Scanning electrochemical microscopy studies for the characterization of localized corrosion reactions at cut edges of coil-coated steel

The local distribution of anodic and cathodic sites in a corroding cut edge using the scanning electrochemical microscope is presented. Platinum and antimony microdiscs were used as tips for combined amperometric/potentiometric operation. Local changes in electrochemical activity, oxygen concentration and pH distribution associated to the onset of localized anodes and cathodes were imaged in situ, as well as their evolution with time. Local alkalization and oxygen consumption related to cathodic activity were detected above the zinc layer covered with the thinner polymeric coating, providing a direct evidence of a differential aeration process effectively operating in an asymmetrical cut edge, in addition to the galvanic coupling of aluzinc and steel. Anodic activity leading to local acidification occurred at the other aluzinc layer at all exposures.