ANODIZING FAQ

 

What is anodizing?
Anodizing is the process of depositing an oxide layer on an aluminum surface which is harder than the original aluminum surface, more corrosion and abrasion resistant, and aesthetically pleasing. This surface is formed by a chemical-electrolytic process that rapidly and evenly oxidizes the aluminum surface. This oxide layer can be further dyed using either organic pigments or inorganic salts.


How is anodizing done?
The aluminum surface is first prepared by rinsing, caustic etching and acidic desmutting stages. It is then dipped in a mild sulfuric acid bath while an electric current is passed through the solution. The aluminum surface effectively becomes the anode (the tank is the cathode) causing the migration of charged oxygen ions towards the surface of the aluminum. The negative oxygen ions bond with the positively charged aluminum ions forming an aluminum oxide layer (Al2O3). The aluminum surface is then sealed to prevent further oxidation and staining.


Can I weld anodized aluminum?
Mechanically fastened parts are always preferable to welding when anodizing. Nevertheless, welding can be done prior to anodizing though the anodized finish in the area around the weld will always be slightly different in appearance. Low heat when welding is highly recommended, as there are slight changes in the metal properties after heating which will affect the shade of the anodized finish. The only welding rod alloy recommended for use is 5356. All other welding rod composites will cause blackening. It is highly recommended that any welding that must be done, is done prior to anodizing. Welding afterwards will burn the surface in the area around the weld.


What alloys are recommended for anodizing?
All alloys of aluminum will build an anodic coat, but not all alloys are suitable for anodizing. In the architectural field the alloys that are best suited for anodizing are the 6000 series for extrusions (most preferably 6063) and the 5000 series for sheet metal (most preferably 5052 or 5005). It is always recommended to use only 1 alloy on a particular job since slight color variances are inherent from alloy to alloy.


Can you anodize cast aluminum?
Cast aluminum is very difficult to anodize and we recommend not to use it for anodizing.


Will anodizing hide imperfections in the metal?
Anodized finishes tend to enhance rather than hide the original surface features of the aluminum substrate. Unlike painting which puts a coating over the surface, the anodized finish is integral with the metal itself and does not hide imperfections.


How do I clean anodized aluminum?
Cleaning anodized surfaces can be achieved by using a mildly abrasive soap. Do not use harsh alkaline or acidic solutions as they may destroy the finish. Always test a small area first to check your results before continuing.