Anodic oxidation is commonly used for the production of protective and decorative films on aluminium. In the anodising process, the thin film of aluminium oxide that forms naturally on the surface providing some degree of corrosion protection for the underlying aluminium is increased to a substantially greater thickness.
In anodising, the articles are made anodic and the oxygen liberated at the anode surface results in the formation of a coherent oxide film which is very adherent to the base metal.
Applications of Anodising:
- Decorative finishes
Anodising provides an attractive decorative finish on variety of aluminium articles. A bright, semi bright or matt effect can be obtained depending on the initial surface condition and alloy composition. A wide range of dye colours are also available for decorative anodised parts.
- Architectural Anodising
This term of anodising refers to thick film anodic films greater than 25 microns, which are necessary to meet the severe conditions of outdoor exposure.
- Hard Anodising
The normal anodic film produced by sulphuric anodising is fairly hard and wear resistant. However, harder and thicker films can be produced for engineering applications by adjusting the anodising conditions.
- Corrosion resistant coatings
Historically, chromic acid anodising has been used for this purpose however due to the drive of eliminating the use of chromic acid from finishing processes, Tartaric systems are now being specified.