An electrochemical framework to explain the intergranular stress corrosion behavior in two Al–Cu–Mg–Ag alloys as a function of aging

Abstract

A modified version of the Cu-depletion electrochemical framework was used to explain the metallurgical factor causal to intergranular stress corrosion cracking (IGSCC) susceptibility in two Al–Cu–Mg–Ag alloys (i.e., Al–5.0%Cu–0.8%Mg–0.5%Ag and Al–5.4%Cu–0.5%Mg–0.5%Ag). This framework was also used to explain the specific cases of IGSCC susceptibility in the under-aged condition and increased IGSCC resistance with over-aging. Susceptibility in the under-aged and T8 (peak-aged) conditions is consistent with the grain boundary Cu-depletion mechanism and high concentrations of Cu in solid solution in grain interiors. Improvement in resistance to IGSCC of the over-aged T8+ condition (i.e., T8 temper followed by an additional thermal exposure of 5000 h at 107.2 °C) can be explained by elimination of the differential Cu concentration adjacent to the grain boundary compared to that of the grain interior. The resultant leveling of Cu concentration leads to the suppression of a preferential dissolution path at the grain boundaries associated with IGSCC.