The corrosion of Zn-11%Al-3%Mg-0.2%Si hot-dip galvanized steel sheet

Abstract

For the improvement on corrosion resistance of Zn-5mass%-0.1mass%Mg hot-dip galvanized steel sheet, it was investigated that the influence of Al and Mg contents and Si addition in coating on the corrosion resistance of the coating. It was found that the corrosion resistance of Zn-11mass%Al-3mass%Mg-0.2mass%Si galvanized steel sheet is more than 5 times superior to Zn-5mass%Al-0.1mass%Mg galvanized steel sheet in the corrosion loss after the SST, and also superior to that in the outdoor exposure test. According to the polarization measurements in the 5mass% NaCl solution, further additions of Al, Mg and Si in the Zn-5mass%Al-0.1mass%Mg coating decreased the both anode and cathode currents. This effect is regarded as one of reasons of enhancement of corrosion resistance in the SST. It is supposed that the increased polarization is related to the thickness and stability of basic zinc chloride as the corrosion product formed on the Zn-11%Al-3%Mg-0.2%Si coating.