Stress corrosion cracking behavior of the wrought magnesium alloy AZ31 under controlled cathodic potentials

Abstract

► We investigated stress corrosion cracking (SCC) behavior in Mg alloy. ► We examine SCC behavior dominated by anodic dissolution and hydrogen embrittlement separately. ► Threshold stress intensity factor is higher in hydrogen embrittlement type SCC. ► Crack propagation rates were accelerated by larger amount of charged hydrogen. Stress corrosion cracking (SCC) tests were performed using compact tension (CT) specimens in a NaCl solution under hydrogen-charged conditions to investigate the SCC behavior of the wrought magnesium alloy AZ31. The effect of NaCl concentration was estimated by conducting the SCC tests under a constant cathodic potential of −1.4 V, with NaCl concentrations of 0.5, 3.0 and 8.0%. The crack propagation rate (d a /d t ) became accelerated with increasing concentration due to the enhanced anodic dissolution by chloride ions. Subsequently, SCC tests were performed using a 3%NaCl solution with cathodic potentials at −1.4, −2.5 and −3.0 V to investigate the effect of cathodic potentials on SCC behavior. According to the Pourbaix diagram, the cathodic potential of −3.0 V corresponds to the immunity region, whereas −1.4 V is within the corrosion region and −2.5 V is the boundary between the two regions. In the immunity region, the SCC due to hydrogen embrittlement occurred when the K Iscc value was higher than that of the SCC dominated by anodic dissolution. The K Iscc value decreased and the crack propagation rate increased with decreasing cathodic potential in the immunity region at which SCC occurred due to hydrogen embrittlement. At the cathodic potential of −3.0 V, the d a /d t was insensitive to the stress intensity factor because highly charged hydrogen gave rise to brittle fracture.