An organic-inorganic hybrid passivation solution and method for blackening resistance of zinc-aluminum-magnesium coatings

Abstract

This invention relates to an organic-inorganic hybrid passivation solution and method for zinc-aluminum-magnesium plating to resist blackening. It primarily aims to provide a novel, pollution-free passivation solution and treatment method for enhancing the anti-blackening and corrosion resistance of zinc-aluminum-magnesium products, belonging to the field of metal material surface treatment technology. The passivation solution contains a key component, an acrylic acid-phosphonic acid copolymer, which chelates with zinc, aluminum, and magnesium ions on the plating surface through phosphonic acid groups in its molecular chain, constructing a chemically bonded organic-inorganic hybrid network that significantly improves the adhesion and corrosion resistance of the passivation film. This copolymer remains stable under strongly acidic conditions with a pH of 1-3 and can form a film normally. The passivation solution of this invention is chromium-free, environmentally friendly and safe, and can be directly applied to continuous zinc plating production lines without a separate degreasing process, simplifying the process flow. Zinc-aluminum-magnesium plating treated with this invention exhibits excellent resistance to white rust and blackening in salt spray tests, effectively replacing traditional chromate passivation processes.

Description

Technical Field

[0001] This invention relates to an organic-inorganic hybrid passivation solution and method for zinc-aluminum-magnesium coatings to resist blackening, mainly to provide a novel pollution-free passivation solution and treatment method for enhancing the blackening resistance and corrosion resistance of zinc-aluminum-magnesium products, belonging to the field of metal material surface treatment technology. Background Technology

[0002] Zinc-aluminum-magnesium alloy coatings, with their excellent corrosion resistance, long service life, and relatively low production cost, have become important materials for coping with harsh corrosive environments and have shown broad application prospects in global industrial manufacturing. Currently, various series of zinc-aluminum-magnesium coatings with low, medium, and high aluminum compositions have been developed. These coatings not only significantly improve the acid and alkali resistance and field corrosion stability of materials but also provide good fracture surface protection. However, when exposed to the atmosphere for extended periods, the magnesium element on the surface of the zinc-aluminum-magnesium coating is highly reactive and easily undergoes oxidation, resulting in blackening. Therefore, surface passivation treatment is usually required to suppress this problem.

[0003] To slow down corrosion and improve resistance to "blackening," surface passivation of zinc-aluminum-magnesium coatings has become an indispensable post-treatment process. Traditional chromate passivation technology has dominated for decades due to its mature technology, low cost, and the resulting passivation film's excellent self-healing ability. However, chromates, especially hexavalent chromium (Cr(VI)) compounds, are highly toxic, carcinogenic, and cause persistent environmental pollution. Their production, use, and wastewater treatment are subject to increasingly stringent international regulations (such as the EU RoHS and ELV directives). Although trivalent chromium (Cr(III)) processes have lower toxicity, their corrosion resistance and self-healing properties are still inferior to hexavalent chromium systems, and there is an environmental risk of conversion to hexavalent chromium, making it impossible to fundamentally meet the requirements of green manufacturing.

[0004] Therefore, developing a chromium-free passivation technology that can completely replace chromates and combines environmental friendliness with high performance has become an urgent need in the surface treatment field. Current mainstream chromium-free technologies, such as phosphates, molybdates, silicates, phytates, organic acids, and organic-inorganic composite systems, aim to block corrosion by forming dense films or releasing corrosion-inhibiting ions. However, these technologies all have limitations: inorganic systems (such as phosphates) form films with weak adhesion, poor flexibility, and porous structures, offering limited effectiveness in inhibiting "blackening" caused by magnesium oxidation; while organic systems form continuous and flexible films, their protection depends on the integrity of the film and has weak adhesion to the substrate, making them prone to peeling in humid and hot environments. To seek synergistic performance, organic-inorganic composite technologies have emerged, aiming to synergistically leverage the passivation ability of the inorganic phase and the barrier effect of the organic phase. However, existing composite technologies are mostly just physical blends with weak interfacial bonding, leading to easy phase separation, unstable performance, and narrow process windows, and have not yet achieved a complete replacement of chromates. Therefore, focusing on the microstructure and corrosion mechanism of zinc-aluminum-magnesium coatings, constructing stable organic-inorganic hybrid networks based on strong chemical bonds (such as coordinate bonds and covalent bonds) through innovative molecular design has become the key to developing next-generation efficient, stable, and environmentally friendly passivation technologies. Summary of the Invention

