Stress corrosion cracking of an aluminum alloy under compressive stress

Abstract

Stress corrosion cracking (SCC) of 7075 aluminum alloy in a 3.5 pet NaCl aqueous solution under compressive stress was investigated using modified WOL notched specimen. The result showed that SCC could occur if an applied compressive displacement was larger than a critical value. Finiteelement analysis indicated that there was a stress concentration and the stress components were negative at the notch tip under the compressive displacement. Since the unloaded displacements were equal but opposite to the loaded ones, no stress relaxation occurred throughout SCC. Thus, the SCC was induced by compressive stress. The threshold stress intensity nucleating SCC from the notch under the compressive applied stress was 27.6 MPa m1/2, but the corresponding value under tensile stress was 8.3 MPa m1/2. Besides, the incubation period for SCC under compressive stress was one order of magnitude longer than that under tensile stress in the sameK1 The fracture surfaces of SCC under compressive stress were quite different from those under tensile stress. The latter was composed of intergranular but the former was quasi-cleavage characterized by parallel striation pattern.