Method for improving surface corrosion resistance of aluminum alloy anode oxide film

Abstract

The invention relates to the technical field of aluminum alloy surface treatment, and discloses a method for improving the surface corrosion resistance of an aluminum alloy anode oxide film, which comprises the following steps: synthesizing a hole sealing agent containing a methoxy functional group; an aluminum alloy anode oxide film is prepared, and the aluminum alloy anode oxide film with the hydroxylated surface is obtained by conducting alkali liquor treatment on the aluminum alloy anode oxide film; a hole sealing agent is used for conducting sealing treatment on the aluminum alloy anode oxide film with the hydroxylated surface, silicon hydroxyl functional groups obtained through hydrolysis reaction of methoxyl functional groups of the hole sealing agent and hydroxyl functional groups on the surface of the aluminum alloy anode oxide film are subjected to dehydration condensation reaction, and the aluminum alloy anode oxide film with the corrosion-resistant surface is obtained. The aluminum alloy anode oxide film is corrected in corrosion potential, lower in corrosion current density, larger in impedance value, capable of remarkably inhibiting corrosion reaction and excellent in corrosion resistance.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloy surface treatment, in particular to a method for improving the surface corrosion resistance of an aluminum alloy anodic oxide film. Background Art

[0002] Aluminum alloys, with their advantages of low density, high specific strength, good processability, and low cost, are widely used in aviation, aerospace, automotive, construction, and energy. To improve the corrosion resistance of aluminum alloys, they are typically protected by pretreatment and surface coating. Anodizing is a common method for aluminum alloy surface pretreatment.

[0003] The anodic oxide film of aluminum alloys consists of an inner dense barrier layer and an outer porous layer. To further enhance the corrosion resistance of the aluminum alloy anodic oxide film, the film is typically sealed. The dichromate and dilute chromic acid used in traditional chromic acid sealing methods contain carcinogenic chromium, while boiling water sealing methods suffer from high energy consumption and insufficient long-term protective performance. Therefore, the development of new sealing processes has been a key focus and hot topic in research on improving the corrosion resistance of aluminum alloy anodic oxide films.

[0004] The present invention cites the following document: A doctoral dissertation from Beijing University of Chemical Technology, titled "Molecular Dynamics Simulation of Cross-linked Epoxy Resins and Study on the Properties of Nanocomposites Containing Heptaphenyl POSS," which discloses the chemical structure and preparation method of vinyl heptaphenyl POSS. Summary of the Invention

[0005] The present invention provides a method for improving the surface corrosion resistance of an aluminum alloy anodized film, wherein a self-synthesized sealing agent is used to seal the surface hydroxylated aluminum alloy anodized film, thereby achieving the beneficial technical effect of significantly improving the surface corrosion resistance of the aluminum alloy anodized film.

[0006] A method for improving the surface corrosion resistance of an aluminum alloy anodic oxide film comprises the following steps:

[0007] Step 1: synthesizing a sealing agent containing a methoxy functional group, wherein the sealing agent is sealing agent I or sealing agent II;

[0008] Step 2: preparing an aluminum alloy anodic oxide film by treating the aluminum alloy anodic oxide film with alkaline solution to obtain an aluminum alloy anodic oxide film with a surface hydroxylation;

[0009] Step 3: Use a sealing agent to seal the surface hydroxylated aluminum alloy anodized film, and the silanol functional groups obtained by the hydrolysis reaction of the methoxy functional groups of the sealing agent undergo a dehydration condensation reaction with the hydroxyl functional groups on the surface of the aluminum alloy anodized film to obtain a surface corrosion-resistant aluminum alloy anodized film.

[0010] Preferably, the preparation method of the sealing agent I is: the alkenyl functional group of the vinyl heptadiphenyl POSS is reacted with the Si-H functional group of 1,1,3,3-tetramethyl-1-[2'-(trimethoxysilyl)ethyl]-disiloxane to undergo an addition reaction, and the amount ratio of the vinyl heptadiphenyl POSS and 1,1,3,3-tetramethyl-1-[2'-(trimethoxysilyl)ethyl]-disiloxane participating in the reaction is controlled to be 1:(1.01-1.05) to generate the sealing agent I.

[0011] Preferably, the preparation method of the sealing agent II is: the alkenyl functional group of octavinyl POSS is reacted with the Si-H functional group of 1,1,3,3-tetramethyl-1-[2'-(trimethoxysilyl)ethyl]-disiloxane by an addition reaction, and the amount ratio of the octavinyl POSS and 1,1,3,3-tetramethyl-1-[2'-(trimethoxysilyl)ethyl]-disiloxane participating in the reaction is controlled to be 1:(8.01-8.04) to generate the sealing agent II.

