CN115216759B - Hydrophilic chemical conversion film forming liquid and aluminum alloy surface treatment method - Google Patents

Abstract

The invention relates to a hydrophilic chemical conversion film forming liquid and an aluminum alloy surface treatment method. Hydrophilic chemical conversion film forming liquid comprising trivalent chromium salt, fluorozirconate, organic complexing agent, inorganic salt additive and water; the organic complexing agent is one or more of polyvinyl alcohol, polyethylene glycol and polyacrylamide; the inorganic salt additive is fluotitanic acid and/or fluotitanate. The invention also provides an aluminum alloy surface treatment method, which comprises the following steps: removing impurities from the surface of the aluminum alloy; placing aluminum alloy into the hydrophilic chemical conversion film forming liquid to perform chemical conversion treatment so as to form a hydrophilic chemical conversion film on the surface of the aluminum alloy; and (3) cleaning the coated aluminum alloy, and naturally aging in a normal-temperature environment. The invention effectively improves the adsorption capacity of the metal surface, and solves the problems of high toxicity, poor corrosion resistance, complex working procedure and poor protection effect of the existing aluminum alloy surface chemical conversion film.

Description

A hydrophilic chemical conversion film-forming liquid and aluminum alloy surface treatment method

Technical field

The invention relates to the technical field of aluminum alloy surface treatment, and specifically relates to a hydrophilic chemical conversion film-forming liquid and an aluminum alloy surface treatment method.

Background technique

Aluminum alloy is currently the most widely used lightweight metal structural material in the world. In order to meet the requirements of mechanical and other properties, various alloying elements such as Cu, Mg, Zn, and Si are usually added to aluminum alloys. However, due to the addition of a large number of alloying elements, the corrosion resistance of most aluminum alloys decreases and cannot meet the requirements of industrial applications. Therefore, most aluminum alloys require certain surface treatments before they can be put into use.

Common aluminum alloy surface treatment processes include: electroplating, chemical conversion, anodizing, micro-arc oxidation, laser cladding and sol-gel, etc. Among them, chemical conversion coating treatment does not require an external power supply, has simple process operations, low production costs, and has no obvious impact on the mechanical properties of the substrate, and is widely used in industrial production. Among them, chromate conversion coating is the chemical conversion coating with the longest application, best corrosion resistance and self-healing function. It has been widely used for a long time in the past.

However, long-term practical research has found that the hexavalent chromium ions contained in chromate are carcinogenic and have serious harm to humans, animals and the natural environment. The European Union environmental protection organization comprehensively banned the commercial application of hexavalent chromium conversion coatings in 2017, and the United States, Japan and other countries also have stricter restrictions on hexavalent chromium. As a result, green and environmentally friendly chromium-free conversion and chemical conversion processes came into being. Among them, chromium-free conversion coatings mainly include zirconate, phosphate, molybdate, titanate, cobaltate and rare earth salt conversion coatings, etc. However, chromium-free conversion coatings are looser, have poor corrosion resistance, or have cumbersome procedures and poor protection. The effect and application range are not as good as chromate conversion coating.

Contents of the invention

The purpose of the present invention is to provide a hydrophilic chemical conversion film-forming liquid to improve the adsorption capacity of the metal surface; the second purpose is to provide an aluminum alloy surface treatment method to improve the adsorption performance of the aluminum alloy surface and also solve the problem of existing problems. There are problems with the chemical conversion coating on the surface of aluminum alloys, such as high toxicity, poor corrosion resistance, cumbersome processes and poor protective effects.

In order to achieve the above objects, the technical solutions adopted by the present invention are as follows:

A hydrophilic chemical conversion membrane liquid includes trivalent chromium salt, fluorozirconate, organic complexing agent, inorganic salt additive and water;

The organic complexing agent is one or more of polyvinyl alcohol, polyethylene glycol and polyacrylamide;

The inorganic salt additive is fluorotitanic acid (H ₂ TiF ₆ ) and/or fluorotitanate.

Preferably, the trivalent chromium salt includes one or more of chromium sulfate (Cr ₂ (SO ₄ ) ₃ ), chromium nitrate (Cr(NO ₃ ) ₃ ) and chromium chloride (CrCl ₃ ).

