Accelerated Grain Boundary Corrosion of Dilute Zinc-Aluminum Alloys Under High Applied Cathodic Currents

Under relatively high applied cathodic current densities (⩾0.5 mA/cm²), hot rolled Zn-Al alloys in hot water suffer very rapid boundary attack and blistering which appear to be caused mainly by hydrogen accumulation within the corroding boundaries. This effect does not occur in pure zinc, but additions of 0.03% Al are sufficient for this attack. The grain boundary corrosion rates have an approximately logarithmic dependence on the current density and a linear dependence on temperature in the range 40 to 90 C. Grain boundary corrosion rates are much less dependent on the alloy purity than is the case for intergranular corrosion when no cathodic current is applied. Instead, the rates are in this case very dependent on the water composition and are particularly sensitive to the presence of carbonates.