STRESS-CORROSION BEHAVIOR OF ALPHA-ALUMINUM BRONZE IN SALINE WATER

Alpha-Aluminum bronze (Copper[Cu]-7% Al) (UNS C61400) was found to be susceptible to stress corrosion cracking (SCC) in 3.4% NaCl under relatively high anodic potentials (greater-than-or-equal-to 300 m V(NHE), i. e., greater than 200 m V more positive than the free-corrosion potential. The time to failure and stress ratio (sigma soln/sigma air) were mildly dependent on potential The fracture mode changed from ductile under open-circuit and mild anodic or cathodic potentials to brittle at 300 m V(NHE). Electrochemical and x-ray diffraction data were obtained to suggest interpretations for the SCC measurements. The bronze's susceptibility to SCC at high anodic potentials was attributed to the presence of cuprous chloride (CuCl) on the surface. CuCl was absent at low potentials. The bronze's resistance to SCC at low potentials was attributed to the presence of theta-aluminum oxide, which was detected by x-ray diffraction on the corroded surface.