Pretreatment method for reducing roughness of hard anodic oxide film

Abstract

The invention provides a pretreatment method for reducing the roughness of a hard anodic oxide film, which comprises the following steps: grinding and polishing a base material to obtain a surface-polished base material; the surface-polished base material is sequentially subjected to first acid pickling, alkali washing and second acid pickling, nitric acid is used for the first acid pickling, nitric acid is used for the second acid pickling, and pretreatment is completed; and the pretreated base material is subjected to hard anodic oxidation and hole sealing. According to the pretreatment method provided by the invention, the surface of the base material is firstly ground and polished, the surface roughness is preliminarily adjusted, and then the microstructure of the surface of the base material is improved through specific acid washing and alkali washing processes, so that the roughness of the generated hard anode oxide film is reduced, and the performance and the appearance of the hard anode oxide film are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of surface treatment, and in particular relates to a pretreatment method for reducing the roughness of a hard anodized film. Background Art

[0002] Hard anodizing is a surface treatment technology that generates a dense alumina ceramic film on the surface of aluminum alloy by electrochemical method. Its principle is to use the aluminum alloy workpiece as the anode and conduct the electrochemical treatment at low temperature (about 0-5℃) and high current density (about 1-5A / dm 2 In an acidic electrolyte containing 20% MgCl2 (20%), the aluminum substrate undergoes an oxidation reaction through electrolysis, forming a mixed-phase oxide film. This film has high hardness, excellent wear resistance, corrosion resistance, and insulation properties, and is widely used in high-end fields such as aviation, automobiles, and precision machinery.

[0003] The surface roughness of hard anodized films plays an important role in their functional properties. Higher roughness will lead to an increase in the friction coefficient, accelerate the wear of the abrasive parts, and reduce the appearance gloss and coating adhesion. However, during the hard anodizing process, the violent oxidation reaction easily forms micropores and columnar crystal structures inside the film layer, which often significantly increases the roughness of the oxide film. Due to the violent oxidation reaction generated during the hard anodizing process and the complex growth mechanism of the oxide film, it is very difficult to control the roughness of the hard anodized film during the hard anodizing process. In addition, after the hard anodized film is generated, conventional mechanical or chemical means are used to improve the roughness of the film layer, which will seriously affect the performance of the hard anodized film and cause a huge waste of resources. Therefore, it is of great technological value to develop pretreatment methods before hard anodizing to reduce the roughness of the hard anodized film.

[0004] However, in the prior art, it is difficult to effectively regulate the microscopic morphology of the substrate surface by pre-treating the aluminum alloy substrate, such as degreasing, deashing, and alkaline etching, thereby improving the roughness of the generated hard anodized film. For example, CN119507003A discloses a method for improving the quality of hard anodized film formation, by machining the substrate surface to a roughness below a preset roughness, thereby improving the porosity and quality of the hard anodized film. The quality of the film layer is improved by controlling the roughness before hard anodizing. The measurement of the roughness has a certain degree of accuracy, is not accurate in reflecting the microscopic appearance of the substrate surface, and has high requirements for the operator. CN110373699A discloses a ZL105 aluminum alloy sand casting hard anodizing electrolyte and oxidation method, which pre-treats the aluminum alloy sand casting by alkaline etching and acid polishing. However, inappropriate pickling and alkaline etching processes can easily cause selective corrosion of grain boundaries, forming pits, or exacerbate the non-uniformity of the initial oxidation reaction, which not only makes it difficult to reduce the roughness of the hard anodized film, but will further increase its roughness.

[0005] Therefore, developing an effective pretreatment method to achieve low-roughness hard anodizing becomes a key challenge for process optimization. Summary of the Invention

[0006] The purpose of the present invention is to provide a pretreatment method for reducing the roughness of a hard anodized film, which effectively reduces the surface roughness and performance of the hard anodized film by pretreating the substrate surface before hard anodization.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] The present invention provides a pretreatment method for reducing the roughness of a hard anodized film, the pretreatment method comprising the following steps:

[0009] (1) grinding and polishing the substrate to obtain a surface-polished substrate;

[0010] (2) performing a first pickling, an alkaline pickling, and a second pickling on the surface-polished substrate in sequence, wherein the first pickling uses nitric acid and the second pickling uses nitric acid to complete pretreatment;

[0011] (3) The pretreated substrate is hard-anodized and sealed.

