A chromium-free passivation solution for zinc alloys

Abstract

This invention discloses a chromium-free passivation solution for zinc alloys, belonging to the field of metal surface treatment technology. The chromium-free passivation solution comprises the following components by weight: 1-10 parts silane coupling agent, 2-20 parts aluminum dihydrogen phosphate, 0.5-5 parts cerium sulfate, 2-20 parts passivation enhancer, 0.5-5 parts corrosion inhibitor, 0.5-5 parts chelating agent, 0.5-5 parts pH adjuster, 10-40 parts acrylic emulsion, and 50-150 parts water; wherein the passivation enhancer is composed of nano-silica, ammonium fluorotitanate, potassium fluorozirconate, and an aqueous solution of tetramethylammonium hydroxide. The chromium-free passivation solution formulation provided by this invention is safe and environmentally friendly, suitable for the protection of zinc alloy workpieces and products, and has advantages such as strong adhesion, good corrosion resistance, and good stability.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment technology, and specifically relates to a chromium-free passivation solution for zinc alloys. Background Technology

[0002] Zinc alloys, as an important coating material for steel protection, are widely used in automotive parts, electronic connectors, building hardware, and daily industrial products. However, zinc alloys are easily corroded in humid and hot environments, resulting in white spots and gray deposits on the surface. Passivation treatment of zinc alloy surfaces can improve their corrosion resistance and aesthetics. Traditional chromate passivation processes passivate zinc alloys with chromate to form a mixed oxide film of chromium and zinc. In particular, hexavalent chromium passivation films, with their excellent self-healing and salt spray resistance, were the preferred choice for industries with high protection requirements for a period of time. However, the high toxicity of hexavalent chromium poses significant safety hazards to the ecological environment and human health, and it has gradually been replaced by trivalent chromium passivation systems. Although the toxicity of trivalent chromium is significantly reduced and it can form a passivation film with a framework-like structure, the film layer may still contain hexavalent chromium, and long-term storage poses a risk of oxidation and transformation, failing to completely solve the chromium pollution problem. Therefore, the development of truly environmentally friendly chromium-free passivation technology has become an urgent need for the industry.

[0003] Currently, chromium-free passivation solution systems mainly focus on silicate, molybdate, and rare earth salt formulations. For example, Chinese patent CN103966585A discloses a silicate passivation solution and a method for passivating the coating on the surface of galvanized steel wire. Its passivation solution formulation mainly includes silicate, sulfuric acid, hydrogen peroxide, aminotrimethylphosphonic acid, nitric acid, phosphoric acid, TMTUP, thiourea, and nano-alumina, with the silicate being sodium silicate. Silicate passivation has attracted much attention due to its low cost, non-toxicity, and easy wastewater treatment, but early versions suffered from defects such as non-dense film formation, insufficient corrosion resistance, and inadequate salt spray resistance. Chinese patent CN102409330A discloses a chromium-free passivation solution, whose raw material composition mainly consists of rare earth salts, inorganic salts, boric acid, nitric acid, and water. The rare earth salts are a mixture of vanadate and cerium salts, and the inorganic salts are sodium chloride or potassium chloride. Rare earth salt passivation relies on the deposition of rare earth ions at the metal interface to form a barrier layer, but the film formation speed is slow and the process window is narrow. Chinese patent CN107090576A discloses a chromium-free passivation solution for zinc alloys, composed of the following components: molybdate, titanium sulfate, surfactant, additives, hydrogen peroxide, stabilizer, and deionized water, wherein the molybdate is sodium molybdate. Although the molybdate system belongs to the same group as chromium and can improve chloride ion resistance by forming zinc-molybdenum composite oxides, its effect when used alone is still not as good as that of chromium-based systems. Therefore, there is an urgent need to develop a novel chromium-free passivation solution for zinc alloys that also possesses advantages such as safety, environmental friendliness, corrosion resistance, and good stability. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention provides a chromium-free passivation solution for zinc alloys. By optimizing the component formulation and adding specific silane coupling agents, passivation enhancers and components such as aluminum dihydrogen phosphate, cerium sulfate, and acrylic emulsion, the passivation film formed on the zinc alloy surface has the advantages of strong adhesion, good corrosion resistance and stability.

