Community Research and Development Information Service - CORDIS

Development of repair procedures and regulations for the repair of corroded aluminium, especially damaged by filiform corrosion

The state-of-the-art in Europe and world-wide is the application of chromated and coated aluminium. In many cases however, above all in maritime climates and in industrial areas, corrosion can occur. The existing repair systems can prevent the renewed corrosion only for a very short time.
Within this project a portable anodizing system was developed. It allows the application of anodic oxide layers on aluminium parts without the need to remove them (eg facades, door-frames and window-frames, caravans, etc). This anodic oxide layer can prevent corrosion, particularly filiform corrosion, completely and is therefore an ideal corrosion-protecting and adhesion-promoting under-layer for organic coatings (even without a primer). All other operations of the repair (mechanical pre-treatment, coating, etc) are the same as for the repair procedures currently in use. The benefit for the user is the much higher lifetime of the parts repaired, compared to all existing repair systems.
The anodizing process developed works according to the so-called brush-anodization or tampon-anodization. This procedure works with a hand-held cathode being moved over the area to be anodized. The (acid) electrolyte is thickened with a special thickening agent, thus vertical areas can also be anodized without the danger of the electrolyte falling from the work-piece.
The corrosion-resistance and the mechanical properties (eg adhesion) of different coatings (PUR, PVDF, etc, with and without different primers) on the anodic oxide layer were tested in different laboratory tests (salt spray, constant moist atmosphere, etc). No corrosion did occur. The repair system is now being tested in field experiments and in long-term outdoor exposure tests at different locations within Europe.
The portable anodizing set, a case with a built-in protective transformer, comprises the rectifier, electrolyte, cathodes, cables, clamps and protection equipment. It is manufactured and distributed (costs about 3000 ECU) by the project participant Munk GmbH.

Reported by

Forschungsinstitut für Edelmetalle und Metallchemie
Katharinenstraße 17
73525 Schwäbisch Gmünd
Germany
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