Preferably, the fluorozirconate includes one or both of potassium fluorozirconate (K ₂ ZrF ₆ ) and sodium fluorozirconate (Na ₂ ZrF ₆ ).

Preferably, the fluorotitanate is potassium fluorotitanate (K ₂ TiF ₆ ).

Preferably, the concentration of the trivalent chromium salt is 0.5-5g/L, the concentration of the fluorozirconate is 1-10g/L, and the concentration of the organic complexing agent is 2-10g/L. The concentration of inorganic salt additive is 0.5~5g/L.

The invention also provides an aluminum alloy surface treatment method, which includes the following steps:

S1. Pretreatment: perform impurity removal treatment on the aluminum alloy surface;

S2. Coating: adjust the pH value of the hydrophilic chemical conversion film-forming liquid of the present invention to acidic, and put the aluminum alloy into the acidic hydrophilic chemical conversion film-forming liquid for chemical conversion treatment to form a hydrophilic film-forming liquid on the surface of the aluminum alloy. Water-based chemical conversion coating;

S3. Natural aging: Clean the coated aluminum alloy and place it in a normal temperature environment for natural aging.

Preferably, after natural aging, an organic sealing treatment is also included, specifically: sealing the naturally aged aluminum alloy in an organic sealing agent.

According to the above technical means, after coating and natural aging, that is, after priming the surface of the aluminum alloy, and then sealing it, the corrosion resistance of the aluminum alloy is greatly improved. Among them, the hydrophilic chemical conversion into a film The aluminum alloy surface is coated with liquid, which effectively improves the adsorption capacity of the aluminum alloy to the organic sealant, thereby further improving the corrosion resistance of the aluminum alloy.

Preferably, in S2, the temperature of the chemical conversion treatment is 20°C to 60°C. In this temperature range, the film formation rate can be controlled to make the film layer grow quickly and uniformly, and the time of the chemical conversion treatment is 60 to 600 seconds.

Preferably, in S1, the pretreatment includes degreasing, alkali washing, pickling and rinsing the aluminum alloy in sequence;

Among them, a degreasing cleaning agent is used for cleaning treatment, the cleaning temperature is 50°C to 60°C, and the cleaning time is 30 to 120 seconds; alkali cleaning (to fully remove the surface rolling deformation layer and part of the second phase particles) uses 5 %~10% (wt.) sodium hydroxide (NaOH) solution is used for treatment, the alkali washing temperature is 30°C~40°C, and the alkali washing time is 10~60 seconds; 30%~40% (vol.) nitric acid is used for pickling (HNO ₃ ) solution, the pickling temperature is 20℃～30℃, the pickling time is 10～60 seconds; the rinsing is treated with deionized water, the rinsing temperature is 70℃～80℃, the rinsing time is 10～60 seconds .

Preferably, in S3, the natural aging time is 4 to 24 hours.

Preferably, the organic blocking agent is a silane blocking agent.

Preferably, the thickness of the chemical conversion film formed on the surface of the aluminum alloy is 50 nm to 150 nm, and the water contact angle of the chemical conversion film is less than 50°.

Beneficial effects of the present invention:

1) The hydrophilic chemical conversion film-forming liquid of the present invention uses chromium salt, fluorozirconate, organic complexing agent and inorganic salt additive as the main components of the film-forming liquid. The chromium salt has low toxicity, good corrosion resistance, and corrosion resistance. It has the advantages of high temperature, certain conductivity and good adhesion. As an oxidant and film-forming agent, fluorozirconate is mainly used to provide fluoride ions to dissolve the aluminum matrix, thereby promoting the film-forming reaction. Organic complexing agents can Prevents the hydrolysis of trivalent chromium, stabilizes and controls the deposition rate of metal ions within a certain pH range, and improves the hydrophilicity of the film. Inorganic salt additives act as film-forming accelerators and can passivate the delicate structure of the film. , the porosity is reduced, and more stable oxides are introduced into the film layer, so that the nanochemical conversion film made on the metal surface has good hydrophilic properties, effectively improving the adsorption performance of the metal surface, and providing a better solution for adsorption on the metal surface. Sealers provide good prerequisites;

