Abstract
Atmospheric corrosion of hot-dip Zn-6%Al-3%Mg alloy coated steel sheet after 5 years of exposure in a severe marine and a rural sites have been investigated compared with Zn-0.2%Al and Zn-4.5%Al-0.1%Mg alloy coated steel sheets.
The corrosion resistance of Zn-6%Al-3%Mg alloy coated steel sheet is more superior than that of Zn-4.5%Al-0.1%Mg alloy coated steel sheet in both exposure sites. An extensive study using XRD and TEM revealed that the corrosion products consisting of amorphous, finecrystal Zn5(OH)8Cl2·H2O and Zn6Al2(OH)16CO3·4H2O are formed on Zn-6%Al-3%Mg alloy coated steel sheet after 1 year of exposure in a severe marine site. Even after 5 years of exposure the formation of zinc oxide, which have little protective action for coatings, is suppressed on Zn-6%Al-3%Mg alloy coated steel sheet.
It is concluded that the surface of Zn-6%Al-3%Mg alloy coated steel sheet is covered with the protective corrosion products in the early stage of exposure, resulting in the remarkably improvement of atmospheric corrosion resistance.
