Aluminum alloy natural color trivalent chromium passivator and preparation method thereof

Abstract

The invention relates to the technical field of passivating agents, and particularly discloses an aluminum alloy natural color trivalent chromium passivating agent which is characterized by comprising the following components in percentage by mass: 3.5-6.5% of chromic nitrate, 6-9% of citric acid, 1.8-3.2% of malic acid, 0.8-1.5% of lanthanum nitrate, 1-2% of cerium chloride, 0.2-0.4% of benzotriazole, 2.5-4.5% of polyvinylpyrrolidone, 0.5-1.2% of triethanolamine and the balance of deionized water, and the pH value of the passivating agent is 3.8-4.2. According to the passivator, the corrosion resistance of metal can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of surface treatment, and particularly to an aluminum alloy trivalent chromium passivator in natural color and a preparation method thereof. Background Art

[0002] Aluminum alloys are widely used due to their light weight, high strength and other characteristics, but they are prone to pitting corrosion and intergranular corrosion in humid and saline environments. The following technical bottlenecks exist in traditional surface treatment technologies: (1) Hexavalent chromium system: Although hexavalent chromium passivators have excellent corrosion resistance, hexavalent chromium is a Class I carcinogen, and the European Union clearly prohibits industrial applications; (2) Trivalent chromium replacement technology: Existing trivalent chromium passivators generally have the following defects: slow film formation speed (usually requiring an immersion time of 120 - 300 seconds), resulting in low production line efficiency, insufficient corrosion resistance of the passivation film (neutral salt spray test is generally less than 240h), the film layer is prone to interference colors or yellowing, affecting the appearance consistency of products, and the use of fluorine-containing compounds leads to easy corrosion of equipment and difficult wastewater treatment.

[0003] In the prior art, it is impossible to solve how to achieve rapid complexation and controlled release of Cr 3+ in a fluorine-free system; the passivation film has poor density and self-healing ability, and has poor corrosion resistance while maintaining the natural color of the aluminum alloy. Summary of the Invention

[0004] Aiming at the defects of the prior art, the purpose of the present invention is to provide an aluminum alloy trivalent chromium passivator in natural color and a preparation method thereof to solve the problems raised in the above background art.

[0005] The present invention adopts the following technical solutions to solve the technical problems: In the first aspect, the present invention provides an aluminum alloy trivalent chromium passivator in natural color, which is composed of the following components in mass percentage: chromium nitrate 3.5 - 6.5%, citric acid 6 - 9%, malic acid 1.8 - 3.2%, lanthanum nitrate 0.8 - 1.5%, cerium chloride 1 - 2%, benzotriazole 0.2 - 0.4%, polyvinylpyrrolidone 2.5 - 4.5%, triethanolamine 0.5 - 1.2%, and the balance is deionized water, and the pH value is 3.8 - 4.2.

[0006] Further, the molar ratio of citric acid to malic acid is (2.8 - 3.2):1.

[0007] Further, it is composed of the following components in mass percentage: chromium nitrate 5%, citric acid 7.5%, malic acid 2.5%, lanthanum nitrate 1.1%, cerium chloride 1.5%, benzotriazole 0.3%, polyvinylpyrrolidone 3.5%, triethanolamine 0.8%, and the balance is deionized water, and the pH value is 4.

[0008] Second aspect, the present application provides a preparation method of trivalent chromium passivating agent for aluminum alloy in its natural color, and the method includes: Weigh components according to the following mass percentages: chromium nitrate 3.5 - 6.5%, citric acid 6 - 9%, malic acid 1.8 - 3.2%, lanthanum nitrate 0.8 - 1.5%, cerium chloride 1 - 2%, benzotriazole 0.2 - 0.4%, polyvinylpyrrolidone 2.5 - 4.5%, triethanolamine 0.5 - 1.2%, and the balance is deionized water; Mix chromium nitrate with deionized water at 40°C in a volume ratio of 1:3, and mechanically stir for 10 minutes until completely dissolved; Add 70% of the total amount of citric acid to the solution, heat up to 50°C, and carry out a constant temperature reaction for 15 minutes; make the solution change from blue to green; Continue to add the remaining citric acid and all malic acid to the solution, cool down to 35°C, and carry out ultrasonic-assisted dispersion for 20 minutes; Dropwise add the lanthanum nitrate solution to the solution at a rate of 0.5 mL / min, and simultaneously introduce nitrogen gas; Continue to add polyvinylpyrrolidone to the solution, and use a high-pressure homogenizer to ensure nanoscale dispersion; Age at 25°C in a brown glass container for 24 - 36 hours, and stir for 5 minutes every 8 hours during this period; Filter successively through a 5 - μm polypropylene filter membrane and a 0.45 - μm ceramic membrane to remove agglomerated particles larger than 100 nm, and then carry out canning.

