Composite passivation agent for aluminum alloy and preparation method thereof

Abstract

The present application relates to the technical field of metal additive, in particular to a passivator for aluminum alloy and a preparation method thereof.The composite passivator is composed of the following raw materials in percentage by weight: 35-45wt% of acrylic resin, 4-8wt% of 3-isocyanate propyl triethoxysilane, 1-3wt% of lanthanum nitrate, 9-15wt% of 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, 1-2wt% of potassium fluozirconate, 0.5-2wt% of disodium edetate, 1-2wt% of aluminum dihydrogen phosphate, and the rest is water.By adding the surfactant potassium fluozirconate, the surface tension of the aluminum alloy can be effectively reduced, the alloy surface is activated, the acrylic resin-silane coupling agent can fully react with the aluminum alloy matrix to form a uniform and dense film, and the corrosion resistance is improved.By selecting a suitable silane coupling agent, the capacity of free lanthanum carried by the composite film can be effectively improved, thereby effectively solving the problem of adhesion reduction caused by the overload of metal elements in the composite film.

Description

Technical Field

[0001] This invention relates to the field of metal additives technology, and in particular to a passivating agent for aluminum alloys and its preparation method. Background Technology

[0002] The molecular formula RSiX3 of silane coupling agents typically refers to organosilicon monomers containing two or more different reactive groups. X represents a hydrolyzable functional group, which can usually couple with inorganic materials such as methoxy, ethoxy, glass, and silica. R represents an organic functional group, which can usually couple with vinyl, ethoxy, various resins, and rubber. Therefore, silane coupling agents often exist as "molecular bridges" between organic and inorganic substances, allowing the prepared new materials to possess both organic and inorganic properties. Zuo Ke et al. prepared cerium-silane-zirconia films on aluminum alloy surfaces, and the results showed that the porosity and microcracks of the film significantly decreased with improved corrosion resistance. Hu Jiming et al. deposited silane films on aluminum alloy surfaces via electrodeposition, and the results showed that silane and aluminum alloy are bonded by -SiOAl bonds, significantly improving the corrosion resistance of the aluminum alloy.

[0003] In recent years, the composite passivation of silanes and inorganic materials has attracted increasing attention from researchers, and there is a wealth of related literature. However, the understanding of the film-forming mechanism is still insufficient, and the currently prepared silane composite passivation films still have defects, such as poor heat resistance and decreased adhesion due to excessively high metal ion concentration. Composite passivation of inorganic and organic resins involves the formation of organic polymers and chromium-free substances on a coating. The microstructure of the mixture coating consists of an organic polymer forming a continuous phase, i.e., a gel phase, as well as a dispersed phase within the continuous phase. The gel is an organic polymer, which can be water-soluble or anhydrous. During the passivation process, the organic polymer forms a continuous phase on the coating. Typically, acrylic polymers, epoxy resins, phenolic resins, and ammonia resins are used as organic film-forming polymers. The dispersed phase is generally a chromium-free salt mixture, such as alkali metal vanadates (e.g., sodium or calcium salts) and alkali metal borates, such as barium borate.

[0004] Based on the above, this invention proposes a composite passivating agent for aluminum alloys and its preparation method. Summary of the Invention

[0005] The purpose of this invention is to provide a composite passivating agent for aluminum alloys and its preparation method.

[0006] To achieve the above objectives, the present invention provides a composite passivating agent for aluminum alloys, wherein the composite passivating agent is composed of the following raw materials in weight percentages: 35-45 wt% acrylic resin, 4-8 wt% silane coupling agent, 1-3 wt% rare earth additive, 9-15 wt% film-forming promoter, 1-2 wt% surfactant, 0.5-2 wt% coordination agent, 1-2 wt% phosphating agent, and the balance being water.

[0007] Preferably, the rare earth additive is a rare earth metal nitrate, and in one embodiment, the rare earth metal nitrate is lanthanum nitrate.

[0008] Preferably, the film-forming promoter is an alcohol ester film-forming promoter. In one embodiment, the alcohol ester film-forming promoter is 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate.

[0009] Preferably, the surfactant is a fluorinated zirconate, and in one embodiment, the fluorinated zirconate is potassium fluorozirconate.

[0010] Preferably, the ligand is a sodium salt of edetate or a sodium / potassium salt of tartaric acid. In one embodiment, the ligand is disodium edetate.

[0011] Preferably, the phosphating agent is aluminum dihydrogen phosphate.

[0012] Preferably, the silane coupling agent is an isocyanate-containing silane coupling agent. In one embodiment, the isocyanate-containing silane coupling agent is 3-isocyanopropyltriethoxysilane.