[0005] The technical solution adopted in this invention is as follows:

[0006] This invention provides a chromium-free passivation solution for zinc alloys, comprising the following components in parts by weight:

[0007] 1-10 parts silane coupling agent, 2-20 parts aluminum dihydrogen phosphate, 0.5-5 parts cerium sulfate, 2-20 parts passivation enhancer, 0.5-5 parts corrosion inhibitor, 0.5-5 parts chelating agent, 0.5-5 parts pH adjuster, 10-40 parts acrylic emulsion, 50-150 parts water.

[0008] Preferably, a chromium-free passivation solution for zinc alloys comprises the following components in parts by weight:

[0009] 2-4 parts silane coupling agent, 6-10 parts aluminum dihydrogen phosphate, 1-2 parts cerium sulfate, 6-10 parts passivation enhancer, 1-3 parts corrosion inhibitor, 1-2.5 parts chelating agent, 1-3 parts pH adjuster, 12-18 parts acrylic emulsion, 60-75 parts water.

[0010] Preferably, the silane coupling agent is any one of 3-aminopropylmethyldiethoxysilane, 3-aminopropyltriethoxysilane, and 3-aminopropyltrimethoxysilane.

[0011] Preferably, the silane coupling agent is 3-aminopropylmethyldiethoxysilane.

[0012] Preferably, the corrosion inhibitor is any one of methylbenzotriazole, 2-mercaptobenzothiazole, and thiosalicylic acid.

[0013] Preferably, the corrosion inhibitor is methylbenzotriazole.

[0014] Preferably, the chelating agent is composed of hydroxyethylidene diphosphonic acid and trisodium citrate; the weight ratio of hydroxyethylidene diphosphonic acid to trisodium citrate is 4-6:1.

[0015] Preferably, the pH adjuster is composed of glacial acetic acid and boric acid; the weight ratio of glacial acetic acid to boric acid is 2-4:1.

[0016] Preferably, the acrylic emulsion is brand name Houxian®5111 and has a solid content of 40-50 wt%.

[0017] Preferably, the passivation enhancer is made from nano-silica, ammonium fluorotitanate, potassium fluorozirconate, and an aqueous solution of tetramethylammonium hydroxide.

[0018] Preferably, the weight ratio of the aqueous solution of nano-silica, ammonium fluorotitanate, potassium fluorozirconate, and tetramethylammonium hydroxide is 1-5:0.01-0.05:0.2-0.8:0.2-0.8.

[0019] The chromium-free passivation solution provided by this invention forms a passivation film with excellent corrosion resistance and adhesion on the zinc alloy surface through the synergistic effect of multiple components. Specifically, the silane coupling agent, after hydrolysis, generates Si-OH groups, which graft onto the zinc alloy surface to form Si-O-Zn covalent bonds, laying the chemical foundation for the chemical bonding between the film layer and the zinc alloy substrate, and simultaneously providing crosslinking sites for subsequent organic / inorganic network structures. Aluminum dihydrogen phosphate decomposes into a porous AlPO4 framework in an acidic environment, and its surface hydroxyl groups crosslink with the silane coupling agent through Si-O-Al / P covalent bonds, forming a three-dimensional network structure that enhances the mechanical strength and density of the passivation film. Ce released from cerium sulfate... 4+ Ions oxidize the surface of zinc alloy under acidic conditions to form a ZnO / CeO2 composite oxide layer, which can not only fill the micropores on the metal surface, but also improve the chemical stability of the film.

