A chromium-free passivation agent for aluminum and aluminum alloys and a method for preparing the same

Abstract

The application discloses a chromium-free passivator for aluminum and aluminum alloy and a preparation method thereof. The chromium-free passivator comprises the following components: cerium nitrate 2.0-5.0 g / L, lanthanum nitrate 1.0-3.0 g / L, yttrium nitrate 0.5-2.0 g / L, fluorosilane modified nano-SiO2 1.0-3.0 g / L, chelate type titanate coupling agent 0.5-1.5 g / L, citric acid 3.0-8.5 g / L, 30% hydrogen peroxide 1.0-3.0 mL / L, potassium fluorozirconate 0.5-2.0 g / L, amino silane coupling agent 1.0-5.0 mL / L, pH regulator 0.01-3.0 mL / L, and the rest is deionized water. The chromium-free passivator has high adhesion and excellent hydrophobicity, is not corroded under neutral salt spray for 500 hours, can resist copper accelerated acetate salt spray for more than 120 hours, and meets the industrial requirements of aluminum alloy product surface treatment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of surface treatment of metal materials, and particularly relates to a chromium-free passivation agent for aluminum and aluminum alloy and a preparation method thereof. BACKGROUND

[0002] Aluminum and its alloys are widely used in aerospace, vehicle manufacturing, household appliances, electronics, building materials and general hardware fields due to their high specific strength, good thermal and electrical conductivity, no magnetism, no low-temperature brittleness, excellent corrosion resistance and excellent processing performance. However, aluminum itself is a kind of active metal, and when it is in contact with a high-potential metal in a humid environment, it is prone to contact corrosion. In addition, various alloying elements are added in the manufacturing process of aluminum alloy to pursue high mechanical properties and other comprehensive properties. The existence of these elements makes the internal chemical composition and structure of aluminum alloy uneven, and the existence of residual stress in the heat treatment and processing process makes the aluminum alloy prone to micro-battery corrosion in the use environment. Moreover, in the use environment of aluminum alloy, the condensation of humid air on the surface of aluminum alloy material forms a water film, and more seriously, there are certain amounts of Cl - , SO2, H2S, CO2 and other substances in the humid air, which makes the aluminum alloy surface more prone to pitting corrosion, intergranular corrosion, stress corrosion and other forms of damage.

[0003] At present, the most simple and effective corrosion protection treatment for aluminum alloy is the metal surface passivation treatment technology, which generates a complete, dense and uniform passivation layer on the surface of aluminum alloy. Traditionally, the aluminum alloy passivation often adopts chromate chemical passivation method. The passivation film obtained by this treatment has good corrosion resistance and strong adhesion to organic coatings. However, hexavalent chromium ions in the chromate treatment have carcinogenic effect on human body, and improper treatment will cause serious pollution to the environment. Therefore, the chromate passivation technology has been strictly controlled, and some countries have limited its use. Developing a non-toxic, environmentally friendly and high corrosion-resistant green passivation technology has become the industry consensus.

[0004] In recent years, a large number of researches on chromium-free passivation process have been carried out at home and abroad, and various passivation liquid treatment systems such as rare earth, cobalt salt, silicate, molybdate, titanium / zirconate have been developed. At present, the researches are more based on fluorozirconate, fluorotitanate, phytic acid, tannic acid, molybdate, rare earth salt and other treatment technologies. For example, there are various types of cerium salt and oxidizing agents, and a composite treatment agent of cerium nitrate and potassium permanganate is used for passivation treatment of aluminum profiles, which obtains good film forming effect and appearance. However, these technologies still have some shortcomings such as uneven passivation film, insufficient density, slow treatment speed and poor corrosion resistance of bare film.

