Compared with aluminum anodizing film, the chemical oxidation film of aluminum plate is much thinner, with lower corrosion resistance and hardness, and is not easy to be colored. The light fastness after coloring is poor, so only anodizing treatment is introduced for coloring and color matching of aluminum plate.
Anodizing process of aluminum plate
1. General principle of anodic aluminum oxide film formation:
The process of taking aluminum plate as anode and putting it in electrolyte solution to form aluminum oxide film on its surface by electrolysis is called anodic oxidation treatment of aluminum plate. Cathodes in the device are materials with high chemical stability in electrolytic solution, such as lead, stainless steel, aluminum, etc. The principle of aluminum anodizing is essentially the principle of water electrolysis. When the current passes through, hydrogen will be released on the cathode; On the anode, the oxygen precipitated is not only molecular oxygen, but also atomic oxygen (O) and ionic oxygen, usually expressed as molecular oxygen in the reaction. The aluminum as anode is oxidized by the oxygen precipitated on it to form an anhydrous aluminum oxide film. The oxygen generated does not interact with aluminum completely, but some of it is precipitated in gaseous form.
2. Selection of electrolytic solution for anodizing aluminum plate:
A prerequisite for the growth of anodic oxide film is that the electrolyte should dissolve the oxide film. However, this does not mean that anodic oxidation can generate oxide film in all electrolytes with dissolution or the oxide film generated has the same properties.
3. Type of anodized aluminum plate:
Anodizing can be divided into DC anodizing, AC anodizing, and pulse current anodizing according to the current form. According to the electrolyte, it can be divided into sulfuric acid, oxalic acid, chromic acid, mixed acid and natural coloring anodic oxidation with sulfonic organic acid as the main solution. According to film properties, it can be divided into ordinary film, hard film (thick film), porcelain film, bright modification layer, semiconductor barrier layer and other anodic oxidation. See Table - 5 for common anodic oxidation methods and process conditions of aluminum and aluminum alloys. Among them, direct current sulfuric acid anodizing is the most common.
4. Structure and property of anodic aluminum oxide film:
