Aluminum alloy surface environment-friendly chemical passivator and preparation method and application thereof

Abstract

The invention relates to an aluminum alloy surface environment-friendly chemical passivator and a preparation method and application thereof, and belongs to the technical field of metal surface treatment. The passivating agent is in a liquid state and is prepared from the following raw materials: 60 g / L-80 g / L of potassium permanganate, 36 g / L-54 g / L of aluminum sulfate, 0.9 g / L-1. 2 g / L of a stabilizer, 100 ml / L-200 ml / L of concentrated sulfuric acid and the balance of water in each liter of solution; the stabilizer is prepared from sodium stannate, sodium pyrosulfate and 8-hydroxyquinoline; the passivator is prepared by fully mixing the raw materials. According to the application method, the aluminum alloy with the clean and dry surface is soaked in the passivating agent, and a passivation layer can be formed on the surface of the aluminum alloy; the treatment time of the application is shortened to 0.5 min-2 min, meanwhile, the applicable temperature range is expanded to 35 DEG C-50 DEG C, and the feasibility of industrial production is greatly improved.

Description

Technical Field

[0001] This invention relates to an environmentally friendly chemical passivating agent for aluminum alloy surfaces, its preparation method, and its application, belonging to the field of metal surface treatment technology. Background Technology

[0002] Aluminum alloys are widely used due to their lightweight, high strength, good thermal and electrical conductivity, excellent corrosion resistance, and good machinability. Aluminum alloys have a relatively low density but high strength, giving them a significant technological advantage and development potential in fields such as aerospace, high-speed shipbuilding, and automotive manufacturing, where weight reduction while maintaining structural strength is crucial. Regarding corrosion resistance, aluminum alloy surfaces spontaneously form a relatively dense oxide film, effectively resisting the erosion of various chemicals and improving the material's corrosion resistance. Aluminum alloys are also easily processed into various shapes and sizes, possessing good plasticity and ductility, making them suitable for manufacturing complex structures.

[0003] However, in service environments containing chloride ions, sulfate ions, heavy metal ions, or extreme pH values ​​(acidic / alkaline), the natural oxide film that spontaneously forms on the surface of aluminum alloys has limited protective capabilities and is prone to problems such as pitting corrosion, intergranular corrosion, and stress corrosion cracking, which seriously threaten the reliability and service life of components.

[0004] To overcome this weakness, passivation has become a key surface protection technology for improving the corrosion resistance of aluminum alloys. This technology involves reacting chemical agents with the metal surface to form a passivation layer that is thicker, denser, and chemically more stable than the natural oxide film, effectively blocking corrosive media. Among various passivation technologies, chromate passivation (especially hexavalent chromium) has long dominated high-end industrial fields such as aerospace and military due to its mature process, relatively low cost, extremely excellent corrosion resistance of the passivation film formed, unique self-healing ability, and excellent adhesion to subsequent coatings. However, chromate passivation technology has serious drawbacks that are difficult to overcome. Hexavalent chromium is an internationally recognized strong carcinogen and allergen, posing a significant threat to the health of operators; the chromium-containing wastewater and waste residue generated during its production and use are difficult and costly to treat, and improper disposal can easily cause serious soil and water pollution. In addition, increasingly stringent environmental regulations worldwide impose strict restrictions or even prohibitions on the use and emission of hexavalent chromium, greatly reducing its application space under the concept of sustainable development.

[0005] Given the environmental and health risks associated with chromate passivation, the development of efficient and environmentally friendly alternative chemical passivation technologies for aluminum alloys has become an urgent industry need. Currently, the most researched non-chromium alternatives include molybdate passivation, rare earth salt (such as cerium salt) passivation, silane / zirconium-titanium passivation, and organic acid / phytic acid passivation. Molybdate passivation operates on a similar principle to chromate passivation, but with reduced toxicity and relatively good corrosion resistance. The process is also relatively mature. However, its main drawbacks are high cost and the fact that the self-healing ability of the passivation film is generally inferior to that of chromate films. High concentrations of molybdate also raise environmental concerns. Rare earth salt passivation provides barrier protection by depositing rare earth oxide / hydroxide films, offering significant environmental benefits. However, its film formation rate is slow, process control (such as pH and temperature) is stringent, and the uniformity and adhesion of the film layer may not meet requirements. The cost-effectiveness of large-scale applications still needs optimization. Silane / zirconium-titanium passivation is based on the formation of a nano-protective layer through organic-inorganic hybrid reactions. It is environmentally friendly and non-toxic, and exhibits excellent adhesion to organic coatings. However, the corrosion resistance of pure silane films, especially long-term corrosion resistance and scratch resistance, is often lower than that of chromate films. Furthermore, this process has extremely strict requirements for pretreatment (surface cleanliness, activation state), and the film stability is significantly affected by environmental factors. Organic acid / phytic acid passivation utilizes functional groups (such as carboxyl and phosphate groups) in organic molecules to chelate with the aluminum matrix to form a protective film. The raw materials can be derived from biomass, making it environmentally friendly. However, the films formed by this type of passivation are usually thin, and their corrosion resistance often fails to meet the requirements of high-end applications. Long-term stability is also questionable, and some organic acids are also relatively expensive.