[0005] This invention addresses the aforementioned technical problems in the prior art by providing a chromium-free passivation solution and passivation method for the surface of zinc-aluminum-magnesium galvanized layers. It mainly provides a novel, pollution-free passivation solution and preparation process for enhancing the anti-blackening and corrosion resistance of zinc-aluminum-magnesium products. At the same time, it also features a simple process flow and significant effects.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: An organic-inorganic hybrid passivation solution and method for zinc-aluminum-magnesium coatings with blackening resistance, wherein the passivation solution raw material formulation consists of the following components: acrylic acid-phosphonic acid copolymer (0.5~5) g / L, citric acid (2~20) g / L, zinc chloride (2~16) g / L, sodium dihydrogen phosphate (4~20) g / L, hydrogen peroxide (4~16) ml / L, the pH value of the passivation solution is adjusted to 1~4 using hydrochloric acid or sodium hydroxide, and the remainder is water.

[0007] The preparation method of the above-mentioned blackening-resistant organic-inorganic hybrid passivation solution includes the following steps: a. Dissolve the acrylic acid-phosphonic acid copolymer and citric acid in half the required volume of water, while stirring with a mixer until homogeneous to obtain an organic solution.

[0008] b. Dissolve zinc chloride and sodium dihydrogen phosphate in a small amount of water. After complete dissolution, add hydrogen peroxide to obtain an inorganic solution.

[0009] c. Mix the organic and inorganic solutions, then bring the volume to the required level and stir for 10-30 minutes until fully mixed to obtain a chromium-free passivation solution.

[0010] The above-mentioned blackening-resistant organic-inorganic hybrid passivation solution and method include the following steps: a. Passivation: Immerse the zinc-aluminum-magnesium galvanized sheet in the prepared chromium-free passivation solution, and after passivation for a period of time, remove it and rinse the surface with water to remove any residual passivation solution.

[0011] b. Drying: The zinc-aluminum-magnesium galvanized sheet after the treatment in step a above is placed in a dryer to dry, and a dry passivated zinc-aluminum-magnesium galvanized sheet is obtained.

[0012] The water mentioned therein is distilled water or deionized water.

[0013] The passivation solution temperature is 25~60℃, and the passivation time is 5~90s.

[0014] The chemical composition of the coating of the zinc-aluminum-magnesium galvanized sheet is as follows by mass percentage: Al: 1%~11%, Mg: 1%~6%, with the balance being Zn and unavoidable impurities; the coating also contains one or more trace elements selected from Si, Re, Fe, Cu and Ni, with each trace element having a mass percentage of no more than 0.1%.

[0015] The drying temperature of the dryer is 40~80℃ and the drying time is 20~90s.

[0016] The acrylic acid-phosphonic acid copolymer has a solid content of 38% to 42%, a molecular weight of 40,000 to 80,000, and a density of about 1.18 g / cm3 at 25°C.

[0017] The present invention has the following advantages over the prior art: 1. Unlike the high toxicity of traditional chromium-containing passivation solutions, this invention uses only biodegradable or easily treated environmentally friendly reagents, which significantly reduces the environmental burden and health risks during production and use.

[0018] 2. The passivation solution of this invention has a lower cost compared to traditional zinc-aluminum-magnesium passivation, and most of the required reagents are commonly used reagents on the market; 3. The passivation process of this invention is simple, fast, and the bath solution is stable. The corrosion resistance and blackening resistance of the passivated solution are greatly improved.

[0019] 4. This invention employs a novel resin, an "acrylic acid-phosphonic acid copolymer," whose mechanism of action differs from the conventional acrylic resin's protection method, which relies solely on physical coating. This copolymer can interact with the Zn²⁺, Al³⁺, and Mg groups on the coating surface through the phosphonic acid groups in its molecular chain. 2+When metal ions chelate, a robust organic-inorganic hybrid network structure is constructed at the interface, achieving strong adhesion primarily through chemical bonding. This significantly improves the adhesion and corrosion resistance of the passivation film. Furthermore, unlike conventional resins that are only suitable for neutral to weakly acidic / alkaline environments, this copolymer remains dissolved or stably dispersed under strongly acidic conditions (pH=1~3), forming a film with good quality, thus broadening the applicability of the passivation process.

