Corrosion of AA2024-T3 Part I: Localised corrosion of isolated IM particles

Polished specimens of AA2024-T3 were immersed for various times up to 120 min in 0.1 M NaCl. The development of corrosion around isolated intermetallic particles was monitored using scanning electron microscopy with energy dispersive X-ray spectroscopy (EDXS). The earliest stages of attack started with localised corrosion of the S-phase particles resulting in dealloying which was followed by trenching around these particles. Subsequently, trenching was observed around cathodic particles where trenching started with AlCuFeMn particles with Cu/Fe ratios typically around 2.5 and then progressed to AlCuFeMnSi particles. This latter category of particles had a much lower Cu/Fe ratio, typically 0.5.

Research highlights
► Corrosion of AA2024-T3 in 0.1 M NaCl was examined after various immersion times up to 120 min.
► It was found that localised corrosion at isolated intermetallic (IM) particles proceeded through a hierarchy of attack.
► Attack began at around 2.5 min on S-phase particles which underwent dealloying and by 15 min had developed trenches around their peripheries. The morphology of the corrosion product changed considerably during this period.
► Attack on cathodic particles appeared to initiate after corrosion had finished at S-phase particles and proceeded to AlCuFeMn IM particles where the attack was complete by 30 min. Corrosion then became active around the (Al,Cu)x(Fe,Mn)ySi. IM particles and was complete by 120 min immersion.