[0020] The role of the passivation enhancer is to achieve structural strengthening through surface modification of nano-SiO2 and synergistic deposition of transition metal ions. After treatment with tetramethylammonium hydroxide, the nano-SiO2 has a negatively charged surface, which first adsorbs Ti released from ammonium fluorotitanate. 4 + Subsequently, potassium fluorozirconate provided Zr 4+ With Ti 4+ Co-deposition forms a Ti-Zr oxide@SiO2 structure, which can achieve nanoscale pore sealing through filling, further improving salt spray resistance. Corrosion inhibitors such as methylbenzotriazole form coordination bonds with the zinc surface through the lone pair electrons of the nitrogen atom, and its hydrophobic benzene ring forms a barrier layer that can inhibit corrosion of Cl. - Medium permeation; the chelating agent composed of hydroxyethylidene diphosphonic acid and trisodium citrate maintains the stability of metal ions in the passivation solution system; the pH adjuster composed of glacial acetic acid and boric acid maintains the pH value of the passivation solution system within a suitable range through buffering, ensuring the appropriate hydrolysis of silane coupling agent and the smooth progress of the passivation process; the acrylic emulsion, as an organic component, can penetrate into the pores of the inorganic network skeleton, thereby forming an organic / inorganic interpenetrating network structure, bridging interface defects, and improving the hardness and corrosion resistance of the film.

[0021] Preferably, the passivation enhancer is prepared by:

[0022] By weight, 1-5 parts of nano-silica and 0.01-0.05 parts of tetramethylammonium hydroxide aqueous solution are added to 5-15 parts of water and ultrasonically treated for 20-40 minutes. Then, 0.2-0.8 parts of ammonium fluorotitanate are added and stirred for 10-20 minutes. Finally, 0.2-0.8 parts of potassium fluorozirconate are added and stirred for 10-20 minutes to obtain a passivation enhancer.

[0023] Preferably, the concentration of the tetramethylammonium hydroxide aqueous solution is 15-25 wt%.

[0024] Preferably, the ultrasonic power is 200-500W and the frequency is 25-45kHz.

[0025] Preferably, the average particle size of the nano-silica is 20-50 nm.

[0026] This invention also provides a method for preparing the above-mentioned chromium-free passivation solution for zinc alloys, comprising the following steps:

[0027] Add silane coupling agent and pH adjuster to water and stir for 10-20 minutes. Add cerium sulfate and stir for 7-12 minutes. Then add aluminum dihydrogen phosphate and passivation enhancer and stir for 7-12 minutes. Finally, add chelating agent, corrosion inhibitor and acrylic emulsion and stir for 20-30 minutes to obtain chromium-free passivation solution for zinc alloy.

[0028] The beneficial effects of this invention are as follows:

[0029] This invention provides a safe and environmentally friendly chromium-free passivation solution for zinc alloys. Through optimized formulation, it achieves synergistic effects of multiple components, forming a passivation film with excellent corrosion resistance and adhesion on the zinc alloy surface. The passivation solution utilizes a silane coupling agent to hydrolyze and generate Si-OH groups, forming Si-O-Zn covalent bonds with the matrix, laying the foundation for film adhesion. Aluminum dihydrogen phosphate decomposes into a porous AlPO4 framework in an acidic environment, forming a Si-O-Al three-dimensional network structure with silane, enhancing the mechanical strength and density of the film. Ce released from cerium sulfate... 4+ Ions can oxidize the zinc surface to form a ZnO / CeO2 composite oxide layer, further improving density and chemical stability. The passivation enhancer, through surface modification with nano-SiO2, interacts with Zr... 4+ / Ti 4+ Co-deposition forms a Ti-Zr oxide@SiO2 structure, which achieves nanoscale pore sealing through filling, further improving salt spray resistance. Corrosion inhibitors such as methylbenzotriazole form a barrier layer with their hydrophobic benzene rings to inhibit the penetration of corrosive media. Hydroxyethylidene diphosphonic acid and trisodium citrate chelating agents maintain component stability. Acrylic emulsion, as an organic component, penetrates into the inorganic network pores, thereby forming an organic / inorganic interpenetrating structure, further enhancing the hardness and corrosion resistance of the film. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Some of the raw materials used in the examples are described below:

[0032] Acrylic emulsion, brand name: Houxian®5111, solid content: 46wt%, manufacturer: Guangdong Huaguoshan Environmental Protection Technology Co., Ltd.

