Preparation method of aluminum alloy conductive corrosion-resistant conversion film

Abstract

The invention provides a preparation method of an aluminum alloy conductive corrosion-resistant conversion film. The preparation method comprises the following steps: step 1, pretreating an aluminum alloy; 2, preparing a tin organic conversion solution; thirdly, the aluminum alloy pretreated in the first step is immersed in the tin organic conversion liquid obtained in the second step, the temperature is controlled to range from 25 DEG C to 65 DEG C, the treatment time ranges from 30 seconds to 240 seconds, a sample is taken out of the solution, the pulling speed for taking out the sample is 9 cm / min to 20 cm / min, then, the sample is naturally aired for 10 min to 20 min at the room temperature, dried for 1 h to 2 h at the temperature of 140 DEG C to 180 DEG C and cooled along with a furnace, and the aluminum alloy is obtained. And the aluminum alloy conductive corrosion-resistant conversion film is prepared. The invention further provides the aluminum alloy conductive corrosion-resistant conversion film prepared through the method. The preparation method of the conversion film with the conductive and corrosion-resistant functions on the aluminum alloy surface is convenient to operate, a workpiece does not need to be washed after being treated, no wastewater is discharged, and the method is green and environmentally friendly. The aluminum alloy conductive corrosion-resistant conversion film prepared by the method comprises the main components of elemental tin and tin dioxide, and is simple in composition, low in drying temperature and excellent in conductivity.

Description

Technical Field

[0001] The present invention relates to the field of electrical and electrochemical corrosion and protection of metal material surfaces, and in particular to a method for preparing a conversion film with conductive and corrosion-resistant functions applied to the surface of an aluminum alloy. Background Art

[0002] Aluminum alloy has excellent comprehensive properties. As a bipolar plate for proton exchange membrane fuel cells, conductive tubes (or rods), anti-static flooring, and electromagnetic shielding lining, it requires not only good corrosion resistance but also good electrical conductivity. This can effectively prevent equipment failures caused by corrosion and poor electrical conductivity, and even avoid catastrophic accidents.

[0003] Among aluminum alloy surface treatment technologies, electroplating and electroless plating provide excellent electrical conductivity, but their potential for galvanic corrosion and process complexity limit their application. Currently, the most mature chromate oxidation process can meet the conductivity requirements of metal surfaces, but the hexavalent chromium ion is carcinogenic and polluting, preventing widespread application. Chemical conversion methods deposit multivalent transition metal oxides on the metal surface, achieving low contact resistance, but their corrosion resistance is suboptimal.

[0004] At present, the main goal of chromium-free conversion coatings for aluminum alloys is to improve the corrosion resistance of the film layer, while the conductivity is relatively ignored. Studies have shown that by depositing multivalent transition metal oxides on the surface of the metal through chemical conversion, the semiconductor properties of the oxides can be used to achieve low contact resistance of the film layer. For example, patent application No. 202111192927.6 proposed adding nano zinc oxide to a conversion solution system containing molybdate and titanate to prepare a conductive corrosion-resistant film on the surface of aluminum alloy. However, the conductivity is still poor (824 to 1054 mΩ·in -2 Separately, patent application number 201810957046.0 proposes a conductive spot design. This utilizes the differing corrosion resistances between the primary α-phase and secondary β-phase of AZ91D magnesium alloy. Through pickling pretreatment, the β-phase is rendered superior to the α-phase, serving as the conductive spot. After chemical conversion, a conductive corrosion-resistant film is obtained. This method produces a film with a thickness of only 200 nm. Its conductivity depends on the pickling pretreatment, resulting in a complex process and unsuitable for alloys with less pronounced secondary phases or pure metals.

