The practice of anodizing, or controlled oxidation, of aluminum and its alloys has been around for more than seven decades. The main intention behind anodizing aluminum and its alloy parts is to protect the highly reactive surface against corrosion in aqueous environments, such as humid air and seawater. Since anodic coating can be produced in a range of colors, painted parts are generally used in architectural applications. Additionally, as the AC aluminum anodizing process would produce a hard ceramic coating, harder than the substrate from which it is formed, anodic coatings are also used to protect aluminum parts from abrasions, especially sand abrasion. The traditional anodizing process is electrochemical oxidation. The part to be anodized is then connected to the positive terminal of a direct current (DC) power source and a non-reactive metal, such as stainless steel, is attached to the negative terminal. The aluminum anode and the stainless steel cathode are then immersed ...
The chromate film will be smooth when it is newly formed, but once it dries and ages, the layer will become more resistant to roughness. Chromate conversion coatings provide excellent corrosion resistance.
Paint, polish, and organic finishes adhere very well to chromate conversion coatings. Additionally, chromate coatings will prevent loss of adhesion due to under-film corrosion.
The most common use of chrome plating is to impart corrosion resistance to zinc-aluminum parts and galvanized steel.
These films will vary in color depending on the chemicals used and the background metal being coated. Colors range from clear to bright to gold.
Greater protection against corrosion is given with formulations that give a golden color, since these coatings tend to be thicker. A multi-colored appearance will be obtained when the base metal is not uniform.
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