Study On Aluminum Hard Anodic Oxidation And Coloring Technology

Aluminum and its alloys could obtain porous oxide film after hard anodic oxidation. It has many strong points such as high hardness, good insulation, high temperature and corrosion resistance, high chemical stability. The oxide film has a good absorption because of its porous and could be used as the base coating film. If we dye and shade the oxide film, its surface decoration performance could be enhanced. Meanwhile, it can be used as insulation and thermal protection layer because of its low thermal conductivity.Sulfuric acid anodizing is the most staple process. This approach costs little and could obtain high porosity oxide film. But sulfuric acid has a great dissolution on the film and results that the oxide film's hardness is not hard enough. However, the oxalic acid anodizing has an advantage in low cost, small solubility of the coating. And the hardness, corrosion resistance, wear resistance and electrical insulation of the oxide film are better than the film formed in sulfuric acid. But the porosity of the film formed in sulfuric acid is lower. At the present time, the most mature coloring approach of aluminum and its alloys is electrolytic coloring. It can bring bright color but the electrolytic coloring process is more complex and time-consuming and strenuous and has a constraint in dyeing color. The easiest way is adsorption coloring. It can be variety colored just by soaking it in coloring liquid. The key to successful Staining is getting a good oxide film. However, the staining of cast aluminum alloy is difficult because the even oxidation itself is very difficult due to the existence of silicon.AC7A is a new aluminum-magnesium casting alloy and has a good corrosion resistance in seawater. It is the better mold aluminum and is more ideal material of tire mold in the world and widely used. Currently, the studying on AC7A aluminum alloy process is relatively few. Therefore, sulfuric-oxalic acid anodic oxidation is chose as the approach to anodizing AC7A combined with the advantages of the two methods. A set of optimum process parameters of anodizing and dyeing was optimized by orthogonal tests. It can promise the formed film to guarantee its hardness and porosity. And make AC7A aluminum alloy achieve good results of anodic oxidation and coloring.