Functions of Anodizing Aluminum Profiles

1. Enhanced Corrosion Resistance:Aluminum profiles extruded from heated aluminum billets have a very thin and soft surface film, only a few micrometers thick. Since aluminum is a highly reactive metal, it easily reacts with oxygen, water, and other substances in the air, forming aluminum oxide and aluminum hydroxide through chemical reactions. This results in poor corrosion resistance. Anodizing treatment can thicken the surface film to over 10 μm, enabling resistance to various acidic and alkaline substances, thereby extending the service life and improving the mechanical properties of aluminum profiles.
2. Improved Decorative Properties:Extruded aluminum profiles typically exhibit the natural silver-white color of aluminum. Through anodizing treatment, the surface can be transformed into various colors, such as gold, brown, or red, using oxidation coloring techniques based on customer requirements and application needs. This enhances the decorative appeal of aluminum profiles.
3. Increased Insulation:Aluminum profiles are alloy materials composed of elements like copper, manganese, and zinc, which inherently conduct electricity. After anodizing, a protective film forms on the surface, creating a new insulating material that lacks electrical conductivity. This ensures the safety of electronic components, making anodized aluminum profiles suitable for use in electronic products.
4. Enhanced Coating Adhesion:The substrate surface of extruded aluminum profiles is covered with a thin layer of aluminum oxide. To facilitate oxidation coloring, anodizing is performed to open the micropores on the aluminum surface, allowing organic dyes and coatings to adhere more effectively. Finally, sealing treatment stabilizes the various properties of the aluminum profile surface.

Principles of Anodizing Aluminum Profiles

Anodizing aluminum profiles involves placing the profiles in sulfuric acid, chromic acid, or oxalic acid solutions. Under an electric current, aluminum acts as the anode and undergoes electrolysis to form an oxide film 5–30 μm thick on the surface. This process improves the corrosion resistance, wear resistance, high-temperature resistance, and decorative properties of aluminum profiles. The process of generating this anodic oxide film is referred to as the anodizing of aluminum profiles. Unless otherwise specified, anodizing typically refers to sulfuric acid anodizing, which is the most widely used method. The chemical reactions occurring in the sulfuric acid solution are as follows:

• 2H⁺ + 2e⁻ → H₂↑
• 4OH⁻ + 4e⁻ → 2H₂O + O₂↑
• 2Al³⁺ + 3O²⁻ → Al₂O₃ + Heat
• Al₂O₃ + 3H₂SO₄ → Al₂(SO₄)₃ + 3H₂O

Anodizing Process Flow

Loading → Mechanical Polishing → Degreasing → Water Rinsing → Acid Washing → Water Rinsing → Alkaline Washing → Water Rinsing → Neutralization → De-smutting → Water Rinsing → Chemical Polishing → Water Rinsing → Anodizing → Water Rinsing → Sealing → Water Rinsing → Drying → Unloading → Inspection → Packaging → Storage

Before anodizing, pre-treatment of aluminum profiles is essential. Mechanical polishing smoothens surface defects such as burrs and pinholes. Degreasing removes oil stains and impurities. This is followed by acid washing, water rinsing, alkaline washing, and water rinsing, then neutralization. It is important to note that the correct sequence involves acid washing first to remove adhered heavy metal ions and inorganic salts, followed by alkaline washing to eliminate organic matter and microorganisms. Reversing this order (alkaline washing first) would cause metal ions to precipitate, rendering acid washing ineffective. After neutralization, further removal of oil stains and dust is performed. The profiles are then placed in a chemical polishing solution to achieve a smoother and more polished surface, laying the foundation for a high-quality anodic oxide film.