[0013] Preferably, the composite passivating agent is composed of the following raw materials in weight percentages: 35-45 wt% acrylic resin, 4-8 wt% 3-isocyanopropyltriethoxysilane, 1-3 wt% lanthanum nitrate, 9-15 wt% 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, 1-2 wt% potassium fluorozirconate, 0.5-2 wt% disodium edetate, 1-2 wt% aluminum dihydrogen phosphate, and the balance being water.

[0014] This invention also provides a method for preparing a composite passivating agent for aluminum alloys, the method comprising the following steps:

[0015] (1) Mix the silane coupling agent with the acrylic resin and stir at 500-550 rpm at 40-45°C for 30-40 min to obtain solution a.

[0016] (2) Add rare earth additives, film-forming promoters, surfactants, complexing agents and phosphating agents to the water of the formula amount, and stir at 150-200 rpm for 15-20 min to obtain solution b.

[0017] (3) While stirring solution a at 500-550 rpm, add solution b to solution a at a rate of 5-6 drops / second. After the addition is complete, continue stirring at 55-60℃ for 50-60 min and let stand at room temperature for 24 h to obtain the solution.

[0018] The present invention also provides a passivation method for aluminum alloys, wherein the passivation method comprises: immersing the aluminum alloy, which has been successively treated by degreasing, rust removal, alkaline etching, and acid etching, in the passivation solution for aluminum alloys, adjusting the pH of the passivation solution to 5-6, and passivating at a temperature of 38-40°C for 4-6 minutes.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. This invention, by adding the surfactant potassium fluorozirconate, effectively reduces the surface tension of aluminum alloys, activates the alloy surface, and promotes the full reaction between the acrylic resin-silane coupling agent and the aluminum alloy substrate to form a uniform and dense film, thereby improving its corrosion resistance. By selecting a suitable silane coupling agent, this invention can effectively increase the capacity of the composite film to carry free lanthanum, thus effectively solving the problem of decreased adhesion caused by overloading of metal elements in the composite film. Simultaneously, the silane coupling agent containing isocyanate groups, due to the presence of C=O and C=N groups, can form ZrN and ZrO2 with zirconium elements respectively, thereby synergistically improving the corrosion resistance of the composite film with lanthanum elements.

[0021] 2. The raw materials for this invention are abundant and reasonably priced in China, which means that there are no high cost restrictions on its large-scale production. At the same time, the preparation method is simple and the overall production cost is not high, which is conducive to large-scale industrial production. Detailed Implementation

[0022] Example 1

[0023] Weigh the specific raw materials according to Table 1. The preparation steps are as follows:

[0024] (1) The silane coupling agent was mixed with the acrylic resin and stirred at 500 rpm at 45°C for 30 min to obtain solution a.

[0025] (2) Add rare earth additives, film-forming promoters, surfactants, complexing agents and phosphating agents to the water of the formula amount, stir at 150 rpm for 20 min to obtain solution b.

[0026] (3) While stirring solution a at 500 rpm, add solution b to solution a at a rate of 5 drops / second. After the addition is complete, continue stirring at 55℃ for 60 min and let stand at room temperature for 24 h to obtain the solution.

[0027] (4) The aluminum alloy that has been degreased, derusted, alkali-etched and acid-etched in sequence is immersed in the passivation solution for aluminum alloy prepared in step (3), the pH of the passivation solution is adjusted to 5, and passivation is carried out at 38°C for 6 minutes.

[0028] Example 2

[0029] Weigh the specific raw materials according to Table 1. The preparation steps are as follows:

[0030] (1) The silane coupling agent was mixed with the acrylic resin and stirred at 550 rpm at 45°C for 30 min to obtain solution a.

[0031] (2) Add rare earth additives, film-forming promoters, surfactants, complexing agents and phosphating agents to the water of the formula amount, stir at 200 rpm for 15 min to obtain solution b.

[0032] (3) While stirring solution a at 550 rpm, add solution b to solution a at a rate of 6 drops / second. After the addition is complete, continue stirring at 60℃ for 50 min and let stand at room temperature for 24 h to obtain the solution.

[0033] (4) The aluminum alloy that has been degreased, derusted, alkali-etched and acid-etched in sequence is immersed in the passivation solution for aluminum alloy prepared in step (3), the pH of the passivation solution is adjusted to 6, and passivation is performed at 40°C for 4 minutes.