[0005] Patent document CN116590699A discloses an aluminum alloy chromium-free passivation agent, a preparation method thereof and an aluminum alloy passivation method. Potassium fluozirconate is 3-5 g / L, complexing agent (succinic acid, citric acid) is 0.5-1 g / L, rare earth alloy (heavy rare earth and gadolinium, terbium, scandium) is 1-2 g / L, and the balance is water. The pH value of the aluminum alloy passivation agent is 4.8-5.2. The aluminum alloy is soaked in the passivation solution, the passivation solution uses the above-mentioned aluminum alloy chromium-free passivation agent, the working temperature is 45°C, the pH value of the aluminum alloy chromium-free passivation agent is 5.2, and the passivation time is 10 min. However, scandium, terbium and the like are rare earth elements with extremely low content in the earth's crust and extremely difficult to extract, and are very expensive (for example, the price of scandium is usually thousands to tens of thousands of times that of cerium), which leads to high raw material cost of the passivation solution of the document and serious lack of economic feasibility for industrial mass production. Moreover, the passivation time of 10 min is too long in modern continuous production line, which seriously affects the production rhythm and efficiency.

[0006] Patent document CN107653449A discloses a chromium-free passivation composition, a chromium-free passivation agent and a preparation method thereof. The composition includes components: 1-3 parts of fluozirconate; 0.1-0.5 parts of corrosion inhibitor (sorbitol and sodium grape carbonate); 0.1-0.2 parts of fluoride compound other than fluozirconate (hydrofluoric acid, fluorosilicic acid, hydrogen fluoride and sodium fluoride); 0.5-1.0 parts of nitrate; 0.1-0.2 parts of silane (vinyl triethoxy silane and 3-(2,3-epoxy propoxy) propyl trimethoxy silane); and 0.01-0.05 parts of rare earth. The document adjusts the pH value of the solution to be between 3.5-4.5 with ammonia water, soaks the cleaned aluminum material in the chromium-free passivation agent at room temperature for 3-5 min, washes it clean with pure water after taking it out, and dries it at 100-120°C. However, the document needs to use highly toxic fluoride compound (hydrofluoric acid), which is harmful to the health of the operators; and needs to be dried at 100-120°C, which cannot be used for large aluminum alloy profiles.

[0007] Patent document CN109943836A discloses an aluminum alloy surface chromium-free passivation agent. The solvent is deionized water, and further includes: 45% of a fluozirconate solution 23-27 g / L, 40% of a hydrofluoric acid solution 13-17 g / L, 99.8% of an ice acetic acid solution 3-5 g / L, citric acid 2-3 g / L, 40% of a fluorotitanate solution 3-6 g / L, corrosion inhibitor (sodium molybdate and / or sodium silicate) 0.3-2 g / L, and modified acrylic resin 18-22 g / L, with a pH value of 2.0-3.5. The aluminum alloy surface is treated at room temperature for 30-60 s, and does not need to be washed after passivation. However, the document also needs to use highly toxic fluoride compound (hydrofluoric acid), which is harmful to the health of the operators. SUMMARY

[0008] The present application aims to provide a chromium-free passivation agent for aluminum and aluminum alloy and a preparation method thereof, so as to solve the problems of high toxicity, high curing temperature and poor corrosion resistance in the prior art, form a multi-level corrosion protection barrier, and balance environmental protection, corrosion resistance and process economy.

[0009] In order to achieve the above-mentioned purpose, the technical scheme of the present application is:

[0010] The chromium-free passivation agent for aluminum and aluminum alloy comprises the following components: cerium nitrate (Ce(NO3)3): 2.0-5.0 g / L, lanthanum nitrate (La(NO3)3): 1.0-3.0 g / L, yttrium nitrate (Y(NO3)3): 0.5-2.0 g / L, fluorosilane modified nano-SiO2: 1.0-3.0 g / L, chelated titanate coupling agent: 0.5-1.5 g / L, citric acid: 3.0-8.5 g / L, 30% hydrogen peroxide: 1.0-3.0 mL / L, potassium fluorozirconate (K2ZrF6): 0.5-2.0 g / L, amino silane coupling agent: 1.0-5.0 mL / L, pH regulator: 0.01-3.0 mL / L, and the balance is deionized water.