[0006] Among numerous environmentally friendly passivation technologies, the cerium nitrate and potassium permanganate composite passivation system is considered one of the most promising alternatives due to its oxidation film-forming mechanism similar to chromates. This system forms a passivation film on the aluminum surface through the oxidation of cerium salts, with potassium permanganate enhancing the film-forming efficiency; its corrosion resistance can reach 60% to 70% of that of chromate processes. However, this technology still has several key drawbacks that severely restrict its large-scale application. The passivation film formed by this system exhibits significant structural defects, often displaying a loose and porous structure, with insufficient density leading to an increased risk of localized corrosion. Furthermore, cerium salt passivation treatment typically requires an immersion time of more than 20 minutes, has a narrow process window, and the pH value must be strictly controlled within the range of 1.8 to 4.5; temperature fluctuations exceeding ±5°C will affect the film quality.

[0007] To address the aforementioned technical bottlenecks, there is an urgent need for an innovative material and preparation method as a systematic solution. Summary of the Invention

[0008] To overcome the shortcomings of existing passivation technologies, one of the objectives of this invention is to provide an environmentally friendly chemical passivating agent for aluminum alloy surfaces. This passivating agent is chromium-free, environmentally friendly, and chemically stable. By using potassium permanganate and aluminum sulfate, the oxidation of potassium permanganate is inhibited by the stabilizer. With its high specific surface area and active sites, the density and uniformity of the passivation film can be improved. Its passivation effect can reach or even exceed the effect of chromate chemical passivating agents on the corrosion resistance of aluminum alloys.

[0009] The second objective of this invention is to provide a method for preparing an environmentally friendly chemical passivating agent for aluminum alloy surfaces.

[0010] The third objective of this invention is to provide an application of an environmentally friendly chemical passivating agent for aluminum alloy surfaces. The application method shortens the processing time to 0.5 min to 2 min and expands the applicable temperature range to 35℃ to 50℃, greatly improving the feasibility of industrial production.

[0011] To achieve the objectives of this invention, the following technical solutions are provided.

[0012] An environmentally friendly chemical passivating agent for aluminum alloy surfaces, wherein the passivating agent is in liquid form and the raw material formula is as follows: per liter of solution, potassium permanganate 60 g / L ~ 80 g / L, aluminum sulfate 36 g / L ~ 54 g / L, stabilizer 0.9 g / L ~ 1.2 g / L, concentrated sulfuric acid 100 ml / L ~ 200 ml / L, and the balance is water.

[0013] The stabilizer consists of sodium stannate, sodium pyrosulfate, and 8-hydroxyquinoline; Concentrated sulfuric acid is a sulfuric acid solution with a mass fraction of 98%.

[0014] A method for preparing an environmentally friendly chemical passivating agent for aluminum alloy surfaces according to the present invention, the method comprising the following steps: (1) Add concentrated sulfuric acid to water and stir until fully mixed to form solution A; Preferably, the mixing time is 20 min to 30 min and the rotation speed is 400 r / min to 500 r / min.

[0015] (2) Add potassium permanganate to solution A and stir to mix thoroughly to form solution B; Preferably, the mixing time is 50 min to 60 min and the rotation speed is 400 r / min to 500 r / min.

[0016] (3) Add a stabilizer to solution B and mix thoroughly to form solution C; Preferably, the mixing time is 5 min to 10 min and the rotation speed is 400 r / min to 500 r / min.

[0017] (4) Add aluminum sulfate to solution C and stir to mix thoroughly to prepare an environmentally friendly chemical passivating agent for aluminum alloy surface; Preferably, the mixing time is 20 min to 30 min and the rotation speed is 400 r / min to 500 r / min.

