Environmentally Assisted Fracture of Aluminum Alloys

Aluminum alloys AA⁽¹⁾ 7017, 7018, and 7475 are known to be susceptible to stress corrosion cracking (SCC) in moist air, but cracking may be enhanced when the alloys are pre-exposed to an aggressive environment before SCC testing. In this study, the fracture morphology has been correlated with the kinetic data of crack velocity and stress intensity. The morphology of all three alloys revealed several interesting features; intergranular fracture was shown frequently to consist of arrest markings, ductile dimpled, and quasi-brittle intergranular fracture. Arrest markings suggest a discontinuous mode of crack growth, and a correlation is sought between the change in the stress intensity range with the distance of arrest markings occurring in Regions II and I of the crack velocity-stress intensity (V-K) curves. Other results are also described, which form the basis of this paper.