[0005] The sol-gel method is another method for preparing conductive membranes. Generally, conductive fillers are introduced into the sol-gel network or metal oxide membranes are prepared to achieve the conductivity of the membrane layer. For example, patent application number CN201711114242.3 uses the sol-gel method to prepare a Ti1-xNbxO2 conductive and corrosion-resistant membrane layer on a proton exchange membrane fuel cell stainless steel bipolar plate, where x represents the atomic percentage of Nb and the thickness is 0.2 to 0.7 μm. Although this method has simple ingredients, the prepared membrane has excellent corrosion resistance and conductivity (the self-corrosion current density is reduced by three orders of magnitude relative to the substrate, and the contact resistance is 20 to 80 mΩ·cm). -2 ), but it is necessary to control the percentage of titanium atoms and to anneal at a high temperature of 400-500°C. The process is relatively complicated, and generally requires multi-layer preparation to ensure the corrosion resistance of the film. Summary of the Invention

[0006] The present invention provides a method for preparing a conversion film with conductive and corrosion-resistant functions on the surface of an aluminum alloy, which solves the problem that the preparation method of the conversion film in the prior art is complicated.

[0007] The present invention also provides an aluminum alloy conductive corrosion-resistant conversion film, which solves the problem of poor corrosion resistance of the film layer in the prior art.

[0008] The technical solution of the present invention is achieved as follows: A method for preparing a conductive and corrosion-resistant conversion film of an aluminum alloy, comprising the following steps: step one, pretreating the aluminum alloy; step two, preparing a tin organic conversion solution; step three, immersing the aluminum alloy pretreated in step one in the tin organic conversion solution obtained in step two, controlling the temperature to 25-65°C, and processing time to 30-240 seconds, taking out a sample from the solution, and pulling the sample at a speed of 9-20 cm / min, then naturally drying at room temperature for 10-20 minutes, drying at 140-180°C for 1-2 hours, and cooling with the furnace to obtain a conductive and corrosion-resistant conversion film of an aluminum alloy.

[0009] Furthermore, the specific method for pre-treating the aluminum alloy is as follows: step S1, mechanically removing the surface oxide film and dirt: polishing the aluminum alloy with sandpaper, and ultrasonically degreasing with anhydrous ethanol for 10-15 minutes; step S2, rinsing with tap water and deionized water once each; step S3, two-step pickling: industrial acid pickling for 1-3 minutes, mixed acid activation for 1-4 minutes; step S4, rinsing with tap water and deionized water once each.

[0010] Furthermore, the industrial acid consists of 100 g / L concentrated sulfuric acid, 20 ml / L H3PO4, 6 ml / L HF, and 0.3 g / L OP-10 (dodecylphenol polyoxyethylene ether).

[0011] Furthermore, the mixed acid consists of 10% by volume of concentrated nitric acid, 2.5% by volume of H3PO4, and 2% by volume of concentrated sulfuric acid.

[0012] Furthermore, step S1 is to grind the aluminum alloy in stages using 400-mesh, 1200-mesh, and 1500-mesh sandpaper.

[0013] Furthermore, the specific preparation method of the tin organic conversion liquid is as follows: dissolving stannous chloride dihydrate in a mixed solution of n-butanol and pure water, magnetically stirring at room temperature for 10-20 minutes, then openly stirring and refluxing in a constant temperature oil bath at 110°C for 2-3 hours, and after the solution is cooled to room temperature to obtain an organic conversion liquid, adjusting the pH value to 0.5-1.6 with hydrochloric acid and ammonia water, and placing it at room temperature for more than 24 hours.

[0014] Furthermore, 1-8 g of stannous chloride dihydrate is dissolved in 120-160 ml of a mixed solution of n-butanol and pure water.

[0015] Furthermore, the concentration of stannous chloride dihydrate is 0.05-0.5 mol / L; the volume ratio of the mixture of n-butanol and pure water is 10-100:1; the volume fraction of hydrochloric acid is 15% and the volume fraction of ammonia water is 25%.

[0016] Furthermore, the stannous chloride dihydrate, the n-butanol, the hydrochloric acid, and the ammonia water are all analytically pure reagents.

[0017] A conductive and corrosion-resistant aluminum alloy conversion film is prepared by the method for preparing the conductive and corrosion-resistant aluminum alloy conversion film.

