Method for improving appearance and corrosion resistance of anodized surface of cast aluminum alloy

Abstract

The invention relates to the technical field of aluminum alloy surface treatment, in particular to a method for improving cast aluminum alloy anodic oxidation surface appearance and corrosion resistance, which comprises the following operation steps: adding a proper amount of Al-10Sr when a cast aluminum alloy sample is prepared, so that the content of Sr in the cast aluminum alloy sample is 100-300ppm; the surface of a cast aluminum alloy sample is firstly subjected to alkali washing treatment and then subjected to acid washing treatment, the surface of the cast aluminum alloy sample is subjected to anodic oxidation, specific pulse voltage is applied, and an oxidation film is generated on the surface of the cast aluminum alloy sample; the cast aluminum alloy sample subjected to anodic oxidation is cleaned; the cleaned cast aluminum alloy sample is subjected to dyeing treatment; and the dyed cast aluminum alloy sample is subjected to hole sealing treatment. The invention provides a simple experiment method, and the whole operation process is convenient. The anodic oxidation treatment is performed by adopting the pulse voltage, so that an oxidation film can uniformly grow, and the surface appearance and the corrosion resistance of the cast aluminum alloy after anodic oxidation are improved.

Description

Technical Field

[0001] The invention relates to the technical field of surface treatment of cast aluminum alloys, and in particular to a method for improving the appearance of anodized surfaces of cast aluminum alloys. Background Art

[0002] Cast aluminum alloys are widely used in aerospace, automobile manufacturing, and 5G base stations due to their light weight, high strength, and corrosion resistance. In order to further improve the corrosion resistance and aesthetics of cast aluminum alloys, anodizing is a commonly used surface treatment method. However, while traditional anodizing improves corrosion resistance, it often fails to effectively improve the surface appearance, resulting in a rough surface of the finished product, which affects the appearance and subsequent use. The main problems with the anodizing of cast aluminum alloys are: 1. Most of the existing anodizing technologies for cast aluminum alloys use higher voltages or mixed acid electrolytes such as sulfuric acid and phosphoric acid or oxalic acid or tartaric acid. Although higher voltages or mixed acid electrolytes can provide faster reaction rates and more high-temperature resistant oxide films, the thickness and temperature control are more complicated due to the violent reaction. In addition, the use of mixed acid electrolytes has higher corrosion resistance requirements for process equipment, increases the difficulty of waste liquid treatment and environmental pressure, and puts higher requirements on the safety of workers. It is still not suitable for large-scale industrial production. 2. The existing pre-treatment of cast aluminum alloy anodizing introduces complex pre-treatments such as multiple pickling and mechanical polishing to improve the surface appearance of cast aluminum. The complex multi-step process not only increases production costs, but also makes quality control more difficult. 3. The existing optimization of cast aluminum alloy anodizing technology is mostly limited to the optimization of anodizing process, without considering the impact of material optimization on anodizing effect, so the improvement of the final corrosion resistance and surface effect of cast aluminum alloy is limited. Therefore, the existing technology needs to be improved and developed. Summary of the invention

[0003] The purpose of the present invention is to provide a method for improving the appearance and corrosion resistance of the anodized surface of cast aluminum alloy in order to solve the above problems. The present invention effectively improves the uniformity and density of the oxide film by adding Sr element and coordinating pulse voltage treatment, improves the chromaticity and brightness of the cast aluminum alloy oxide film surface after dyeing, and improves the appearance and corrosion resistance of the oxide film surface.

[0004] The technical solution to achieve the purpose of the present invention is: a method for improving the appearance of anodized surface of cast aluminum alloy, comprising the following steps:

[0005] Step 1, adding an appropriate amount of Al-10Sr when preparing a cast aluminum alloy sample;

[0006] Step 2, the surface of the cast aluminum alloy sample is first subjected to alkali washing and then to acid washing to remove surface oil, impurities, oxides, etc.;

[0007] Step 3, anodizing the surface of the cast aluminum alloy sample and applying a specific pulse voltage to form an oxide film on the surface of the cast aluminum alloy;

[0008] Step 4, cleaning the cast aluminum alloy sample after anodizing;

[0009] Step 5, dyeing the cast aluminum alloy sample after cleaning;

[0010] Step 6, sealing the cast aluminum alloy sample after the dyeing treatment.