2) The aluminum alloy surface treatment method of the present invention puts the aluminum alloy into a hydrophilic chemical conversion film liquid, so that the chemical conversion film liquid reacts with the aluminum alloy surface, thereby forming a layer of chemical conversion on the aluminum alloy surface. Film, experimental studies have proven that the chemical conversion film formed on the surface of aluminum alloy has good hydrophilic properties, significantly improves the adsorption performance of the aluminum alloy surface, and provides a good basis for subsequent organic sealing treatment, and the preparation method has It has the advantages of simple process, mild conditions, short film formation time, green environmental protection, and low production cost. It is suitable for industrial production and has promotion and application value in the field of aluminum alloy surface treatment technology.

Description of drawings

Figure 1 is a scanning electron microscope morphology (10 μm) of the 5056 aluminum foil treated in Examples 1 to 4;

Figure 2 is a scanning electron microscope morphology image (1 μm) of the 5056 aluminum foil treated in Examples 1 to 4;

Figure 3 is a macroscopic morphology diagram of the 5056 aluminum foil treated in Example 1 and Example 4 after being subjected to a 5% neutral salt spray test;

Figure 4 is a graph showing the results of the water contact angle test on the treated 5056 aluminum foil in Example 1, Example 2, Example 4 and Comparative Example 1;

Figure 5 is an electrochemical polarization curve measured in a 3.5% (wt%) NaCl aqueous solution of the 5056 aluminum foil treated in Examples 1 to 3;

Figure 6 is a graph showing the results of a potassium dichromate drop test on uncoated 5056 aluminum foil and the treated 5056 aluminum foil in Example 1, Example 5 and Example 6;

Figure 7 is a diagram showing the results of a potassium dichromate drop test on the 5056 aluminum foil treated in Example 4 and Comparative Example 1.

Detailed ways

The implementation of the present invention will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention.

Example 1

An aluminum alloy surface treatment method includes the following steps:

S1. Preprocessing:

1) Degreasing treatment: Put the entire 5056 aluminum foil into 10wt.% degreasing cleaning agent, keep it at a constant temperature of 60°C for 30 seconds to remove oil and degreasing, take it out and rinse it in deionized water at 80°C for 30 seconds. ;

2) Alkali washing treatment: Put the deoiled 5056 aluminum foil into a 10wt.% NaOH aqueous solution, keep it at a constant temperature of 40°C for 30s, take it out and rinse it in deionized water at 80°C for 30s;

3) Pickling treatment: Put the alkali-washed 5056 aluminum foil into a 30 vol.% HNO ₃ aqueous solution for 30 seconds of deoxidation and ash removal, then take it out and rinse it in 80°C deionized water for 30 seconds;

4) Rinsing treatment: Rinse the pickled 5056 aluminum foil with deionized water, and finally dry it naturally to obtain pretreated 5056 aluminum foil;

S2. Coating: Use 1wt.% H ₂ SO ₄ solution to adjust the pH value of the hydrophilic chemical conversion film-forming liquid to 3.5, and place the pretreated 5056 aluminum foil in S1 into the acidic hydrophilic chemical conversion film-forming liquid. Carry out chemical conversion treatment to form a hydrophilic chemical conversion film on the surface of 5056 aluminum foil. The temperature of chemical conversion treatment is 40°C and the time of chemical conversion treatment is 90S;

Among them, the components of the hydrophilic chemical conversion film-forming liquid in Example 1 are Cr ₂ (SO ₄ ) ₃ , K ₂ ZrF ₆ , polyvinyl alcohol, H ₂ TiF ₆ and water, and Cr ₂ (SO ₄ ) ₃ The concentration is 2g/L, the concentration of K ₂ ZrF ₆ is 4g/L, the concentration of polyvinyl alcohol is 6g/L, and the concentration of H ₂ TiF ₆ is 2g/L;

S3. Natural aging: After the coating is completed, rinse the 5056 aluminum foil with deionized water, and then place it in a normal temperature environment for natural air drying and aging for 8 hours to obtain a 5056 aluminum foil with a colorless chemical conversion film formed on the surface.

