film, and completing the anti-corrosion treatment of aluminum alloy after high temperature curing;

[0009] The usage of the slow-release particles is 120g-200g / L.

[0010] The treatment of this application is mainly divided into three steps. The first step is to grind and chemically polish the surface of the aluminum alloy to remove various factors that affect the combination of the aluminum alloy surface and the protective layer, grind to remove protrusions and depressions, flatten the molecular surface, alkaline wash to remove the loose oxide layer on the surface, deoxidize to remove excess alkaline substances, and then passivate the treated surface with metal acid salts to form a relatively complete and uniform anti-oxidation film;

[0011] The second step is to encapsulate the phytic acid to prevent excessive phytic acid from contacting the metal salt film layer at the same time. The concentration of phosphate groups on the phytic acid is too high, and after chelating with metal ions, the metal salt film layer is destroyed. After encapsulation, the slow-release particles will not directly release phytic acid, but in the subsequent treatment, the cavitation effect of ultrasonic treatment will open the structure of the encapsulated material particles, so that the phytic acid is slowly released. Phytic acid chelates with metal ions evenly on the surface of the aluminum alloy. After phytic acid chelates a part of the metal, it is ultrasonically treated again to release phytic acid. Repeated chelation of phytic acid can avoid the occurrence of the phenomenon that the metal salt film layer is destroyed due to excessive phytic acid concentration in local areas, thereby ensuring that the internal aluminum alloy is not oxidized. After multiple phytic acid chelations, the formed organic film layer will be thicker and have more active sites for further processing.

[0012] The last step is to coat the surface with a thicker organic film layer with a maleic acid resin film. Maleic acid resin, also known as maleic acid alkyd resin, contains carboxyl groups in its molecular structure, which can stably react with the phosphate groups in phytic acid to form stable chemical bonds. This effective connection can not only stabilize the overly thick organic film layer, but also strengthen the connection between the outer resin coating and the aluminum alloy. It has a strong electronic isolation ability, which greatly improves the corrosion resistance of the organic film layer and improves the resistance of the aluminum alloy to external corrosion.

[0013] Furthermore, the specific steps of the phytic acid embedding treatment are as follows:

[0014] A1, placing ethyl cellulose in anhydrous ethanol and stirring to dissolve, then adding polyethylene glycol by dropwise addition to obtain an embedding base solution, and finally adding phytic acid to the embedding base solution for homogenization to obtain an embedding solution;

[0015] A2, spray drying the embedding solution to form sustained-release particles containing phytic acid;

[0016] The mass ratio of the phytic acid to the ethyl cellulose is 1:3-10.

[0017] The embedding material used in the present application is ethyl cellulose, which does not react with the effective groups on phytic acid and is not soluble in water. Therefore, when ultrasonic treatment is not performed, the phytic acid can be effectively isolated from the outside world. However, when ultrasonic treatment is performed, the microcapsule structure of ethyl cellulose will be affected to a certain extent, thereby causing the destruction of the capsule wall and releasing the core material-phytic acid embedded inside. Step-by-step ultrasound can release a certain amount of phytic acid from the outside to the inside, thereby preventing excessive phytic acid and controlling the uniform formation of the organic acid sealing membrane.

[0018] Furthermore, the solid-liquid ratio of the ethyl cellulose to the anhydrous ethanol is 1:20-30, and the added amount of the polyethylene glycol is 1%-5% of the anhydrous ethanol.

[0019] Furthermore, the coating composition for forming the maleic acid resin film is 40-60 parts of fatty acid, 3-10 parts of maleic anhydride, 20-35 parts of rosin and 10-20 parts of pentaerythritol.

[0020] Furthermore, the preparation method of the coating is as follows: heating rosin to a molten state and stirring, adding maleic anhydride during the stirring process, heating to 200°C and then keeping warm for standby use; mixing fatty acid and pentaerythritol and heating to perform a first esterification reaction, then adding the reactants after the esterification reaction to a mixture containing maleic anhydride and rosin for a second esterification reaction, refluxing xylene to remove water, cooling and filtering after no water is produced to obtain the coating.

[0021] Furthermore, the temperature of the first esterification reaction is 215-255° C., the reaction time is 1 hour, the temperature of the second esterification reaction is 225-235° C., and the termination criterion of the second esterification reaction is that no water is produced during the reflux of xylene.