[0012] Preferably, the preparation method of the surface corrosion-resistant aluminum alloy anodized film is: mix the sealing agent, methanol and deionized water evenly to prepare a 0.01-0.1 g / mL sealing agent solution, add 30-40wt% glacial acetic acid to adjust the solution pH to 8, heat to 30-40°C and stir to react until the sealing agent is completely hydrolyzed, immerse the surface hydroxylated aluminum alloy anodized film in the sealing agent system, immerse for 3-5 hours, take out and blow dry with cold air, and vacuum dry to obtain the surface corrosion-resistant aluminum alloy anodized film.

[0013] Beneficial effects:

[0014] The present invention first designs and synthesizes two sealing agents, and then based on the condensation reaction of silanol and hydroxyl groups, the surface hydroxylated aluminum alloy anodized film is sealed with the sealing agents. Compared with the aluminum alloy anodized film that has not been sealed, the aluminum alloy anodized film thus obtained has a more positive corrosion potential, a lower corrosion current density, and a larger impedance value, can significantly inhibit the corrosion reaction, and exhibits excellent corrosion resistance. DETAILED DESCRIPTION

[0015] Experimental Example 1:

[0016] Preparation of Sealing Agent I: The alkenyl functional group of vinyl heptaphenyl POSS reacts with the Si-H functional group of 1,1,3,3-tetramethyl-1-[2'-(trimethoxysilyl)ethyl]-disiloxane through an addition reaction, and the molar ratio of vinyl heptaphenyl POSS and 1,1,3,3-tetramethyl-1-[2'-(trimethoxysilyl)ethyl]-disiloxane participating in the reaction is controlled to be 1:1.03 to produce Sealing Agent I, whose chemical structure is:

[0017] ;

[0018] The specific experimental steps for preparing sealing agent I are as follows: under nitrogen protection, 4.9 g of vinyl heptaphenyl POSS and 50 mL of anhydrous tetrahydrofuran were added to a three-necked flask and stirred at room temperature until completely dissolved. Then, 10 mL of an anhydrous tetrahydrofuran solution containing 1.4 g of 1,1,3,3-tetramethyl-1-[2'-(trimethoxysilyl)ethyl]-disiloxane and 2 drops of Custer's catalyst were added dropwise to the three-necked flask. The temperature was raised to 70°C and stirred under reflux for 6 h. The reaction was cooled to room temperature, the solvent was removed by rotary evaporation, and the pore sealing agent I was obtained.

[0019] The H NMR spectrum of sealing agent I is characterized as follows: 1 H NMR (CDCl3, 400MHz) δ: 0.03 (s, 6H), 0.08 (s, 6H), 0.71-0.85 (m, 8H), 3.57 (s, 9H), 7.32-7.55 (m, 35H, Ar-H).

[0020] Experimental Example 2:

[0021] Preparation of Sealing Agent II: The alkenyl functional group of octavinyl POSS (purchased from Forsman Technology (Beijing) Co., Ltd., product number 9502034) was reacted with the Si-H functional group of 1,1,3,3-tetramethyl-1-[2'-(trimethoxysilyl)ethyl]-disiloxane by addition reaction, and the molar ratio of octavinyl POSS and 1,1,3,3-tetramethyl-1-[2'-(trimethoxysilyl)ethyl]-disiloxane participating in the reaction was controlled to be 1:8.04 to produce Sealing Agent II, whose chemical structure is:

[0022] ;

[0023] The specific experimental steps for preparing sealing agent I are as follows: under nitrogen protection, 1.6 g of octavinyl POSS and 20 mL of anhydrous tetrahydrofuran were added to a three-necked flask and stirred at room temperature until completely dissolved. Then, 30 mL of anhydrous tetrahydrofuran solution containing 5.7 g of 1,1,3,3-tetramethyl-1-[2'-(trimethoxysilyl)ethyl]-disiloxane and 5 drops of Custer's catalyst were added dropwise to the three-necked flask. The temperature was raised to 70°C, stirred and refluxed for 8 h, cooled to room temperature, the solvent was removed by rotary evaporation, and vacuum dried to obtain sealing agent II.

[0024] The nuclear magnetic resonance hydrogen spectrum of sealing agent II is characterized as follows: 1H NMR (CDCl3, 400MHz) δ: 0.04 (s, 48H), 0.10 (s, 48H), 0.64-0.86 (m, 64H), 3.57 (s, 72H).

[0025] Example 1:

[0026] Preparation of aluminum alloy anodic oxide film: 50mm×50mm×5mm aluminum alloy (purchased from Ningbo Qingyun Metal Co., Ltd., model 2195) was heated at 1200 # The surface was mechanically polished with sandpaper and cleaned with acetone for 5 minutes to remove oil. It was then immersed in a sodium hydroxide solution at 60°C and a mass concentration of 50 g / L for 5 minutes for alkaline washing. It was then washed with hot water and cold water for 5 minutes in sequence and immersed in a 25% volume fraction nitric acid solution until it was polished. Finally, it was rinsed with deionized water at room temperature and immediately immersed in an electrolyte for anodization. After the oxidation was completed, it was taken out and rinsed with deionized water and vacuum dried to obtain an aluminum alloy anodized film.