Example 2

An aluminum alloy surface treatment method includes the following steps:

S1. Preprocessing:

1) Degreasing treatment: Put the entire 5056 aluminum foil into 10wt.% degreasing cleaning agent, keep it at a constant temperature of 60°C for 30 seconds to remove oil and degreasing, take it out and rinse it in deionized water at 80°C for 30 seconds. ;

2) Alkali washing treatment: Put the deoiled 5056 aluminum foil into a 10wt.% NaOH aqueous solution, keep it at a constant temperature of 40°C for 30s, take it out and rinse it in deionized water at 80°C for 30s;

3) Pickling treatment: Put the alkali-washed 5056 aluminum foil into a 30 vol.% HNO ₃ aqueous solution for 30 seconds of deoxidation and ash removal, then take it out and rinse it in 80°C deionized water for 30 seconds;

4) Rinsing treatment: Rinse the pickled 5056 aluminum foil with deionized water, and finally dry it naturally to obtain pretreated 5056 aluminum foil;

S2. Coating: Use 1wt.% H ₂ SO ₄ solution to adjust the pH value of the hydrophilic chemical conversion film-forming liquid to 4.5, and place the pretreated 5056 aluminum foil in S1 into the acidic hydrophilic chemical conversion film-forming liquid. Carry out chemical conversion treatment to form a hydrophilic chemical conversion film on the surface of 5056 aluminum foil. The temperature of chemical conversion treatment is 40°C and the time of chemical conversion treatment is 90S;

Among them, the components of the hydrophilic chemical conversion membrane-forming liquid in Example 2 are Cr(NO ₃ ) ₃ , Na ₂ ZrF ₆ , polyvinyl alcohol, H ₂ TiF ₆ and water, and the concentration of Cr(NO ₃ ) ₃ is 2g/L, the concentration of Na ₂ ZrF ₆ is 4g/L, the concentration of polyvinyl alcohol is 6g/L, and the concentration of H ₂ TiF ₆ is 2g/L;

S3. Natural aging: After the coating is completed, rinse the 5056 aluminum foil with deionized water, and then place it in a normal temperature environment for natural air drying and aging for 8 hours to obtain a 5056 aluminum foil with a colorless chemical conversion film formed on the surface.

Example 3

An aluminum alloy surface treatment method includes the following steps:

S1. Preprocessing:

1) Degreasing treatment: Put the entire 5056 aluminum foil into 10wt.% degreasing cleaning agent, keep it at a constant temperature of 60°C for 30 seconds to remove oil and degreasing, take it out and rinse it in deionized water at 80°C for 30 seconds. ;

2) Alkali washing treatment: Put the deoiled 5056 aluminum foil into a 10wt.% NaOH aqueous solution, keep it at a constant temperature of 40°C for 30s, take it out and rinse it in deionized water at 80°C for 30s;

3) Pickling treatment: Put the alkali-washed 5056 aluminum foil into a 30 vol.% HNO ₃ aqueous solution for 30 seconds of deoxidation and ash removal, then take it out and rinse it in 80°C deionized water for 30 seconds;

4) Rinsing treatment: Rinse the pickled 5056 aluminum foil with deionized water, and finally dry it naturally to obtain pretreated 5056 aluminum foil;

S2. Coating: Use 1wt.% H ₂ SO ₄ solution to adjust the pH value of the hydrophilic chemical conversion film-forming liquid to 5.5, and place the pretreated 5056 aluminum foil in S1 into the acidic hydrophilic chemical conversion film-forming liquid. Carry out chemical conversion treatment to form a hydrophilic chemical conversion film on the surface of 5056 aluminum foil. The temperature of chemical conversion treatment is 40°C and the time of chemical conversion treatment is 90S;

Among them, the components of the hydrophilic chemical conversion film-forming liquid in Example 3 are CrCl ₃ , Na ₂ ZrF ₆ , polyvinyl alcohol, H ₂ TiF ₆ and water. The concentration of CrCl ₃ is 2g/L, and the concentration of Na ₂ ZrF ₆ The concentration of polyvinyl alcohol is 4g/L, the concentration of polyvinyl alcohol is 6g/L, and the concentration of H ₂ TiF ₆ is 2g/L;

S3. Natural aging: After the coating is completed, rinse the 5056 aluminum foil with deionized water, and then place it in a normal temperature environment for natural air drying and aging for 8 hours to obtain a 5056 aluminum foil with a colorless chemical conversion film formed on the surface.