[0022] Furthermore, the passivation reagent used in S1 is a mixed solution of sodium fluoride and titanyl sulfate, the pH of the passivation treatment is 5-6, the temperature of the passivation treatment is 40-50°C, the reaction time is 30 minutes, and the mass ratio of sodium fluoride to titanyl sulfate is 6-10:1.

[0023] Furthermore, the concentration of sodium fluoride in the passivation treatment is 1-10 g / L.

[0024] Furthermore, the thickness of the phytic acid sealing film is 17.5-19.0 μm.

[0025] The anti-corrosion treatment method of the present application can be applied to the surface treatment of aluminum alloys.

[0026] The beneficial effects of the present invention are:

[0027] The anti-corrosion treatment method of the present application can effectively improve the isolation ability against oxygen and electrons, thereby improving the corrosion resistance of the aluminum alloy by first converting a passivation film on the surface of the aluminum alloy and forming a thicker organic acid film layer on the outside of the passivation film.

[0028] The present application uses an embedding technology to limit the concentration of phytic acid to increase the thickness of the organic acid film layer, thereby reducing excessive chelation of phytic acid and metal ions in local areas and avoiding damage to the passivation film. The phytic acid substance is then slowly released under ultrasonic treatment to form a relatively uniform organic film layer. During the film formation process of the organic film layer, the phytic acid concentration will not be too high and will be dispersed in the sealing liquid at a low concentration. This uniform state of phytic acid will not damage the metal acid film layer, thereby ensuring that the corrosion resistance of the aluminum alloy after sealing will not decrease. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a bar graph of the corrosion resistance time of the embodiments of the present invention and the comparative examples in salt spray. DETAILED DESCRIPTION

[0030] The following will refer to the attached Figure 1 The embodiments of the present invention are described in detail. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0031] Preparation Example 1

[0032] Preparation of sustained-release particles: Ethyl cellulose is placed in anhydrous ethanol at a solid-liquid ratio of 1:25 and stirred to dissolve, polyethylene glycol with a volume of 3% of anhydrous ethanol is added dropwise to the solution of anhydrous ethanol and ethyl cellulose to obtain an embedding base liquid, and finally phytic acid is added to the embedding base liquid for homogenization to obtain an embedding solution, wherein the mass ratio of phytic acid to ethyl cellulose is 1:5, and the embedding solution is spray-dried, with a feed rate of 100 ml per hour, an inlet air temperature of 130°C, and an outlet air temperature of 70°C, to form sustained-release particles containing phytic acid.

[0033] Preparation Example 2:

[0034] Preparation of sustained-release particles: Ethyl cellulose is placed in anhydrous ethanol at a solid-liquid ratio of 1:20 and stirred to dissolve, polyethylene glycol with a volume of 1% of anhydrous ethanol is added dropwise to the solution of anhydrous ethanol and ethyl cellulose to obtain an embedding base liquid, and finally phytic acid is added to the embedding base liquid for homogenization to obtain an embedding solution, wherein the mass ratio of phytic acid to ethyl cellulose is 1:10, and the embedding solution is spray-dried, with a feed rate of 100 ml per hour, an inlet air temperature of 130°C, and an outlet air temperature of 70°C, to form sustained-release particles containing phytic acid.

[0035] Preparation Example 3:

[0036] Preparation of sustained-release particles: Ethyl cellulose is placed in anhydrous ethanol at a solid-liquid ratio of 1:30 and stirred to dissolve, polyethylene glycol with a volume of 5% of anhydrous ethanol is added dropwise to the solution of anhydrous ethanol and ethyl cellulose to obtain an embedding base liquid, and finally phytic acid is added to the embedding base liquid for homogenization to obtain an embedding solution, wherein the mass ratio of phytic acid to ethyl cellulose is 1:3, and the embedding solution is spray-dried, with a feed rate of 100 ml per hour, an inlet air temperature of 130°C, and an outlet air temperature of 70°C, to form sustained-release particles containing phytic acid.

