Systematic Evaluation of Strain Rate and Environmental Conditions Effects on Stress Corrosion Cracking of an Al-Cu Alloy

The aim of this study is to comprehensively investigate and quantify the effect of strain rate (SR) and environmental parameters on the stress corrosion cracking (SCC) behavior of a high-strength, aluminum–copper alloy. Slow strain rate (SSR) tests were carried out in air at 25 °C, over a SR range from 10−4 to 10−7 s−1 and controlled relative humidity (RH) between 40% and 80%. The influence of the pre-soaking period in 3.5 wt.% NaCl solution was also assessed. A major effect of pre-soaking was identified, as it was necessary for the onset of SCC. Increasing RH over 40% and decreasing SR below 10−5 s−1 significantly intensified SCC susceptibility, leading to ductility loss up to 84%. SSR test results were supported by microstructural investigations, with particular emphasis on the role of second phases. Their electrochemical activity was examined by scanning Kelvin probe force microscopy (SKPFM), while intergranular corrosion (IGC) susceptibility was evaluated according to the ISO 11846 standard. The pronounced IGC susceptibility of the alloy led to predominantly intergranular fracture morphologies in cross-section peripheral areas after SSR testing. The results confirmed the synergistic effect among microstructure, IGC susceptibility and SCC behavior, identifying a critical window of mechanical and environmental parameters governing SCC.