Direct observations of microstructure-resolved corrosion initiation in AA7075-T651 at the nanoscale using vertical scanning interferometry (VSI)

Early stage micro-galvanic corrosion attack at and around different intermetallic compounds (IMC) present on the pristine surface of AA7075-T651 was investigated using multiple microscopy-based modalities. The microstructural surface features and chemical compositions of the major constituent of AA7075-T651 were analyzed using scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy (EDS) and electron backscattered diffraction (EBSD). Exposure at free potential was conducted in 3.5 wt% NaCl aqueous solution for 1 h. At every 10 minute interval, the sample was rinsed and corrosion attacks were visualized using vertical scanning interferometry (VSI). The localized dissolution rate and morphology of the alloy matrix adjacent to cathodic and anodic inclusions was rationalized to obtain virtual corrosion metrology. Subsequently, the self-dissolution and variations in corrosion attack at and around the major cathodic and anodic area were examined using cross-section focused ion beam (FIB). Combing with previous investigations on similar Al alloys, the understanding of the localized dissolution associated with micro-galvanic corrosion was advanced.