[0037] Preparation Example 4: Using chitosan instead of ethyl cellulose

[0038] Preparation of sustained-release particles: chitosan is placed in anhydrous ethanol at a solid-liquid ratio of 1:25 and stirred to dissolve, polyethylene glycol with a volume of 3% of anhydrous ethanol is added dropwise to the solution of anhydrous ethanol and chitosan to obtain an embedding base liquid, and finally phytic acid is added to the embedding base liquid for homogenization to obtain an embedding solution, wherein the mass ratio of phytic acid to chitosan is 1:5, and the embedding solution is spray-dried, with a feed rate of 100 ml per hour, an inlet air temperature of 130°C, and an outlet air temperature of 70°C, to form sustained-release particles containing phytic acid.

[0039] Preparation Example 5: Instead of using phytic acid for embedding, benzotriazole

[0040] Preparation of sustained-release particles: Ethyl cellulose is placed in anhydrous ethanol at a solid-liquid ratio of 1:25 and stirred to dissolve, polyethylene glycol with a volume of 3% of anhydrous ethanol is added dropwise to the solution of anhydrous ethanol and ethyl cellulose to obtain an embedding base liquid, and finally benzotriazole is added to the embedding base liquid for homogenization to obtain an embedding solution, wherein the mass ratio of benzotriazole to ethyl cellulose is 1:5, and the embedding solution is spray-dried, with a feed rate of 100 ml per hour, an inlet air temperature of 130°C, and an outlet air temperature of 70°C, to form sustained-release particles containing benzotriazole.

[0041] Preparation Example 6: The mass ratio of phytic acid to ethyl cellulose is 1:2

[0042] Preparation of sustained-release particles: Ethyl cellulose is placed in anhydrous ethanol at a solid-liquid ratio of 1:25 and stirred to dissolve, polyethylene glycol with a volume of 3% of anhydrous ethanol is added dropwise to the solution of anhydrous ethanol and ethyl cellulose to obtain an embedding base liquid, and finally phytic acid is added to the embedding base liquid for homogenization to obtain an embedding solution, wherein the mass ratio of phytic acid to ethyl cellulose is 1:2, and the embedding solution is spray-dried, with a feed rate of 100 ml per hour, an inlet air temperature of 130°C, and an outlet air temperature of 70°C, to form sustained-release particles containing phytic acid.

[0043] Example 1

[0044] S1. Use sandblasting to remove impurities from the surface of the aluminum alloy to be treated, use 5% sodium hydroxide to alkaline wash the surface of the aluminum alloy for 5 minutes, and then use 5% nitric acid solution to deoxidize and clean the surface of the aluminum alloy for 3 minutes, and then prepare a passivation agent with a concentration of 8g / L NaF solution and 1g / L TiOSO4 in the solution. The pH of the passivation agent is 5, and the aluminum alloy surface is passivated at 45°C for 30 minutes to form a passivation film.

[0045] S2, formation of phytic acid sealing film, using the slow-release particles prepared in Preparation Example 1, preparing a sealing solution, the amount of the slow-release particles is 150g / L, the pH of the sealing solution is 3.0, the surface of the passivation film is placed in the sealing solution for ultrasonic treatment, the ultrasonic power is 180w, the treatment temperature is 55°C, the ultrasonic treatment time is 2min, the reaction is performed after ultrasonic treatment for 5min, and then the ultrasonic treatment and reaction after ultrasonic treatment are repeated for 5 times.

[0046] S3, coating of maleic acid resin film, heat 30 parts of rosin by weight to a molten state and stir, add 5 parts of maleic anhydride during the stirring process, heat to 200°C and keep warm for use; mix 50 parts of fatty acid and 15 parts of pentaerythritol and heat to carry out the first esterification reaction, the reaction temperature is 235°C, the reaction time is 1h, then add the reactants after the esterification reaction to a mixture containing maleic anhydride and rosin for a second esterification reaction, the reaction temperature is 230°C, use xylene to reflux and remove water, after no water is produced, cool and filter to obtain maleic acid coating, apply the coating containing maleic acid alkyd resin on the surface of phytic acid sealing film, and complete the anti-corrosion treatment of aluminum alloy after high-temperature curing.

[0047] Example 2

[0048] S1. Use sandblasting to remove impurities from the surface of the aluminum alloy to be treated, use 5% sodium hydroxide to alkaline wash the surface of the aluminum alloy for 5 minutes, and then use 5% nitric acid solution to deoxidize and clean the surface of the aluminum alloy for 3 minutes, and then prepare a passivation agent with a concentration of 8g / L NaF solution and 1g / L TiOSO4 in the solution. The pH of the passivation agent is 5, and the aluminum alloy surface is passivated at 45°C for 30 minutes to form a passivation film.

