| Understanding of localized corrosion and its growth kinetics is critical from both scientific and practical points of view, since the high strength Al alloys widely used in aircraft structures are extremely susceptible to localized corrosion. In this dissertation, the foil penetration technique, an non-electrochemical method for studying the growth kinetics of the fastest-growing localized corrosion site (pit, crevice, or intergranular attack), combined with electrochemical techniques, metallographic cross-sections, and other materials characterization tools such as SEM, TEM, and microfocal X-ray radiography, were used to address the effects of alloy microstructure, sample orientation, and artificial aging, potential, and environmental factors on the kinetics and morphology of localized corrosion in AA2024 (Al-4.5%Cu-1.5%Mg).; Localized corrosion kinetics in T3 temper exhibited a strong anisotropy. Growth in the short transverse direction was found to be much slower than that in either the longitudinal or long transverse direction. The anisotropy occurred because pits that initiated on the surface often developed into intergranular corrosion (IGC) as they grew into the microstructure. Metallographic cross sections confirmed that the growth rate anisotropy was a result of microstructural anisotropy. The anisotropy of the kinetics was found to be different for various forms of AA2024-T3 having different microstructures.; Artificial aging had a strong effect on polarization behavior and corrosion morphology. AA2024 in the solution heat treated and water quenched condition, T3, and T3+ tempers exhibited two breakdown potentials, whereas overaged AA2024-T8, T8+ exhibited only one breakdown potential. When two breakdown potentials were observed, the more active one was found to be related to the transient dissolution of S-phase Al2CuMg particles leading to pitting while the noble one was thought to result from initiation of IGC or the transition of pits to IGC. The aging did not have a significant effect on the localized corrosion kinetics at −580 mV SCE and open circuit. Finally, a statistical model was developed for IGC growth kinetics on the basis of the Al alloy microstructure. |
