Atmospheric Corrosion of Zinc-Aluminum Alloyed Coated Steel in Depleted Carbon Dioxide Environments

NaCl induced corrosion of Zn-0.2Al, Zn-5Al and Zn-55Al coated steel was investigated at low and ambient CO 2 levels. Weight loss measurements revealed an enhancement of the corrosion of Zn-0.2Al and particularly Zn-5Al in low CO 2 . This was connected to an increase of surface pH in a low CO 2 atmosphere promoting the formation of ZnO and layered double hydroxide for Zn-5Al. For Zn-55Al, CO 2 depletion did not affect the surface pH due to the acidification effect of Al 3 + . Preferential dissolution of zinc rich phase was observed on cross-sections, particularly in depleted CO 2 experiments. Different sequences of corrosion product formation were proposed for the different Zn-Al coatings.