Stress corrosion crack initiation and propagation characteristics of 7xxx high-strength Al alloy plate: Experiments and modeling

High-strength 7xxx aluminum (Al) alloy is widely used in aerospace and ocean engineering as a structural material, causing a risk of stress corrosion crack (SCC) in equipment. Mechanical experiments equipped with in-situ electrochemical measurements and finite element modeling were conducted on 7xxx Al alloy in 3.5 wt% NaCl solution to research the effect of elastic–plastic deformation on SCC mechanism. The grain structure, corrosion pits, surface cracks and electrochemical behavior of the SCC samples were compared. A model for pit-crack transformation was proposed that considered the combined effects of constant load and slow strain rate tensile. Findings demonstrated that the stress induced a variation in the microstructure of the 7xxx Al alloy, which indicated an increase in the proportion of low angle grain boundaries (LAGBs) and a rise in the kernel average misorientation (KAM) value. The strain concentration coefficient ($K_{\epsilon }$) of the plastic deformation sample was higher than that of the elastic deformation sample, due to the larger aspect ratio (width D/depth d) of its pits. The severe plastic deformation sample (ε_s = 12.5 %) had the highest SCC susceptibility, exhibiting large-scale and dense SCC crack generation due to microstructure transformation and passive film defects.