Secondary closed passivation method for aluminum alloy die casting

Abstract

The invention discloses a secondary closed passivation method for an aluminum alloy die casting, which is characterized by comprising the following steps of: removing oil, namely removing oil stains and smudginess attached to the surface of a product; washing with water, cleaning surface process liquid medicine, activating, removing surface oxides and organic matters, and roughening the surface; washing with water, passivating, and generating a conductive oxide film with good corrosion resistance on the aluminum base material; washing with water and sealing to generate a conductive protective film with good corrosion resistance; washing with water and sealing to generate a hydrophobic protective film; and drying and baking. The method has the beneficial effects that the passivated surface is free of spots, white spots, pinholes and bubbles, the surface is smooth and clean, and the corrosion resistance is high.

Description

Technical Field

[0001] The invention relates to the technical field of passivation treatment of aluminum alloy castings, and in particular to a secondary closed passivation method for aluminum alloy die castings. Background Art

[0002] The engine compartment, crankcase, air-cooled cylinder, and wheel hubs of existing automotive components are all made from die-cast aluminum alloys, which are not only aesthetically pleasing but also offer excellent practical value. To ensure effective pretreatment, existing die-cast aluminum alloy pretreatment methods often use chromization, a process that contains hexavalent chromium, a hazardous substance banned by most countries worldwide. Furthermore, existing passivation processes are prone to delamination, with the oxide layer separating and detaching from the aluminum alloy under external forces. Therefore, improved process methods are needed. Summary of the Invention

[0003] In view of the above-mentioned deficiencies in the prior art, the present invention provides a secondary closed passivation method for aluminum alloy die castings, which has a better coating effect and improves the corrosion resistance of the aluminum alloy die castings.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A secondary closed passivation method for aluminum alloy die castings, characterized by comprising the following steps:

[0006] S1. Degreasing: Add degreasing agent to the process tank, use ultrasonic pre-degreasing, then use tap water to clean the product surface, add degreasing agent again, use ultrasonic main degreasing to remove oil and dirt attached to the product surface;

[0007] S2, water washing, use tap water to wash the product to remove dirt and residual liquid from the previous process;

[0008] S3, activation, add activator to the process tank, adjust the pH value to 1-3, soak the product in the process tank to remove surface oxides and organic matter, and roughen the surface;

[0009] S4, water washing, first use tap water overflow water washing, then through two pure water washing, use pure water overflow product surface to remove the residual liquid from the previous process on the product surface;

[0010] S5, passivation, add passivating agent into the process tank, adjust the Ph value to 3-4, maintain the temperature at 40℃±5℃, and form a conductive oxide film with good corrosion resistance on the aluminum substrate;

[0011] S6, water washing, using pure water to wash the product twice to remove dirt and liquid medicine from the previous process;

[0012] S7. Sealing: Add sealing agent to the process tank, adjust the Ph value to 2-5, maintain the temperature at 30℃±5℃, immerse the product in the process tank, and then form a conductive protective film with good corrosion resistance on the product surface;

[0013] S8, water washing, using pure water to wash the product twice to remove dirt and liquid medicine from the previous process;

[0014] S9, sealing, add sealing agent to the process tank, adjust the Ph value to 5.5-6.5, maintain the temperature at 30℃±5℃, and form a hydrophobic film on the product surface;

[0015] S10, blow dry, use an air gun to blow dry the water stains on the surface of the product;

[0016] S11. Drying: The product is hung in a baking oven for drying at a temperature of 100°C ± 10°C to remove residual chemical solution and water and stabilize the passivation film.

[0017] Furthermore, the groove concentration ratio of the passivating agent in step S5 is 9-12%.

[0018] Furthermore, the groove concentration ratio of the passivating agent in step S9 is 9-12%.

[0019] The beneficial effects of the present invention include: the passivated surface is free of spots, white spots, pinholes, bubbles, a smooth surface, and high corrosion resistance. DETAILED DESCRIPTION

[0020] The present invention will be further described in detail below with reference to specific embodiments.

[0021] A secondary closed passivation method for aluminum alloy die castings, characterized by comprising the following steps:

[0022] S1. Degreasing: Add degreasing agent to the process tank, use ultrasonic pre-degreasing, then use tap water to clean the product surface, add degreasing agent again, use ultrasonic main degreasing to remove oil and dirt attached to the product surface; Ph value is 7-11, temperature is 60℃±5℃, and time is 180±30S.

[0023] S2. Wash with tap water to clean the product to remove dirt and residual liquid from the previous process; the washing time is 60±30S.

[0024] S3, activation, add activator to the process tank, adjust the pH value to 1-3, soak the product in the process tank to remove surface oxides and organic matter, and roughen the surface;

[0025] S4, water washing, first use tap water overflow water washing, then through two pure water washing, use pure water overflow product surface to remove the residual liquid from the previous process on the product surface;

[0026] S5. Passivation: Add a passivator to the process tank with a concentration of 9-12%. Adjust the Ph value to 3-4 and maintain the temperature at 40°C ± 5°C to form a corrosion-resistant conductive oxide film on the aluminum substrate.

