Bright anodising (Topic: 14121)

Bright anodising is a special type of anodising (in combination with polishing) when glossy or shiny surfaces are required. The pre-treatment before anodising may be mechanical -, chemical, or electrolytic polishing. A combination of mechanical and electrolytic or chemical polishing can be used, mainly a combination of mechanical and chemical polishing. Very often only chemical polishing is used because of difficult profile geometry and labour costs. The polishing method is also dependent on the surface requirements.

After polishing the profiles are anodised to increase the wear and corrosion resistance. It is important to put on a thin anodic oxide layer, because the brightness drops when the thickness of the oxide coating increase. To achieve both good abrasion resistance and good reflectivity an oxide coating thickness of approximately 10 µm is suitable. The resistance to abrasion and corrosion is better after anodising at low acid concentrations and high voltages, while reflectivity is higher after anodising at high acid concentrations and lower voltages. Usually bright anodising is carried out with a lower current density than normal anodising.

In order to obtain colours the bright anodised profiles could be dyed or electrolytic coloured prior to the sealing operation.

Pure aluminium is excellent for bright anodising ,but alloys with low values of alloying elements are also very suitable, i.e. AW 1050, 1070, and 1370. In addition AW 6463 is very good for bright anodising due to an optimum copper content (max. 0,20%). Too much copper and silicon give alloys unsuitable for bright anodising due to formation of intermetallic particles. See also Chemical composition and Strength level of main alloy groups-table.

Bright anodised extrusions are widely used for finishing trim components, particularly for domestic appliances and automotive applications like window trims and bumpers.