Surface Treatments: Anodising and Alochroming
Anodising uses electrolysis to produce a thick hard transparent oxide coating that increases corrosion resistance and protects the surface of the casting. Sulphuric acid and chromic acid anodising are the two most popular techniques.
Sulphuric acid anodising
The most common form of anodising because of the durability and corrosion resistance it offers, sulphuric acid anodising provides an additional anodic film thickness of 3 to 25 microns.
Chromic acid anodising
Chromic acid anodising produces a much thinner anodic film of 3 to 7 microns. It therefore does not provide the same levels of wear resistance but is more able to be deformed without losing toughness and provides a good key for painting.
This finishing process involves coating the casting in a chemical solution to form a protective film. Known also as chromating the protective film is not particularly durable and therefore is good for decorative finishes but not for components experiencing significant abrasion.