Example 4

An aluminum alloy surface treatment method includes the following steps:

S1. Preprocessing:

1) Degreasing treatment: Put the entire 5056 aluminum foil into 10wt.% degreasing cleaning agent, keep it at a constant temperature of 60°C for 30 seconds to remove oil and degreasing, take it out and rinse it in deionized water at 80°C for 30 seconds. ;

2) Alkali washing treatment: Put the deoiled 5056 aluminum foil into a 10wt.% NaOH aqueous solution, keep it at a constant temperature of 40°C for 30s, take it out and rinse it in deionized water at 80°C for 30s;

3) Pickling treatment: Put the alkali-washed 5056 aluminum foil into a 30 vol.% HNO ₃ aqueous solution for 30 seconds of deoxidation and ash removal, then take it out and rinse it in 80°C deionized water for 30 seconds;

4) Rinsing treatment: Rinse the pickled 5056 aluminum foil with deionized water, and finally dry it naturally to obtain pretreated 5056 aluminum foil;

S2. Coating: Use 1wt.% H ₂ SO ₄ solution to adjust the pH value of the hydrophilic chemical conversion film-forming liquid to 3.5, and place the pretreated 5056 aluminum foil in S1 into the acidic hydrophilic chemical conversion film-forming liquid. Carry out chemical conversion treatment to form a hydrophilic chemical conversion film on the surface of 5056 aluminum foil. The temperature of chemical conversion treatment is 40°C and the time of chemical conversion treatment is 90S;

Among them, the components of the hydrophilic chemical conversion membrane-forming liquid in Example 4 are Cr ₂ (SO ₄ ) ₃ , K ₂ ZrF ₆ , polyvinyl alcohol, H ₂ TiF ₆ and water, and Cr ₂ (SO ₄ ) ₃ The concentration is 2g/L, the concentration of K ₂ ZrF ₆ is 2g/L, the concentration of polyvinyl alcohol is 6g/L, and the concentration of H ₂ TiF ₆ is 2g/L;

S3. Natural aging: After the coating is completed, rinse the 5056 aluminum foil with deionized water, and then place it in a normal temperature environment for natural air drying and aging for 8 hours to obtain a 5056 aluminum foil with a colorless chemical conversion film formed on the surface;

S4. Place the naturally air-dried and aged 5056 aluminum foil in a silane sealant for sealing treatment. After taking it out, dry it in an oven to obtain a sealed 5056 aluminum foil.

Example 5

An aluminum alloy surface treatment method includes the following steps:

S1. Preprocessing:

5) Degreasing treatment: Put the entire 5056 aluminum foil into 10wt.% degreasing cleaning agent, keep it at a constant temperature of 60°C for 30 seconds to perform degreasing treatment, take it out and rinse it in deionized water at 80°C for 30s. ;

6) Alkali washing treatment: Put the deoiled 5056 aluminum foil into a 10wt.% NaOH aqueous solution, keep it at a constant temperature of 40°C for 30s, take it out and rinse it in deionized water at 80°C for 30s;

7) Pickling treatment: Put the alkali-washed 5056 aluminum foil into a 30 vol.% HNO ₃ aqueous solution for 30 seconds of deoxidation and ash removal, then take it out and rinse it in 80°C deionized water for 30 seconds;

8) Rinsing treatment: Rinse the pickled 5056 aluminum foil with deionized water, and finally dry it naturally to obtain pretreated 5056 aluminum foil;

S2. Coating: Use 1wt.% H ₂ SO ₄ solution to adjust the pH value of the hydrophilic chemical conversion film-forming liquid to 3.5, and place the pretreated 5056 aluminum foil in S1 into the acidic hydrophilic chemical conversion film-forming liquid. Carry out chemical conversion treatment to form a hydrophilic chemical conversion film on the surface of 5056 aluminum foil. The temperature of chemical conversion treatment is 40°C and the time of chemical conversion treatment is 90S;

