FIB/SEM study of AA2024 corrosion under a seawater drop, part II

The dissolution of S-phase clusters in aluminium alloy 2024 (AA2024) exposed to a 0.5 μl seawater droplet is presented. Foils for transmission electron microscopy (TEM) were made from local attack sites using a focussed ion beam/scanning electron microscope (FIB/SEM). The sections showed that clusters of S-phase particles underwent dealloying. The resulting copper sponge morphology, banding, preferred orientation and crystal defect structure as a result of plastic deformation have been characterised. With build-up of amorphous corrosion product, physical and electrical isolation of parts of the clusters developed, with the result of copper dissolution from the S-phase remnants.

► Dealloying has a directional nature, exhibits banding.
► Oxidation state of copper in sponge remnants found to be variable.
► Dissolution and breakdown of copper sponge structure observed.
► Crystalline defects imaged in dealloyed S-phase.