[0034] Example 3

[0035] Weigh the specific raw materials according to Table 1. The preparation steps are as follows:

[0036] (1) The silane coupling agent was mixed with the acrylic resin and stirred at 550 rpm at 45°C for 40 min to obtain solution a.

[0037] (2) Add rare earth additives, film-forming promoters, surfactants, complexing agents and phosphating agents to the water of the formula amount, stir at 200 rpm for 20 min to obtain solution b.

[0038] (3) While stirring solution a at 550 rpm, add solution b to solution a at a rate of 6 drops / second. After the addition is complete, continue stirring at 60℃ for 60 min and let stand at room temperature for 24 h to obtain the solution.

[0039] (4) The aluminum alloy that has been degreased, derusted, alkali-etched and acid-etched in sequence is immersed in the passivation solution for aluminum alloy prepared in step (3), the pH of the passivation solution is adjusted to 6, and passivation is carried out at 40°C for 6 minutes.

[0040] Comparative Example 1

[0041] Weigh the specific raw materials according to Table 1. Unlike Example 3, K2ZrF6 was not added. The remaining preparation steps are the same as in Example 3.

[0042] Comparative Example 2

[0043] Weigh the specific raw materials according to Table 1. The difference from Example 3 is that the silane coupling agent is KH560, and the other preparation steps are the same as in Example 3.

[0044] Comparative Example 3

[0045] Weigh the specific raw materials according to Table 1. The difference from Example 3 is that the silane coupling agent is N-2-aminoethyl-3-aminopropyltrimethoxysilane, and the other preparation steps are the same as in Example 3.

[0046] Comparative Example 4

[0047] Weigh the specific raw materials according to Table 1. The difference from Example 3 is that the silane coupling agent is 3-aminopropyltriethoxysilane, and the other preparation steps are the same as in Example 3.

[0048] Table 1

[0049]

[0050] Performance Evaluation

[0051] All aluminum alloy sheets used in this performance evaluation were 7075 aluminum alloy, and were passivated according to the methods of Examples 1-3 and Comparative Examples 1-4, respectively. Neutral salt spray performance was tested using an XHM / Q-750 neutral salt spray tester according to ASTM B117: temperature (35±1)℃, 5% NaCl solution, pH of the collected solution 6.5–7.2, and the angle of the specimen to the vertical direction 15°–30°. The salt spray time was defined as the time when the corrosion area of ​​the sample fell below 1% of the total area. The results are shown in Table 2.

[0052] The adhesion between the passivation film and the aluminum alloy substrate was tested using the cross-cut adhesion test. Eighty-one 1mm × 1mm grids were etched onto the sample surface using a cross-cut adhesion tester, with each etch reaching the bottom layer of the film. The grids were then firmly adhered with 3M 600 tape, and the tape was quickly torn off vertically by holding one end. The adhesion between the passivation film and the aluminum alloy substrate was evaluated based on the degree of film peeling off within the grid. The results are shown in Table 2.

[0053] Table 2

[0054]

[0055] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A composite passivating agent for aluminum alloys, characterized in that, The composite passivating agent for aluminum alloys is composed of the following raw materials in weight percentage: 35-45 wt% acrylic resin, 4-8 wt% 3-isocyanopropyltriethoxysilane, 1-3 wt% lanthanum nitrate, 9-15 wt% 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, 1-2 wt% potassium fluorozirconate, 0.5-2 wt% disodium edetate, 1-2 wt% aluminum dihydrogen phosphate, and the balance being water.

2. A method for preparing the composite passivating agent for aluminum alloys as described in claim 1, characterized in that, The method includes the following steps: (1) Mix 3-isocyanopropyltriethoxysilane with acrylic resin and stir at 500-550 rpm at 40-45°C for 30-40 min to obtain solution a; (2) Add lanthanum nitrate, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, potassium fluorozirconate, disodium edetate, and aluminum dihydrogen phosphate to the water in the formula amount, and stir at 150-200 rpm for 15-20 min to obtain solution b; (3) While stirring solution a at 500-550 rpm, add solution b to solution a at a rate of 5-6 drops / second. After the addition is complete, continue stirring at 55-60℃ for 50-60 min and let stand at room temperature for 24 h to obtain the solution.

3. A passivation method for aluminum alloys, characterized in that, The passivation method is as follows: the aluminum alloy that has been successively degreased, derusted, alkali-etched, and acid-etched is immersed in the composite passivating agent for aluminum alloys as described in claim 1, the pH of the composite passivating agent for aluminum alloys is adjusted to 5-6, and passivation is performed at a temperature of 38-40℃ for 4-6 minutes.

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