[0049] S2, formation of phytic acid sealing film, using the slow-release particles prepared in Preparation Example 2, preparing a sealing solution, the amount of slow-release particles is 120g / L, the pH of the sealing solution is 2.5, the surface of the passivation film is placed in the sealing solution for ultrasonic treatment, the ultrasonic power is 120w, the treatment temperature is 50°C, the ultrasonic treatment time is 1min, the reaction is performed after ultrasonic treatment for 4min, and then the ultrasonic treatment and the reaction after ultrasonic treatment are repeated for 5 times.

[0050] S3, coating of maleic acid resin film, heat 20 parts of rosin by weight to a molten state and stir, add 3 parts of maleic anhydride during the stirring process, heat to 200°C and keep warm for use; mix 40 parts of fatty acid and 10 parts of pentaerythritol and heat to carry out the first esterification reaction at 215°C for 1h, then add the reactants after the esterification reaction to a mixture containing maleic anhydride and rosin for a second esterification reaction at 225°C, use xylene to reflux and remove water, cool and filter after no water is produced to obtain maleic acid coating, apply the coating containing maleic acid alkyd resin on the surface of phytic acid sealing film, and complete the anti-corrosion treatment of aluminum alloy after high-temperature curing.

[0051] Example 3

[0052] S1. Use sandblasting to remove impurities from the surface of the aluminum alloy to be treated, use 5% sodium hydroxide to alkaline wash the surface of the aluminum alloy for 5 minutes, and then use 5% nitric acid solution to deoxidize and clean the surface of the aluminum alloy for 3 minutes, and then prepare a passivation agent with a concentration of 8g / L NaF solution and 1g / L TiOSO4 in the solution. The pH of the passivation agent is 5, and the aluminum alloy surface is passivated at 45°C for 30 minutes to form a passivation film.

[0053] S2, formation of phytic acid sealing film, using the slow-release particles prepared in Preparation Example 3, preparing a sealing solution, the amount of slow-release particles is 200g / L, the pH of the sealing solution is 3.0, the surface of the passivation film is placed in the sealing solution for ultrasonic treatment, the ultrasonic power is 200w, the treatment temperature is 60°C, the ultrasonic treatment time is 2min, the reaction is performed after ultrasonic treatment for 6min, and then the ultrasonic treatment and the reaction after ultrasonic treatment are repeated for 5 times.

[0054] S3, coating of maleic acid resin film, heat 35 parts of rosin by weight to a molten state and stir, add 10 parts of maleic anhydride during the stirring process, heat to 200°C and keep warm for use; mix 60 parts of fatty acid and 20 parts of pentaerythritol and heat to carry out the first esterification reaction at 255°C for 1h, then add the reactants after the esterification reaction to a mixture containing maleic anhydride and rosin for a second esterification reaction at 235°C, use xylene to reflux and remove water, cool and filter after no water is produced to obtain maleic acid coating, apply the coating containing maleic acid alkyd resin on the surface of phytic acid sealing film, and complete the anti-corrosion treatment of aluminum alloy after high-temperature curing.

[0055] Comparative Example 1

[0056] The difference between this comparative example and Example 1 is that the sustained-release granules used are the sustained-release granules prepared in Preparation Example 4.

[0057] Comparative Example 2

[0058] The difference between this comparative example and Example 1 is that the sustained-release granules used are the sustained-release granules prepared in Preparation Example 5.

[0059] Comparative Example 3

[0060] The difference between this comparative example and Example 1 is that the sustained-release granules used are the sustained-release granules prepared in Preparation Example 6.

[0061] Comparative Example 4

[0062] The difference between this comparative example and Example 1 is that the phytic acid is not embedded, but the passivation film is directly sealed. The specific differences are as follows:

[0063] S1. Use sandblasting to remove impurities from the surface of the aluminum alloy to be treated, use 5% sodium hydroxide to alkaline wash the surface of the aluminum alloy for 5 minutes, and then use 5% nitric acid solution to deoxidize and clean the surface of the aluminum alloy for 3 minutes, and then prepare a passivation agent with a concentration of 8g / L NaF solution and 1g / L TiOSO4 in the solution. The pH of the passivation agent is 5, and the aluminum alloy surface is passivated at 45°C for 30 minutes to form a passivation film.