[0012] The pretreatment method provided by the present invention first grinds and polishes the surface of the substrate to preliminarily adjust the surface roughness. Under the condition of adjusting the surface roughness, the microstructure of the substrate surface is improved through two acid washing and alkaline washing processes, thereby reducing the roughness of the generated hard anodized film.

[0013] Preferably, the substrate comprises aluminum and / or an aluminum alloy.

[0014] Preferably, the aluminum alloy includes 6 series aluminum alloy.

[0015] Preferably, the surface roughness of the surface polished substrate is 0.1-0.4 μm, for example, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm or 0.4 μm, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0016] Preferably, the temperature of the first pickling is 15-20°C, for example, 15°C, 16°C, 17°C, 18°C, 19°C or 20°C, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0017] Preferably, the mass concentration of nitric acid in the first pickling is 10-20%, for example, it can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0018] Preferably, the first pickling time is 5-15 min, for example, it can be 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min or 15 min, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0019] Preferably, the first pickling method includes soaking.

[0020] Preferably, sodium hydroxide is used for the alkali washing.

[0021] Preferably, the mass concentration of the sodium hydroxide is 5-10%, for example, 5%, 6%, 7%, 8%, 9% or 10%, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0022] Preferably, the temperature of the alkali washing is 15-20°C, for example, 15°C, 16°C, 17°C, 18°C, 19°C or 20°C, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0023] Preferably, the alkali washing time is 1-5 min, for example, 1 min, 2 min, 3 min, 4 min or 5 min, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0024] Preferably, the alkali washing method includes soaking.

[0025] Preferably, the mass concentration of nitric acid in the second pickling is 10-20%, for example, it can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0026] Preferably, the temperature of the second pickling is 15-20°C, for example, 15°C, 16°C, 17°C, 18°C, 19°C or 20°C, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0027] Preferably, the second pickling time is 5-15 min, for example, it can be 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min or 15 min, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0028] Preferably, the second pickling method includes soaking.

[0029] Preferably, the pretreatment method further comprises: performing a first water wash after the first acid wash, performing a second water wash after the alkali wash, and performing a third water wash after the second acid wash.

[0030] Preferably, the first water washing time is 1-5 min, for example, 1 min, 2 min, 3 min, 4 min or 5 min, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0031] Preferably, the second water washing time is 1-5 min, for example, 1 min, 2 min, 3 min, 4 min or 5 min, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0032] Preferably, the time of the third water wash is 5-15 min, for example, it can be 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min or 15 min, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0033] As a preferred technical solution of the pretreatment method provided by the present invention, the pretreatment method comprises the following steps:

[0034] (1) After grinding and polishing the substrate, the surface roughness of the substrate is controlled to be 0.1-0.4 μm to obtain a surface-polished substrate;

[0035] (2) performing a first acid wash, a first water wash, an alkali wash, a second water wash, a second acid wash and a third water wash on the surface polished substrate in sequence to complete pretreatment, wherein the first acid wash is performed by soaking in nitric acid with a mass concentration of 10-20%, the temperature of the first acid wash is 15-20°C, the time of the first acid wash is 5-15min, the time of the first water wash is 1-5min, the alkali wash is performed by soaking in sodium hydroxide with a mass concentration of 5-10%, the temperature of the alkali wash is 15-20°C, the time of the alkali wash is 1-5min, the time of the second water wash is 1-5min, the second acid wash is performed by soaking in nitric acid with a mass concentration of 10-20%, the temperature of the second acid wash is 15-20°C, the time of the second acid wash is 5-15min, and the time of the third water wash is 5-15min;

[0036] (3) The pretreated substrate is hard-anodized and sealed.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The pretreatment method provided by the present invention first grinds and polishes the surface of the substrate to preliminarily adjust the surface roughness, and then improves the microstructure of the substrate surface through specific acid and alkali washing processes, thereby reducing the roughness of the generated hard anodized film and improving the performance and appearance of the hard anodized film. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0040] Example 1

[0041] This embodiment provides a pretreatment method for reducing the roughness of a hard anodized film, the pretreatment method comprising the following steps:

