The electrochemical oxidation of metals or alloys is known as anodizing. Aluminum and its alloys form an oxide deposit on aluminum products (anodes) due to the applied current under the appropriate electrolyte and process conditions. Usually refers to anodized sulfuric acid. Aluminum is anodized by an electrolytic oxidation process. The surface of aluminum and aluminum alloys is usually converted into an oxide coating during this process, which serves as a protective, aesthetic, and functional layer. By electrolysis, metal or alloy pieces are utilized as anodes to create oxide deposits on the surface. Metal oxide layers alter the condition and qualities of the metal surface, such as surface coloration, corrosion resistance, wear resistance, and hardness, and protect the metal surface.
The oxide film obtained by anodizing is usually 5 – 20 m thick. It also possesses the following characteristics:
Strong absorption capacity
Because the anodize oxide surface on aluminum and aluminum alloys is porous and has a high adsorption capacity, filling the hole with different pigments, lubricants, and resins can increase the protection, insulation, wear resistance, and ornamental features of aluminum products.
High corrosion resistance
It is due to the chemical stability of the anodize oxide coating. After testing, the pure aluminum anodize oxide film outperforms the aluminum alloy anodize oxide film in terms of corrosion resistance. This is because the alloy composition inclusion or the production of metal compounds cannot be oxidized or dissolved, causing the oxide film to become discontinuous or void-filled, reducing the oxide film's corrosion resistance. As a result, the anodized film must be sealed to improve its corrosion resistance.
High level of hardness
Aluminum alloy oxide film has a higher hardness than pure aluminum oxide film. Its hardness is usually determined by the aluminum alloy composition and the technical electrolyte conditions during anodization. The anodize oxide film is robust and wear-resistant. The porous oxide covering on the surface, in particular, has the capacity to adsorb lubricants, improving the surface's wear resistance.