[0064] S2, formation of phytic acid blocking film, prepare a blocking solution with a phytic acid concentration of 35g / L, the pH of the blocking solution is 4.0, place the surface of the passivation film in the blocking solution for ultrasonic treatment, the ultrasonic power is 180w, the treatment temperature is 55℃, the ultrasonic treatment time is 2min, the reaction is performed after ultrasonic treatment for 5min, and then the ultrasonic treatment and reaction after ultrasonic treatment are repeated for 5 times.

[0065] S3, coating of maleic acid resin film, heat 30 parts of rosin by weight to a molten state and stir, add 5 parts of maleic anhydride during the stirring process, heat to 200°C and keep warm for use; mix 50 parts of fatty acid and 15 parts of pentaerythritol and heat to carry out the first esterification reaction, the reaction temperature is 235°C, the reaction time is 1h, then add the reactants after the esterification reaction to a mixture containing maleic anhydride and rosin for a second esterification reaction, the reaction temperature is 230°C, use xylene to reflux and remove water, after no water is produced, cool and filter to obtain maleic acid coating, apply the coating containing maleic acid alkyd resin on the surface of phytic acid sealing film, and complete the anti-corrosion treatment of aluminum alloy after high-temperature curing.

[0066] Comparative Example 5

[0067] The difference between this comparative example and Example 1 is that no maleic acid resin film coating is performed, and the specific differences are as follows:

[0068] S1. Use sandblasting to remove impurities from the surface of the aluminum alloy to be treated, use 5% sodium hydroxide to alkaline wash the surface of the aluminum alloy for 5 minutes, and then use 5% nitric acid solution to deoxidize and clean the surface of the aluminum alloy for 3 minutes, and then prepare a passivation agent with a concentration of 8g / L NaF solution and 1g / L TiOSO4 in the solution. The pH of the passivation agent is 5, and the aluminum alloy surface is passivated at 45°C for 30 minutes to form a passivation film.

[0069] S2, formation of phytic acid sealing film, using the slow-release particles prepared in Preparation Example 1, preparing a sealing solution, the amount of the slow-release particles is 150g / L, the pH of the sealing solution is 3.0, the surface of the passivation film is placed in the sealing solution for ultrasonic treatment, the ultrasonic power is 180w, the treatment temperature is 55°C, the ultrasonic treatment time is 2min, the reaction is performed after ultrasonic treatment for 5min, and then the ultrasonic treatment and reaction after ultrasonic treatment are repeated for 5 times.

[0070] S3. Coating of ethylene resin anti-corrosion paint film: Use commercially available ethylene resin anti-corrosion paint to coat the ethylene resin anti-corrosion paint on the surface of the phytic acid sealing film, and complete the anti-corrosion treatment of the aluminum alloy after high-temperature curing.

[0071] Comparative Example 6

[0072] The difference between this comparative example and Example 1 is that multi-stage ultrasonic treatment is not performed, and the specific differences are as follows:

[0073] S1. Use sandblasting to remove impurities from the surface of the aluminum alloy to be treated, use 5% sodium hydroxide to alkaline wash the surface of the aluminum alloy for 5 minutes, and then use 5% nitric acid solution to deoxidize and clean the surface of the aluminum alloy for 3 minutes, and then prepare a passivation agent with a concentration of 8g / L NaF solution and 1g / L TiOSO4 in the solution. The pH of the passivation agent is 5, and the aluminum alloy surface is passivated at 45°C for 30 minutes to form a passivation film.

[0074] S2, formation of phytic acid blocking film, using the slow-release particles prepared in Preparation Example 1, preparing blocking solution, the amount of slow-release particles is 150g / L, the pH of the blocking solution is 3.0, the surface of the passivation film is placed in the blocking solution for ultrasonic treatment, the ultrasonic power is 180w, the treatment temperature is 55°C, the ultrasonic treatment time is 15min, and the reaction is carried out for 5min after ultrasonic treatment.