[0009] Further, in the step of mixing chromium nitrate with deionized water at 40°C in a volume ratio of 1:3 and mechanically stirring for 10 minutes until completely dissolved, the rotation speed of the mechanical stirring is 300 rpm.

[0010] Further, in the step of continuing to add the remaining citric acid and all malic acid to the solution, cooling down to 35°C, and carrying out ultrasonic-assisted dispersion for 20 minutes, the ultrasonic power is 200 W and the ultrasonic frequency is 40 kHz.

[0011] Further, in the step of dropwise adding the lanthanum nitrate solution to the solution at a rate of 0.5 mL / min and simultaneously introducing nitrogen gas, the rate of introducing nitrogen gas is 2 L / min.

[0012] Further, in the step of aging at 25°C in a brown glass container for 24 - 36 hours and stirring for 5 minutes every 8 hours during this period, the stirring rotation speed is 60 rpm.

[0013] Further, in the step of continuing to add polyvinylpyrrolidone to the solution and using a high-pressure homogenizer to ensure nanoscale dispersion, the pressure of the high-pressure homogenizer is 150 MPa.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The trivalent chromium passivating agent for aluminum alloy in its natural color and its preparation method provided by this application adopt the following raw materials in parts by weight: chromium nitrate 3.5 - 6.5%, citric acid 6 - 9%, malic acid 1.8 - 3.2%, lanthanum nitrate 0.8 - 1.5%, cerium chloride 1 - 2%, benzotriazole 0.2 - 0.4%, polyvinylpyrrolidone 2.5 - 4.5%, triethanolamine 0.5 - 1.2%, and the balance is deionized water, with a pH value of 3.8 - 4.2; through the synergistic effect of citric acid (CA) and malic acid (MA), the [Cr(CA)(MA)]²⁻ intermediate is constructed, and the pyrrolidone ring of PVP is adsorbed on the crystal plane of Cr(OH)3 through hydrogen bonds, reducing the grain size from the micron level to the nanometer level; the passivating agent of this application can effectively improve the corrosion resistance of metals. Detailed implementation manners

[0015] The following combines specific embodiments to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0016] The present invention provides a trivalent chromium passivating agent for aluminum alloy in its natural color, which is composed of the following components in mass percentages: chromium nitrate 3.5 - 6.5%, citric acid 6 - 9%, malic acid 1.8 - 3.2%, lanthanum nitrate 0.8 - 1.5%, cerium chloride 1 - 2%, benzotriazole 0.2 - 0.4%, polyvinylpyrrolidone 2.5 - 4.5%, triethanolamine 0.5 - 1.2%, and the balance is deionized water, with a pH value of 3.8 - 4.2.

[0017] Further, the molar ratio of the citric acid to the malic acid is (2.8 - 3.2):1.

[0018] Further, it is composed of the following components in mass percentages: chromium nitrate 5%, citric acid 7.5%, malic acid 2.5%, lanthanum nitrate 1.1%, cerium chloride 1.5%, benzotriazole 0.3%, polyvinylpyrrolidone 3.5%, triethanolamine 0.8%, and the balance is deionized water, with a pH value of 4.

[0019] This application also provides a preparation method for the trivalent chromium passivating agent for aluminum alloy in its natural color, and the method includes: Weigh the components according to the following mass percentages: chromium nitrate 3.5 - 6.5%, citric acid 6 - 9%, malic acid 1.8 - 3.2%, lanthanum nitrate 0.8 - 1.5%, cerium chloride 1 - 2%, benzotriazole 0.2 - 0.4%, polyvinylpyrrolidone 2.5 - 4.5%, triethanolamine 0.5 - 1.2%, and the balance is deionized water; Mix chromium nitrate with deionized water at 40°C in a volume ratio of 1:3, and mechanically stir for 10 minutes until completely dissolved; Add 70% of the total amount of citric acid to the solution, heat up to 50°C, and carry out a constant temperature reaction for 15 minutes; the solution changes from blue to green; Continue to add the remaining citric acid and all malic acid to the solution, cool down to 35°C, and disperse by ultrasonic assistance for 20 minutes; Drop the lanthanum nitrate solution into the solution at a rate of 0.5 mL / min, and simultaneously introduce nitrogen; Continue to add polyvinylpyrrolidone to the solution and treat it with a high-pressure homogenizer (150 MPa, 3 cycles) to ensure nano-scale dispersion; Age at 25°C in a brown glass container for 24 - 36 hours, and stir for 5 minutes every 8 hours during this period; Filter successively through a 5 μm polypropylene filter membrane and a 0.45 μm ceramic membrane to remove agglomerated particles larger than 100 nm, and then carry out canning.

