Multianalytical and in situ studies of localized corrosion of EN AW-3003 alloy - Influence of intermetallic particles

The influence of intermetallic particles (IMPs) on the localized corrosion behavior of an EN AW-3003 alloy was investigated in situ by conventional electrochemical measurements and high-resolution local probing techniques in chloride solutions with and without acetic acid. The open-circuit potential (OCP) fluctuations indicate local activities on the surface, and electrochemical impedance spectroscopy measurements suggest active dissolution in acidic solutions but a passivelike behavior in near-neutral solutions. Integrated atomic force microscopy/ scanning electrochemical microscopy (AFM/SECM) was used to investigate the localized activities on the surface in a diluted chloride solution. The concurrent AFM and SECM images reveal cathodic activity of the IMPs and enhanced anodic current due to localized dissolution adjacent to some large IMPs upon anodic polarization. Moreover, in situ AFM imaging at OCP in solutions containing acetic acid show localized dissolution around the IMPs, leading to formation of deposits of ringlike corrosion products. The in situ observations reveal the microgalvanic effect of the IMPs, and the large IMPs are more prone to initiate localized corrosion compared to submicrometer dispersoids. Infrared absorption spectroscopy measurements after the exposure and thermodynamic calculations suggest the formation of mixtures of aluminum oxihydroxide and acetate on the surface in the presence of acetic acid. (c) 2008 The Electrochemical Society.