[0027] A programmable DC regulated anodic oxidation power supply was used for the anodic oxidation reaction. The pretreated aluminum alloy was used as the anode and the lead plate was used as the cathode. The electrolyte was 180 g / L concentrated sulfuric acid solution. The anodic oxidation process parameters were set as follows: temperature 20 °C, current density 1.5 A / dm 2 , time is 50 minutes.

[0028] Example 2:

[0029] Preparation of surface hydroxylated aluminum alloy anodized film: The aluminum alloy anodized film prepared in Example 1 was ultrasonically cleaned in deionized water for 5 minutes, taken out and dried, and then placed in a 1 mol / L sodium hydroxide solution, reacted at room temperature for 4 hours, activated by ultrasonication for 30 minutes, taken out and dried to obtain a surface hydroxylated aluminum alloy anodized film.

[0030] Example 3:

[0031] Preparation of a surface corrosion-resistant aluminum alloy anodic oxide film I: Using a sealing agent I to seal the surface hydroxylated aluminum alloy anodic oxide film, and allowing the silanol functional groups obtained by the hydrolysis reaction of the sealing agent I to undergo a dehydration condensation reaction with the hydroxyl functional groups on the surface of the aluminum alloy anodic oxide film, thereby obtaining the surface corrosion-resistant aluminum alloy anodic oxide film I;

[0032] The specific experimental steps for preparing surface corrosion-resistant aluminum alloy anodized film I are as follows: add 1 g of sealing agent I, 40 mL of methanol and 10 mL of deionized water into a beaker, stir at room temperature for 1 hour, adjust the solution pH to 8 with 36 wt% glacial acetic acid, heat to 35°C and stir for 6 hours for hydrolysis, then put the surface hydroxylated aluminum alloy anodized film prepared in Example 2 into the completely hydrolyzed silanol solution, immerse for 4 hours, take out and blow dry with cold air, and vacuum dry to obtain surface corrosion-resistant aluminum alloy anodized film I.

[0033] Example 4:

[0034] Preparation of surface corrosion-resistant aluminum alloy anodic oxide film II: Using sealing agent II to seal the surface hydroxylated aluminum alloy anodic oxide film, the silanol functional groups obtained by hydrolysis of sealing agent II react with the hydroxyl functional groups on the surface of the aluminum alloy anodic oxide film to produce a surface corrosion-resistant aluminum alloy anodic oxide film II;

[0035] The specific experimental steps for preparing surface corrosion-resistant aluminum alloy anodic oxide film II refer to the preparation experiment of surface corrosion-resistant aluminum alloy anodic oxide film I, and the only difference is that sealing agent II is used instead of sealing agent I.

[0036] Performance testing:

[0037] (1) The corrosion resistance of aluminum alloy anodic oxide film in 3.5wt% NaCl solution was studied using a CHI 660E electrochemical workstation. Polarization curves and frequency-impedance spectroscopy were tested. The scanning rate for the polarization curve test was 1mV / s. The electrochemical corrosion parameters, corrosion potential and corrosion current density, were obtained using the Tafel epitaxy method. The more negative the corrosion potential and the greater the corrosion current density, the faster the metal corrodes. Conversely, the more positive the corrosion potential and the smaller the corrosion current density, the better the protection effect on the metal.

[0038] During the frequency-impedance spectrum test, a 10mV sinusoidal potential disturbance was applied and the scanning frequency was 10 -2 -10 5 Hz, recording frequency is 10 -2 The impedance value at Hz, the larger the impedance value, the better the corrosion resistance of the anodic oxide film;

[0039] (2) A full immersion corrosion test was conducted in accordance with GB 10124-1988. The corrosive medium was 3 wt% NaCl solution and the immersion time was 14 days. After the experiment, the samples were washed with deionized water at room temperature and the corrosion morphology was observed.

[0040] (3) Contact angle test was performed using a JC2000D1 contact angle meter, and the test solution was deionized water;

[0041] The above experimental results are shown in Table 1 below.

