Hard-Coat designates a procedure in which the surface of aluminium articles is provided with a protective layer by electro-chemical processes. It is an option to the regular anodizing process, which is used for a variety of parts made of aluminium.
Basically, in both of these procedures no impurity layer is applied to the surface of an item. Instead, it is a conversion of the aluminium-surface into an aluminium-oxide, which is microporous and therefore dyeable. With the standard anodizing procedure, aside from the protection of the surface against corrosion, an optically attractive appearance can be reached by using a corresponding pre-treatment. Simultaneously, there is a possibility of many different colourings.
Contrary to the standard anodizing process the protective layers, the protective layers obtainable with hard-coating are considerably harder and thicker - comparable to hard chrome layers - and hence they are preferably used for parts where it is specified by their technical application. Hard-coated layers possess a self-colouring capacity depending on the alloy and the layer thickness. Moreover, their porosity (absorbency of colourings) is significantly lower than with the regular anodizing procedure so that the possibility of the additional colouring is heavily reduced and limited to dark colour tones.
Hard-anodized layers possess no levelling effect, too, so that pits, scratches and damages will be visible after anodizing - therefore, as a rule, likewise a mechanical and/or chemical surface treatment is applied before, in order to eliminate such faults if high optical requirements are demanded. Both pre-treatment procedures involve material removal, though. Previously invisible inhomogeneities of the alloys also appear beyond the anodizing process and may cause optically disturbing structures.