[0027] S6, water washing, using pure water to wash the product twice to remove dirt and liquid medicine from the previous process;

[0028] S7. Sealing: Add sealing agent to the process tank, adjust the Ph value to 2-5, maintain the temperature at 30℃±5℃, immerse the product in the process tank, and then form a conductive protective film with good corrosion resistance on the product surface;

[0029] S8, water washing, using pure water to wash the product twice to remove dirt and liquid medicine from the previous process;

[0030] S9, sealing, add sealing agent to the process tank, the passivation agent slot concentration ratio is 9-12%. Adjust the Ph value to 5.5-6.5, maintain the temperature at 30℃±5℃, and form a hydrophobic film on the product surface;

[0031] S10, blow dry, use an air gun to blow dry the water stains on the surface of the product;

[0032] S11. Drying: The product is hung in a baking oven for drying at a temperature of 100°C ± 10°C to remove residual chemical solution and water and stabilize the passivation film.

[0033] Product Inspection

[0034] 1. The surface of the passivated product is free of spots, white spots, black spots, pinholes, different colors, bubbles, deformation, fog, watermarks, foreign matter, qualified roughness, and scratches. The surface appearance of the workpiece with high corrosion resistance passivation process is uniform.

[0035] Corrosion resistance test:

[0036] The corrosion resistance of the conversion film is tested by titration in the chemical conversion area of ​​the sample. The test solution is titrated on the test sample using a burette, usually 5 locations are evenly selected for titration. After titration, the color change of the substrate at the titration location is observed, and the titration time (the time from the start of titration to the beginning of substrate color change) is recorded using a stopwatch. This time must be greater than 15s. The titration solution consists of: 4.1g copper sulfate pentahydrate (CuSO4.5H2O), 3.5g sodium chloride (NaCl), 1.3mL concentrated hydrochloric acid (HCl, concentration of 36-38%) and water. The total volume of the solution is 100mL, and the solution is weakly acidic. The test sample must be stored at room temperature for at least 24 hours before testing.

[0037] Neutral salt spray test method

[0038] Salt spray test: After the salt spray test, the workpiece surface must be intact, free of cracks, breakage, and other defects, and must meet airtightness requirements. The salt spray test method for artificial atmosphere corrosion testing is conducted according to GB / T10125-2012, "Artificial Atmosphere Corrosion Test Salt Spray Test," with a neutral salt spray for 240 hours. The rating is less than mild according to GB / T6461-2002.

[0039] 960H alternating salt spray test

[0040] Test method: According to the test procedure 5.1.5 in Q / BYD-A1901.959-2020 "Corrosion Resistance Test and Evaluation Specification for Automotive Aluminum Parts", 10 cycles, a total of 960 hours

[0041] Evaluation criteria: After 3 cycles, the corrosion area of ​​the test surface is ≤10%; after 10 cycles, the function does not fail after the test, and there should be no salt water entering or salt crystallizing inside the parts; the mass loss is ≤2%, and the corrosion depth does not exceed 5% of the thinnest part.

[0042] Adhesion requirements

[0043] Use 3M standard transparent tape. When applying the tape, ensure it adheres tightly to the test area without any bubbles or wrinkles. After 2-5 minutes, quickly pull the tape back, ensuring there are no particles or metal particles on the surface.

[0044] The technical solutions provided by the embodiments of the present invention are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the embodiments of the present invention. The description of the above embodiments is only applicable to help understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, according to the embodiments of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the contents of this specification should not be understood as limiting the present invention.

Claims

1. A secondary closed passivation method for aluminum alloy die castings, characterized in that: The following steps are included: S1, degreasing, add degreasing agent into the process tank, use ultrasonic pre-degreasing, then use tap water to clean the product surface, add degreasing agent again, use ultrasonic main degreasing to remove oil and dirt attached to the product surface; S2, water washing, use tap water to wash the product to remove dirt and residual liquid from the previous process; S3, activation, add activator into the process tank, adjust the pH value to 1-3, soak the product in the process tank to remove surface oxides and organic matter, and roughen the surface; S4, water washing, first use tap water overflow water washing, then wash twice with pure water, use pure water overflow product surface to remove the residual liquid from the previous process on the product surface; S5, passivation, add passivating agent into the process tank, adjust the Ph value to 3-4, maintain the temperature at 40℃±5℃, and form a conductive oxide film with good corrosion resistance on the aluminum substrate; S6, water washing, using pure water to wash the product twice to remove dirt and liquid medicine from the previous process; S7, sealing, add sealing agent into the process tank, adjust the Ph value to 2-5, maintain the temperature at 30℃±5℃, immerse the product in the process tank, and then form a conductive protective film with good corrosion resistance on the surface of the product; S8, water washing, using pure water to wash the product twice to remove dirt and liquid medicine from the previous process; S9, sealing, add sealing agent into the process tank, adjust the Ph value to 5.5-6.5, maintain the temperature at 30℃±5℃, and form a hydrophobic film on the product surface; S10, Blow dry, use an air gun to blow dry the water stains on the surface of the product; S11, drying: the product is hung down and placed in a baking oven for drying. The baking temperature is 100℃±10℃ to remove the residual liquid medicine and water and stabilize the passivation film.

2. The secondary closed passivation method for aluminum alloy die casting according to claim 1, characterized in that: The groove concentration ratio of the passivating agent in step S5 is 9-12%.

3. The secondary closed passivation method for aluminum alloy die casting according to claim 1, characterized in that: The groove concentration ratio of the passivating agent in step S9 is 9-12%.