Surface treatment process for an aluminum alloy

Abstract

This invention relates to a surface treatment process for aluminum alloys, comprising the following steps: S1 degreasing; S2 alkaline etching; S3 neutralization; S4 chemical polishing; S5 anodizing: placing the aluminum alloy substrate after the chemical polishing treatment in step S4 into an anodizing solution for anodizing, wherein the anodizing solution is a sulfuric acid solution with a mass concentration of 180-190 g / L; S6 electrolysis: placing the aluminum alloy substrate after anodizing in step S5 into a potassium sodium tartrate solution with a mass concentration of 10-13 g / L for electrolysis; S7 sealing: placing the electrolyzed aluminum alloy substrate into a sealing agent with a mass concentration of 12-15 g / L for sealing. The surface treatment process for aluminum alloys described in this invention, by placing the aluminum alloy substrate after anodizing with sulfuric acid into a potassium sodium tartrate solution for electrolysis, reduces the obscuring of the aluminum alloy's natural color by the oxide film, resulting in an appearance color effect of the aluminum alloy product that is close to or consistent with the natural color of the aluminum alloy; the surface treatment process for aluminum alloys is easy to control and readily available.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy product processing technology, and in particular to a surface treatment process for aluminum alloys. Background Technology

[0002] With the diversification of metal surface treatment colors and the demand for personalization, aluminum alloy profiles that closely resemble or match the natural color of aluminum alloy are widely favored by consumers due to their unique metallic luster. However, during the surface treatment of aluminum alloys, the oxide film formed on the surface of the aluminum alloy substrate through anodizing can obscure the original color of the aluminum alloy substrate to varying degrees, preventing the final aluminum alloy product from achieving the desired technical effect. Summary of the Invention

[0003] The purpose of this invention is to solve the above-mentioned problems and provide a surface treatment process for aluminum alloys.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0005] A surface treatment process for aluminum alloys includes the following steps:

[0006] S1 Degreasing: The aluminum alloy substrate is immersed in a degreasing agent for degreasing;

[0007] S2 Alkaline Etching: The aluminum alloy substrate degreased in step S1 is placed in an alkaline solution for alkaline etching.

[0008] S3 Neutralization: The aluminum alloy substrate after alkaline etching in step S2 is immersed in a desiccant for neutralization;

[0009] S4 Chemical Polishing: The aluminum alloy substrate after the neutralization treatment in step S3 is placed in a chemical polishing agent for chemical polishing.

[0010] S5 Anodizing: The aluminum alloy substrate after the chemical polishing treatment in step S4 is placed in an anodizing solution for anodizing treatment. The anodizing solution is a sulfuric acid solution with a mass concentration of 180-190 g / L.

[0011] S6 Electrolysis: The aluminum alloy substrate anodized in step S5 is placed in a 10-13 g / L sodium potassium tartrate (NaKC4H4O6) solution for electrolysis. Sodium potassium tartrate is a colorless, semi-transparent crystalline powder with a pH of 6.8-8, is weakly alkaline, and is readily soluble in water. During electrolysis, the overall reaction is 2H2O → 2H2 + O2, and the reaction at the anode is 4OH-. - -4e - →O2 + 2H2O; Cathode reaction: 4H2O → 2H2 + 4OH- -When an anodized aluminum alloy substrate is placed in a potassium sodium tartrate solution and an electric current is passed through it, Al₂O₃ + 2OH⁻ → Al₂O₃ + 2OH⁻ - +3H₂O→2[Al(OH)₄] - ;

[0012] S7 Sealing: The electrolyzed aluminum alloy substrate is placed in a sealing agent with a mass concentration of 12-15 g / L for sealing.

[0013] Preferably, in step S1, the degreasing temperature is 55-65℃, the degreasing time is 4-6 min, and the mass concentration of the degreasing agent is 50-60 g / L.

[0014] Preferably, in step S1, the aluminum alloy substrate is made of 6-series aluminum alloy.

[0015] More preferably, the aluminum alloy substrate is made from alloy type 6023. In practical operation, the inventors discovered that the oxide film formed after anodizing an aluminum alloy substrate made from aluminum-manganese alloy is brownish-yellow or even brown; the oxide film formed after anodizing an aluminum alloy substrate made from aluminum-zinc alloy is opaque grayish-black; and the oxide film formed after anodizing an aluminum alloy substrate made from aluminum-silicon alloy or aluminum-copper alloy is gray, and when the silicon mass fraction is greater than 2%, the oxide film appears gray to black.