[0033] Nano silica, model: DK-SiO2-30, average particle size: 30nm, manufacturer: Suzhou Meibang Nanomaterials Co., Ltd.

[0034] Example 1

[0035] A chromium-free passivation solution for zinc alloys comprises the following components in parts by weight:

[0036] 3 parts silane coupling agent, 8 parts aluminum dihydrogen phosphate, 1.5 parts cerium sulfate, 8 parts passivation enhancer, 2 parts corrosion inhibitor, 1.8 parts chelating agent, 2 parts pH adjuster, 15 parts acrylic emulsion, and 68 parts deionized water.

[0037] The silane coupling agent is 3-aminopropylmethyldiethoxysilane.

[0038] The passivation enhancer is prepared by:

[0039] By weight, 3 parts of nano-silica and 0.04 parts of 25wt% tetramethylammonium hydroxide aqueous solution were added to 8 parts of deionized water and ultrasonically treated for 30 min at an ultrasonic power of 300W and a frequency of 40kHz. Then, 0.5 parts of ammonium fluorotitanate were added and stirred for 10 min, followed by 0.5 parts of potassium fluorozirconate and stirred for 10 min to obtain a passivation enhancer.

[0040] The corrosion inhibitor is methylbenzotriazole.

[0041] The chelating agent is composed of hydroxyethylidene diphosphonic acid and trisodium citrate in a weight ratio of 5:1.

[0042] The pH adjuster is composed of glacial acetic acid and boric acid in a weight ratio of 3:1.

[0043] A method for preparing the above-mentioned chromium-free passivation solution for zinc alloy includes the following steps:

[0044] Add silane coupling agent and pH adjuster to deionized water and stir for 15 min. Add cerium sulfate and stir for 10 min. Add aluminum dihydrogen phosphate and passivation enhancer and stir for 10 min. Add chelating agent, corrosion inhibitor and acrylic emulsion and stir for 25 min to obtain chromium-free passivation solution for zinc alloy.

[0045] Example 2

[0046] A chromium-free passivation solution for zinc alloys comprises the following components in parts by weight:

[0047] 2 parts silane coupling agent, 6 parts aluminum dihydrogen phosphate, 1 part cerium sulfate, 6 parts passivation enhancer, 1 part corrosion inhibitor, 1 part chelating agent, 1 part pH adjuster, 12 parts acrylic emulsion, 60 parts deionized water.

[0048] The silane coupling agent is 3-aminopropylmethyldiethoxysilane.

[0049] The preparation method of the passivation enhancer is the same as that in Example 1.

[0050] The corrosion inhibitor is methylbenzotriazole.

[0051] The chelating agent is composed of hydroxyethylidene diphosphonic acid and trisodium citrate in a weight ratio of 4:1.

[0052] The pH adjuster is composed of glacial acetic acid and boric acid in a weight ratio of 2:1.

[0053] A method for preparing the above-mentioned chromium-free passivation solution for zinc alloy includes the following steps:

[0054] Add silane coupling agent and pH adjuster to deionized water and stir for 10 min. Add cerium sulfate and stir for 7 min. Add aluminum dihydrogen phosphate and passivation enhancer and stir for 7 min. Add chelating agent, corrosion inhibitor and acrylic emulsion and stir for 20 min to obtain chromium-free passivation solution for zinc alloy.

[0055] Example 3

[0056] A chromium-free passivation solution for zinc alloys comprises the following components in parts by weight:

[0057] 4 parts silane coupling agent, 10 parts aluminum dihydrogen phosphate, 2 parts cerium sulfate, 10 parts passivation enhancer, 3 parts corrosion inhibitor, 2.5 parts chelating agent, 3 parts pH adjuster, 18 parts acrylic emulsion, and 75 parts deionized water.

[0058] The silane coupling agent is 3-aminopropylmethyldiethoxysilane.

[0059] The preparation method of the passivation enhancer is the same as that in Example 1.

[0060] The corrosion inhibitor is methylbenzotriazole.

[0061] The chelating agent is composed of hydroxyethylidene diphosphonic acid and trisodium citrate in a weight ratio of 6:1.