[0018] The beneficial effects of the present invention are as follows: the method for preparing a conversion film having conductive and corrosion-resistant functions on the surface of an aluminum alloy according to the present invention is easy to operate, does not require water washing after workpiece processing, does not discharge wastewater, and is green and environmentally friendly. The main components of the aluminum alloy conductive and corrosion-resistant conversion film prepared by the present invention are elemental tin and tin dioxide, with a simple composition, low drying temperature, and excellent conductivity. The tin organic conversion liquid prepared by the present invention comprises stannous chloride dihydrate, n-butanol, and water, with simple ingredients and low cost. The prepared conversion liquid has excellent stability and can be stored for a long time. The prepared aluminum alloy conductive and corrosion-resistant conversion film showed no corrosion spots after being soaked in 5% salt water for 45 days, and has good corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Attachment Figure 1 This is an SEM image of the conversion film with conductive and corrosion-resistant functions on the aluminum alloy surface prepared in Example 1 of the present invention.

[0021] Attachment Figure 2 These are the polarization curve test results of the conversion film with conductive and corrosion-resistant functions on the aluminum alloy surface prepared in Example 1 of the present invention.

[0022] Attachment Figure 3 Corrosion diagrams of the conversion film with conductive and corrosion-resistant functions on the aluminum alloy surface prepared in Example 1 of the present invention after being immersed in 3.5% NaCl solution for different times. DETAILED DESCRIPTION

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0024] Example 1 According to the preparation method of the present invention, a conversion film having conductive and corrosion-resistant functions is prepared on the surface of an aluminum alloy, and the steps are as follows: Step 1: Aluminum alloy pretreatment: Mechanically remove the surface oxide film and dirt, polish the aluminum alloy with 400#, 1200#, and 1500# sandpaper in stages, and ultrasonically degrease with anhydrous ethanol for 10 minutes; Rinse once with tap water and once with deionized water; Two-step pickling: industrial acid (composed of 100 g / L concentrated sulfuric acid, 20 ml / L H3PO4, 6 ml / L HF and 0.3 g / L OP-10) pickling for 1 minute, mixed acid (composed of 10% by volume concentrated nitric acid, 2.5% by volume H3PO4 and 2% by volume concentrated sulfuric acid) activation for 2 minutes; Rinse once with tap water and once with deionized water; blow dry with cold air and set aside; Step 2, preparation of tin organic conversion solution: 3.55 g of stannous chloride dihydrate was dissolved in a mixed solution of 150 ml of n-butanol and 7.5 ml of pure water (the volume ratio of n-butanol to water was 20:1) to prepare a 0.1 mol / L tin solution, magnetically stirred at room temperature for 15 minutes, then refluxed in an open oil bath at 110°C for 3 hours with stirring. After the solution was cooled to room temperature, the organic conversion solution was obtained, and the pH value was adjusted to 1.2 with hydrochloric acid and aqueous ammonia, and the solution was aged at room temperature for more than 24 hours before use; Step 3, preparation of conductive corrosion-resistant film: immerse the aluminum alloy pretreated in step 1 in the tin organic conversion solution obtained in step 2 at a temperature of 25°C for 60 seconds, and remove the sample from the solution at a pulling speed of 18 cm / min; dry it naturally at room temperature for 10 minutes, dry it at 150°C for 1 hour, and cool it in the furnace to obtain the conductive corrosion-resistant conversion film of the aluminum alloy.

[0025] Polarization curves and salt water immersion experiments are effective tools commonly used in corrosion science to characterize the corrosion rate of metal electrodes covered by films, coatings, conversion films, etc. The conversion film on the surface of aluminum alloy was subjected to salt water immersion experiments and electrochemical corrosion resistance tests. A standard three-electrode system was used (the conversion film sample was the research electrode, the platinum electrode was the auxiliary electrode, and the saturated calomel electrode was the reference electrode). NaCl with a mass percentage concentration of 3.5% was used as the electrolyte, and a dynamic potential polarization curve scan was performed. A salt water immersion corrosion experiment was carried out using a NaCl solution with a mass percentage concentration of 5% to simulate seawater, and the corrosion of the sample was observed after immersion for different times. The results are shown in Table 1. The polarization curve test results of the conversion film with conductive and corrosion-resistant functions on the surface of aluminum alloy are shown in Table 1. Figure 2 The SEM image of the conversion film with conductive and corrosion-resistant functions on the surface of the aluminum alloy is shown in Figure 1 As shown, Figure 1 ) a is the SEM image before immersion, Figure 1 ) b SEM image after immersion, the surface still shows no corrosion effect after immersion.