[0011] In step 1 of the above technical solution, a proper amount of Al-10Sr is added when preparing the cast aluminum alloy sample, so that the Sr content in the cast aluminum alloy sample is 100-300ppm. The cast aluminum alloy is an Al-Si cast aluminum alloy with a silicon content of 2.5% to 12.5%.

[0012] The present invention has found that after adding 100-300ppm Sr in coordination with pulse voltage oxidation treatment, defects and holes in the anodized layer are reduced, the oxide film is more conducive to improving the chromaticity, and exhibits higher corrosion resistance.

[0013] In step 2 of the above technical scheme, the cast aluminum alloy sample is immersed in an alkaline solution for alkaline washing, and the alkaline washing uses a 5vt% NaOH solution to remove surface oil stains, impurities, etc.; after the alkaline washing is completed, the cast aluminum alloy sample is immersed in an acidic solution for pickling, and the pickling uses a mixed acid of sulfuric acid-phosphoric acid-hydrofluoric acid, with a hydrofluoric acid concentration of 1.5vt%, a sulfuric acid concentration of 20vt%, a phosphoric acid concentration of 60vt%, and a pH value controlled between 1.5-2 (if the pH value is lower than 1.5, it will cause excessive corrosion to the matrix), and pickling can remove surface oxides.

[0014] In step 3 of the above technical solution, the cast aluminum alloy sample is anodized by sulfuric acid method, the sulfuric acid concentration is 9.8vt%, the temperature is 17-18°C, and the current density is about 1A / dm 2 , pulse voltage (E1 = 10 ~ 25V, t1 = 50s; E2 = 5 ~ 15V, t2 = 50s; f = 0.01Hz), high and low potential difference is 5V, oxidation time is 15-45min. Further, the preferred pulse voltage is E1 = 25V, t1 = 50s; E2 = 15V, t2 = 50s; f = 0.01Hz.

[0015] In step 4 of the above technical solution, the cast aluminum alloy sample is cleaned using an ultrasonic cleaner and deionized water for 10 to 20 minutes.

[0016] In step 5 of the above technical solution, the cleaned cast aluminum alloy sample is immersed in a dye for dyeing, the dye mass concentration is 2-3%, the dyeing temperature is 50-60°C, and the dyeing time is 10-20 minutes.

[0017] In step 6 of the above technical solution, the cast aluminum alloy sample after dyeing is quickly immersed in distilled water, and then placed in distilled water at 95 to 98° C. for sealing treatment for 25 to 35 minutes.

[0018] After adopting the above technical solution, the present invention has the following positive effects:

[0019] By adding the Sr element during the preparation of the cast aluminum alloy and combining it with a pulse voltage treatment during anodizing, the oxide film can be effectively grown uniformly, thereby improving the uniformity of the oxide film. This method can form a uniform and dense oxide film on the surface of the cast aluminum alloy, further improving the surface appearance of the cast aluminum alloy, and the corrosion resistance is significantly improved after adding Sr. The technical solution described in the present invention is simple to operate, does not rely on expensive advanced equipment, reduces production costs and process complexity, can effectively improve the surface appearance and corrosion resistance of the cast aluminum alloy, and provides a better foundation for subsequent use. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The surface morphology of an aluminum-silicon alloy with a silicon content of 5wt% observed using an optical microscope after anodization using the method provided by the present invention;

[0021] Figure 2 For Al-Si alloy with 5wt% silicon content, the morphology of anodized film after different Sr contents is shown. It can be seen that the addition of Sr element can significantly reduce the defects of the oxide film and improve the surface appearance of the oxide film;

[0022] Figure 3 This is a voltage diagram. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments.