[0018] An application of an environmentally friendly chemical passivating agent for aluminum alloy surfaces, the application method of which is as follows: By immersing a clean and dry aluminum alloy in the environmentally friendly chemical passivating agent for aluminum alloy surfaces described in this invention, a passivation layer can be formed on the surface of the aluminum alloy.

[0019] Preferably, the soaking temperature is 35 ℃ ~ 50 ℃, and the soaking time is 30 s ~ 120 s.

[0020] A clean and dry aluminum alloy surface can be obtained by degreasing, wiping clean, and drying the aluminum alloy surface.

[0021] Beneficial effects (1) This invention provides an environmentally friendly chemical passivating agent for aluminum alloy surfaces. The passivating agent is not only made from green and environmentally friendly raw materials and has long-term stable performance, eliminating the toxicity of chromium, but is also not limited by the size and shape of the aluminum alloy surface, has a long service life, and is easy to maintain and manage. (2) This invention provides an environmentally friendly chemical passivating agent for aluminum alloy surfaces. The components in the passivating agent raw material formulation work together through synergistic coexistence and synergistic effects to construct a stable passivation layer system, thereby improving the service life of the passivation layer and further enhancing the corrosion resistance of the aluminum alloy. The oxidizing properties of potassium permanganate enable the formation of the passivation layer and impart stability and hydrophobicity to it. Concentrated sulfuric acid promotes the oxidizing properties of potassium permanganate; Stabilizers ensure the long-term stability of the passivation solution; sodium stannate prevents decomposition and precipitation, keeping the solution clear and transparent; sodium pyrosulfate preferentially reacts with oxygen in the solution, consuming it; 8-hydroxyquinoline is an organic chelating agent that can react with various metal ions (such as Al). 3+ Fe 3+ Cu 2+ Sn 4+ (etc.) form stable complexes, providing certain antioxidant auxiliary effects; Aluminum sulfate increases the mobility of ions, further enhancing the interaction and bonding force of the components in the passivation layer, thereby enhancing the stability and durability of the passivation layer. (3) This invention provides a method for preparing an environmentally friendly chemical passivating agent for aluminum alloy surfaces. The preparation process is simple, does not require complex production equipment, and is suitable for large-scale industrial production. (4) The present invention provides an application of an environmentally friendly chemical passivating agent for aluminum alloy surfaces. The preferred immersion temperature in the application method is 35 ℃ ~ 50 ℃, and the immersion time is 30 s ~ 120 s, which significantly improves the density and uniformity of the passivation film. Attached Figure Description

[0022] Figure 1 This is a scanning electron microscope (SEM) image of the environmentally friendly chemical passivation layer on the surface of the aluminum alloy prepared in Example 1.

[0023] Figure 2 The chart shows the durability test results of the environmentally friendly chemical passivation layer on the aluminum alloy surface prepared in Examples 1 to 3.

[0024] Figure 3 The chart shows the durability test results of the environmentally friendly chemical passivation layers on the aluminum alloy surfaces prepared in Comparative Examples 1 to 3. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the present invention.

[0026] In the following examples and comparative examples, the concentrated sulfuric acid is a commercially available sulfuric acid solution with a mass fraction of 98%.

[0027] Example 1 A method for preparing an environmentally friendly chemical passivating agent for aluminum alloy surfaces, comprising the following steps: (1) Add 100 ml of concentrated sulfuric acid to 900 ml of deionized water and stir at 400 r / min for 20 min to mix thoroughly to form solution A; (2) Add 60 g of potassium permanganate in 30 portions, 2 g each time, to solution A, and stir at 400 r / min for 50 min to mix thoroughly to form solution B; (3) Add 0.3 g sodium stannate, 0.3 g sodium pyrosulfate and 0.3 g 8-hydroxyquinoline to solution B in sequence, and stir at 400 r / min for 5 min to mix thoroughly to form solution C; (4) 36 g of aluminum sulfate was added to solution C in 18 portions, 2 g each time, and stirred at 400 r / min for 20 min to mix thoroughly, thus preparing an environmentally friendly chemical passivating agent for aluminum alloy surfaces.

[0028] An application of an environmentally friendly chemical passivating agent for aluminum alloy surfaces, the application method of which is as follows: The aluminum alloy surface is degreased, wiped clean and dried to obtain a clean and dry aluminum alloy. It is then immersed in the environmentally friendly chemical passivating agent for aluminum alloy surface prepared in this embodiment. The immersion temperature is 35 ℃ and the immersion time is 120 s, forming an environmentally friendly chemical passivation layer on the aluminum alloy surface.