[0020] Further, in the step of mixing chromium nitrate with deionized water at 40°C in a volume ratio of 1:3 and mechanically stirring for 10 minutes until completely dissolved, the rotation speed of the mechanical stirring is 300 rpm.

[0021] Further, in the step of continuing to add the remaining citric acid and all malic acid to the solution, cooling down to 35°C, and dispersing by ultrasonic assistance for 20 minutes, the ultrasonic power is 200 W and the ultrasonic frequency is 40 kHz.

[0022] Further, in the step of dropping the lanthanum nitrate solution into the solution at a rate of 0.5 mL / min and simultaneously introducing nitrogen, the rate of introducing nitrogen is 2 L / min.

[0023] Further, in the step of continuing to add polyvinylpyrrolidone to the solution and treating it with a high-pressure homogenizer to ensure nano-scale dispersion, the pressure of the high-pressure homogenizer is 150 MPa.

[0024] Example 1. The preparation method of the trivalent chromium passivating agent for the natural color of aluminum alloy in this example, the method includes: Weigh the components according to the following mass percentages: chromium nitrate 3.5%, citric acid 6%, malic acid 1.8%, lanthanum nitrate 0.8%, cerium chloride 1%, benzotriazole 0.2%, polyvinylpyrrolidone 2.5%, triethanolamine 0.5%, the balance is deionized water, and the pH value is 4; Mix chromium nitrate with deionized water at 40°C in a volume ratio of 1:3, and mechanically stir for 10 minutes until completely dissolved, and the rotation speed of the mechanical stirring is 300 rpm; Add 70% of the total amount of citric acid to the solution, heat up to 50 °C, and carry out a constant-temperature reaction for 15 minutes; the solution changes from blue to green; Continue to add the remaining citric acid and all malic acid to the solution, cool down to 35 °C, and disperse it by ultrasonic assistance for 20 minutes. The ultrasonic power is 200 W, and the ultrasonic frequency is 40 kHz; Drop the lanthanum nitrate solution into the solution at a rate of 0.5 mL / min, and at the same time introduce nitrogen gas at a rate of 2 L / min; Continue to add polyvinylpyrrolidone to the solution, and process it with a high-pressure homogenizer. The pressure of the high-pressure homogenizer is 150 MPa to ensure nanoscale dispersion; Age at 25 °C in a brown glass container for 24 hours, stir for 5 minutes every 8 hours during this period, and the stirring speed is 60 rpm; Filter successively through a 5-μm polypropylene filter membrane and a 0.45-μm ceramic membrane to remove agglomerated particles larger than 100 nm, and then carry out canning.

[0025] Example 2. The preparation method of the trivalent chromium passivation agent for the natural color of aluminum alloy in this example, the method includes: Weigh the components according to the following mass percentages: chromium nitrate 6.5%, citric acid 9%, malic acid 3.2%, lanthanum nitrate 1.5%, cerium chloride 2%, benzotriazole 0.4%, polyvinylpyrrolidone 4.5%, triethanolamine 1.2%, and the balance is deionized water, and the pH value is 4; Mix chromium nitrate and deionized water at 40 °C in a volume ratio of 1:3, and mechanically stir for 10 minutes until completely dissolved. The rotation speed of the mechanical stirring is 300 rpm; Add 70% of the total amount of citric acid to the solution, heat up to 50 °C, and carry out a constant-temperature reaction for 15 minutes; the solution changes from blue to green; Continue to add the remaining citric acid and all malic acid to the solution, cool down to 35 °C, and disperse it by ultrasonic assistance for 20 minutes. The ultrasonic power is 200 W, and the ultrasonic frequency is 40 kHz; Drop the lanthanum nitrate solution into the solution at a rate of 0.5 mL / min, and at the same time introduce nitrogen gas at a rate of 2 L / min; Continue to add polyvinylpyrrolidone to the solution, and process it with a high-pressure homogenizer. The pressure of the high-pressure homogenizer is 150 MPa to ensure nanoscale dispersion; Age at 25 °C in a brown glass container for 24 hours, stir for 5 minutes every 8 hours during this period, and the stirring speed is 60 rpm; Filter successively through a 5-μm polypropylene filter membrane and a 0.45-μm ceramic membrane to remove agglomerated particles larger than 100 nm, and then carry out canning.

