The effect of exfoliation corrosion on the fracture and fatigue behaviour of 7178-T6 aluminium

The effect of pre-existing exfoliation corrosion on the fracture toughness and fatigue crack growth of a high-strength structural aluminium alloy (7178-T6) is considered. The material tested is in sheet form and the toughness of the alloy is measured using the R-curve approach. Before testing, exfoliation corrosion is introduced in the crack tip region of the toughness specimens and ahead of the notch in the fatigue specimens using a solution recommended for accelerated corrosion testing. The toughness of the alloy is shown to be only slightly reduced by the presence of exfoliation corrosion at the crack tip, and this slight reduction is modelled by thinning of the material at the crack tip. Fatigue experiments show that the presence of exfoliation corrosion enhances the fatigue crack growth rate at intermediate ΔK values.