1996 Volume 45 Issue 7 Pages 432-438
Corrosion behavior of Zn (EG) and Zn-Fe alloy (Zn-Fe) electroplated steel sheets in atmospheric exposure test was investigated by observation of the appearance, polarization measurement, anodic dissolution analysis, and corrosion products analysis. Corrosion resistance of EG and Zn-Fe changed as follows with increasing Fe content in deposit; nearly constant in 0-10 mass%Fe, decreasing in 10-20 mass%Fe, nearly constant in 20-30 mass%Fe, decreasing over 30 mass%Fe. Corrosion rate of the coating was 12.3g/m2·year and 22.9g/m2·year for 0-10 mass% and 20-30 mass%Fe, respectively. The mechanism of the corrosion behavior was considered as follows; Uniformly formed zinc corrosion products such as 4ZnO⋅CO2⋅4H2O, etc. suppress diffusion of oxygen through the corrosion product layer in the range of 0-10 mass%Fe, whereas α-FeOOH formed in the corrosion products promotes the oxygen diffusion in the range over 10 mass%Fe, thus resulting in decrease in corrosion resistance.
