Transition from Localized Corrosion to Stress Corrosion Cracking in an Al-Li-Cu-Ag Alloy

Abstract

Abstract The early stages of stress-assisted corrosion and stress corrosion crack (SCC) initiation from machine-notched aluminum alloy (AA) 2096 (UNS A92096) specimens, lacking prefatigue cracks, were investigated. Double-notched tensile specimens of an extremely SCC-susceptible underaged (i.e., 4-h artificially aging at 160°C) temper of AA2096 were exposed in an alternate immersion (A/I) 0.6 sodium chloride (NaCl) environment. Focused ion beam (FIB) sectioning/secondary electron imaging methods were used to study and document the earliest stages of pit, intersubgranular corrosion, corrosion fissure, and SCC development starting from LT surfaces. SCC in machine-notched AA2096 involved several stages: trenching of the alloy matrix along bands of constituent particles, constituent particle-induced pit or trench coalescence, elongated corrosion fissure growth initially by general dissolution on the length scale of subgrains and the transition to intersubgranular attack, followed by the initiation/transition ...