Abstract
Cadmium coatings have in the past been frequently used as protective coatings against corrosion of metallic structures, but cadmium is now known to be a polluting substance, dangerous for human health and the environment. Since 1991, a European directive has regulated the use of cadmium coatings in industry. Other coatings, such as Zn electrodeposited alloys or metallic coatings deposited by PVD techniques, are under development to replace cadmium. This study discusses first the behaviour of bare low alloy steel, Ti, and Al in 3%NaCI solution, which is necessary for the understanding of monolayer coating behaviour. Various electrochemical techniques are used to distinguish the behaviour of each metal. Then, a thorough investigation is carried out to characterise the galvanic corrosion between a steel substrate and bulk metal coatings. The overall corrosion behaviour of the coated steel depends not only on the electrochemical properties of the deposited metal, but also on surface defects such as roughness, droplets deposited during PVD, and, in particular, porosity, cracks, and scratches.
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