[0016] Preferably, in step S2, the alkaline etching temperature is 50-60℃, the alkaline etching time is 8-15s, and the alkaline solution includes a sodium hydroxide (NaOH) solution with a mass concentration of 50-60g / L.

[0017] Preferably, in step S3, the ash removal agent includes a nitrogen-free ash removal agent with a mass concentration of 180-200 g / L and a neutralization time of 3-5.5 min.

[0018] Preferably, in step S4, the chemical polishing agent includes one or a mixture of sulfuric acid solution and phosphoric acid solution, with a mass concentration of 170-200 g / L; the chemical polishing temperature is 75-80℃, the chemical polishing time is 45-55 s, and the gloss of the aluminum alloy substrate at 60° after chemical polishing is 70±5%. Too short a polishing time will not achieve the desired polishing effect, while too long a polishing time will affect the important dimensions of the aluminum alloy. Higher sulfuric acid concentration and higher temperature result in faster polishing speed, but excessively high sulfuric acid concentration can lead to uneven gloss in the product due to excessively fast polishing speed. To increase the aluminum ion content during chemical polishing, it can be incorporated into the aluminum plate to provide an appropriate aluminum ion content, depending on the actual operating conditions.

[0019] Preferably, the anodizing temperature is 15-20℃, the anodizing voltage is 10-15V, and the anodizing time is 50-60min.

[0020] Preferably, the electrolysis temperature is 15-20℃, the electrolysis voltage is 10-15V (DC), and the electrolysis time is 5-8min. The electrolysis voltage and time should not be too high, as excessively high voltage and temperature will result in a b-value greater than 2.5.

[0021] Preferably, the sealing temperature is 85-95℃ and the sealing time is 60-90 min. The sealing time affects the stability of the b-value. If the sealing time is too short, the b-value is unstable. When the sealing temperature is greater than 60 min, the b-value is stable. Considering the final quality of aluminum alloy products and energy conservation and environmental protection, the sealing time is preferably 60-90 min.

[0022] The beneficial effects of this invention include at least the following:

[0023] The surface treatment process for aluminum alloys described in this invention involves electrolyzing an aluminum alloy substrate that has undergone sulfuric acid anodizing in a potassium sodium tartrate solution. This reduces the current in the oxide film during electrolysis, thereby lowering the b-value of the aluminum alloy product's color. This, in turn, reduces the yellow tint of the oxide film formed after anodizing, lessening the obscuring of the aluminum alloy's natural color by the anodized film. This results in an appearance color effect that closely resembles or matches the natural color of the aluminum alloy. Furthermore, potassium sodium tartrate is a colorless, semi-transparent crystalline powder, preventing the introduction of other impurities into the oxide film during electrolysis. The surface treatment process for aluminum alloys described in this invention is easy to control and readily available. Attached Figure Description

[0024] Figure 1 This is a flowchart of the surface treatment process for the aluminum alloy of the present invention; Detailed Implementation

[0025] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0027] Example 1

[0028] like Figure 1 As shown, a surface treatment process for aluminum alloy includes the following steps:

[0029] S1 Degreasing: The aluminum alloy substrate is immersed in a degreasing agent for degreasing; wherein, the aluminum alloy substrate is made of alloy of type 6023; the degreasing temperature is 55℃, the degreasing time is 5min, the mass concentration of the degreasing agent is 50g / L, and the degreasing agent is preferably Okuno 161 degreasing powder; Okuno 161 degreasing powder is a weakly alkaline and low-corrosive degreasing agent. During use, due to its low corrosiveness, it will not damage the gloss of the aluminum alloy substrate. At the same time, due to its low foaming properties, it can be operated by air agitation or spraying, and the requirements for the degreasing treatment environment are low.

[0030] S2 Alkaline Etching: The aluminum alloy substrate after degreasing in step S1 is placed in an alkaline solution for alkaline etching; the alkaline etching temperature is 55℃ and the alkaline etching time is 10s, and the alkaline solution includes a NaOH solution with a mass concentration of 60g / L.