[0026] Table 1 From the test data, it can be seen that the self-corrosion current density of the conversion film on the aluminum alloy surface is 2.06 μA·cm -2 , which is higher than 39.4 μA·cm on the blank aluminum alloy surface. -2 , which is reduced by about one order of magnitude, and the salt water immersion corrosion test lasts for more than 1000h.

[0027] like Figure 3 As shown in Figure 2, the corrosion diagram of the conversion film on the aluminum alloy surface with conductive and corrosion-resistant functions is immersed in 3.5% NaCl solution for different times, as shown in Figure 2. Figure 3 (a) is a blank sample, such as Figure 3 (b) Conversion coating test specimens, such as Figure 3 (c) Corrosion diagram of blank sample (after immersion for 12 h), as shown in Figure 3 (d) Corrosion image of the conversion coating (after 1080 h of immersion). The conductive, corrosion-resistant conversion coating on aluminum alloy exhibited excellent corrosion resistance after immersion in 5% salt water for 45 days, showing no corrosion spots.

[0028] Surface contact resistance refers to the additional resistance generated when current passes through two rough interfaces in contact with each other, which can characterize the conductive properties of the coating. The conductivity test system of the conversion film is designed in accordance with the military standard SJ20813-2002 "Specifications for Chemical Conversion Films of Aluminum and Aluminum Alloys" of the electronics industry of the People's Republic of China, and the test temperature is room temperature. Because the four-wire Kelvin test technology is more accurate than the two-wire method, and the reference current can effectively eliminate the resistance of the power supply wire and has no effect on the reference current, the reliability of the surface contact resistance measurement can be ensured. A DC low resistance tester (RK2512N+) is selected to measure the contact resistance. The electrode material is a highly conductive copper alloy, and the area of the upper electrode is 1 cm 2 , the lower electrode area is 1.96 cm 2 A self-assembled pressure testing machine was used to provide a constant load pressure of 1.4 MPa, with pressure fluctuations within 1.5% of the predetermined pressure. To minimize error, each sample was tested four times in parallel. The results are shown in Table 2.

[0029] Table 2 The test results show that the contact resistance of the conversion coating is 1.87 mΩ·cm higher than that of the aluminum alloy without the coating. 2 As for conductivity, the difference between the two is not much, that is, the conductive conversion film of the present invention has good conductivity.

[0030] Example 2 Steps 1 and 2 are the same as Example 1 Step 3. Preparation of conductive corrosion-resistant film: Immerse the aluminum alloy pretreated in step 1 in the tin organic conversion solution obtained in step 2 at 35°C for 120 seconds. Take out the sample from the solution at a pulling speed of 20 cm / min, dry it naturally at room temperature for 12 minutes, dry it at 160°C for 1.5 hours, and cool it in the furnace.

[0031] The corrosion resistance test and conductivity test results are shown in Table 3 and Table 4.

[0032] Table 3 From the test data, it can be seen that the self-corrosion current density of the conversion film on the aluminum alloy surface is 1.70 μA·cm -2 , which is higher than 39.4 μA·cm on the blank aluminum alloy surface. -2 , reduced by an order of magnitude, and the salt water immersion corrosion test lasted for more than 200 h.

[0033] Table 4 From the test results, it can be seen that the conductivity of the conversion film on the aluminum alloy surface is not much different from that of the blank aluminum alloy sample, indicating that the conversion film of the present invention has good conductivity.

[0034] Example 3 Steps 1 and 3 are the same as Example 1 Step 2, Preparation of Tin Organic Conversion Solution: Dissolve 7.11 g of stannous chloride dihydrate in a mixed solution of 150 ml of n-butanol and 7.5 ml of water (the volume ratio of n-butanol to water is 20:1) to prepare a 0.2 mol / L tin solution. Stir magnetically at room temperature for 15 minutes, then reflux in an open oil bath at 110°C for 3 hours with stirring. After the solution is cooled to room temperature, an organic conversion solution is obtained. Adjust the pH to 0.8 with hydrochloric acid and aqueous ammonia, and let it stand at room temperature for more than 24 hours before use. The corrosion resistance test and conductivity test results are shown in Table 5 and Table 6.