[0026] Example 3. The preparation method of the trivalent chromium passivating agent for the natural color of aluminum alloy in this embodiment, the method includes: Weigh the components according to the following mass percentages: chromium nitrate 5%, citric acid 7.5%, malic acid 2.5%, lanthanum nitrate 1.1%, cerium chloride 1.5%, benzotriazole 0.3%, polyvinylpyrrolidone 3.5%, triethanolamine 0.8%, and the balance is deionized water, with a pH value of 4; Mix chromium nitrate with deionized water at 40°C in a volume ratio of 1:3, and mechanically stir for 10 minutes until completely dissolved. The rotation speed of the mechanical stirring is 300 rpm; Add 70% of the total amount of citric acid to the solution, heat up to 50°C, and keep the temperature constant for reaction for 15 minutes; make the solution change from blue to green; Continue to add the remaining citric acid and all malic acid to the solution, cool down to 35°C, and disperse for 20 minutes by ultrasonic assistance. The ultrasonic power is 200 W and the ultrasonic frequency is 40 kHz; Drop the lanthanum nitrate solution into the solution at a rate of 0.5 mL / min, and at the same time introduce nitrogen gas at a rate of 2 L / min; Continue to add polyvinylpyrrolidone to the solution and process it with a high-pressure homogenizer. The pressure of the high-pressure homogenizer is 150 MPa to ensure nanoscale dispersion; Age at 25°C in a brown glass container for 24 hours, and stir for 5 minutes every 8 hours during this period. The stirring speed is 60 rpm; Filter successively through a 5 μm polypropylene filter membrane and a 0.45 μm ceramic membrane to remove agglomerated particles larger than 100 nm, and then carry out canning.

[0027] Comparative Example 1. The difference from Example 1 is that citric acid is not added.

[0028] Comparative Example 2. The difference from Example 1 is that malic acid is not added.

[0029] Comparative Example 3. The difference from Example 1 is that cerium chloride is not added.

[0030] Comparative Example 4. The difference from Example 1 is that polyvinylpyrrolidone is not added.

[0031] Comparative Example 5. The difference from Example 1 is that triethanolamine is not added.

[0032] Use the passivating agents prepared in Examples 1 to 3 and Comparative Examples 1 to 5 to perform surface treatment on the aluminum alloy. The specific method is to immerse the clean aluminum alloy in the passivating solution for 5 minutes, then rinse with water and dry. Perform corrosion performance tests on the surface of the aluminum alloy after surface treatment with the passivating agent. The test results are as follows: Results of neutral salt spray test (test standard: GB6458-86) Example 1 Corrosion started after 96 hours Example 2 Corrosion started after 99 hours Example 3 Corrosion started after 97 hours Comparative Example 1 Corrosion started after 70 hours Comparative Example 2 Corrosion started after 67 hours Comparative Example 3 Corrosion started after 81 hours Comparative Example 4 Corrosion started after 66 hours Comparative Example 5 Corrosion started after 68 hours The trivalent chromium passivating agent for aluminum alloy in its natural color and its preparation method provided by this application adopt the following raw materials in parts by weight: chromium nitrate 3.5 - 6.5%, citric acid 6 - 9%, malic acid 1.8 - 3.2%, lanthanum nitrate 0.8 - 1.5%, cerium chloride 1 - 2%, benzotriazole 0.2 - 0.4%, polyvinylpyrrolidone 2.5 - 4.5%, triethanolamine 0.5 - 1.2%, with the balance being deionized water and the pH value being 3.8 - 4.2; through the synergistic effect of citric acid (CA) and malic acid (MA), the [Cr(CA)(MA)]²⁻ intermediate is constructed, and the pyrrolidone ring of PVP is adsorbed on the crystal plane of Cr(OH)3 through hydrogen bonds, reducing the grain size from the micron level to the nanometer level; the passivating agent of this application can effectively improve the corrosion resistance of metals.

