The sealing treatment of anodized aluminum is a crucial post-anodizing process designed to enhance the protective and aesthetic properties of the porous oxide layer formed during anodization. This treatment closes the pores in the anodic film, improving its resistance to corrosion, wear, and contamination.

1. Characteristics of Anodic Oxide Layer

During the anodization process, a porous aluminum oxide (Al₂O₃) layer forms on the surface of the aluminum. This layer has the following

features:

Porous Structure: The surface contains numerous microscopic pores, which can trap contaminants and be susceptible to corrosion.

High Hardness: The oxide layer increases the material's hardness, enhancing its wear resistance.

However, the porous nature of the layer can reduce its effectiveness in protecting against environmental damage unless sealed.

2. Purpose of Sealing Treatment

The main objectives of sealing the anodized layer include:

2.1. Enhanced Corrosion Resistance: Sealing the pores prevents corrosive substances from penetrating, thereby improving the layer's durability.

2.2. Improved Contamination Resistance: Reducing the absorption of pollutants makes the surface easier to clean and maintain.

2.3. Increased Wear Resistance: Sealing can further harden the surface, reducing wear over time.

2.4. Aesthetic Improvement: It enhances the surface finish, making it more visually appealing.

3. Common Sealing Methods

Several methods are used to seal anodized coatings, each with its advantages and disadvantages:

a. Hot Water Sealing

- Process: Immersion of the anodized aluminum in hot water (above 90°C) causes the pores to swell and close.

- Advantages: Simple, cost-effective, suitable for large-scale production.

- Disadvantages: May not provide as high corrosion resistance as other methods.

b. Acid Sealing

- Process: The anodized aluminum is submerged in an acidic solution, such as acetic or oxalic acid, to chemically seal the pores.

- Advantages: Provides good sealing and corrosion resistance.

- Disadvantages: More complex and potentially hazardous to handle.

c. Metal Salt Sealing

- Process: Use of metal salts like nickel or chromium salts to seal the anodized layer, often applied for products requiring high corrosion resistance.

- Advantages: Excellent sealing performance and enhanced corrosion protection.

- Disadvantages: Higher cost and more stringent environmental controls needed.

d. Organic Sealing

- Process: Coating the anodized surface with organic materials such as polymers or oils to fill and seal the pores.

- Advantages: Good decorative effects and strong contamination resistance.

- Disadvantages: Potentially less durable than inorganic sealing methods.

4. Applications of Sealing Treatment

Sealing treatments are essential in various industries, such as:

4.1. Aerospace and Automotive: For parts that require long-term durability and resistance to harsh environments.

4.2. Electronics: To protect aluminum casings from corrosion and wear.

4.3. Architecture: Enhancing the aesthetic and functional lifespan of aluminum facades and decorative elements.

Conclusion

Sealing treatment is a vital process in ensuring the functionality and longevity of anodized aluminum products. By selecting the appropriate sealing method based on specific application needs and environmental factors, manufacturers can significantly enhance the performance and appearance of their aluminum components.

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