[0062] The pH adjuster is composed of glacial acetic acid and boric acid in a weight ratio of 4:1.

[0063] A method for preparing the above-mentioned chromium-free passivation solution for zinc alloy includes the following steps:

[0064] Add silane coupling agent and pH adjuster to deionized water and stir for 20 min. Add cerium sulfate and stir for 12 min. Add aluminum dihydrogen phosphate and passivation enhancer and stir for 12 min. Add chelating agent, corrosion inhibitor and acrylic emulsion and stir for 30 min to obtain chromium-free passivation solution for zinc alloy.

[0065] Example 4

[0066] A chromium-free passivation solution for zinc alloys comprises the following components in parts by weight:

[0067] 3 parts silane coupling agent, 8 parts aluminum sulfate, 1.5 parts high cerium sulfate, 8 parts passivation enhancer, 2 parts corrosion inhibitor, 1.8 parts chelating agent, 2 parts pH adjuster, 15 parts acrylic emulsion, and 68 parts deionized water.

[0068] The silane coupling agent is 3-aminopropylmethyldiethoxysilane.

[0069] The preparation method of the passivation enhancer is the same as that in Example 1.

[0070] The corrosion inhibitor is methylbenzotriazole.

[0071] The chelating agent is composed of hydroxyethylidene diphosphonic acid and trisodium citrate in a weight ratio of 5:1.

[0072] The pH adjuster is composed of glacial acetic acid and boric acid in a weight ratio of 3:1.

[0073] A method for preparing the above-mentioned chromium-free passivation solution for zinc alloy includes the following steps:

[0074] Add silane coupling agent and pH adjuster to deionized water and stir for 15 min. Add cerium sulfate and stir for 10 min. Add aluminum sulfate and passivation enhancer and stir for 10 min. Add chelating agent, corrosion inhibitor and acrylic emulsion and stir for 25 min to obtain chromium-free passivation solution for zinc alloy.

[0075] Example 5

[0076] A chromium-free passivation solution for zinc alloys comprises the following components in parts by weight:

[0077] 3 parts silane coupling agent, 8 parts aluminum dihydrogen phosphate, 8 parts passivation enhancer, 2 parts corrosion inhibitor, 1.8 parts chelating agent, 2 parts pH adjuster, 15 parts acrylic emulsion, 69.5 parts deionized water.

[0078] The silane coupling agent is 3-aminopropylmethyldiethoxysilane.

[0079] The preparation method of the passivation enhancer is the same as that in Example 1.

[0080] The corrosion inhibitor is methylbenzotriazole.

[0081] The chelating agent is composed of hydroxyethylidene diphosphonic acid and trisodium citrate in a weight ratio of 5:1.

[0082] The pH adjuster is composed of glacial acetic acid and boric acid in a weight ratio of 3:1.

[0083] A method for preparing the above-mentioned chromium-free passivation solution for zinc alloy includes the following steps:

[0084] Add silane coupling agent and pH adjuster to deionized water and stir for 15 min. Then add aluminum dihydrogen phosphate and passivation enhancer and stir for 10 min. Finally add chelating agent, corrosion inhibitor and acrylic emulsion and stir for 25 min to obtain chromium-free passivation solution for zinc alloy.

[0085] Example 6

[0086] A chromium-free passivation solution for zinc alloys comprises the following components in parts by weight:

[0087] 3 parts silane coupling agent, 8 parts aluminum dihydrogen phosphate, 1.5 parts cerium sulfate, 8 parts passivation enhancer, 2 parts corrosion inhibitor, 1.8 parts chelating agent, 2 parts pH adjuster, 15 parts acrylic emulsion, and 68 parts deionized water.

[0088] The silane coupling agent is 3-aminopropylmethyldiethoxysilane.

[0089] The passivation enhancer is prepared by:

[0090] By weight, 3 parts of nano-silica and 0.04 parts of 25wt% tetramethylammonium hydroxide aqueous solution were added to 8 parts of deionized water and ultrasonically treated for 30 minutes at an ultrasonic power of 300W and a frequency of 40kHz to obtain a passivation enhancer.