[0042] Table 1 Experimental results of surface corrosion resistance of aluminum alloy anodic oxide films

[0043] Product Type Corrosion potential (V) <![CDATA[Corrosion current density (A·cm -2 )]]> <![CDATA[Impedance value (Ω·cm 2 )]]> Corrosion morphology Contact angle (°) Surface corrosion resistance of aluminum alloy anodic oxide film Ⅰ -0.527 <![CDATA[3.09×10 -7 ]]> <![CDATA[1.8×10 6 ]]> The surface is still relatively flat and dense, without significant unevenness 66.2 Surface corrosion resistance of aluminum alloy anodic oxide film Ⅱ -0.510 <![CDATA[2.96×10 -7 ]]> <![CDATA[2.1×10 6 ]]> The surface is still relatively flat and dense, without significant unevenness 70.1 Comparative Example (Aluminum Alloy Anodic Oxide Film) -0.608 <![CDATA[3.21×10 -6 ]]> <![CDATA[3.4×10 5 ]]> Large areas of pitting and severe bubbling appear on the surface 33.5

[0044] By comprehensively analyzing the above experimental results, the following conclusions can be drawn:

[0045] Conclusion 1: Compared with the aluminum alloy anodic oxide film that has not been sealed, the aluminum alloy anodic oxide film with hydroxylation on its surface obtained by sealing with the self-synthesized sealing agent has a more positive corrosion potential, a lower corrosion current density, and a larger impedance value. This shows that sealing with the sealing agent can significantly inhibit the corrosion reaction and improve the surface corrosion resistance of the anodic oxide film on the aluminum-lithium alloy surface.

[0046] The mechanism of the above experimental results may be that after the anodic oxide film on the surface of the lithium alloy is sealed, the pore defects of the anodic oxide film are effectively filled and sealed, thereby blocking the corrosive medium and increasing the corrosion resistance;

[0047] Conclusion 2: The contact angle of the surface corrosion-resistant aluminum alloy anodized film prepared by the present invention is greater than 65°, which can effectively block the adhesion of corrosive solutions and prevent corrosive ions from entering the pores of the anodized film to damage the aluminum alloy.

Claims

1. A method for improving the corrosion resistance of the surface of anodized aluminum alloy film, characterized in that: The steps include: Step 1: synthesizing a sealing agent containing a methoxy functional group, wherein the sealing agent is sealing agent I or sealing agent II; Step 2: preparing an aluminum alloy anodic oxide film by treating the aluminum alloy anodic oxide film with alkaline solution to obtain an aluminum alloy anodic oxide film with a surface hydroxylation; Step 3: Use a sealing agent to seal the surface hydroxylated aluminum alloy anodized film, and the silanol functional groups obtained by the hydrolysis reaction of the methoxy functional groups of the sealing agent undergo a dehydration condensation reaction with the hydroxyl functional groups on the surface of the aluminum alloy anodized film to obtain a surface corrosion-resistant aluminum alloy anodized film.

2. A method for improving the surface corrosion resistance of anodized aluminum alloy films according to claim 1, characterized in that: The chemical structural formula of the sealing agent I is: 。 3. A method for improving the surface corrosion resistance of anodized aluminum alloy films according to claim 2, characterized in that: The preparation method of the sealing agent I is as follows: the alkenyl functional group of the vinyl heptadiphenyl POSS is subjected to an addition reaction with the Si-H functional group of 1,1,3,3-tetramethyl-1-[2'-(trimethoxysilyl)ethyl]-disiloxane, and the molar ratio of the vinyl heptadiphenyl POSS and the 1,1,3,3-tetramethyl-1-[2'-(trimethoxysilyl)ethyl]-disiloxane participating in the reaction is controlled to be 1:(1.01-1.05), thereby generating the sealing agent I.

4. The method for improving the surface corrosion resistance of anodized aluminum alloy films according to claim 1, wherein: The chemical structural formula of the sealing agent II is: 。 5. A method for improving the surface corrosion resistance of anodized aluminum alloy films according to claim 4, characterized in that: The preparation method of the sealing agent II comprises: an addition reaction between the alkenyl functional group of octavinyl POSS and the Si-H functional group of 1,1,3,3-tetramethyl-1-[2'-(trimethoxysilyl)ethyl]-disiloxane, and controlling the molar ratio of the octavinyl POSS and 1,1,3,3-tetramethyl-1-[2'-(trimethoxysilyl)ethyl]-disiloxane participating in the reaction to be 1:(8.01-8.04) to generate the sealing agent II.

6. The method for improving the surface corrosion resistance of anodized aluminum alloy films according to claim 1, wherein: The preparation method of the surface corrosion-resistant aluminum alloy anodized film is as follows: a sealing agent, methanol and deionized water are evenly mixed to prepare a 0.01-0.1 g / mL sealing agent solution, 30-40 wt% glacial acetic acid is added to adjust the solution pH to 8, the temperature is raised to 30-40° C. and stirred to react until the sealing agent is completely hydrolyzed, the surface hydroxylated aluminum alloy anodized film is immersed in the sealing agent system, immersed for 3-5 hours, taken out and blown dry with cold air, and vacuum dried to obtain the surface corrosion-resistant aluminum alloy anodized film.

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