Evolution of Surface Changes and Corrosion Kinetics During Atmospheric Corrosion in Seacoast Environment, Part I: AA2024-T3 Available to Purchase

This study examines the anodic and cathodic reactions on AA2024-T3 during seacoast exposure using potentiodynamic polarization and a modified droplet cell method, which creates a surface electrolyte by adding water to the contaminated surface. Corrosion kinetics were determined over the exposure period of 1 y at the seacoast. Ion chromatography was used to track the concentration of the soluble species on the surface, while optical microscopy and scanning electron microscopy (SEM)-energy dispersive spectroscopy were used to document the corrosion morphology. Early exposure conditions, particularly relative humidity (RH) and temperature, strongly influenced initial corrosion kinetics. Dealloying of the S-phase and copper redistribution increased the corrosion potential during the first 2 d, with limited wet conditions sustaining higher corrosion rates for the first 4 d. By day seven, increased RH and chloride deposition promoted oxide formation around the cathodic intermetallic particles, reducing cathodic kinetics. Mud cracking was evident in SEM images after 7 d, and chloride dominated in the early stages, while sulfate increased later, slowing corrosion until 90 d. Over time, accumulated damage led to higher corrosion rates, with chloride and sulfate concentrations increasing after 6 month of exposure, while sodium and calcium ion concentrations showed no clear trend. The corrosion morphology shifted from chloride-rich pits to sulfur-rich cracked corrosion products over the exposure period.