[0091] The corrosion inhibitor is methylbenzotriazole.

[0092] The chelating agent is composed of hydroxyethylidene diphosphonic acid and trisodium citrate in a weight ratio of 5:1.

[0093] The pH adjuster is composed of glacial acetic acid and boric acid in a weight ratio of 3:1.

[0094] A method for preparing the above-mentioned chromium-free passivation solution for zinc alloy includes the following steps:

[0095] Add silane coupling agent and pH adjuster to deionized water and stir for 15 min. Add cerium sulfate and stir for 10 min. Add aluminum dihydrogen phosphate and passivation enhancer and stir for 10 min. Add chelating agent, corrosion inhibitor and acrylic emulsion and stir for 25 min to obtain chromium-free passivation solution for zinc alloy.

[0096] Example 7

[0097] A chromium-free passivation solution for zinc alloys comprises the following components in parts by weight:

[0098] 3 parts silane coupling agent, 8 parts aluminum dihydrogen phosphate, 1.5 parts cerium sulfate, 8 parts passivation enhancer, 2 parts corrosion inhibitor, 1.8 parts chelating agent, 2 parts pH adjuster, 15 parts acrylic emulsion, and 68 parts deionized water.

[0099] The silane coupling agent is 3-aminopropylmethyldiethoxysilane.

[0100] The passivation enhancer is prepared by:

[0101] By weight, 3 parts of nano-silica were added to 8 parts of deionized water and ultrasonically treated for 30 minutes with an ultrasonic power of 300W and a frequency of 40kHz. 0.5 parts of ammonium fluorotitanate were added and stirred for 10 minutes, followed by 0.5 parts of potassium fluorozirconate and stirred for another 10 minutes to obtain the passivation enhancer.

[0102] The corrosion inhibitor is methylbenzotriazole.

[0103] The chelating agent is composed of hydroxyethylidene diphosphonic acid and trisodium citrate in a weight ratio of 5:1.

[0104] The pH adjuster is composed of glacial acetic acid and boric acid in a weight ratio of 3:1.

[0105] A method for preparing the above-mentioned chromium-free passivation solution for zinc alloy includes the following steps:

[0106] Add silane coupling agent and pH adjuster to deionized water and stir for 15 min. Add cerium sulfate and stir for 10 min. Add aluminum dihydrogen phosphate and passivation enhancer and stir for 10 min. Add chelating agent, corrosion inhibitor and acrylic emulsion and stir for 25 min to obtain chromium-free passivation solution for zinc alloy.

[0107] Example 8

[0108] A chromium-free passivation solution for zinc alloys comprises the following components in parts by weight:

[0109] 3 parts silane coupling agent, 8 parts aluminum dihydrogen phosphate, 1.5 parts cerium sulfate, 8 parts passivation enhancer, 2 parts corrosion inhibitor, 1.8 parts chelating agent, 2 parts pH adjuster, and 83 parts deionized water.

[0110] The silane coupling agent is 3-aminopropylmethyldiethoxysilane.

[0111] The preparation method of the passivation enhancer is the same as that in Example 1.

[0112] The corrosion inhibitor is methylbenzotriazole.

[0113] The chelating agent is composed of hydroxyethylidene diphosphonic acid and trisodium citrate in a weight ratio of 5:1.

[0114] The pH adjuster is composed of glacial acetic acid and boric acid in a weight ratio of 3:1.

[0115] A method for preparing the above-mentioned chromium-free passivation solution for zinc alloy includes the following steps:

[0116] Add silane coupling agent and pH adjuster to deionized water and stir for 15 min, add cerium sulfate and stir for 10 min, then add aluminum dihydrogen phosphate and passivation enhancer and stir for 10 min, then add chelating agent and corrosion inhibitor and stir for 25 min to obtain chromium-free passivation solution for zinc alloy.