[0029] Example 2 A method for preparing an environmentally friendly chemical passivating agent for aluminum alloy surfaces, comprising the following steps: (1) Add 150 ml of concentrated sulfuric acid to 850 ml of deionized water and stir at 400 r / min for 25 min to mix thoroughly to form solution A; (2) Add 70 g of potassium permanganate in 35 portions, 2 g each time, to solution A, and stir at 400 r / min for 55 min to mix thoroughly to form solution B; (3) Add 0.35 g sodium stannate, 0.35 g sodium pyrosulfate and 0.35 g 8-hydroxyquinoline to solution B in sequence, and stir at 400 r / min for 8 min to mix thoroughly to form solution C; (4) 45 g of aluminum sulfate was added to solution C in 20 portions of 2.25 g each time, and stirred at 400 r / min for 25 min to mix thoroughly, thus preparing an environmentally friendly chemical passivating agent for aluminum alloy surfaces.

[0030] An application of an environmentally friendly chemical passivating agent for aluminum alloy surfaces, the application method of which is as follows: The aluminum alloy surface was degreased, wiped clean, and dried to obtain a clean and dry aluminum alloy. It was then immersed in the environmentally friendly chemical passivating agent for aluminum alloy surface prepared in this embodiment at a immersion temperature of 45 ℃ for 60 s to form an environmentally friendly chemical passivation layer on the aluminum alloy surface.

[0031] Example 3 (1) Add 200 ml of concentrated sulfuric acid to 800 ml of deionized water and stir at 500 r / min for 30 min to mix thoroughly to form solution A; (2) Add 80 g of potassium permanganate in 40 portions, 2 g each time, to solution A, and stir at 500 r / min for 60 min to mix thoroughly to form solution B; (3) Add 0.4 g sodium stannate, 0.4 g sodium pyrosulfate and 0.4 g 8-hydroxyquinoline to solution B in sequence, and stir at 500 r / min for 10 min to mix thoroughly to form solution C; (4) 54 g of aluminum sulfate was added to solution C in 27 portions, 2 g each time, and stirred at 500 r / min for 30 min to mix thoroughly, thus preparing an environmentally friendly chemical passivating agent for aluminum alloy surfaces.

[0032] An application of an environmentally friendly chemical passivating agent for aluminum alloy surfaces, the application method of which is as follows: The aluminum alloy surface is degreased, wiped clean and dried to obtain a clean and dry aluminum alloy. It is then immersed in the environmentally friendly chemical passivating agent for aluminum alloy surface prepared in this embodiment. The immersion temperature is 50 ℃ and the immersion time is 30 s, forming an environmentally friendly chemical passivation layer on the aluminum alloy surface.

[0033] Comparative Example 1 Concentrated sulfuric acid was not used in this comparative example; otherwise, it was the same as in Example 1.

[0034] Comparative Example 2 Potassium permanganate was not used in this comparative example; otherwise, it was the same as in Example 2.

[0035] Comparative Example 3 Aluminum sulfate was not used in this comparative example; otherwise, it was the same as in Example 3.

[0036] Performance testing: (1) Scanning electron microscope The environmentally friendly chemical passivation layers on the surface of aluminum alloys prepared in Examples 1-3 and Comparative Examples 1-3 were observed using scanning electron microscopy, and the results are as follows: The scanning electron microscope image of the passivation layer described in Example 1 is as follows: Figure 1 As shown, the passivation layer is a dense oxide film with a thickness of 1.5 μm, which makes the aluminum alloy surface more uniform and effectively improves the corrosion resistance and chemical stability of the aluminum alloy. The scanning electron microscope images of the passivation layers in Examples 2 and 3 are similar to those in Example 1, showing that the passivation layer is a dense oxide film with a thickness of 1.5 μm.

[0037] The passivation layer obtained in Comparative Example 1 is not a dense passivation film. This is because acidity promotes the oxidation reaction, but the lack of sulfuric acid solution in the passivating agent of Comparative Example 1 significantly reduces its reaction rate. In Comparative Example 2, no passivation layer was observed on the aluminum alloy surface. This is because the lack of potassium permanganate prevents the oxidation reaction from occurring on the aluminum alloy surface. The passivation layer in Comparative Example 3 is not a complete and dense passivation film; the lack of aluminum sulfate also weakens the ion migration rate during passivation.