[0020] 5. The passivation process of this invention is specifically designed for continuous galvanizing production lines and can directly treat the surface of the strip steel on the production line. Compared with traditional processes, it eliminates the separate chemical degreasing step, simplifies the process, improves production efficiency, and reduces overall operating costs. Attached Figure Description

[0021] Figure 1 This is a macroscopic image after the boiling water acceleration experiment. Detailed Implementation Example

[0022] An organic-inorganic hybrid passivation solution for zinc-aluminum-magnesium plating with blackening resistance, comprising the following components and proportions: 0.5 g / L citric acid-phosphonic acid copolymer, 2 g / L citric acid, 2 g / L zinc chloride, 8 g / L sodium dihydrogen phosphate, 4 ml / L hydrogen peroxide, with the pH of the passivation solution adjusted to 1-4 using hydrochloric acid or sodium hydroxide, and the remainder being water.

[0023] The chemical composition of the zinc-aluminum-magnesium galvanized sheet coating, by mass percentage, is: Al: 1%~11%, Mg: 1%~6%, with the balance being Zn and unavoidable impurities.

[0024] Detailed operation steps: a. Dissolve the acrylic acid-phosphonic acid copolymer and citric acid in half the required volume of water, while stirring with a mixer until homogeneous to obtain an organic solution.

[0025] b. Dissolve zinc chloride and sodium dihydrogen phosphate in a small amount of water. After complete dissolution, add hydrogen peroxide to obtain an inorganic solution.

[0026] c. Mix the organic and inorganic solutions, then bring the volume to the required level and stir until fully mixed to obtain a chromium-free passivation solution.

[0027] A blackening-resistant organic-inorganic hybrid passivation method, the specific steps of which are as follows: a. Passivation: Immerse the zinc-aluminum-magnesium galvanized sheet in the prepared chromium-free passivation solution, control the temperature of the passivation solution to 50℃, and after passivation for 25 seconds, take it out and rinse the surface with water to remove any residual passivation solution.

[0028] b. Drying: Place the zinc-aluminum-magnesium galvanized sheet processed in step a above into a dryer and dry it. Set the drying temperature to 60℃ and the drying time to 30s to obtain a dry passivated zinc-aluminum-magnesium galvanized sheet. Example

[0029] This embodiment is basically the same as the steps in Embodiment 1, with the following differences: An organic-inorganic hybrid passivation solution for zinc-aluminum-magnesium coatings, comprising the following components and proportions: 1 g / L acrylic acid-phosphonic acid copolymer, 2 g / L citric acid, 4 g / L zinc chloride, 12 g / L sodium dihydrogen phosphate, and 8 ml / L hydrogen peroxide. The pH of the passivation solution is adjusted to 2 using hydrochloric acid or sodium hydroxide, with the remainder being distilled water or deionized water.

[0030] A blackening-resistant organic-inorganic hybrid passivation method, the specific steps of which are as follows: a. Passivation: Immerse the zinc-aluminum-magnesium galvanized sheet in the prepared chromium-free passivation solution, control the temperature of the passivation solution to 40℃, and after passivation for 40 seconds, take it out and rinse the surface with water to remove any residual passivation solution.

[0031] b. Drying: Place the zinc-aluminum-magnesium galvanized sheet processed in step a above into a dryer and dry it. Set the drying temperature to 50℃ and the drying time to 60s to obtain a dry passivated zinc-aluminum-magnesium galvanized sheet. Example

[0032] This embodiment is basically the same as the previous embodiment in terms of steps, with the following differences: An organic-inorganic hybrid passivation solution for zinc-aluminum-magnesium plating with blackening resistance, comprising the following components and proportions: 1.5 g / L acrylic acid-phosphonic acid copolymer, 6 g / L citric acid, 8 g / L zinc chloride, 8 g / L sodium dihydrogen phosphate, 8 ml / L hydrogen peroxide, with the pH of the passivation solution adjusted to 2.5 using hydrochloric acid or sodium hydroxide, and the remainder being distilled water or deionized water.

[0033] A blackening-resistant organic-inorganic hybrid passivation method, the specific steps of which are as follows: a. Passivation: Immerse the zinc-aluminum-magnesium galvanized sheet in the prepared chromium-free passivation solution, control the temperature of the passivation solution at 55℃, and after passivation for 60 seconds, take it out and rinse the surface with water to remove any residual passivation solution.

[0034] b. Drying: Place the zinc-aluminum-magnesium galvanized sheet processed in step a above into a dryer and dry it. Set the drying temperature to 60℃ and the drying time to 40s to obtain a dry passivated zinc-aluminum-magnesium galvanized sheet.

[0035] Performance testing This test aims to determine the corrosion resistance and anti-blackening properties of the coating on zinc-aluminum-magnesium galvanized steel sheets before and after passivation. The corrosion resistance was assessed and evaluated according to the methods and conditions specified in GB / T10125.

