Insights into the cut edge corrosion of 55% Al–Zn metal coating on steel from simultaneous electrochemical polarization and localised pH sensing experiments

Band microelectrode arrays were used to model the cut edge corrosion behaviour of 55% Al–Zn (Galvalume/Zincalume) and Zn coated steels in chloride and sulfate electrolytes. Simultaneous electrochemical polarization experiments revealed increased cathodic current on the steel during anodic dissolution of neighbouring Al–Zn alloy electrodes. The increased cathodic current on the steel was shown to be a result of pH buffering by Al3+, enhancing the rate of hydrogen evolution. A large negative shift of the corrosion potential of the Al–Zn alloy electrodes was observed during cathodic polarization on neighbouring steel electrodes and was attributed to alkaline pH generated from cathodic processes.

► 55% Al–Zn coated steel as electrode arrays.
► Al3+ and Zn2+ ions buffered the pH within hundreds of microns of the surface.
► pH buffering from Al3+ ions enhanced cathodic processes on steel.
► Zn2+ ions did not significantly affect cathodic current densities on steel.