What is anodising?
Anodising is the process by which the natural film on aluminium is greatly increased in thickness.
Aluminium metal is on the anodic side of the galvanic series. Its position is similar to zinc and magnesium, ie it is readily oxidised. The oxide on aluminium is naturally corrosion resistant, very hard, abrasion resistant, an insulator and very tenacious. In its natural form the oxide film on aluminium is less than 0.50 microns thick.
Because the naturally occurring film is very thin and attached to a soft ductile metal, it is easily damaged. Building up this coating provides very useful properties for the aluminium surface.
The basis of every good coating is preparation. In anodising, good preparation is essential. Oils and greases are removed in weak alkali solutions and the surface is etched to remove heavy oxides. After rinsing, the aluminium is dipped into a desmut solution to remove the insoluble components of the aluminium which remain on the surface after etching, rinsed and presented for anodising.
How is it done?