Anodizing Aluminum and How It Works

Exposed to the earth's atmosphere, aluminum combines with oxygen to form a protective surface film which inhibits further oxidation of the aluminum. Unlike steel or iron alloys, aluminum will not continue to oxidize (rust) once this protective layer is formed. This natural oxide is extremely thin and loosely adhered to the aluminum surface, however, and is easily removed by handling. Anodizing is a process which thickens the natural oxide film resulting in a heavy aluminum oxide film of controlled thickness having the hardness similar to that of a ruby or sapphire.

When aluminum is anodized conventionally, direct electrical current (DC) is passed through a bath of sulfuric acid -- the electrolyte -- while the aluminum being treated serves as the anode. This produces a clear film of aluminum oxide on the aluminum's surface. Electron microscopy indicates that this layer is mostly porous with a very thin barrier layer at the base. This structure lends itself very well to electrolytic coloring or absorptive dying.

During the anodizing process, several controls are critical to assure the specified film thickness, its abrasion resistance and density. These controls include a precise combination of chemical concentration, temperature and current density. In the production of quality anodized products, there is no alternative to having sophisticated monitoring equipment and highly-trained, experienced personnel. The company you choose for your anodizing projects must be able to demonstrate these qualities.

For a view of an actual anodizing process in action, view our anodizing video.

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AACOA is a leader in aluminum extrusion and fabrication, as well as aluminum anodizing. Operating state-of-the-art plants in Niles, Michigan and Elkhart, Indiana, AACOA serves customers throughout the Midwest and the entire U.S.

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