Abstract:
The study investigates the effect of prior corrosive exposure on crack growth resistance behaviour of
thin sheet (3 mm thick) aluminium alloy 2024-T3 at slow strain rates. Compact tension specimens were
exposed to standard corrosive environments that simulate accelerated atmospheric corrosion attack.
Two corrosive environments were considered – an exfoliation corrosion (EXCO) solution and a 3.5 wt%
sodium chloride solution. The unloading compliance R-curves of the two-hour EXCO-exposed specimens
revealed a significant degradation of approximately 11% in the crack growth resistance behaviour
(Kc_e values) compared to the baseline (air-exposed) values. Furthermore, secondary intergranular
crack formation was also revealed in the plastic zone ahead of, and adjacent to, the crack tip of these
specimens; which formed during the crack growth resistance loading. It is postulated that the observed
degradation of the Kc_e values of the EXCO-exposed material is due to hydrogen embrittlement since
the exposure times for the EXCO evaluation were limited to ensure that uniform corrosion dominated;
that is, significant penetration of corrosion damage and pitting due to localized corrosive attack did not
occur. The sodium chloride-exposed specimens revealed a similar degradation (13%) after 24 hours
exposure. However, slight intergranular corrosive attack and isolated pitting were observed on the
exposed surfaces prior to crack growth resistance loading, resulting in notch effects that could assist in
crack growth. Pitting and intergranular corrosion were, however, not observed at the pre-crack tip. The
relative contributions of the notch effects and the hydrogen embrittlement during the degradation of the
KR performance are, therefore, unclear.
