What is the anodizing process of alumina plate?

The core of anodic oxidation process of alumina plate is to generate a dense and stable oxide film (mainly composed of Al₂O₃) on the surface of aluminum plate by electrochemical method, so as to improve its performance. The whole process is usually divided into three core links: pretreatment, anodic oxidation and post-treatment. The specific process is as follows:

1. Pretreatment: Laying the foundation of oxidation

This stage aims to remove impurities on the surface of aluminum plate and ensure the uniform adhesion of oxide film, including three steps:

Deoiling: Soak the aluminum plate with alkaline solution (such as sodium hydroxide solution) or organic solvent (such as ethanol) to remove oil stains such as rolling oil and dust on the surface to avoid pinholes and blisters on the oxide film.

Pickling: treat with dilute hydrochloric acid or dilute sulfuric acid solution to remove the oxide scale (loose film layer formed by natural oxidation) on the surface of aluminum plate, so that the substrate can be exposed to a clean and uniform metal surface.

Polishing (optional): Carry out mechanical polishing (to improve the smoothness) or chemical polishing as required to make the surface of aluminum plate smoother and lay the foundation for subsequent coloring and oxide film uniformity.

2. Anodizing: forming a core oxide film.

This is the key to the process. An oxide film is formed on the surface of aluminum plate through electrolytic reaction, and the specific process is as follows:

Put the pretreated aluminum plate as anode and inert metal such as lead plate as cathode into electrolyte solution (sulfuric acid solution, oxalic acid and chromic acid solution can also be used, corresponding to oxide films with different properties).

After electrifying, the anode (aluminum plate) undergoes an oxidation reaction: 2Al+3H₂O → Al₂O₃+6H⁺+6e⁻, and the generated ALO gradually deposits on the aluminum plate surface to form an oxide film.

By adjusting the current density (usually 1-3a/dm), electrolysis time (10-60min) and temperature (15-25℃), the thickness of oxide film (usually 5-20μm, especially above 50μm) can be controlled.

3. Post-treatment: Improve performance and appearance.

Sealing: There are tiny pores on the surface of the oxide film, which need to be treated with hot water, steam or special sealing agent (such as nickel salt solution) to close the pores and enhance the corrosion resistance, pollution resistance and insulation of the oxide film.

Coloring (optional): By electrolytic coloring (depositing metal ions in the pores of the oxide film, such as copper ions in red and nickel ions in gold), chemical coloring or electrophoretic painting, various colors of the alumina plate can be realized, giving consideration to decoration and functionality.