Electrolytic and chemical polishing (Topic: 14050)

Electropolishing and chemical polishing are selective dissolution processes by means of which the high points of the rough surface are dissolved faster than the depressions. Negative and positive effects of the two processes are mentioned in "Which method to use?" Industrial electrolytic and chemical polishing processes for aluminium are of two types:

a. Processes designed to replace or reduce mechanical polishing

These provide a smooth, bright, though not a "mirror" finish, and are characterised by high dissolution rates. In most cases the best results are obtained on high purity aluminium or its alloys, but some processes may be employed on commercial purity based grades of aluminium (AW 1050, 1070, and 1370), producing a correspondingly lower grade of finish.

b. Processes employed after mechanical polishing

These processes have a low rate of attack and are employed on components which require a higher specular reflectivity than is obtained by mechanical methods alone. Their use is generally restricted to high-purity based materials as reflectivity falls off sharply as the quantity of second-phase constituents present increases.