Corrosion behaviour of Al Ti coating elaborated by cathodic are PVD process onto mild steel substrate

The use of cadmium coatings in industry is strongly restricted by an European directive, cadmium being dangerous for human health and the environment. Aluminium-based coatings are potential candidates for replacing cadmium coatings. In this paper. we compare the corrosion behaviour of Al and Al/Ti coated steel. We demonstrate that the galvanic effect through the open porosity of the Al coating leads to a rapid loss of sacrificial protection during long immersion time. It is shown that the double-layer coating Al/Ti/steel presents a better corrosion resistance than monolayer in coating in saline solution. The intermediate titanium layer permits the reduction of the open porosity and also allows the reduction of the galvanic effect between steel and aluminium. In order to enhance the electrochemical properties of the: double-layer coating we also investigated the effect of PVD post-oxidation treatments. (C) 1999 Elsevier Science S.A. All rights reserved.