[0075] S3, coating of maleic acid resin film, heat 30 parts of rosin by weight to a molten state and stir, add 5 parts of maleic anhydride during the stirring process, heat to 200°C and keep warm for use; mix 50 parts of fatty acid and 15 parts of pentaerythritol and heat to carry out the first esterification reaction, the reaction temperature is 235°C, the reaction time is 1h, then add the reactants after the esterification reaction to a mixture containing maleic anhydride and rosin for a second esterification reaction, the reaction temperature is 230°C, use xylene to reflux and remove water, after no water is produced, cool and filter to obtain maleic acid coating, apply the coating containing maleic acid alkyd resin on the surface of phytic acid sealing film, and complete the anti-corrosion treatment of aluminum alloy after high-temperature curing.

[0076] Experiments and data

[0077] The aluminum alloys after the anti-corrosion treatment in the above embodiment and the comparative example were subjected to a neutral salt spray test and an organic film thickness test. The test method is as follows:

[0078] The anti-corrosion effect is tested according to the standard of GB6458-86.

[0079] Test standard: 2, 6, 16, 24, 48, 96, 240, 480, 720h rust

[0080] The test results are shown in Table 1 below:

[0081] Table 1

[0082]

[0083] The experimental results of neutral salt spray resistance of Examples 1-3 and Comparative Examples 1-6 are as follows: Figure 1 shown.

[0084] analyze

[0085] According to the data in Table 1 of Example 1 to Example 3, after using the anti-corrosion treatment method of the present application, the aluminum alloy exhibits excellent salt spray resistance and can remain rust-free for 480 hours in the salt spray test. The thickness of the organic film is also improved, which can effectively reduce the corrosion current density and has strong corrosion resistance.

[0086] According to Table 1, in terms of salt spray resistance, the aluminum alloy of Comparative Example 1 rusted after 96 hours of testing, and the thickness of the organic film layer was extremely small, far from meeting the standard for blocking electrochemical corrosion, indicating that the use of ethyl cellulose can effectively maintain the structure and characteristics of phytic acid molecules and will not affect the chelation of phytic acid molecules with metal ions.

[0087] According to Table 1, the aluminum alloy of Comparative Example 2 has a relatively high improvement in salt spray resistance. Rust appeared after 480 hours, and its film thickness increased compared with Comparative Example 1, but did not increase significantly compared with Example 1, indicating that the organic film layer constructed by phytic acid molecules has a significant advantage in film thickness. The use of phytic acid molecules can increase the thickness of the organic film layer, increase resistance to electrochemical corrosion, and correspondingly improve corrosion resistance.

[0088] According to Table 1, the aluminum alloy of Comparative Example 3 has no obvious improvement in salt spray resistance, but has a relatively high improvement in the thickness of the organic film layer, indicating that excessive use of phytic acid will cause the metal salt film layer to be damaged and the salt spray resistance is poor, proving that the use of an appropriate amount of phytic acid and ethyl cellulose can effectively improve the corrosion resistance of the aluminum alloy.

[0089] According to the data in Table 1, the aluminum alloy of Comparative Example 4 has extremely poor salt spray resistance test, and the aluminum alloy is easily corroded. The thickness of the organic film of Comparative Example 4 is relatively high, indicating that the formed film layer is not uniform and the local film layer is damaged. This proves that embedding phytic acid molecules can effectively solve the damage of high concentration phytic acid to the metal acid salt film layer and ensure the uniform formation of the organic acid film layer.

[0090] According to the data in Table 1, the aluminum alloy of Comparative Example 5 rusted after 480 hours of testing in the salt spray resistance test, and the thickness of its organic film layer was low, indicating that the corrosion resistance had a certain improvement, and the film layer was relatively uniform. The corrosion resistance could not be improved due to the thickness of the organic film chelation. Combined with the film thickness of Comparative Example 2, it can be seen that the use of phytic acid and maleic acid resin coatings, the combination of the two can significantly increase the thickness of phytic acid and ensure the presence of the phytic acid organic layer, which confirms that the combination of phytic acid and maleic acid resin can significantly improve the electrochemical corrosion resistance of aluminum alloys.