Among them, the components of the hydrophilic chemical conversion membrane-forming liquid in Example 4 are Cr ₂ (SO ₄ ) ₃ , K ₂ ZrF ₆ , polyvinyl alcohol, H ₂ TiF ₆ and water, and Cr ₂ (SO ₄ ) ₃ The concentration is 0.5g/L, the concentration of K ₂ ZrF ₆ is 1g/L, the concentration of polyvinyl alcohol is 2g/L, and the concentration of H ₂ TiF ₆ is 0.5g/L;

S3. Natural aging: After the coating is completed, rinse the 5056 aluminum foil with deionized water, and then place it in a normal temperature environment for natural air drying and aging for 8 hours to obtain a 5056 aluminum foil with a colorless chemical conversion film formed on the surface;

S4. Place the naturally air-dried and aged 5056 aluminum foil in a silane sealant for sealing treatment. After taking it out, dry it in an oven to obtain a sealed 5056 aluminum foil.

Example 6

An aluminum alloy surface treatment method includes the following steps:

S1. Preprocessing:

9) Degreasing treatment: Put the entire 5056 aluminum foil into 10wt.% degreasing cleaning agent, keep it at a constant temperature of 60°C for 30 seconds to remove oil and degreasing, take it out and rinse it in deionized water at 80°C for 30s. ;

10) Alkali washing treatment: Put the deoiled 5056 aluminum foil into a 10wt.% NaOH aqueous solution, keep it at a constant temperature of 40°C for 30s, take it out and rinse it in deionized water at 80°C for 30s;

11) Pickling treatment: Put the alkali-washed 5056 aluminum foil into a 30 vol.% HNO ₃ aqueous solution for 30 seconds of deoxidation and ash removal, then take it out and rinse it in 80°C deionized water for 30 seconds;

12) Rinsing treatment: Rinse the pickled 5056 aluminum foil with deionized water, and finally dry it naturally to obtain pretreated 5056 aluminum foil;

S2. Coating: Use 1wt.% H ₂ SO ₄ solution to adjust the pH value of the hydrophilic chemical conversion film-forming liquid to 3.5, and place the pretreated 5056 aluminum foil in S1 into the acidic hydrophilic chemical conversion film-forming liquid. Carry out chemical conversion treatment to form a hydrophilic chemical conversion film on the surface of 5056 aluminum foil. The temperature of chemical conversion treatment is 40°C and the time of chemical conversion treatment is 90S;

Among them, the components of the hydrophilic chemical conversion membrane-forming liquid in Example 4 are Cr ₂ (SO ₄ ) ₃ , K ₂ ZrF ₆ , polyvinyl alcohol, H ₂ TiF ₆ and water, and Cr ₂ (SO ₄ ) ₃ The concentration is 5g/L, the concentration of K ₂ ZrF ₆ is 10g/L, the concentration of polyvinyl alcohol is 10g/L, and the concentration of H ₂ TiF ₆ is 5g/L;

S3. Natural aging: After the coating is completed, rinse the 5056 aluminum foil with deionized water, and then place it in a normal temperature environment for natural air drying and aging for 8 hours to obtain a 5056 aluminum foil with a colorless chemical conversion film formed on the surface;

S4. Place the naturally air-dried and aged 5056 aluminum foil in a silane sealant for sealing treatment. After taking it out, dry it in an oven to obtain a sealed 5056 aluminum foil.

Comparative Example 1

An aluminum alloy surface treatment method includes the following steps:

S1. Preprocessing:

1) Degreasing treatment: Put the entire 5056 aluminum foil into 10wt.% degreasing cleaning agent, keep it at a constant temperature of 60°C for 30 seconds to remove oil and degreasing, take it out and rinse it in deionized water at 80°C for 30 seconds. ;

2) Alkali washing treatment: Put the deoiled 5056 aluminum foil into a 10wt.% NaOH aqueous solution, keep it at a constant temperature of 40°C for 30s, take it out and rinse it in deionized water at 80°C for 30s;

3) Pickling treatment: Put the alkali-washed 5056 aluminum foil into a 30 vol.% HNO ₃ aqueous solution for 30 seconds of deoxidation and ash removal, then take it out and rinse it in 80°C deionized water for 30 seconds;

4) Rinsing treatment: Rinse the pickled 5056 aluminum foil with deionized water, and finally dry it naturally to obtain pretreated 5056 aluminum foil;

S2. Put the rinsed and air-dried 5056 aluminum foil directly into the silane sealant for sealing treatment, take it out and dry it in an oven to obtain the sealed 5056 aluminum foil.