[0042] (1) Grinding and polishing the aluminum alloy substrate;

[0043] (2) Soak the polished aluminum alloy substrate in a 15% nitric acid solution at 20°C for 10 minutes, and then rinse it in bubbling water for 3 minutes;

[0044] (3) Soak the pickled aluminum alloy substrate in a sodium hydroxide solution with a temperature of 20°C and a mass concentration of 8% for 3 minutes, and then rinse it in bubbling water for 3 minutes;

[0045] (4) Soaking the alkali-washed aluminum alloy substrate in a nitric acid solution with a temperature of 20° C. and a mass concentration of 15% for 10 minutes, and then washing it in bubbling water for 10 minutes to complete the pretreatment;

[0046] (5) The pre-treated aluminum alloy substrate is hard anodized and sealed.

[0047] In this embodiment, six test points were evenly distributed on the surface of the aluminum alloy substrate after grinding and polishing in step (1) for roughness testing, and the results were 0.279, 0.295, 0.306, 0.272, 0.361, and 0.416, respectively. The average value of the surface roughness of the aluminum alloy substrate was calculated to be 0.322.

[0048] The process parameters of hard anodizing in step (5) include: the electrolyte is a sulfuric acid solution with a concentration of 150g / L, the current density is 4A / dm 2 , temperature is 5℃, time is 60min.

[0049] The surface roughness of the hard anodized film obtained by hard anodizing and sealing in step (5) was evenly dispersed at 6 test points for testing. The results were 1.371, 1.115, 0.981, 1.013, 1.009, and 0.989, respectively. The average value of the surface roughness of the hard anodized film was calculated to be 1.080.

[0050] Example 2

[0051] This embodiment provides a pretreatment method for reducing the roughness of a hard anodized film, the pretreatment method comprising the following steps:

[0052] (1) Grinding and polishing the aluminum alloy substrate;

[0053] (2) Soaking the polished aluminum alloy substrate in a nitric acid solution with a temperature of 15° C. and a mass concentration of 20% for 5 minutes, and then washing it in bubbling water for 5 minutes;

[0054] (3) Soak the pickled aluminum alloy substrate in a 5% sodium hydroxide solution at 15°C for 5 minutes, and then rinse it in bubbling water for 1 minute;

[0055] (4) Soaking the alkali-washed aluminum alloy substrate in a 10% nitric acid solution at 15°C for 15 minutes, and then rinsing it in bubbling water for 5 minutes to complete the pretreatment;

[0056] (5) The pre-treated aluminum alloy substrate is hard anodized and sealed.

[0057] Example 3

[0058] This embodiment provides a pretreatment method for reducing the roughness of a hard anodized film, the pretreatment method comprising the following steps:

[0059] (1) Grinding and polishing the aluminum alloy substrate;

[0060] (2) Soak the polished aluminum alloy substrate in a 10% nitric acid solution at 18°C for 15 minutes, and then rinse it in bubbling water for 1 minute;

[0061] (3) Soak the pickled aluminum alloy substrate in a 10% sodium hydroxide solution at 18°C for 1 minute, and then rinse it in bubbling water for 5 minutes;

[0062] (4) Soaking the alkali-washed aluminum alloy substrate in a nitric acid solution with a temperature of 18° C. and a mass concentration of 20% for 5 minutes, and then washing it in bubbling water for 15 minutes to complete the pretreatment;

[0063] (5) The pre-treated aluminum alloy substrate is hard anodized and sealed.

[0064] Example 4

[0065] This embodiment provides a pretreatment method for reducing the roughness of a hard anodized film. Compared with Example 1, the temperatures of the pickling in step (2), the alkaline washing in step (3), and the pickling in step (4) are all controlled to be room temperature (25°C), and the rest are the same as in Example 1.

[0066] Example 5

[0067] This embodiment provides a pretreatment method for reducing the roughness of a hard anodized film. Compared with Example 1, the concentration of sodium hydroxide in step (3) is controlled to be 2%, and the rest is the same as Example 1.

[0068] Example 6

[0069] This embodiment provides a pretreatment method for reducing the roughness of a hard anodized film. Compared with Example 1, the concentration of sodium hydroxide in step (3) is controlled to be 13%, and the rest is the same as Example 1.