[0031] S3 Neutralization: The aluminum alloy substrate after alkaline etching in step S2 is immersed in a desiccant for neutralization; the desiccant includes a nitrogen-free desiccant with a mass concentration of 200 g / L, the neutralization time is 3 min, and the neutralization process is carried out at room temperature;

[0032] S4 Chemical Polishing: The aluminum alloy substrate, after neutralization treatment in step S3, is placed in a chemical polishing agent for chemical polishing. The chemical polishing agent is a mixed solution of sulfuric acid and phosphoric acid, with a mass concentration of 180 g / L. The phosphoric acid has a mass concentration of 1000-1200 g / L, and the sulfuric acid has a mass concentration of 150-250 g / L. The chemical polishing temperature is 78℃, the polishing time is 45 seconds, and the gloss level of the aluminum alloy substrate after chemical polishing is 70±5% at 60°. The gloss level is measured using a German BYK gloss meter at a 60° illumination angle.

[0033] S5 Anodizing: The aluminum alloy substrate after the chemical polishing treatment in step S4 is placed in an anodizing solution for anodizing treatment. The anodizing solution is a sulfuric acid solution with a mass concentration of 180 g / L. The anodizing temperature is 17℃, the anodizing voltage is 12V, and the anodizing time is 50 min.

[0034] S6 Electrolysis: The aluminum alloy substrate after anodizing in step S5 is placed in a potassium sodium tartrate solution with a mass concentration of 10 g / L for electrolysis; the electrolysis temperature is 15-18℃, the electrolysis voltage is 15V (DC), and the electrolysis time is 5 min.

[0035] S7 Sealing: To improve the corrosion resistance, stain resistance, stability, light resistance, and weather resistance of the wood grain aluminum alloy, a sealing treatment is performed. The electrolyzed aluminum alloy substrate is placed in a sealing agent with a mass concentration of 15 g / L for sealing; the sealing temperature is 90℃, and the sealing time is 40 min; preferably, the sealing agent is a nickel-free sealing agent, and more preferably, the nickel-free sealing agent includes Okuno E110 sealing agent. The aluminum alloy product obtained through the surface treatment process of the aluminum alloy described in this invention can be used in the housing of electronic devices, such as the cover or frame of a mobile phone.

[0036] Optionally, the sealing process may include a drying or baking step to dry the aluminum alloy.

[0037] Example 2

[0038] Compared with Example 1, the surface treatment process of aluminum alloy described in Example 2 includes the same steps, but the difference is:

[0039] S1 Degreasing: The degreasing temperature is 65℃, the degreasing time is 4min, the mass concentration of the degreasing agent is 60g / L, and the degreasing agent is preferably Okuno 161 degreasing powder;

[0040] S2 Alkaline Etching: The alkaline etching temperature is 60℃, and the alkaline etching time is 8s. The alkaline solution includes a NaOH solution with a mass concentration of 50g / L.

[0041] S3 Neutralization: The ash removal agent includes a nitrogen-free ash removal agent with a mass concentration of 180 g / L, and the neutralization time is 4 min. The neutralization treatment step is carried out at room temperature.

[0042] S4 Chemical Polishing: The aluminum alloy substrate, after neutralization treatment in step S3, is placed in a chemical polishing agent for chemical polishing. The chemical polishing agent is a mixed solution of sulfuric acid and phosphoric acid, with a mass concentration of 190 g / L. Specifically, the mass concentration of phosphoric acid is 1000-1200 g / L, and the mass concentration of sulfuric acid is 150-250 g / L. The chemical polishing temperature is 80℃, the polishing time is 50 seconds, and the gloss level of the aluminum alloy substrate after chemical polishing is 70±5% at 60°. The gloss level is measured using a German BYK gloss meter at a 60° illumination angle.

[0043] S5 Anodizing: The anodizing solution is a sulfuric acid solution with a mass concentration of 190 g / L; the anodizing temperature is 15℃, the anodizing voltage is 15V, and the anodizing time is 55 min;

[0044] S6 Electrolysis: The aluminum alloy substrate after anodizing in step S5 is placed in a potassium sodium tartrate solution with a mass concentration of 13 g / L for electrolysis; the electrolysis temperature is 15℃, the electrolysis voltage is 8V (DC), and the electrolysis time is 8 min.

[0045] S7 Sealing: The electrolyzed aluminum alloy substrate is placed in a sealing agent with a mass concentration of 12g / L for sealing; the sealing temperature is 84℃ and the sealing time is 30min; preferably, the sealing agent is a nickel-free sealing agent, and more preferably, the nickel-free sealing agent includes Okuno E110 sealing agent.