[0036] The blackening resistance test conditions are boiling water accelerated test. The test method is to vertically immerse a 150mm×75mm sample in boiling water, take it out after 2 hours, and observe the black spots on the plate surface. The specific evaluation is the black spot area ratio.

[0037] Less than 5%; £: Greater than 5%, less than 10% ×: Greater than 15% Fingerprint resistance is determined by the change in color difference before and after applying Vaseline to the sample surface: if the change in color difference is less than 1, it is grade A; if the change in color difference is greater than 1 but less than 2, it is grade B; if the change in color difference is greater than 2 but less than 4, it is grade C; if the change in color difference is greater than 4, it is grade D.

[0038] Water resistance is determined by dropping 100°C deionized water onto the sample: if the sample is completely free of water, it is grade A; if there is slight water, it is grade B; and if there is obvious water, it is grade C.

[0039] Comparative Example 1 is a zinc-aluminum-magnesium galvanized sheet treated with commercially available trivalent chromium passivating agent.

[0040] Comparative Example 2 is an untreated zinc-aluminum-magnesium galvanized sheet.

[0041] The performance test results are shown in Table 1.

[0042] Macroscopic image after boiling water acceleration experiment is shown below Figure 1 The performance test results are shown in the table below:

Claims

1. An organic-inorganic hybrid passivation solution and method for preventing blackening of zinc-aluminum-magnesium coatings, characterized in that, The passivation solution raw material formula consists of the following components Composition: Acrylic acid-phosphonic acid copolymer (0.5~5) g / L, citric acid (2~8) g / L, zinc chloride (2~8) g / L, sodium dihydrogen phosphate (8~20) g / L, hydrogen peroxide (4~16) ml / L, the passivation solution pH is adjusted to 1~4 using hydrochloric acid or sodium hydroxide, and the remainder is water.

2. The method for preparing the organic-inorganic hybrid passivation solution according to claim 1, characterized in that, The operation steps are as follows: a. Dissolve the acrylic acid-phosphonic acid copolymer and citric acid in half the required volume of water, while stirring with a glass rod until the mixture is homogeneous, to obtain an organic solution. b. Dissolve zinc chloride and sodium dihydrogen phosphate in a small amount of water. After complete dissolution, add hydrogen peroxide to obtain an inorganic solution. c. Mix the organic and inorganic solutions, then bring the volume to the required level and stir until fully mixed to obtain a chromium-free passivation solution.

3. The method for zinc-aluminum-magnesium coating according to claim 1, characterized in that, The operation steps are as follows: a. Passivation: Immerse the zinc-aluminum-magnesium galvanized sheet in the prepared organic-inorganic hybrid passivation solution, and after passivation for a period of time, remove it and rinse the surface with water to remove any residual passivation solution. b. Drying: The zinc-aluminum-magnesium galvanized sheet after the treatment in step a above is placed in a dryer to dry, and a dry passivated zinc-aluminum-magnesium galvanized sheet is obtained.

4. The organic-inorganic hybrid passivation solution for zinc-aluminum-magnesium coatings to resist blackening as described in claim 1 or 2, characterized in that, The passivation solution temperature is 25~60℃, and the passivation time is 5~90s.

5. The organic-inorganic hybrid passivation solution according to claim 1 or 2, characterized in that, The water is distilled water or deionized water.

6. The organic-inorganic hybrid passivation solution for zinc-aluminum-magnesium coatings to resist blackening according to claim 1 or 2, characterized in that, The chemical composition of the zinc-aluminum-magnesium coating, by mass percentage, is: Al: 1%~11%, Mg: 1%~6%, with the balance being Zn and unavoidable impurities; the coating also contains one or more trace elements selected from Si, Re, Fe, Cu, and Ni, with each trace element having a mass percentage of no more than 0.1%.

7. The organic-inorganic hybrid passivation solution and method for zinc-aluminum-magnesium coatings with resistance to blackening as described in claim 1 or 2, characterized in that, The drying temperature in step c is 40~80℃, and the drying time is 20~90s.

8. The organic-inorganic hybrid passivation solution and method for zinc-aluminum-magnesium coatings with resistance to blackening as described in claim 1 or 2, characterized in that, The copolymer comprises an acrylic acid-phosphonic acid copolymer that is stable in an acidic medium with a pH of 1.0 to 3.0, wherein the side chains or ends contain phosphonic acid groups (-PO(OH)2) or phosphate ester groups, the acrylic acid-phosphonic acid copolymer has a solid content of 38% to 42%, a molecular weight of 40,000 to 80,000, and a density of approximately 1.18 g / cm³ at 25°C. 3 .

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