Evaluation of Stress Corrosion Cracking Susceptibility of 2195-T8 Al-Li Alloy in Propellant Environment Using Slow Strain Rate Testing

The stress corrosion cracking (SCC) susceptibility of 2195-T8 Al-Li alloy in N2O4 medium was evaluated using slow strain rate testing (SSRT). The electrochemical corrosion behavior and morphological evolution of the alloy under different conditions were further examined through potentiodynamic polarization measurements. The results indicate that with the increase in electrochemical corrosion rate, the corrosion morphology of the alloy extends from localized pitting and intergranular corrosion to severe exfoliation corrosion. In the N2O4 medium, the alloy exhibits significant susceptibility to SCC at tensile rates of ε ≥ 5 × 10−6 s−1. However, when strained at ε = 10−6 s−1, a sudden increase in ISCC is observed accompanied by a transition to brittle intergranular fracture mediated by anodic dissolution. At the same stretch rate (ε = 10−6 s−1), the susceptibility to SCC of the alloy in N2O4 medium increased with higher water content ω(H2O). This trend is attributed to enhanced generation of HNO3 and HNO2, as well as increased diffusion of hydrogen—produced by the cathodic reaction—to the crack tip. The synergistic interaction between anodic dissolution and hydrogen embrittlement ultimately promotes the initiation and propagation of SCC in the alloy.