[0011] The fluorosilane modified nano-SiO2 is nano-silicon dioxide modified by fluorosilane on the surface, and the particle size is 10-80 nm; the hydrophobicity and dispersibility are improved, the physical barrier of the coating can be enhanced, the micro-defects of the coating can be filled, and the method disclosed in document CN104445218A can be used for preparation, or commercially available products such as hydrophobic fumed silica of models HB-132, HB-151 and HB-612 of Hubei HuiFu Nanometer Material Co., Ltd.

[0012] The chelated titanate coupling agent is an alcohol amine aqueous chelated titanate coupling agent (such as a chelate solution of bis(dioctyloxy pyrophosphato) ethylene titanate and triethanolamine) or / and a chelated phosphate titan coupling agent quaternary amine salt, which is a dispersant and adhesion promoter for the fluorosilane modified nano-SiO2, can improve the adhesion of the coating to the substrate, and promote the dispersion of nanoparticles, such as Kenrich KR-238T aqueous titanate coupling agent (domestic corresponding model HY311W).

[0013] The amino silane coupling agent is 3-aminopropyl triethoxysilane (KH-550) or / and 3-aminopropyl trimethoxysilane (KH-540); and the pH regulator is nitric acid and / or ammonia.

[0014] The aluminum or aluminum alloy refers to pure aluminum or various series or types of aluminum alloy, especially 5 series, 6 series and 7 series aluminum alloy.

[0015] The preparation method of the chromium-free passivation agent for aluminum and aluminum alloy comprises the following steps:

[0016] S1, by volume ratio: deionized water: ethanol: amino silane coupling agent = (3.5-4.5): (4.5-5.5): 1, mix deionized water and ethanol, adjust pH value to 4.5-5.0 with acetic acid; slowly add the formula amount of amino silane coupling agent under stirring, continue stirring for 25 min or more, seal, hydrolyze at room temperature for at least 24 h, to obtain a pre-hydrolyzed silane solution;

[0017] S2, add 8%-15% of deionized water to the total water to the container, then add the formula amount of chelated titanate coupling agent, stir to dissolve; slowly add the formula amount of fluorosilane modified nano-SiO2 under high-speed stirring, continue to disperse for 20-50 min under high-speed stirring until the slurry is uniform and fine without visible particles; obtain a stable nano-SiO2 pre-dispersed slurry for standby;

[0018] S3, add 10%-20% of deionized water to the total water to the reactor, add the formula amount of citric acid, stir to dissolve completely; slowly add the formula amount of cerium nitrate, lanthanum nitrate and yttrium nitrate, stir to dissolve completely; slowly adjust the pH value of the solution to 3.0-3.5 with ammonia water, to obtain a rare earth complex solution for standby;

[0019] S4, add 40%-60% of deionized water to the total water to the main preparation tank, add the formula amount of potassium fluorozirconate, stir to dissolve completely; slowly add the nano-SiO2 pre-dispersed slurry under stirring and stir to mix evenly; slowly add the rare earth complex solution and stir to mix evenly; add the hydrogen peroxide; add the pre-hydrolyzed silane solution, continue to stir for 15-40 min; add the remaining deionized water;

[0020] S5, adjust the final pH value of the working solution of step S4 to 4.0±0.2 with the pH adjuster, stand for 2-5 h to obtain a chromium-free passivator.

[0021] The rotation speed of the high-speed stirring is ≥5000 rpm; the rotation speed of the medium-speed stirring is 500-1000 rpm;

[0022] Preferably, the temperature of the reactor of step S3 should be controlled at ≤40℃.

[0023] The application method of the chromium-free passivator for aluminum and aluminum alloy, comprising the following steps: D1, pretreatment: the aluminum or aluminum alloy workpiece is subjected to alkaline degreasing or neutral degreasing, then is subjected to water washing, then is subjected to acid etching treatment, then is subjected to water washing, and finally is washed with deionized water; D2, passivation treatment: the cleaned workpiece is completely immersed in the chromium-free passivator, and is soaked at a temperature of 30-40℃ for 3-6 min; D3, post-treatment: the workpiece is directly dried at 80-100℃.

[0024] Preferably, in the step D1, the alkaline or neutral degreasing should be carried out at 40-60℃; the water washing is two-stage countercurrent rinsing.