Detection and analysis

1. Morphological observation

A scanning electron microscope was used to observe the morphology of the 5056 aluminum foil treated in Examples 1 to 4. The results are shown in Figures 1 and 2.

It can be seen from Figures 1 and 2 that the chemical conversion films formed on the surface of the 5056 aluminum foil treated in Examples 1 to 4 are dense and uniform. Due to the generation of hydrogen during the coating process, a small number of pores appeared on the surface of the 5056 aluminum foil. , but the overall shape is relatively smooth, and no defects such as cracking are found.

2. Salt spray test

The 5056 aluminum foil that has not been coated and the 5056 aluminum foil that has been treated in Example 1 and Example 4 are subjected to a salt spray test. The results are shown in Figure 3.

From the observation in Figure 3, it can be seen that the surface of the uncoated 5056 aluminum foil substrate has obvious corrosion spots and corrosion products after 48 hours, while the surface film layer of the coated 5056 aluminum foil still does not show obvious signs of corrosion after 480 hours. , the surface of the 5056 aluminum foil that was further sealed with a silane sealer did not show any obvious signs of corrosion after 1,200 hours, which effectively proved that the 5056 aluminum foil that was coated and sealed with a silane sealer has very excellent corrosion resistance.

3. Contact angle test

The 5056 aluminum foil treated in Example 1, Example 2, Example 4 and Comparative Example 1 was subjected to multiple water contact angle tests, and the results are shown in Figure 4.

From the analysis in Figure 4, it can be seen that the average water contact angle on the surface of the 5056 aluminum foil treated in Example 1 is about 45°, and the average water contact angle on the surface of the 5056 aluminum foil treated in Example 2 is about 33°. It shows good hydrophilic properties. The average water contact angle on the surface of the 5056 aluminum foil treated in Example 4 is about 65°. The average water contact angle on the surface of the 5056 aluminum foil treated in Comparative Example 1 is 69°. about.

4. Electrochemical polarization test

The uncoated 5056 aluminum foil and the 5056 aluminum foil treated in Examples 1 to 3 were subjected to electrochemical polarization tests. The results are shown in Figure 5.

From the analysis in Figure 5, it can be seen that in 3.5% NaCl solution, the self-corrosion potential of the 5056 aluminum foil treated in Example 1 is -0.84V, which is 0.42V higher than that of the uncoated 5056 aluminum foil substrate; Example The self-corrosion current density of the 5056 aluminum foil treated in 2 is less than 10 ^-6 Acm ^-2 , which is significantly higher than that of the uncoated 5056 aluminum foil substrate, and its self-corrosion potential is -0.86V, which is lower than that of the uncoated 5056 aluminum foil. The substrate increased by 0.4V; the self-corrosion current density of the 5056 aluminum foil treated in Example 3 was less than 10 ^-6 Acm ^-2 , which was significantly higher than that of the uncoated 5056 aluminum foil substrate, and its self-corrosion potential was -0.90V, which was relatively high. Compared with the uncoated 5056 aluminum foil substrate, it is 0.36V higher.

5. Potassium dichromate drop test

The uncoated 5056 aluminum foil, as well as the treated 5056 aluminum foil in Example 1, Example 4 to Example 6 and Comparative Example 1 were subjected to a potassium dichromate drop test at 25°C. The results are shown in Figure 6 and Figure 7 shown.

From the analysis in Figure 6 and Figure 7, it can be seen that the 5056 aluminum foil treated in Example 1 and Example 5 can withstand the potassium dichromate titration test for 3 minutes, and the 5056 aluminum foil treated in Example 6 can withstand the potassium dichromate titration test for 60 seconds. Test, in Example 4, the potassium dichromate titration resistance after silane sealing treatment was extended to 13 minutes, and the uncoated 5056 aluminum foil can only withstand the potassium dichromate titration test for 30 seconds, thus proving that 5056 after coating and silane sealing agent sealing treatment The corrosion resistance of aluminum foil is significantly improved.

