A method for improving the appearance and corrosion resistance of anodized surfaces of cast aluminum alloys

Abstract

The present application relates to the technical field of aluminum alloy surface treatment, and particularly relates to a method for improving the surface appearance and corrosion resistance of cast aluminum alloy anodic oxidation, and the operation steps are as follows: when preparing the cast aluminum alloy sample, a proper amount of Al-10Sr is added, so that the content of Sr in the cast aluminum alloy sample is 100-300 ppm; the surface of the cast aluminum alloy sample is first 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, a specific pulse voltage is applied, and an oxide film is generated on the surface; the cast aluminum alloy sample after the anodic oxidation is completed is subjected to cleaning treatment; the cast aluminum alloy sample after the cleaning is completed is subjected to dyeing treatment; and the cast aluminum alloy sample after the dyeing is completed is subjected to sealing treatment. The present application provides a simple experimental method, and the overall operation process is convenient. Through the anodic oxidation treatment by using the pulse voltage, the oxide film can be uniformly grown, so that the surface appearance and corrosion resistance of the cast aluminum alloy after the anodic oxidation are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cast aluminum alloy surface treatment, and particularly relates to a method for improving the surface appearance of anodized cast aluminum alloy. BACKGROUND

[0002] Cast aluminum alloy is widely used in the fields of aerospace, automobile manufacturing and 5G base station due to its light weight, high strength and corrosion resistance. In order to further improve the corrosion resistance and aesthetics of cast aluminum alloy, anodizing is a commonly used surface treatment method. However, the traditional anodizing, while improving the corrosion resistance, often fails to effectively improve the surface appearance, resulting in a rough surface of the finished product, thereby affecting the appearance and subsequent use. The main problems existing in the anodizing of cast aluminum alloy are as follows: 1. The existing anodizing technology for cast aluminum alloy mostly uses a high voltage or a mixed acid electrolyte such as sulfuric acid and phosphoric acid or oxalic acid or tartaric acid. Although a higher voltage or a mixed acid electrolyte can provide a faster reaction rate and a more high-temperature-resistant oxide film, the thickness and temperature control are more complex due to the violent reaction. In addition, the use of a mixed acid electrolyte requires a higher corrosion resistance of the process equipment, increases the difficulty of waste liquid treatment and environmental protection pressure, and puts forward higher requirements for the safety of workers, which is still not suitable for large-scale industrial production. 2. The existing pretreatment for cast aluminum alloy anodizing for improving the surface appearance of cast aluminum introduces a complex pretreatment such as multiple pickling and mechanical polishing. The complex multi-step process not only increases the production cost but also increases the difficulty of quality control. 3. The optimization of the existing cast aluminum alloy anodizing technology is mostly limited to the optimization of the anodizing process without considering the influence of material optimization on the anodizing effect, so the improvement of the final corrosion resistance and surface effect of the cast aluminum alloy is limited. Therefore, the existing technology needs to be improved and developed. SUMMARY

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

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

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

[0006] Step 2, performing alkali washing treatment on the surface of the cast aluminum alloy sample and then performing acid washing treatment to remove surface oil stains, impurities and oxides, etc.

[0007] Step 3, the surface of the cast aluminum alloy sample is anodized, a specific pulse voltage is applied, and an oxide film is generated on the surface of the cast aluminum alloy;

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

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

[0010] Step 6, the cast aluminum alloy sample after dyeing is sealed.

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

[0012] The present application researches and finds that after adding 100-300 ppm of Sr and cooperating with pulse voltage treatment and oxidation treatment, the defects and pores in the anodic oxidation layer are reduced, the oxide film is more beneficial to color improvement, and higher corrosion resistance is exhibited.

[0013] In the above technical solution step 2, the cast aluminum alloy sample is soaked in an alkaline solution for alkaline washing. The alkaline washing uses 5vt% NaOH solution, which can remove surface oil stains, impurities, etc. After alkaline washing, the cast aluminum alloy sample is soaked in an acidic solution for acid washing. The acid washing uses a mixed acid of sulfuric acid-phosphoric acid-hydrofluoric acid, the concentration of hydrofluoric acid is 1.5vt%, the concentration of sulfuric acid is 20vt%, the concentration of phosphoric acid is 60vt%, and the pH value is controlled between 1.5-2 (if the pH value is lower than 1.5, the substrate will be excessively eroded). The acid washing can remove surface oxides.

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

[0015] In the above technical solution step 4, the cast aluminum alloy sample is cleaned using an ultrasonic cleaning machine and deionized water, and the cleaning time is 10-20min.

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

[0017] In step 6 of the above technical solution, the cast aluminum alloy sample after dyeing is quickly soaked in distilled water, and then is put into distilled water at 95-98 DEG C for sealing treatment for 25-35 min.

[0018] After the above technical solution is adopted, the present application has the following positive effects:

[0019] By adding Sr element in the preparation process of the cast aluminum alloy, and combining with the pulse voltage treatment in the anodic oxidation, the uniformity of the oxidation film can be effectively improved. This method can form a uniform and dense oxidation film on the surface of the cast aluminum alloy, further improve the surface appearance of the cast aluminum alloy, and the corrosion resistance is obviously improved after adding Sr. The technical solution of the present application has the advantages of simple operation, no dependence on high-end advanced equipment, reduced production cost and process complexity, and can effectively improve the surface appearance and corrosion resistance of the cast aluminum alloy, providing a better foundation for subsequent use. BRIEF DESCRIPTION OF DRAWINGS

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

[0021] Figure 2 The anodic oxidation film morphology after adding different Sr contents for the aluminum-silicon alloy with a silicon content of 5wt%, it can be seen that the addition of Sr element can significantly reduce the defects of the oxidation film and improve the surface appearance of the oxidation film;

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

[0023] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all the embodiments.

