Investigation into crack initiation from corrosion pit in 7075-T6 under ambient laboratory and saltwater environments

• Characterized experimentally transition of a corrosion pit to a crack under fatigue.
• Two types of corrosion pit (through and corner) at the hole were studied.
• Transition of pit to crack was studied in two environments (ambient and salt water).
• 2- and 3-dim finite element analyses were used to compute stress intensity factors.
• Stress intensity factor vs crack initiation cycle relations were analyzed & compared.

Transition of corrosion pit to crack was studied. Fatigue cycles to initiate 250 μm crack from two corrosion pit configurations under ambient laboratory and saltwater environments were correlated with stress intensity factor range (ΔKI) and applied stress range. Stress to initiate crack from through-pit was less than from corner-pit in both environments. ΔKI to initiate crack from corner-pit was less than from through-pit in both environments. However, stress or ΔKI to initiate crack was less in saltwater than ambient environment for both pit configurations. Fatigue damage mechanism was similar in both pit configurations and under both test environments.