[0091] According to the data in Table 1, the improvement in the salt spray resistance test of Comparative Example 6 is not obvious, and the improvement strength is moderate. The thickness of the organic film of Comparative Example 6 is good, indicating that the multi-stage ultrasound will not destroy the integrity of the metal acid salt film layer. It is also possible that the multi-stage ultrasound treatment will not destroy the capsule wall of the ethyl cellulose microcapsule at one time and will not release too much phytic acid at one time. It proves that the multi-stage ultrasound treatment can ensure the integrity of other film layers, thereby improving the corrosion resistance of the aluminum alloy surface.

[0092] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A method for anti-corrosion treatment of aluminum alloy surface, characterized in that: The processing steps include: S1, passivation pretreatment, after grinding, alkali washing and deoxidation of the aluminum alloy surface, passivation of the aluminum alloy surface using a passivation agent to form a passivation film; S2, formation of phytic acid blocking film, embedding treatment of phytic acid to obtain slow-release particles, preparing blocking solution containing slow-release particles, wherein the pH of the blocking solution is 2.5-3.0, placing the surface of the passivation film in the blocking solution for multi-stage ultrasonic treatment, the ultrasonic power is 120w-200w, the treatment temperature is 50-60°C, the ultrasonic treatment time of a single stage of the multi-stage ultrasonic treatment is 1-2min, and the interval time of the single stage ultrasonic treatment is 4-6min; S3, coating of maleic acid resin film, coating a coating containing maleic acid alkyd resin on the surface of the phytic acid sealing film, and completing the anti-corrosion treatment of the aluminum alloy after high-temperature curing; The usage amount of the slow-release granules is 120g-200g / L; The specific steps of the phytic acid embedding treatment are as follows: A1, placing ethyl cellulose in anhydrous ethanol and stirring to dissolve, then adding polyethylene glycol by dropwise addition to obtain an embedding base solution, and finally adding phytic acid to the embedding base solution for homogenization to obtain an embedding solution; A2, spray drying the embedding solution to form sustained-release particles containing phytic acid; The mass ratio of the phytic acid to the ethyl cellulose is 1:3-10.

2. The method for anticorrosion treatment of aluminum alloy surface according to claim 1, characterized in that: The solid-liquid ratio of the ethyl cellulose to the anhydrous ethanol is 1:20-30, and the added amount of the polyethylene glycol is 1%-5% of the volume of the anhydrous ethanol.

3. The method for anticorrosion treatment of aluminum alloy surface according to claim 1, characterized in that: The coating composition for forming the maleic acid resin film is 40-60 parts of fatty acid, 3-10 parts of maleic anhydride, 20-35 parts of rosin and 10-20 parts of pentaerythritol.

4. The method for anticorrosion treatment of aluminum alloy surface according to claim 3, characterized in that: The preparation method of the coating comprises the following steps: heating rosin to a molten state and stirring the mixture, adding maleic anhydride during the stirring process, heating the mixture to 200° C. and then keeping the mixture warm for later use; mixing fatty acid and pentaerythritol and heating the mixture for a first esterification reaction, then adding the reactant after the esterification reaction to a mixture containing maleic anhydride and rosin for a second esterification reaction, refluxing xylene to remove water, cooling and filtering the mixture after no water is produced to obtain the coating.

5. The method for anticorrosion treatment of aluminum alloy surface according to claim 4, characterized in that: The temperature of the first esterification reaction is 215-255° C., the reaction time is 1 hour, the temperature of the second esterification reaction is 225-235° C., and the termination criterion of the second esterification reaction is that no water is produced in the reflux of xylene.

6. The method for anticorrosion treatment of aluminum alloy surface according to claim 1, characterized in that: The passivation reagent used in S1 is a mixed solution of sodium fluoride and titanyl sulfate, the pH of the passivation treatment is 5-6, the temperature of the passivation treatment is 40-50° C., the reaction time is 30 min, and the mass ratio of sodium fluoride to titanyl sulfate is 6-10:

1.

7. The method for anticorrosion treatment of aluminum alloy surface according to claim 6, characterized in that: The concentration of sodium fluoride in the passivation treatment is 1-10 g / L.

8. The method for anticorrosion treatment of aluminum alloy surface according to claim 1, characterized in that: The thickness of the phytic acid sealing film is 17.5-19.0 μm.

9. Application of the anti-corrosion treatment method according to any one of claims 1 to 8 in anti-corrosion treatment of aluminum alloy surfaces.

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