A novel coating process allows aluminium alloys to be sealed in such a way that their corrosion resistance and resistance to alkalis can be improved considerably. It enables these light metals to be used in areas with a high pH.

Untreated aluminium alloys form a natural oxide layer when they come into contact with air and this provides protection in aqueous media in the medium pH range. A special process can be used to seal the oxidised layer that improves the resistance to acids and alkalis to a limited extent. Sealing with an electropheretic dipping lacquer using the Sila-Coat 5000 process from AHC Oberflächentechnik of Kerpen, Germany, offers a significant improvement. The corrosion resistance is increased and, most notably, the resistance to alkalis is improved significantly. The dipping lacquer’s regularly formed structure seals and smoothes the surface. Very uniform layers are formed, even on complex components with internal surfaces like drilled holes or cavities.

With regards the safety of foodstuffs for human consumption, the coating fulfils the marketability requirements demanded by the Food and Drug Administration (FDA) regulations and the Directive on Materials and Articles (Bedarfsgegenständeverordnung). Furthermore, Sila-Coat 5000 is biocompatible, which means it does not damage tissue cells.

As a result of its properties, dip lacquering, possibly with an intermediate anodised layer, is used where aluminium components have to be cleaned with alkaline or acidic media, for example in food processing, packing machines, laboratories, medical technology or catering. Above all, those areas of components that are difficult to access, such as cavities and drilled holes, can be coated uniformly with a smooth layer.

Fig.: Shaft feedthroughs that have been sealed with Sila-Coat 5000 for protection against alkaline cleaners (with a conversion coating, on left, and an intermediate hard-anodised layer, on right)