Effect of carbon dioxide on the atmospheric corrosion of Zn–Mg–Al coated steel

• ZnMgAl material was significantly more affected than GI, and in the range of the Galfan coating.
• An obvious pH effect was underlined in low CO2 conditions.
• Layered double hydroxide and simonkolleite were mainly formed on ZnMgAl coating in the absence of CO2.
• Hydroxycarbonate and simonkolleite were dominating in ambient air, as for GI.

The atmospheric corrosion of line hot dip ZnMgAl coating was investigated at low and ambient concentration of CO2 as a function surface chloride concentration and temperature and compared to conventional hot dip galvanised (GI) and Galfan coatings. The corrosion of zinc coatings was enhanced in low CO2 conditions and ZnMgAl material was more affected than GI, and in the range of the Galfan coating. An obvious pH effect was underlined in low CO2 conditions. Layered double hydroxide (LDH) and simonkolleite were mainly formed on ZnMgAl coating in the absence of CO2 while hydroxycarbonate and simonkolleite were dominating in ambient air.