Effect of temperature on the localized corrosion of AA2024-T3 and the electrochemistry of intermetallic compounds during exposure to a dilute NaCl solution

In this study, the electrochemical properties of synthesized intermetallic compounds (IMCs) similar to those commonly found in AA2024-T3 were studied in neutral 0.1 M NaCl at 10, 30, 50, and 70°C using the electrochemical microcell method. Results on the synthesized IMCs were combined with and supported by analysis of free corrosion experiments performed on AA2024-T3. Results reveal that, in general, corrosion rates of the IMCs increase with temperature and pitting potentials of most IMCs show a slight decrease with temperature. Increased dealloying kinetics of S-phase with increasing temperature was evident in both open-circuit potential transients and post-exposure corrosion morphology characteristics, leading to increased Cu surface areas and a higher likelihood of the propagation of localized corrosion into the matrix. The corrosion potential of synthesized Al-Cu-Mn-Fe type particles was found to be cathodic to the matrix at low temperatures, but anodic to the matrix at high temperatures. This hightemperature behavior led to dissolution of Al-Cu-Mn-Fe type particles, not commonly found under ambient conditions. After dealloying, these particles became cathodic to the matrix, leading to trenching similar to that found under lowtemperature conditions. The limiting current density on most synthesized IMCs, as a result of the oxygen reduction reaction, was maximized at around 50°C, consistent with calculations using a simplified Cottrell equation and based on the temperature dependence of oxygen solubility and oxygen diffusion.