Anodic oxidation process optimization method for high-strength 7-series aluminum alloy

Abstract

The invention relates to an anodic oxidation process optimization method for a high-strength 7-series aluminum alloy, in particular to the technical field of aluminum alloy materials. The process sequentially comprises the steps of alkaline degreasing, electrochemical polishing, nitric acid bright dipping, anodic oxidation and nickel-free sealing. Wherein the anodic oxidation adopts a sulfuric acid-oxalic acid mixed electrolyte and is combined with a pulse direct-current power supply; the nickel-free sealing adopts zirconium-titanium composite salt and nano silicon dioxide sol for cooperative treatment. Through collaborative optimization of the process, the comprehensive effects that the oxidation time is shortened by 33%, the surface gloss is improved to 450-550 GS, and the method is completely free of nickel, environmentally friendly and excellent in corrosion resistance are successfully achieved, and the method is particularly suitable for manufacturing high-end electronic equipment appearance parts.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy materials technology, and in particular to an optimized method for the anodizing process of high-strength 7-series aluminum alloys. Background Technology

[0002] 7xxx series aluminum alloys (with Zn-Mg-Cu as the main strengthening elements) are widely used in aerospace, high-end electronic equipment, and precision machinery due to their ultra-high strength (tensile strength ≥480MPa), excellent mechanical properties, and lightweight characteristics. With the increasing demands of the consumer electronics industry for metal exterior components, the demand for anodized aluminum alloys, which combine high strength and excellent surface finish, has surged.

[0003] Existing anodizing processes have many problems: Efficiency bottleneck: Traditional sulfuric acid anodizing requires 50-60 minutes, has high energy consumption and limited production capacity, making it difficult to meet the needs of large-scale production; Environmental risks: The closed process generally uses nickel-containing solutions, which pose environmental pollution and compliance risks; Insufficient surface quality: It cannot meet the requirements of high-end electronic products for "mirror effect" (>500GS); Limited corrosion resistance: When the nickel salt-sealed oxide film is used for a long time in harsh environments (such as high humidity and high salt), there is still a risk of microporous corrosion. Summary of the Invention

[0004] (1) Technical solution To address the aforementioned technical problems, this invention provides an optimized method for the anodizing process of high-strength 7-series aluminum alloys, comprising the following steps: (1) Degreasing treatment: The aluminum alloy workpiece is treated with an alkaline degreasing solution containing 40-50 g / L sodium carbonate, 40-50 g / L sodium phosphate, 80-100 g / L sodium pyrophosphate, and 0.1-0.5 g / L OP-10 surfactant; the treatment temperature is 40-60℃ and the treatment time is 3-8 minutes. (2) Electrochemical polishing: The workpiece treated in step (1) is placed in an electrochemical polishing solution for electrochemical polishing. The polishing solution is a mixed acid solution composed of phosphoric acid and sulfuric acid in a volume ratio of 3:1. The current density is controlled at 12A / dm² and the polishing time is 2 minutes. (3) Neutralization and brightening: Immerse the workpiece treated in step (2) in a nitric acid solution with a concentration of 100-120 g / L and treat it at room temperature for 30-40 seconds; (4) Anodizing: The workpiece treated in step (3) is used as the anode and placed in an anodizing electrolyte for oxidation; the electrolyte contains 160-180 g / L of sulfuric acid and 15-25 g / L of oxalic acid; a pulsed DC power supply is used, the voltage is applied at 16-18V, the duty cycle is 70%, the electrolyte temperature is controlled at 18±1℃, and the oxidation time is 30-40 minutes; (5) Nickel-free sealing: The workpiece after oxidation in step (4) is immersed in a nickel-free sealant for sealing treatment; the sealant contains Zr 4 ⁺0.8-1.2g / L, Ti 4 Add 0.3-0.6 g / L of ⁺ and 5-10 g / L of nano silica sol as an additive; control the pH of the sealing tank solution to 5.0-6.0, the temperature to 40-45℃, and the sealing time to 15-20 minutes.

[0005] Preferably, the high-strength 7-series aluminum alloy comprises the following chemical composition by mass percentage: Si < 0.07%, Fe ≤ 0.12%, Cu 1.2-1.6%, Mn 0.07-0.17%, Mg 2.10-2.40%, Zr 0.003-0.012%, Zn 6.2-6.5%, Ti 0.003-0.020%, with the remainder being aluminum and unavoidable impurities.