[0070] Example 7

[0071] This embodiment provides a pretreatment method for reducing the roughness of a hard anodized film. Compared with Example 1, the concentration of nitric acid in step (4) is controlled to be 5%, and the rest is the same as Example 1.

[0072] Example 8

[0073] This embodiment provides a pretreatment method for reducing the roughness of a hard anodized film. Compared with Example 1, the concentration of nitric acid in step (4) is controlled to be 25%, and the rest is the same as Example 1.

[0074] Comparative Example 1

[0075] This comparative example provides a pretreatment method for hard anodizing. Compared with Example 1, the polishing in step (1) is not performed, and the rest is the same as Example 1.

[0076] In this comparative example, the average roughness of the surface of the aluminum alloy substrate that was not polished was 0.9 μm.

[0077] Comparative Example 2

[0078] This comparative example provides a pretreatment method for hard anodizing. Compared with Example 1, the nitric acid pickling in step (2) is not performed, and the rest is the same as Example 1.

[0079] Comparative Example 3

[0080] This comparative example provides a pretreatment method for hard anodizing. Compared with Example 1, the nitric acid solution in step (2) is replaced by a sulfuric acid solution of equal concentration, and the rest is the same as Example 1.

[0081] Comparative Example 4

[0082] This comparative example provides a pretreatment method for hard anodizing. Compared with Example 1, the alkaline washing in step (3) is not performed, and the rest is the same as Example 1.

[0083] Comparative Example 5

[0084] This comparative example provides a pretreatment method for hard anodizing, which comprises the following steps:

[0085] (1) Grinding and polishing the aluminum alloy substrate;

[0086] (2) Soak the polished substrate in a degreasing agent solution with a temperature of 45°C and a mass concentration of 10% for 5 minutes. The degreasing agent is trisodium phosphate;

[0087] (3) Soak the degreased substrate in a mixed solution of nitric acid and hydrofluoric acid for 60 seconds, where the mass concentration of the mixed solution is 10% and the mass ratio of nitric acid to hydrofluoric acid is 1:1, and then rinse in bubbling water for 3 minutes;

[0088] (4) Soak the pickled substrate in a mixed solution of nitric acid and ferric sulfate for 3 minutes, where the mass concentration of the mixed solution is 10% and the mass ratio of nitric acid to ferric sulfate is 1:1, and then rinse in bubbling water for 3 minutes;

[0089] (5) Soak the substrate after cleaning with the mixed solution in a sodium hydroxide solution with a temperature of 45°C and a mass concentration of 8% for 50 seconds, and then rinse it in bubbling water for 3 minutes;

[0090] (6) The alkali-washed substrate was immersed in a mixed solution of nitric acid and ferric sulfate for 3 minutes, wherein the mass concentration of the mixed solution was 10% and the mass ratio of nitric acid to ferric sulfate was 1:1, and then placed in bubbling water for washing for 10 minutes.

[0091] In the examples and comparative examples, the surfaces of the ground and polished aluminum alloy substrate and the generated hard anodized film were uniformly distributed at 6 test points for roughness testing, and the average roughness value was calculated. The results are listed in Table 1.

[0092] The process parameters of hard anodizing include: the electrolyte is a sulfuric acid solution with a concentration of 150g / L, the current density is 4A / dm 2 , temperature is 5℃, time is 60min.

[0093] Table 1

[0094] Substrate roughness Hard anodized film roughness Example 1 0.322 1.080 Example 2 0.314 1.201 Example 3 0.304 1.102 Example 4 0.324 1.348 Example 5 0.341 1.304 Example 6 0.326 1.345 Example 7 0.334 1.325 Example 8 0.324 1.301 Comparative Example 1 0.9 2.057 Comparative Example 2 0.319 1.684 Comparative Example 3 0.337 1.598 Comparative Example 4 0.321 1.978 Comparative Example 5 0.333 1.310

[0095] As can be seen from Table 1:

