Mapping initial stages of localized corrosion of AA6061-T6 in diluted substitute ocean water by LEIS and SKP

Localized Electrochemical Impedance Spectroscopy (LEIS) and Scanning Kelvin Probe (SKP) maps were acquired to characterize the initial corrosion activity of 6061-T6 aluminum alloy in diluted substitute ocean water up to 24 h, simulating low polluted atmospheric environment in chlorides. Both measurements were performed in situ at open circuit potential. LEIS maps showed the distribution of the impedance magnitude |Z| on the alloy surface, suggesting a heterogeneity in development of corrosion-active sites (first pits). SKP maps evidenced the appearance of anodic (with more negative potential) and cathodic sites on the alloy surface, which confirmed the localized character of the corrosion. SEM-EDX analysis revealed the initiation of localized aluminum dissolution in the vicinity of iron-rich intermetallic particles of Al-Fe-Si and in areas with segregated carbon, all acting as cathodes and remaining on the surface with the advance of the process.