[0046] Example 3

[0047] Compared with Example 1, the surface treatment process of aluminum alloy described in Example 3 includes the same steps, but the difference is:

[0048] S1 Degreasing: The degreasing temperature is 60℃, the degreasing time is 6min, the mass concentration of the degreasing agent is 55g / L, and the degreasing agent is preferably Okuno 161 degreasing powder;

[0049] S2 Alkaline Etching: The alkaline etching temperature is 50℃, the alkaline etching time is 15s, and the alkaline solution includes a NaOH solution with a mass concentration of 55g / L;

[0050] S3 Neutralization: The ash removal agent includes a nitrogen-free ash removal agent with a mass concentration of 190 g / L, and the neutralization time is 5.5 min. The neutralization treatment step is carried out at room temperature.

[0051] S4 Chemical Polishing: The aluminum alloy substrate, after neutralization treatment in step S3, is placed in a chemical polishing agent for chemical polishing. The chemical polishing agent is a mixed solution of sulfuric acid and phosphoric acid, with a mass concentration of 200 g / L. The phosphoric acid has a mass concentration of 1000-1200 g / L, and the sulfuric acid has a mass concentration of 150-250 g / L. The chemical polishing temperature is 75℃, the polishing time is 55 seconds, and the gloss level of the aluminum alloy substrate after chemical polishing is 70±5% at 60°. The gloss level is measured using a German BYK gloss meter at a 60° illumination angle.

[0052] S5 Anodizing: The anodizing solution is a sulfuric acid solution with a mass concentration of 180 g / L; the anodizing temperature is 20℃, the anodizing voltage is 10V, and the anodizing time is 60 min;

[0053] S6 Electrolysis: The aluminum alloy substrate after anodizing in step S5 is placed in a potassium sodium tartrate solution with a mass concentration of 12 g / L for electrolysis; the electrolysis temperature is 20℃, the electrolysis voltage is 10V (DC), and the electrolysis time is 7 min.

[0054] S7 Sealing: The electrolyzed aluminum alloy substrate is placed in a sealing agent with a mass concentration of 14 g / L for sealing; the sealing temperature is 95°C and the sealing time is 60 min; preferably, the sealing agent is a nickel-free sealing agent, and more preferably, the nickel-free sealing agent includes Okuno E110 sealing agent.

[0055] Comparative Example 1

[0056] Compared with Example 1, the surface treatment process of aluminum alloy in Comparative Example 1 includes the same steps, except that: during electrolysis, the aluminum alloy substrate after anodizing in step S5 is placed in a mixed solution of potassium sodium tartrate with a mass concentration of 10 g / L and sulfuric acid with a mass concentration of 90 g / L.

[0057] Comparative Example 2

[0058] Compared with Example 1, the surface treatment process of aluminum alloy in Comparative Example 2 includes the same steps, except that: during electrolysis, the aluminum alloy substrate after anodizing in step S5 is placed in a mixed solution of potassium sodium tartrate with a mass concentration of 10 g / L and boric acid with a mass concentration of 5 g / L.

[0059] Comparative Example 3

[0060] Compared with Example 1, the surface treatment process of aluminum alloy in Comparative Example 3 includes the same steps, except that: during electrolysis, the aluminum alloy substrate after anodizing in step S5 is placed in an ammonium tartrate solution with a mass concentration of 10 g / L.

[0061] Comparative Example 4

[0062] Compared with Example 1, the surface treatment process of aluminum alloy in Comparative Example 4 includes the same steps, except that: during electrolysis, the aluminum alloy substrate after anodizing in step S5 is placed in a mixed solution of ammonium tartrate with a mass concentration of 10 g / L and citric acid with a mass concentration of 10 g / L.

[0063] Comparative Example 5

[0064] Compared with Example 1, the difference in the surface treatment process of aluminum alloy in Comparative Example 5 is that Comparative Example 5 does not include an electrolysis step, and the aluminum alloy substrate after anodizing in step S5 is directly sealed.

[0065] The appearance and color of aluminum alloy products obtained using the surface treatment processes described in Examples 1-3 and Comparative Examples 1-5 were tested, and the color parameters were expressed in Lab mode. The b-values ​​of the aluminum alloy products obtained in Examples 1-3 were 1.57, 1.64, and 1.75, respectively; it can be seen that the b-value of the aluminum alloy products obtained using the technical solution of the present invention is less than 1.8, and can reach as low as about 1.5; the b-values ​​of the aluminum alloy products obtained in Comparative Examples 1-5 were 1.9, 1.82, 1.92, 2.08, and 2.84, respectively.