[0024] Example 1

[0025] The above method is used to anodize the cast aluminum alloy plate. The specific operation steps are as follows:

[0026] (1) Cast aluminum-silicon alloy plates with silicon contents of 2.5 wt-%, 5 wt-% and 12.5 wt-% were prepared, and an appropriate amount of Al-10Sr was added to make the Sr content in the cast aluminum alloy plates 150 ppm; and a cast aluminum-silicon alloy with an Sr content of 0 wt-% was used as a comparison.

[0027] (2) First, immerse the cast aluminum alloy plate in an alkaline solution for alkaline washing, using a 5vt% NaOH solution. Alkaline washing can remove surface oil stains, impurities, etc. After alkaline washing, immerse the cast aluminum alloy plate in an acidic solution for pickling. Pickling uses a mixed acid of sulfuric acid, phosphoric acid, and hydrofluoric acid, with a hydrofluoric acid concentration of 1.5vt%, a nitric acid concentration of 20vt%, a phosphoric acid concentration of 60vt%, and a pH value controlled between 1.5-2 (if the pH value is lower than 1.5, it will cause excessive corrosion to the substrate). Pickling can remove surface oxides.

[0028] (3) The cast aluminum alloy plate is anodized by sulfuric acid method: the electrolyte is 9.8vt% sulfuric acid, the temperature is 17-18°C, a specific pulse voltage is applied (E1=25V, t1=50s; E2=15V, t2=50s; f=0.01Hz), the current density is about 1A / dm2, and the oxidation time is 15-45min according to the silicon content in the cast aluminum alloy, so that a layer of uniform and dense oxide film with a thickness of about 10μm is generated on the surface of the cast aluminum alloy.

[0029] (4) Clean the surface of the anodized cast aluminum alloy plate: use an ultrasonic cleaner and deionized water for cleaning, and set the cleaning time to 15 minutes to ensure sufficient cleaning.

[0030] (5) The cleaned cast aluminum alloy plate is immersed in a dye for dyeing: the dye is prepared by dissolving 8 g of red dye (Sanodal Red B3LW) in 400 ml of distilled water, the dyeing temperature is 50-60° C., and the dyeing time is 15 min.

[0031] (6) Sealing the cast aluminum alloy plate: After dyeing, the cast aluminum alloy plate is quickly immersed in distilled water, and then placed in 97° C. distilled water for sealing for 30 minutes.

[0032] Example 1 The chromaticity, brightness and corrosion resistance data of the cast aluminum alloy after dyeing and immersion for 12 hours are shown in Table 1 below:

[0033] The color and brightness of cast aluminum alloys were measured using a spectrophotometer CM-2600d based on high-energy xenon flash illumination and a high-resolution monolithic double-beam monochromator.

[0034] The corrosion resistance test method of cast aluminum alloy after anodization is to use an electrochemical workstation to measure the electrochemical impedance spectrum of the anodized film in a solution with a NaCl concentration of 3wt%, and use the impedance data to fit the equivalent circuit R el (Q ox R ox )(Q in R po ) to fit the data, and finally use R po (i.e. polarization resistance) as a corrosion resistance parameter.

[0035] Table 1

[0036]

[0037] Example 2

[0038] The difference between Example 2 and Example 1 is that the pulse voltage is E1=10V, t1=50s; E2=5V, t2=50s; f=0.01Hz; and the other conditions are the same as those of Example 1.

[0039] Example 2 The chromaticity, brightness and corrosion resistance data of the cast aluminum alloy plate after dyeing and immersion for 12 hours are shown in Table 2 below:

[0040] Table 2

[0041]

[0042] Example 3

[0043] The difference between Example 3 and Example 1 is that the pulse voltage is E1=15V, t1=50s, E2=10V, t2=50s, and f=0.01Hz. The other conditions are the same as those of Example 1.