The aluminum alloy surface treatment method of the present invention places the aluminum alloy in the hydrophilic chemical conversion film-forming liquid of the present invention at a lower temperature of 20 to 60° C., within a short time of 60 to 600 seconds, and under atmospheric environmental conditions. , which can be converted into a layer of chemical conversion film with a water contact angle less than 50° and a thickness of 50-150nm on the surface of the aluminum alloy. It shows good adsorption performance and provides good prerequisites for the subsequent adsorption of organic sealants. Experimental studies have proven that aluminum alloys with a chemical conversion film on their surfaces can withstand a 480-hour neutral salt spray test. Furthermore, after organic sealing treatment is performed on the aluminum alloys with a chemical conversion film on their surfaces, the neutral salt spray test is extended to 1,200 hours. hour, it shows very excellent corrosion resistance, and the self-corrosion current is significantly higher than that of the substrate, thereby effectively improving the corrosion resistance of the aluminum alloy, and the treatment method has the advantages of being simple, easy, green and environmentally friendly. In the field of aluminum alloy surface treatment technology, it has promotion and application value. In the field of aluminum alloy surface treatment technology, it has promotion and application value.

The above embodiments are only preferred embodiments to fully illustrate the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are within the protection scope of the present invention.

Claims (8)

1. The aluminum alloy surface treatment method is characterized by comprising the following steps of:

s1, pretreatment: removing impurities from the surface of the aluminum alloy;

s2, coating: adjusting the pH value of the hydrophilic chemical conversion film-forming liquid to be acidic, and then placing the aluminum alloy into the acidic hydrophilic chemical conversion film-forming liquid for chemical conversion treatment so as to form a hydrophilic chemical conversion film on the surface of the aluminum alloy;

hydrophilic chemical conversion film forming liquid comprising trivalent chromium salt, fluorozirconate, organic complexing agent, additive and water;

the organic complexing agent is one or more of polyvinyl alcohol, polyethylene glycol and polyacrylamide;

the additive is fluotitanic acid and/or fluotitanate;

s3, natural aging: cleaning the coated aluminum alloy, and naturally aging in a normal temperature environment;

in the step S1, the pretreatment comprises the steps of sequentially degreasing, alkaline washing, acid washing and rinsing the aluminum alloy;

the degreasing is carried out by adopting a degreasing cleaning agent for cleaning, the cleaning temperature is 50-60 ℃, and the cleaning time is 30-120 seconds; the alkali washing is carried out by adopting 5-10 wt.% of sodium hydroxide solution, the alkali washing temperature is 30-40 ℃, and the alkali washing time is 10-60 seconds; the pickling is carried out by adopting 30-40 vol.% nitric acid solution, the pickling temperature is 20-30 ℃, and the pickling time is 10-60 seconds; the rinsing is carried out by adopting deionized water, the rinsing temperature is 70-80 ℃, and the rinsing time is 10-60 seconds;

the thickness of the chemical conversion film formed on the surface of the aluminum alloy is 50 nm-150 nm.

2. The aluminum alloy surface treatment method according to claim 1, wherein the trivalent chromium salt includes one or more of chromium sulfate, chromium nitrate, and chromium chloride.

3. The aluminum alloy surface treatment method according to claim 1, wherein the fluorozirconate includes one or both of potassium fluorozirconate and sodium fluorozirconate.

4. The method of claim 1, wherein the fluorotitanate is potassium fluorotitanate.

5. The aluminum alloy surface treatment method according to claim 1, wherein the concentration of trivalent chromium salt is 0.5-5 g/L, the concentration of fluorozirconate is 1-10 g/L, the concentration of organic complexing agent is 2-10 g/L, and the concentration of additive is 0.5-5 g/L.

6. The method for treating the surface of the aluminum alloy according to claim 1, further comprising an organic sealing treatment after natural aging, specifically: and sealing the naturally aged aluminum alloy in an organic sealing agent.

7. The method for treating an aluminum alloy surface according to claim 1, wherein in S2, the chemical conversion treatment is performed at a temperature of 20 ℃ to 60 ℃ for a time of 60 to 600 seconds.

8. The method for treating an aluminum alloy surface according to claim 6, wherein in S3, the natural aging time is 48 to 120 hours;

the organic blocking agent is a silane blocking agent.