[0006] Preferably, the aluminum ion concentration in the anodic oxidation electrolyte in step (4) is controlled to be ≤18g / L.

[0007] Preferably, the SiO2 particles in the nano-silica sol in step (5) have a particle size of 10-50 nm.

[0008] Preferably, the frequency of the pulsed DC power supply in step (4) is 50-100Hz.

[0009] Preferably, the high-strength 7-series aluminum alloy product obtained by the optimized anodizing process of the high-strength 7-series aluminum alloy has an anodized film on its surface, the thickness of the anodized film is 8-15μm, and the surface gloss is 450-550GS.

[0010] (2) Beneficial effects This invention optimizes the anodizing process, improving the efficiency, environmental friendliness, and alloy surface quality, achieving a short-process, pollution-free, and high-gloss anodizing effect for high-strength 7-series aluminum alloys.

[0011] 1. Significantly improve production efficiency: By adopting a sulfuric acid-oxalic acid mixed acid system and cooperating with pulse power supply technology, the anodizing time is shortened from the traditional 50-60 minutes to 30-40 minutes, improving efficiency by about 33%, and significantly reducing energy consumption and unit production costs.

[0012] 2. Achieving ultra-high surface gloss: The innovative introduction of electrochemical polishing as a pretreatment step fundamentally eliminates surface micro-defects caused by mechanical processing, laying a flat base for subsequent anodizing; combined with the more uniform and dense film structure generated by pulse oxidation and the filling polishing effect of nano-SiO2 particles, the final surface gloss reaches a high mirror effect of 450-550GS, which is about 20% higher than the traditional process.

[0013] 3. Excellent environmental friendliness and safety: Using zirconium-titanium / nano SiO2 composite nickel-free sealant, the toxic nickel salt is completely eliminated, thus eliminating the risk of heavy metal pollution and environmental compliance issues from the source, making it safer and more environmentally friendly.

[0014] 4. Enhanced corrosion resistance: The synergistic effect of nano-SiO2 sol and zirconium-titanium composite salt can more effectively fill the micropores of the oxide film, resulting in an extremely high sealing rate. This significantly improves the corrosion resistance of the oxide film under harsh environments, with no signs of corrosion after more than 500 hours of neutral salt spray testing.

[0015] 5. Excellent overall surface quality: The final anodic oxide film thickness is 8-15μm, the film layer is uniform, without color difference, and without defects such as "cloudiness" or "dullness", and the appearance quality is consistent. Detailed Implementation

[0016] To facilitate a better understanding of the present invention, the following examples are provided. These examples fall within the scope of protection of the present invention, but do not limit the scope of protection of the present invention. Example 1:

[0017] Take a sample of 7-series aluminum alloy that meets the composition requirements (Si: 0.05%, Fe: 0.10%, Cu: 1.5%, Mn: 0.12%, Mg: 2.25%, Zr: 0.008%, Zn: 6.4%, Ti: 0.015%, Al: balance).

[0018] Degreasing: Treat in an alkaline solution containing 45 g / L sodium carbonate, 45 g / L sodium phosphate, 90 g / L sodium pyrophosphate, and 0.3 g / L OP-10 at 50°C for 5 minutes, then wash with water.

[0019] Electrochemical polishing: Polish for 2 minutes in a phosphoric acid-sulfuric acid (3:1 volume ratio) mixture at a current density of 12 A / dm², followed by rinsing with water.

[0020] Neutralization and brightening: Soak in 110 g / L nitric acid solution at room temperature for 35 seconds, then wash with water.

[0021] Anodizing: In an electrolyte containing 170 g / L sulfuric acid and 20 g / L oxalic acid, oxidize at 18°C ​​for 35 minutes (Al ion concentration maintained at 15 g / L) using a pulsed DC power supply (voltage 17 V, duty cycle 70%), followed by rinsing with water.

[0022] Nickel-free sealing: In Zr-containing 4 ⁺1.0g / L, Ti 4 The sample was placed in a blocking solution of 0.5 g / L nano-SiO2 sol (particle size 20 nm) and 8 g / L (pH=5.5) at 42°C for 18 minutes, then washed with water and dried.