[0038] (2) Durability test The passivation layers prepared in Examples 1-3 were subjected to durability tests, and the results are as follows: Figure 2As shown, the passivation layers all have a smooth appearance, and the color gradually deepens. The passivation layer of Example 1 has a longer salt spray resistance time (neutral, 192 hours) and a longer resistance time to a 3.5% NaCl solution (240 hours) than the passivation layers of Examples 2 and 3, respectively. This indicates that the passivation layer formed in Example 1 has the best corrosion resistance and chemical stability.

[0039] The passivation layers prepared in Comparative Examples 1 to 3 were subjected to durability tests, and the results are as follows: Figure 3 As shown. The surfaces of Comparative Examples 1-3 are all smooth, and the passivation layer surfaces of Comparative Examples 1 and 3 are light yellow in color. The salt spray resistance time of Comparative Examples 1-3 does not exceed 96 hours, and the resistance time to 3.5% NaCl solution does not exceed 120 hours, indicating that the corrosion resistance and chemical stability of the passivation layers prepared in Comparative Examples 1-3 are worse than those prepared in Examples 1-3.

[0040] The comparison of the experimental results in Example 1 with those in Comparative Examples 1-3 shows that sulfuric acid, potassium permanganate, and potassium sulfate are crucial to the durability of the passivation layer formed on aluminum alloys using environmentally friendly chemical passivating agents. In the raw material formulation of the passivating agent, the various raw material components complement each other, and their synergistic effect determines the corrosion resistance of the passivation layer. The absence of any single raw material component will affect the durability of the passivation layer.

[0041] In summary, the environmentally friendly chemical passivating agent for aluminum alloy surfaces provided by this invention can be applied to aluminum alloy surface treatment, and the resulting passivation layer has better corrosion resistance and chemical stability. The presence of the passivation layer can isolate the metal from direct contact with the external environment, thereby slowing down or preventing metal corrosion and oxidation, which is of great significance for extending the service life of the metal and maintaining its performance.

[0042] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. An environmentally friendly chemical passivating agent for aluminum alloy surfaces, characterized in that: The passivating agent is liquid, and the raw material formula is as follows: per liter of solution, potassium permanganate 60 g / L ~ 80 g / L, aluminum sulfate 36 g / L ~ 54 g / L, stabilizer 0.9 g / L ~ 1.2 g / L, concentrated sulfuric acid 100 ml / L ~ 200 ml / L, and the balance is water; The stabilizer consists of sodium stannate, sodium pyrosulfate, and 8-hydroxyquinoline; Concentrated sulfuric acid is a sulfuric acid solution with a mass fraction of 98%.

2. A method for preparing an environmentally friendly chemical passivating agent for aluminum alloy surfaces as described in claim 1, characterized in that: (1) Add concentrated sulfuric acid to water and stir until fully mixed to form solution A; (2) Add potassium permanganate to solution A and stir to mix thoroughly to form solution B; (3) Add a stabilizer to solution B and mix thoroughly to form solution C; (4) Add aluminum sulfate to solution C and stir to mix thoroughly to prepare an environmentally friendly chemical passivating agent for aluminum alloy surface.

3. The method for preparing an environmentally friendly chemical passivating agent for aluminum alloy surfaces according to claim 2, characterized in that: In step (1), the mixing time is 20 min ~ 30 min, and the rotation speed is 400 r / min ~ 500 r / min; In step (2), the mixing time is 50 min ~ 60 min, and the rotation speed is 400 r / min ~ 500 r / min; In step (3), the mixing time is 5 min ~ 10 min, and the rotation speed is 400 r / min ~ 500 r / min; In step (4), the mixing time is 20 min ~ 30 min and the rotation speed is 400 r / min ~ 500 r / min.

4. The application of an environmentally friendly chemical passivating agent for aluminum alloy surfaces as described in claim 1, characterized in that: A clean and dry aluminum alloy is immersed in the environmentally friendly chemical passivating agent for aluminum alloy surfaces as described in claim 1, thereby forming a passivation layer on the aluminum alloy surface.

5. The application of the environmentally friendly chemical passivating agent for aluminum alloy surfaces according to claim 4, characterized in that: The soaking temperature is 35 ℃ ~ 50 ℃, and the soaking time is 30 s ~ 120 s.

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