Corrosion of AA2024-T3 Part II: Co-operative corrosion

Polished specimens of AA2024-T3 alloy were immersed for up to 120 min in 0.1 M NaCl. The development of corrosion was monitored using scanning electron microscopy with energy dispersive X-ray spectroscopy (EDXS) and particle induced X-ray emission spectroscopy (PIXE). Both techniques revealed the intermetallic (IM) particle distributions and attack sites as distinguished by detection of chloride species. The earliest stages of attack involved localized attack around isolated IM particles as reported in Part I. Additionally attack occurred on a larger scale developing rapidly with rings of corrosion product surrounding clusters of IM particles. There were significantly higher numbers of IM particles within the corrosion rings, indicating that local clustering played an important role in co-operative corrosion.

Research highlights
► Corrosion of AA2024 in 0.1 M NaCl was examined for immersion times up to 120 min.
► Rings of corrosion products with H2 evolution developed as early as 5 min after immersion.
► The rings were distinct from corrosion around isolated intermetallics elsewhere on the surface.
► Analyses of chloride containing sites (red) showed a significant level of IM particle clustering.
► The number of neighbors was much higher at these sites than the average particle number density.