[0033] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non - restrictive. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention.

[0034] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. Trivalent chromium passivating agent for the natural color of aluminum alloy, characterized in that, It consists of the following components by mass percentage: chromium nitrate 3.5 - 6.5%, citric acid 6 - 9%, malic acid 1.8 - 3.2%, lanthanum nitrate 0.8 - 1.5%, cerium chloride 1 - 2%, benzotriazole 0.2 - 0.4%, polyvinylpyrrolidone 2.5 - 4.5%, triethanolamine 0.5 - 1.2%, the balance being deionized water, and the pH value is 3.8 - 4.

2.

2. The trivalent chromium passivating agent for natural-colored aluminum alloy according to claim 1, wherein, The molar ratio of the citric acid to the malic acid is (2.8 - 3.2):

1.

3. The trivalent chromium passivating agent for the natural color of aluminum alloy according to claim 1, characterized in that, It consists of the following components by mass percentage: chromium nitrate 5%, citric acid 7.5%, malic acid 2.5%, lanthanum nitrate 1.1%, cerium chloride 1.5%, benzotriazole 0.3%, polyvinylpyrrolidone 3.5%, triethanolamine 0.8%, the balance being deionized water, and the pH value is 4.

4. Preparation method of trivalent chromium passivating agent for aluminum alloy in natural color, characterized in that The method includes: Weigh the components according to the following mass percentage: chromium nitrate 3.5 - 6.5%, citric acid 6 - 9%, malic acid 1.8 - 3.2%, lanthanum nitrate 0.8 - 1.5%, cerium chloride 1 - 2%, benzotriazole 0.2 - 0.4%, polyvinylpyrrolidone 2.5 - 4.5%, triethanolamine 0.5 - 1.2%, the balance being deionized water; Mix chromium nitrate with deionized water at 40°C in a volume ratio of 1:3, and mechanically stir for 10 minutes until completely dissolved; Add 70% of the total amount of citric acid to the solution, raise the temperature to 50°C, and carry out a constant-temperature reaction for 15 minutes; make the solution change from blue to green; Continue to add the remaining citric acid and all the malic acid to the solution, cool down to 35°C, and carry out ultrasonic-assisted dispersion for 20 minutes; Drop the lanthanum nitrate solution into the solution at a rate of 0.5 mL / min while introducing nitrogen; Continue to add polyvinylpyrrolidone to the solution and use a high-pressure homogenizer to ensure nano-scale dispersion; Age at 25°C in a brown glass container for 24 - 36 hours, and stir for 5 minutes every 8 hours during this period; Filter successively through a 5 - μm polypropylene filter membrane and a 0.45 - μm ceramic membrane to remove agglomerated particles larger than 100 nm, and then carry out canning.

5. The preparation method of the trivalent chromium passivating agent for the natural color of aluminum alloy according to claim 4, wherein, In the step of mixing chromium nitrate with deionized water at 40°C in a volume ratio of 1:3 and mechanically stirring for 10 minutes until completely dissolved, the rotation speed of the mechanical stirring is 300 rpm.

6. The preparation method of the trivalent chromium passivation agent for the natural color of aluminum alloy according to claim 4, wherein, In the step of continuing to add the remaining citric acid and all the malic acid to the solution, cooling down to 35°C, and carrying out ultrasonic-assisted dispersion for 20 minutes, the ultrasonic power is 200 W and the ultrasonic frequency is 40 kHz.

7. The preparation method of the trivalent chromium passivating agent for the natural color of aluminum alloy according to claim 4, characterized in that, In the step of dropping the lanthanum nitrate solution into the solution at a rate of 0.5 mL / min while introducing nitrogen, the rate of introducing nitrogen is 2 L / min.

8. The preparation method of the trivalent chromium passivating agent for aluminum alloy in its natural color according to claim 4, characterized in that, In the step of aging at 25°C in a brown glass container for 24 - 36 hours and stirring for 5 minutes every 8 hours during this period, the rotation speed of the stirring is 60 rpm.

9. The preparation method of the trivalent chromium passivation agent for the natural color of aluminum alloy according to claim 4, characterized in that, In the step of continuing to add polyvinylpyrrolidone to the solution and using a high-pressure homogenizer to ensure nano-scale dispersion, the pressure of the high-pressure homogenizer is 150 MPa.