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 degrees 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 high-temperature 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 low-temperature conditions. The limiting current density on most synthesized IMCs, as a result of the oxygen reduction reaction, was maximized at around 50 degrees C, consistent with calculations using a simplified Cottrell equation and based on the temperature dependence of oxygen solubility and oxygen diffusion.