[0096] The pretreatment method provided by the present invention first controls the surface roughness of the substrate by grinding and polishing, and then combines the pretreatment process of pickling-alkali washing-pickling to achieve the regulation and improvement of the surface microstructure of the substrate. On this basis, a hard anodized film is plated, and the roughness of the obtained hard anodized film is low, which effectively improves the performance and appearance of the hard anodized film. In Examples 1-3, the roughness of the hard anodized film is effectively controlled below 1.2, which effectively solves the technical problem of improving the roughness and appearance of the film layer after hard anodizing. Compared with Example 1, in Examples 4-8, when the temperature and the concentration of the acid or alkali in the pretreatment process are adjusted, even if the roughness of the substrate is maintained at a considerable level, the roughness of the obtained hard anodized film is still increased, and its effect on improving the surface microstructure of the substrate is low. In Comparative Examples 1-5, when the pretreatment process is changed, the roughness of the obtained hard anodized film is significantly deteriorated, making it difficult to meet the use requirements.

[0097] In summary, the pretreatment method provided by the present invention first grinds and polishes the surface of the substrate to preliminarily adjust the surface roughness, and then improves the microstructure of the substrate surface through specific acid washing and alkali washing processes, thereby reducing the roughness of the generated hard anodized film and improving the performance and appearance of the hard anodized film.

[0098] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A pretreatment method for reducing the roughness of a hard anodized film, characterized in that: The pretreatment method comprises the following steps: (1) grinding and polishing the substrate to obtain a surface-polished substrate; (2) performing a first pickling, an alkaline pickling, and a second pickling on the surface-polished substrate in sequence, wherein the first pickling uses nitric acid and the second pickling uses nitric acid to complete pretreatment; (3) The pretreated substrate is hard-anodized and sealed.

2. The pretreatment method according to claim 1, characterized in that The surface roughness of the surface polishing substrate is 0.1-0.4 μm.

3. The pretreatment method according to claim 1 or 2, characterized in that The temperature of the first pickling is 15-20°C; Preferably, the mass concentration of nitric acid in the first pickling is 10-20%.

4. The pretreatment method according to any one of claims 1 to 3, characterized in that The first pickling time is 5-15 minutes; Preferably, the first pickling method includes soaking.

5. The pretreatment method according to any one of claims 1 to 4, characterized in that The alkali washing uses sodium hydroxide; Preferably, the mass concentration of the sodium hydroxide is 5-10%.

6. The pretreatment method according to any one of claims 1 to 5, characterized in that: The temperature of the alkali washing is 15-20°C; Preferably, the alkali washing time is 1-5 min; Preferably, the alkali washing method includes soaking.

7. The pretreatment method according to any one of claims 1 to 6, characterized in that: The mass concentration of nitric acid in the second pickling is 10-20%; Preferably, the temperature of the second pickling is 15-20°C.

8. The pretreatment method according to any one of claims 1 to 7, characterized in that: The second pickling time is 5-15min; Preferably, the second pickling method includes soaking.

9. The pretreatment method according to any one of claims 1 to 8, characterized in that: The pretreatment method further comprises: performing a first water wash after the first acid wash, performing a second water wash after the alkali wash, and performing a third water wash after the second acid wash; Preferably, the first water washing time is 1-5 min; Preferably, the second water washing time is 1-5 min; Preferably, the third water washing time is 5-15 minutes.

10. The pretreatment method according to any one of claims 1 to 9, characterized in that: The pretreatment method comprises the following steps: (1) After grinding and polishing the substrate, the surface roughness of the substrate is controlled to be 0.1-0.4 μm to obtain a surface-polished substrate; (2) performing a first acid wash, a first water wash, an alkali wash, a second water wash, a second acid wash and a third water wash on the surface polished substrate in sequence to complete pretreatment, wherein the first acid wash is performed by soaking in nitric acid with a mass concentration of 10-20%, the temperature of the first acid wash is 15-20°C, the time of the first acid wash is 5-15min, the time of the first water wash is 1-5min, the alkali wash is performed by soaking in sodium hydroxide with a mass concentration of 5-10%, the temperature of the alkali wash is 15-20°C, the time of the alkali wash is 1-5min, the time of the second water wash is 1-5min, the second acid wash is performed by soaking in nitric acid with a mass concentration of 10-20%, the temperature of the second acid wash is 15-20°C, the time of the second acid wash is 5-15min, and the time of the third water wash is 5-15min; (3) The pretreated substrate is hard-anodized and sealed.