[0044] Example 3 The chromaticity, brightness and corrosion resistance data of the cast aluminum alloy plate after dyeing and immersion for 12 hours are shown in Table 3 below:

[0045] Table 3

[0046]

[0047] Example 4

[0048] The difference between Example 4 and Example 1 is that pulse voltage anodization is not used, but conventional oxidation is used instead, and the specific condition is a constant voltage of 25V; other conditions are the same as those in Example 1.

[0049] Example 4 The chromaticity and brightness data of the cast aluminum alloy plate after dyeing are shown in Table 4 below:

[0050] Table 4

[0051]

[0052] Example 5

[0053] The difference between Example 5 and Example 1 is that Al-10Sr is added when preparing the cast aluminum alloy plate so that the Sr content in the cast aluminum alloy plate is 300 ppm. Other operations are the same as Example 1.

[0054] Example 5 The chromaticity, brightness and corrosion resistance data of the cast aluminum alloy plate after dyeing and immersion for 12 hours are shown in Table 5 below:

[0055] Table 5

[0056]

[0057]

[0058] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving the appearance and corrosion resistance of anodized surface of cast aluminum alloy, characterized in that: The steps are as follows: Step 1, when preparing a cast aluminum alloy sample, add an appropriate amount of Al-10Sr to make the Sr content in the cast aluminum alloy sample be 100-300ppm; Step 2, firstly performing an alkali washing treatment and then an acid washing treatment on the surface of the cast aluminum alloy sample; Step 3, anodizing the surface of the cast aluminum alloy sample and applying a specific pulse voltage to form an oxide film on the surface of the cast aluminum alloy; Step 4, cleaning the cast aluminum alloy sample after anodizing; Step 5, dyeing the cast aluminum alloy sample after cleaning; Step 6, sealing the cast aluminum alloy sample after the dyeing treatment.

2. The method for improving the appearance and corrosion resistance of anodized surface of cast aluminum alloy according to claim 1, characterized in that: In step 2, the alkaline washing treatment is to immerse the cast aluminum alloy sample in an alkaline solution for alkaline washing, the alkaline washing solution is a 5vt% NaOH solution; the pickling solution is a mixed acid of sulfuric acid-phosphoric acid-hydrofluoric acid, the hydrofluoric acid concentration is 1.5vt%, the nitric acid concentration is 20vt%, the phosphoric acid concentration is 60vt%, and the pH value is controlled between 1.5-2.

3. The method for improving the appearance and corrosion resistance of anodized surface of cast aluminum alloy according to claim 1, characterized in that: In step 3, the cast aluminum alloy sample is anodized by sulfuric acid method, the sulfuric acid concentration is 9.8vt%, the temperature is 17-18°C, and the current density is about 1A / dm 2 , pulse voltage E1=10~25V, t1=50s; E2=5~15V, t2=50s; f=0.01Hz, oxidation time 15-45min.

4. The method for improving the appearance and corrosion resistance of anodized surface of cast aluminum alloy according to claim 3, characterized in that: In step 3, the pulse voltage is E125V, t1=50s; E215V, t2=50s; f=0.01Hz.

5. The method for improving the appearance and corrosion resistance of anodized surface of cast aluminum alloy according to claim 1, characterized in that: In step 4, the cast aluminum alloy sample is cleaned using an ultrasonic cleaner and deionized water for 10 to 20 minutes.

6. The method for improving the appearance and corrosion resistance of anodized surface of cast aluminum alloy according to claim 1, characterized in that: In step 5, the cleaned cast aluminum alloy sample is immersed in a dye for dyeing at a temperature of 50-60° C. for a dyeing time of 10 to 20 minutes.

7. The method for improving the appearance and corrosion resistance of anodized surface of cast aluminum alloy according to claim 1, characterized in that: In step 6, the cast aluminum alloy sample after dyeing is quickly immersed in distilled water and then placed in distilled water at 95 to 98° C. for sealing treatment for 25 to 35 minutes.

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