Abstract
Thus far the formulae shown the physical shape of coating corrosion circuit are reported. These are required to describe (1) the effective length (lc) of steel substrate contributing the formation of corrosion circuit between coating and steel substrate and (2) the distribution ratio (α) of corrosion current by way of circuit on coating to total coating corrosion current.
In this study, the effect of coating weight and corrosive environment on under-film corrosion of Zn, Zn-Fe alloy coated steel sheets is investigated quantitatively to use these formulae.
In Zn coated steel sheet, lc was independent on coating weight and constant, and a increased with an increase of coating weight on under-film corrosion in exposure environment. In Zn-Fe (15%) alloy coated steel sheet, lc was decreased and α increased with an increase of coating weight.
On the contrary, the coating corrosion rate and lc increased and α decreased with an increase of wet time in corrosive environment.