[0023] Performance testing: The sample surface gloss was 510GS, the oxide film thickness was 12μm, the color was uniform, and there were no defects. After 528 hours of neutral salt spray testing (ASTM B117), no pitting or corrosion spots were observed, demonstrating excellent corrosion resistance. Example 2:

[0024] Aluminum alloy composition: Same as in Example 1.

[0025] Degreasing: Sodium carbonate 40g / L, sodium phosphate 40g / L, sodium pyrophosphate 80g / L, OP-10 0.1g / L, treated at 40℃ for 8 minutes.

[0026] Electrochemical polishing: Same as in Example 1.

[0027] Neutralization and luminescence: 100 g / L nitric acid, treated at room temperature for 40 seconds.

[0028] Anodizing: The electrolyte is 160g / L sulfuric acid + 15g / L oxalic acid; pulse voltage 16V, duty cycle 70%, bath temperature 17℃, oxidation for 40 minutes (Al ion concentration ≦10g / L).

[0029] Nickel-free sealing: sealing solution contains Zr 4 ⁺0.8g / L,Ti 4 ⁺ 0.3 g / L, nano SiO2 sol 5 g / L, pH=5.0, blocked at 40℃ for 20 minutes.

[0030] Results: Gloss level 465GS, film thickness 9μm, uniform surface. Passed NSS test after 500 hours. This demonstrates that superior results compared to traditional processes can still be achieved at the lower limit of parameters. Example 3:

[0031] Aluminum alloy composition: Same as in Example 1.

[0032] Degreasing: Sodium carbonate 50g / L, sodium phosphate 50g / L, sodium pyrophosphate 100g / L, OP-10 0.5g / L, treated at 60℃ for 3 minutes.

[0033] Electrochemical polishing: Same as in Example 1.

[0034] Neutralization and brightening: 120 g / L nitric acid, treated at room temperature for 30 seconds.

[0035] Anodizing: The electrolyte is 180g / L sulfuric acid + 25g / L oxalic acid; pulse voltage 18V, duty cycle 70%, bath temperature 19℃, oxidation for 30 minutes (Al ion concentration ≈ 18g / L).

[0036] Nickel-free sealing: sealing solution contains Zr 4 ⁺1.2g / L,Ti 4 ⁺ 0.6 g / L, nano SiO2 sol 10 g / L, pH=6.0, blocked at 45℃ for 15 minutes.

[0037] Results: Gloss level 495GS, film thickness 14.5μm, dense film layer. No corrosion after 550 hours of NSS testing. This demonstrates that a thicker, highly corrosion-resistant film layer can be obtained at the upper limit of the parameters, with higher efficiency (30 minutes). Example 4:

[0038] Aluminum alloy composition (mass percentage, slightly adjusted to verify suitability): Si: 0.06%, Fe: 0.12%, Cu: 1.2%, Mn: 0.17%, Mg: 2.10%, Zr: 0.012%, Zn: 6.2%, Ti: 0.020%, Al: balance. (The composition is within the boundaries of the claims.) Process parameters: Same as in Example 1.

[0039] Results: Gloss level 500GS, film thickness 11μm. No corrosion observed after 515 hours of NSS testing. This demonstrates that the process of this invention still provides excellent and stable treatment results for alloys with compositions finely adjusted within the required range. Example 5:

[0040] Aluminum alloy composition: Same as in Example 1.

[0041] Degreasing, polishing, and brightening: Same as in Example 1.

[0042] Anodizing: The electrolyte is 165g / L sulfuric acid + 22g / L oxalic acid; pulse voltage 17V, duty cycle 70%, bath temperature 18℃, oxidation for 38 minutes.

[0043] Nickel-free sealing: sealing solution contains Zr 4 ⁺0.9g / L,Ti 4 ⁺ 0.4 g / L, nano-SiO2 sol (particle size 10 nm) 9 g / L, pH=5.2, blocked at 41℃ for 19 minutes. (Note: The amount of nano-SiO2 added and the particle size were slightly increased, focusing on improving gloss.) Results: Gloss reached 545GS (excellent mirror finish), film thickness 13μm. Passed NSS test after 510 hours. This demonstrates that gloss performance can be further optimized by fine-tuning the sealing agent parameters.

[0044] Comparative Example Aluminum alloy composition: Same as in Example 1.

[0045] Degreasing and light extraction: same as Example 1.