[0035] Table 5 From the test data, it can be seen that the self-corrosion current density of the conversion film on the aluminum alloy surface is 2.13 μA·cm -2 , which is higher than 39.4 μA·cm on the blank aluminum alloy surface. -2 , reduced by an order of magnitude, and the salt water immersion corrosion test lasted for more than 500 h.

[0036] Table 6 From the test results, it can be seen that the conductivity of the conversion film on the aluminum alloy surface is not much different from that of the blank aluminum alloy sample, which shows that the conversion film of the present invention has high conductivity.

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a conductive corrosion-resistant conversion film of an aluminum alloy, characterized in that: The following steps are involved: Step 1, pretreating the aluminum alloy; step 2, preparing a tin organic conversion solution; step 3, immersing the aluminum alloy pretreated in step 1 into the tin organic conversion solution obtained in step 2, controlling the temperature to 25-65°C, and treating for 30-240 seconds, taking out the sample from the solution, and pulling the sample at a speed of 9-20 cm / min, then naturally drying it at room temperature for 10-20 minutes, drying it at 140-180°C for 1-2 hours, and cooling it in the furnace to obtain a conductive and corrosion-resistant conversion film for the aluminum alloy.

2. The method for preparing the conductive corrosion-resistant conversion film of aluminum alloy according to claim 1, characterized in that: The specific method for pre-treating the aluminum alloy is as follows: step S1, mechanically removing the surface oxide film and dirt: polishing the aluminum alloy with sandpaper, and ultrasonically degreasing with anhydrous ethanol for 10-15 minutes; step S2, rinsing with tap water and deionized water once each; step S3, two-step pickling: industrial acid pickling for 1-3 minutes, mixed acid activation for 1-4 minutes; step S4, rinsing with tap water and deionized water once each.

3. The method for preparing the conductive corrosion-resistant conversion film of aluminum alloy according to claim 2, wherein: The industrial acid consists of 100 g / L concentrated sulfuric acid, 20 ml / L H3PO4, 6 ml / L HF and 0.3 g / L OP-10.

4. The method for preparing the conductive corrosion-resistant conversion film of aluminum alloy according to claim 2, wherein: The mixed acid consists of 10% by volume of concentrated nitric acid, 2.5% by volume of H3PO4 and 2% by volume of concentrated sulfuric acid.

5. The method for preparing the conductive corrosion-resistant conversion film of aluminum alloy according to claim 2, wherein: Step S1 is to grind the aluminum alloy in stages using 400-mesh, 1200-mesh, and 1500-mesh sandpaper.

6. The method for preparing the conductive corrosion-resistant conversion film of aluminum alloy according to claim 1, wherein: The specific preparation method of the tin organic conversion liquid is as follows: dissolving stannous chloride dihydrate in a mixed solution of n-butanol and pure water, magnetically stirring at room temperature for 10-20 minutes, then openly stirring and refluxing in a constant temperature oil bath at 110°C for 2-3 hours, and after the solution is cooled to room temperature to obtain an organic conversion liquid, adjusting the pH value to 0.5-1.6 with hydrochloric acid and ammonia water, and placing it at room temperature for more than 24 hours.

7. The method for preparing the conductive corrosion-resistant conversion film of aluminum alloy according to claim 6, characterized in that: Dissolve 1-8 g of stannous chloride dihydrate in 120-160 ml of a mixture of n-butanol and pure water.

8. The method for preparing the conductive corrosion-resistant conversion film of aluminum alloy according to claim 6, wherein: The concentration of stannous chloride dihydrate is 0.05-0.5 mol / L; the volume ratio of the mixture of n-butanol and pure water is 10-100:1; the volume fraction of hydrochloric acid is 15% and the volume fraction of ammonia water is 25%.

9. The method for preparing the conductive corrosion-resistant conversion film of aluminum alloy according to claim 6, wherein: The stannous chloride dihydrate, the n-butanol, the hydrochloric acid, and the ammonia water are all analytically pure reagents.

10. A conductive, corrosion-resistant conversion film on an aluminum alloy, characterized by: The conductive and corrosion-resistant conversion film of aluminum alloy is prepared by the preparation method of any one of claims 1 to 9.

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