[0117] Test Example 1

[0118] Zinc alloy samples were pretreated using conventional processes (including degreasing, washing, and drying). They were then immersed in the chromium-free passivation solutions (30°C) prepared in Examples 1-8 for 20 minutes each, and dried at 80°C to obtain the passivation film. The chromium-free passivation solutions were stored at room temperature in the dark for 90 days to observe storage stability. The adhesion of the passivation film was determined according to standard GB / T 9286-2021. The corrosion resistance (neutral salt spray) of the passivation film was determined according to standard GB / T 10125-2021, and the time of first white rust appearance was recorded at 24-hour intervals. The test results are shown in Table 1.

[0119] Table 1. Performance test results of chromium-free passivation solution for zinc alloys

[0120]

[0121] The test results above show that the passivation film formed by the zinc alloy chromium-free passivation solution described in Examples 1-3 after zinc alloy passivation treatment exhibits excellent corrosion resistance (neutral salt spray) and high adhesion, while also maintaining stable performance. Compared to the passivation solution formulations of Examples 1-3, aluminum sulfate was used instead of aluminum dihydrogen phosphate in Example 4, cerium sulfate was not added in Example 5, no specific passivation enhancer was used in Examples 6-7, and acrylic emulsion was not added in Example 8. As a result, the corrosion resistance and adhesion of the passivation solutions corresponding to Examples 4-8 decreased significantly. This demonstrates that the zinc alloy chromium-free passivation solution formulations disclosed in Examples 1-3 of this invention achieve beneficial technical effects through the synergistic effect of optimized aluminum dihydrogen phosphate, cerium sulfate, passivation enhancer, acrylic emulsion, and other components.

[0122] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A chromium-free passivation solution for zinc alloys, characterized in that: Includes the following components by weight: 1-10 parts silane coupling agent, 2-20 parts aluminum dihydrogen phosphate, 0.5-5 parts cerium sulfate, 2-20 parts passivation enhancer, 0.5-5 parts corrosion inhibitor, 0.5-5 parts chelating agent, 0.5-5 parts pH adjuster, 10-40 parts acrylic emulsion, 50-150 parts water; The passivation enhancer is prepared by: By weight, 1-5 parts of nano-silica and 0.01-0.05 parts of tetramethylammonium hydroxide aqueous solution are added to 5-15 parts of water and ultrasonically treated for 20-40 min. Then, 0.2-0.8 parts of ammonium fluorotitanate are added and stirred for 10-20 min, followed by 0.2-0.8 parts of potassium fluorozirconate and stirred for 10-20 min to obtain a passivation enhancer. The concentration of the tetramethylammonium hydroxide aqueous solution is 15-25 wt%. The corrosion inhibitor is any one of methylbenzotriazole, 2-mercaptobenzothiazole, and thiosalicylic acid; The chelating agent is composed of hydroxyethylidene diphosphonic acid and trisodium citrate; the weight ratio of hydroxyethylidene diphosphonic acid to trisodium citrate is 4-6:1; The pH adjuster is composed of glacial acetic acid and boric acid; the weight ratio of glacial acetic acid to boric acid is 2-4:

1.

2. The zinc alloy chromium-free passivation solution according to claim 1, characterized in that: Includes the following components by weight: 2-4 parts silane coupling agent, 6-10 parts aluminum dihydrogen phosphate, 1-2 parts cerium sulfate, 6-10 parts passivation enhancer, 1-3 parts corrosion inhibitor, 1-2.5 parts chelating agent, 1-3 parts pH adjuster, 12-18 parts acrylic emulsion, 60-75 parts water.

3. The zinc alloy chromium-free passivation solution according to claim 1, characterized in that: The silane coupling agent is any one of 3-aminopropylmethyldiethoxysilane, 3-aminopropyltriethoxysilane, and 3-aminopropyltrimethoxysilane.

4. The method for preparing the chromium-free passivation solution for zinc alloys according to any one of claims 1-3, characterized in that: The silane coupling agent and pH adjuster were added to water and stirred. Cerium sulfate was added and stirred. Aluminum dihydrogen phosphate and passivation enhancer were added and stirred. Then, chelating agent, corrosion inhibitor and acrylic emulsion were added and stirred to obtain the chromium-free passivation solution of zinc alloy.

Images