[0024] Embodiment 1

[0025] The cast aluminum alloy plate is anodized by the above method, and the specific operation steps are as follows:

[0026] (1) Prepare cast aluminum alloy plates with silicon content of 2.5wt-%, 5wt-% and 12.5wt-%, add appropriate amount of Al-10Sr to make the content of Sr in the cast aluminum alloy plate 150ppm; and use cast aluminum alloy with 0wt-% of Sr content as a comparison.

[0027] (2) First, immerse the cast aluminum alloy plate in an alkaline solution for alkaline cleaning. Use 5wt-% NaOH solution, which can remove surface oil, impurities, etc. After alkaline cleaning, immerse the cast aluminum alloy plate in an acidic solution for acid cleaning. The acid used is a mixture of sulfuric acid, phosphoric acid and hydrofluoric acid, with a hydrofluoric acid concentration of 1.5wt-%, a nitric acid concentration of 20wt-% and a phosphoric acid concentration of 60wt-%, and the pH value is controlled between 1.5 and 2 (if the pH value is lower than 1.5, it will cause excessive erosion of the substrate). Acid cleaning can remove surface oxides.

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

[0029] (4) Cleaning treatment of the surface of the cast aluminum alloy plate after anodizing: ultrasonic cleaning machine and deionized water are used for cleaning, and the cleaning time is set to 15min to ensure sufficient cleaning.

[0030] (5) Dyeing treatment of the cleaned cast aluminum alloy plate by immersing it in a dyeing agent: the dyeing agent is prepared by dissolving 8g of red dye (Sanodal Red B3LW) in 400ml of distilled water, the dyeing temperature is 50-60℃, and the time is 15min.

[0031] (6) Sealing treatment of the cast aluminum alloy plate: after dyeing, the cast aluminum alloy plate is quickly immersed in distilled water, and then placed in distilled water at 97℃ for 30min for sealing treatment.

[0032] The color, brightness and corrosion resistance data of the cast aluminum alloy after dyeing in Example 1 are shown in Table 1 as follows:

[0033] The detection method of the color and brightness of the cast aluminum alloy is to use a spectrophotometer CM-2600d based on high-energy xenon flash illumination and high-resolution single-piece double-beam monochromator.

[0034] The method for testing the corrosion resistance of the anodized cast aluminum alloy is to measure the electrochemical impedance spectrum of the anodized film in a solution with a 3 wt% NaCl concentration using an electrochemical workstation, and to fit the equivalent circuit R el (Q ox R ox )(Q in R po ) to the data, and finally use R po (i.e., the polarization resistance) after 12 hours of immersion as the corrosion resistance parameter.

[0035] Table 1

[0036]

[0037] Example 2

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

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

[0040] Table 2

[0041]

[0042] Example 3

[0043] Example 3 differs from Example 1 in that the pulse voltage is E1 = 15 V, t1 = 50 s; E2 = 10 V, t2 = 50 s; f = 0.01 Hz. The other conditions are the same as in Example 1.

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

[0045] Table 3

[0046]

[0047] Example 4

[0048] Example 4 differs from Example 1 in that the pulse voltage anodization is not used, and is replaced by conventional oxidation, with the specific conditions being a constant voltage of 25 V; and the other conditions are the same as in Example 1.

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

[0050] Table 4

[0051]

[0052] Example 5

[0053] Example 5 is compared with Example 1, the difference is that Al-10Sr is added in the preparation of cast aluminum alloy plate, the content of Sr in the cast aluminum alloy plate is 300 ppm, and other operations are the same as those in Example 1.

[0054] The color, brightness and corrosion resistance data of the cast aluminum alloy plate after dyeing in Example 5 are shown in Table 5:

[0055] Table 5

[0056]

[0057]

[0058] The above specific examples further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for improving the surface appearance and corrosion resistance of anodized cast aluminum alloys, characterized in that, The operation steps are as follows: Step 1: When preparing the cast aluminum alloy sample, add an appropriate amount of Al-10Sr to make the Sr content in the cast aluminum alloy sample between 100-300ppm. Step 2: The surface of the cast aluminum alloy sample is first treated with alkaline washing and then with acid washing. Step 3: Anodize the surface of the cast aluminum alloy sample by applying a specific pulse voltage to generate an oxide film on the surface of the cast aluminum alloy. The anodizing method uses sulfuric acid; the specific pulse voltage conditions are: pulse voltage E1=10~25V, t1=50s; E2=5~15V, t2=50s; f=0.01Hz, oxidation time 15-45min; Step 4: Clean the cast aluminum alloy sample after anodizing. Step 5: Perform a staining treatment on the cleaned cast aluminum alloy sample. Step 6: Seal the holes in the cast aluminum alloy sample after the dyeing treatment is completed.

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

3. The method for improving the surface appearance and corrosion resistance of anodized cast aluminum alloys according to claim 1, characterized in that: In step 3, the cast aluminum alloy sample was anodized using the sulfuric acid method. The sulfuric acid concentration was 9.8 wt%, the temperature was 17-18℃, and the current density was 1 A / dm³. 2 .

4. The method for improving the surface appearance and corrosion resistance of anodized cast aluminum alloys according to claim 1, characterized in that: In step 3, the pulse voltages are E1=25V, t1=50s; E2=15V, t2=50s; and f=0.01Hz.

5. The method for improving the surface appearance and corrosion resistance of anodized cast aluminum alloys 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 10-20 minutes.

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

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

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