[0046] Anodizing: The electrolyte is sulfuric acid 180g / L; DC power supply is used, voltage is 16V, bath temperature is 20℃, and oxidation time is 55 minutes.

[0047] Sealing: Traditional nickel acetate sealing solution (Ni²⁺: 5g / L, 80℃, 20 minutes, pH 5.6) was used.

[0048] Results: Gloss level 380GS, film thickness 15μm, surface slightly hazy. Obvious pitting appeared after 360 hours of NSS testing.

[0049] Conclusion: The comparison between Examples 2-5 and the comparative examples fully demonstrates that the process solution provided by this invention has excellent reproducible effects over a wide range of parameters and compositions. Whether using the upper limit, lower limit, or intermediate values ​​of the parameters, a high-quality surface with a gloss level exceeding 450GS and resistance to neutral salt spray corrosion exceeding 500 hours can be consistently obtained. The overall performance significantly surpasses traditional nickel sealing processes, perfectly achieving the design objectives of this invention: short process, high gloss, no pollution, and high corrosion resistance.

[0050] The above content should not be construed as limiting the specific implementation of this invention to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of this invention, and all such deductions or substitutions should be considered as falling within the patent protection scope defined by the submitted claims.

Claims

1. An optimized method for the anodizing process of high-strength 7-series aluminum alloys, characterized in that, Includes the following steps: (1) Degreasing treatment: The aluminum alloy workpiece is treated with an alkaline degreasing solution containing 40-50 g / L sodium carbonate, 40-50 g / L sodium phosphate, 80-100 g / L sodium pyrophosphate, and 0.1-0.5 g / L OP-10 surfactant; the treatment temperature is 40-60℃ and the treatment time is 3-8 minutes. (2) Electrochemical polishing: The workpiece treated in step (1) is placed in an electrochemical polishing solution for electrochemical polishing. The polishing solution is a mixed acid solution composed of phosphoric acid and sulfuric acid in a volume ratio of 3:

1. The current density is controlled at 12A / dm² and the polishing time is 2 minutes. (3) Neutralization and brightening: Immerse the workpiece treated in step (2) in a nitric acid solution with a concentration of 100-120 g / L and treat it at room temperature for 30-40 seconds; (4) Anodizing: The workpiece treated in step (3) is used as the anode and placed in an anodizing electrolyte for oxidation; the electrolyte contains 160-180 g / L of sulfuric acid and 15-25 g / L of oxalic acid; a pulsed DC power supply is used, the voltage is applied at 16-18V, the duty cycle is 70%, the electrolyte temperature is controlled at 18±1℃, and the oxidation time is 30-40 minutes; (5) Nickel-free sealing: The workpiece after oxidation in step (4) is immersed in a nickel-free sealant for sealing treatment; the sealant contains Zr 4 ⁺0.8-1.2g / L, Ti 4 Add 0.3-0.6 g / L of ⁺ and 5-10 g / L of nano silica sol as an additive; control the pH of the sealing tank solution to 5.0-6.0, the temperature to 40-45℃, and the sealing time to 15-20 minutes.

2. The method for optimizing the anodizing process of high-strength 7-series aluminum alloys as described in claim 1, characterized in that, The high-strength 7-series aluminum alloy comprises the following chemical composition by mass percentage: Si < 0.07%, Fe ≤ 0.12%, Cu 1.2-1.6%, Mn 0.07-0.17%, Mg 2.10-2.40%, Zr 0.003-0.012%, Zn 6.2-6.5%, Ti 0.003-0.020%, with the remainder being aluminum and unavoidable impurities.

3. The optimized anodizing process method for high-strength 7-series aluminum alloys according to claim 1, characterized in that, The aluminum ion concentration in the anodic oxidation electrolyte in step (4) is controlled to be ≤18g / L.

4. The optimized anodizing process method for high-strength 7-series aluminum alloys according to claim 1, characterized in that, The SiO2 particles in the nano silica sol described in step (5) have a particle size of 10-50 nm.

5. The optimized anodizing process method for high-strength 7-series aluminum alloys according to claim 1, characterized in that, The frequency of the pulsed DC power supply mentioned in step (4) is 50-100Hz.

6. The high-strength 7-series aluminum alloy product obtained by the optimization method according to any one of claims 1-5, characterized in that, Its surface has an anodic oxide film with a thickness of 8-15 μm and a surface gloss of 450-550 GS.