[0025] The acid etching treatment in the step D1 is an optional step, which is selected or omitted according to specific conditions, and preferably, a nitric acid aqueous solution or a non-chromium acid oxidant with a mass concentration of 3%-15% is used for acid etching treatment.

[0026] Compared with the prior art, the positive effects of the present application are:

[0027] The present application adopts the multi-rare earth synergy of Ce / La / Y combination, Ce is the main passivator, cathode inhibition, providing basic protection; La and Y synergistically form a film, which can fill the defects on the surface of the aluminum alloy workpiece, improve the compactness, and stabilize the structure of the passivation film, enhance the heat resistance and long-term performance; hydrogen peroxide is a mild oxidant, which is used to promote the conversion of Ce 3+ to Ce 4+ , forming a more stable CeO2 film; potassium fluozirconate can form a Zr / O / F network, which cooperates with the rare earth film to improve uniformity; through the bridging action of chelating titanate, fluorosilane modified nano-SiO2 is introduced to fill the pores of the passivation film, enhance the hydrophobicity, and provide a physical barrier; citric acid can complex rare earth ions, prevent nanoparticles and rare earth precipitation, control the hydrolysis film formation rate, and improve the stability of the chromium-free passivator; the amino group of the amino silane coupling agent can be complexed with the -OH group formed after hydrolysis and the rare earth elements through complexation synergy, improving the adhesion of the film base and improving the compatibility with the subsequent coating; the acid-base balance, pH 4.0 is more suitable for various aluminum alloys, and the film formation efficiency is high. DETAILED DESCRIPTION

[0028] A person of ordinary skill in the art should recognize that the embodiments are only used to illustrate the present application, and are not used as a limitation to the present application, and as long as the embodiments are changed and modified within the scope of the present application, they can be within the scope of the claims of the present application.

[0029] Examples 1-5 and Comparative Examples 1-3

[0030] The chromium-free passivators for aluminum and aluminum alloys of Examples 1-5 and Comparative Examples 1-3 are listed in Table 1, and the preparation method includes the following steps:

[0031] S1, take deionized water: ethanol: KH-550=4:5:1 by volume ratio, mix deionized water and ethanol, adjust the pH value to 4.6 with acetic acid; slowly add KH-550 under stirring, continue stirring for 30 min, seal, and hydrolyze at room temperature for at least 24 h to obtain a pre-hydrolyzed silane solution;

[0032] S2, add 10% of the total water amount of deionized water to a container with a high-speed disperser, then add chelated titanate coupling agent (Kanrich KR-238T), and stir at medium speed (600 rpm) for 5 min to fully dissolve; under high-speed stirring (6000 rpm), slowly add fluorosilane modified nano-SiO2 (Hui Fu Nano HB-132) in batches, continue to stir at high speed for 30 min until the slurry is uniform and fine without visible particles; obtain a stable nano-SiO2 pre-dispersed slurry for standby;

[0033] S3, add 15% of the total water amount of deionized water to the reactor, control the temperature of the reactor at 35℃, add citric acid, and stir until completely dissolved; slowly add cerium nitrate, lanthanum nitrate and yttrium nitrate, and stir until completely dissolved; slowly adjust the pH value of the solution to 3.2 with ammonia water to obtain a rare earth complex solution for standby;

[0034] S4, add 50% of the total water amount of deionized water to the main preparation tank, add potassium fluorozirconate, and stir until completely dissolved; under medium-speed stirring (800 rpm), slowly add the nano-SiO2 pre-dispersed slurry, continue to stir for 15 min after adding until the mixture is uniform; slowly add the rare earth complex solution, continue to stir for 10 min after adding until the mixture is uniform; add hydrogen peroxide, and mix for 5 min with slight stirring; wash the container with pre-hydrolyzed silane solution and add it all to the tank, continue to stir for 30 min; add the remaining deionized water;

[0035] S5, adjust the final pH value of the working solution of step S4 to 4.0±0.2 with a pH adjuster, and stand for 3 h to obtain a chromium-free passivator.