[0066] Comparing the b-values ​​of Comparative Examples 3 and 4 with those of Example 1, it can be seen that under the same electrolysis conditions, the aluminum alloy product with and without potassium sodium tartrate has a lower b-value. This is because potassium sodium tartrate, as a carboxylate containing two hydroxyl groups, partially reacts to form tartaric acid under acidic conditions. Tartaric acid has excellent complexing and buffering properties, and its addition as an organic acid effectively reduces the dissolution of the generated oxide film by sulfuric acid. Furthermore, the conductivity of organic acids is significantly lower than that of sulfuric acid. In summary, under the same voltage conditions, the current is relatively lower with and without potassium sodium tartrate, naturally resulting in a lower b-value.

[0067] As can be seen from the b-value of Comparative Example 5, the b-value reaches 2.5 or higher without electrolytic treatment. Therefore, compared with Example 1, the b-values ​​of the aluminum alloy products obtained in the comparative examples are all greater than 1.8. A smaller b-value results in a lighter yellow hue in the oxide film formed after anodizing. This allows the oxide film to protect the aluminum alloy substrate while reducing the yellow hue's obscuring of the substrate's color. Consequently, the appearance of the aluminum alloy product obtained by this invention is closer to or consistent with the natural color of aluminum alloy, giving it a metallic silver appearance.

[0068] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0069] The above embodiments merely illustrate preferred implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention should be determined by the appended claims.

Claims

1. A surface treatment process for aluminum alloys, characterized in that, Including the following steps: S1 Degreasing: The aluminum alloy substrate is immersed in a degreasing agent for degreasing; S2 Alkaline Etching: The aluminum alloy substrate degreased in step S1 is placed in an alkaline solution for alkaline etching. S3 Neutralization: The aluminum alloy substrate after alkaline etching in step S2 is immersed in a desiccant for neutralization; S4 Chemical Polishing: The aluminum alloy substrate after the neutralization treatment in step S3 is placed in a chemical polishing agent for chemical polishing. S5 Anodizing: The aluminum alloy substrate after the chemical polishing treatment in step S4 is placed in an anodizing solution for anodizing treatment. The anodizing solution is a sulfuric acid solution with a mass concentration of 180-190 g / L. S6 Electrolysis: The aluminum alloy substrate after anodizing in step S5 is placed in a potassium sodium tartrate solution with a mass concentration of 10-13 g / L for electrolysis. S7 Sealing: The electrolyzed aluminum alloy substrate is placed in a sealing agent with a mass concentration of 12-15 g / L for sealing. The anodizing temperature is 15-20℃, the anodizing voltage is 10-15V, and the anodizing time is 50-60min. The electrolysis temperature is 15-20℃, the electrolysis voltage is 10-15V, and the electrolysis time is 5-8min.

2. The surface treatment process for aluminum alloys according to claim 1, characterized in that: In step S1, the degreasing temperature is 55-65℃, the degreasing time is 4-6 min, and the mass concentration of the degreasing agent is 50-60 g / L.

3. The surface treatment process for aluminum alloys according to claim 1, characterized in that: In step S1, the aluminum alloy substrate is made of 6-series aluminum alloy.

4. The surface treatment process for aluminum alloys according to claim 1, characterized in that: The aluminum alloy substrate is made from alloy with model number 6023.

5. The surface treatment process for aluminum alloys according to claim 1, characterized in that: In step S2, the alkaline etching temperature is 50-60℃, the alkaline etching time is 8-15s, and the alkaline solution includes a sodium hydroxide solution with a mass concentration of 50-60g / L.

6. The surface treatment process for aluminum alloys according to claim 1, characterized in that: In step S3, the ash removal agent includes a nitrogen-free ash removal agent with a mass concentration of 180-200 g / L and a neutralization time of 3-5.5 min.

7. The surface treatment process for aluminum alloys according to claim 1, characterized in that: In step S4, the chemical polishing agent includes one or a mixture of sulfuric acid solution or phosphoric acid solution, and the mass concentration of the chemical polishing agent is 170-200 g / L; the chemical polishing temperature is 75-80℃, the chemical polishing time is 45-55s, and the gloss of the aluminum alloy substrate after chemical polishing is 70±5% at 60°.

8. The surface treatment process for aluminum alloys according to claim 1, characterized in that: The sealing temperature is 85-95℃, and the sealing time is 60-90 minutes.

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