Fractography of Stress Corrosion Cracks in Aluminum Alloy 7075

As suggested by Evans¹  and demonstrated by Meyn,²  propagation of a stress corrosion crack can be irregular, with corrosion occurring at some points of high susceptibility, while other points along the crack front remain intact. When the local load sustained by these bridges of sound material rise above a critical level by reason of their decreased size and position at the rear of the more advanced corrosion front, they rupture mechanically. Hence, the relative proportions of fracture surface which show features characteristic of corrosion processes on the one hand and mechanical rupture on the other will depend upon the crack tip stress or stress intensity. When the average crack tip stress is low, so that the bridges of more corrosion resistant material become quite small before rupturing, features characteristic of corrosion processes should predominate. When the crack tip stress level is nearer the higher value necessary for dry...