[0036] Comparative Examples 1-3 are comparative examples of Example 3. In Comparative Example 1, silane coupling agent KH-550 is not added, and step S1 is omitted; in Comparative Example 2, fluorosilane modified nano-SiO2 and chelated titanate coupling agent are not added, and step S2 is omitted; in Comparative Example 3, citric acid is not added.

[0037] Table 1: Pretreatment agent ratio of Examples 1-5 and Comparative Examples 1-3, unit wt%

[0038]

[0039] Test Experimental Example

[0040] The chromium-free passivators of Examples 1-5 and Comparative Examples 1-3 were respectively used to passivate aluminum alloy plate samples, and the application method included the following steps: D1, pretreatment: the 6061 aluminum alloy workpiece was degreased with an alkaline degreasing agent (10 min at 50℃), then washed thoroughly (two-stage countercurrent rinsing), then treated with 8% nitric acid aqueous solution for acid etching, then washed thoroughly (two-stage countercurrent rinsing), and finally washed with deionized water; D2, passivation treatment: the cleaned workpiece was completely immersed in the chromium-free passivator, and soaked at a temperature of 35℃ for 5 min; D3, post-treatment: the workpiece was directly dried by heating at 90℃ for 10 min.

[0041] The surface of the passivated aluminum alloy plate sample was a uniform iridescent film or a light golden yellow film; the film weight, adhesion, hydrophobicity (water contact angle), neutral salt spray resistance, and copper-accelerated acetic acid salt spray resistance of the passivation film were respectively determined, and the results are shown in Table 2.

[0042] Adhesion: determined according to GB / T 9286-2021 grid method, no falling off after the cross-cut knife cutting.

[0043] Contact angle: according to ASTM D7334 static water drop method.

[0044] Neutral salt spray resistance (NSS): according to GB / T 1771-2007, each sample had 6 test samples, and the prepared sample plate was placed in a salt spray chamber at a temperature of 35℃, and sprayed with 5wt% sodium chloride brine with a pH of 7.0 at an air pressure of 1.0kgf / cm 2 After spraying the sample plate for 150h and 360h, 3 samples were taken out respectively, washed with water and dried, and then the surface corrosion of the sample plate was observed, and the percentage of the corrosion area to the total area of the product was calculated.

[0045] Copper-accelerated acetic acid salt spray resistance: according to GBT 12967.3-2008, 5wt% sodium chloride brine was added with 2±0.2g / L CuCl2·2H2O, the pH value was 3.0-3.1, and the gas source pressure was 100kPa; the test temperature was 50℃.

[0046] Table 2 Performance of passivation films of Examples 1-5 and Comparative Examples 1-3

[0047]

[0048] As can be seen from Table 2, the chromium-free passivators of Examples 1-5 have high adhesion and excellent hydrophobicity, no corrosion under neutral salt spray for 500h, can resist copper-accelerated acetic acid salt spray for more than 120h, and meet the industrial needs of aluminum alloy product surface treatment.

[0049] Compared with Example 3, in Comparative Example 1, the silane coupling agent KH-550 is not added, step S1 is omitted, the adhesion and hydrophobicity of the base film decrease, and the salt spray resistance of the passivation film is also affected; in Comparative Example 2, the fluorosilane modified nano-SiO2 and the chelate type titanate coupling agent are not added, step S2 is omitted, the porosity in the passivation film increases, the hydrophobicity decreases, and the salt spray resistance sharply decreases; in Comparative Example 3, citric acid is not added.

Claims

1. A chromium-free passivating agent for aluminum and aluminum alloys, characterized in that, It comprises the following components: Cerium nitrate: 2.0-5.0 g / L, lanthanum nitrate: 1.0-3.0 g / L, yttrium nitrate: 0.5-2.0 g / L, fluorosilane modified nano-SiO2: 1.0-3.0 g / L, chelated titanate coupling agent: 0.5-1.5 g / L, citric acid: 3.0-8.5 g / L, 30% hydrogen peroxide: 1.0-3.0 mL / L, potassium fluozirconate: 0.5-2.0 g / L, amino silane coupling agent: 1.0-5.0 mL / L, pH regulator: 0.01-3.0 mL / L, and the rest is deionized water.

