Stress Corrosion Cracking of Sensitized AA5083 in NaCl Solution

In this study, commercial AA5083 aluminum alloy was sensitized at 175^oC, in order to create a two-phase microstructure that is highly susceptible to stress corrosion cracking (SCC).  To characterize the SCC behavior of these sensitized AA5083 alloy in NaCl solution, open circuit continuous immersion SCC tests were conducted on pre-cracked double lever cantilever beam (DCB) specimens with an initial stress intensity factor (K_I) of 15 ksi√in, in NaCl solutions with five different concentrations, i.e. 0.01, 0.1, 0.6, 1, and 3 mol/L.  Three SCC characteristics, incubation time, initial crack growth rate, and total crack growth, were found strongly dependent on solution concentration:  incubation time decreased with increasing NaCl concentration, while both initial crack growth rate and total crack growth increased with solution concentration.  A linear relationship between initial crack growth rate and NaCl concentration, as well as between total crack growth and NaCl concentration, was also found.  Since the growth of cracks under fixed loading line displacement decreases the applied K, the arrest of cracks that limits the total crack growth may be interpreted as a concentration dependent threshold stress intensity, K_ISCC. Fracture surfaces produced by SCC in NaCl solutions with different concentrations and on different values of K, when investigated by scanning electron microscopy, all demonstrated intergranular cracking with similar characteristics.  Discussion centers on relative contributions to SCC from mechanical driving forces and chemical driving forces.