2. The chromium-free passivant for aluminum and aluminum alloys according to claim 1, characterized by, The fluorosilane modified nano-SiO2 is nano-silicon dioxide modified by fluorosilane on the surface, and the particle size is 10-80 nm.

3. The chromium-free passivant for aluminum and aluminum alloys according to claim 1, characterized by, The chelated titanate coupling agent is an alcohol amine aqueous chelated titanate coupling agent or / and a chelated phosphate ester titanium coupling agent quaternary amine salt.

4. The chromium-free passivant for aluminum and aluminum alloys according to claim 1, characterized by, The amino silane coupling agent is 3-aminopropyl triethoxysilane or / and 3-aminopropyl trimethoxysilane; and the pH regulator is nitric acid and / or ammonia.

5. The production method of the chromium-free passivation agent for aluminum and aluminum alloys according to any one of claims 1 to 4, characterized by, It comprises the following steps: S1, by volume ratio: deionized water: ethanol: amino silane coupling agent = (3.5-4.5): (4.5-5.5): 1, mix deionized water and ethanol, adjust the pH value to 4.5-5.0 with acetic acid; slowly add the formula amount of amino silane coupling agent under stirring, continue stirring for more than 25 min, seal, and stand for hydrolysis at room temperature for at least 24 h to obtain a pre-hydrolyzed silane solution; S2, add 8%-15% of deionized water to the total water amount to the container, then add the formula amount of chelated titanate coupling agent, and stir to fully dissolve; slowly add the formula amount of fluorosilane modified nano-SiO2 in batches under high-speed stirring, continue to disperse for 20-50 min under high-speed stirring until the slurry is uniform and fine without visible particles; obtain a stable nano-SiO2 pre-dispersed slurry; S3, add 10%-20% of deionized water to the total water amount to the reactor, add the formula amount of citric acid, and stir to fully dissolve; slowly add the formula amount of cerium nitrate, lanthanum nitrate and yttrium nitrate, and stir to fully dissolve; slowly adjust the pH value of the solution to 3.0-3.5 with ammonia water to obtain a rare earth complex solution; S4, add 40%-60% of deionized water to the total water amount to the main preparation tank, add the formula amount of potassium fluozirconate, and stir to fully dissolve; slowly add the nano-SiO2 pre-dispersed slurry under stirring and stir evenly; slowly add the rare earth complex solution and stir evenly; add the hydrogen peroxide; add the pre-hydrolyzed silane solution, continue to stir for 15-40 min; add the remaining deionized water; S5, adjust the final pH value of the working solution of step S4 to 4.0±0.2 with the pH regulator, and stand for curing for 2-5 h to obtain a chromium-free passivator.

6. The production method of the chromium-free passivant for aluminum and aluminum alloys according to claim 5, characterized by, The temperature of the reactor of step S3 should be controlled at ≤40℃.

7. The application method of the chromium-free passivation agent for aluminum and aluminum alloys according to any one of claims 1 to 4, characterized by, It comprises the following steps: D1, pretreatment: the aluminum or aluminum alloy workpiece is subjected to alkaline degreasing or neutral degreasing, then fully washed with water, then subjected to acid etching treatment, then fully washed with water, and finally washed with deionized water; D2, passivation treatment: completely immerse the cleaned workpiece in the chromium-free passivation agent, soak for 3-6 min at a temperature of 30-40 DEG C; D3, post-treatment: directly dry the workpiece at 80-100 DEG C.

8. The application method of the chromium-free passivating agent for aluminum and aluminum alloys according to claim 7, characterized by, In the step D1, the alkaline or neutral degreasing should be carried out at 40-60 DEG C; the water washing is two-stage countercurrent rinsing.

9. The application method of the chromium-free passivation agent for aluminum and aluminum alloys according to claim 7, characterized by, In the step D1, the acid etching treatment is carried out using a nitric acid aqueous solution or a non-chromium acid oxidizing agent with a mass concentration of 3-15%.

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