Effects of Potential and Material Anisotropy on Fatigue Crack Growth Characteristics of 7075-T6 Aluminum Alloy in 3.5% Saltwater

Fatigue crack growth tests were made in air and in 3.5% saltwater on 7075-T6 aluminum alloy specimens extructed in LT and TL directions. The testing in saltwater was made under the application of anodic and cathodic potentials. The test results showed that the crack growth rate in saltwater was higher than that in air under all the conditions tested, regardless of the applied potential and the specimen orientation. Although an appreciable effect of the applied potential was observed in the lower ΔKI range of the da/dN-ΔKI relation for LT specimen, almost no effect of potential was observed in both the da/dN-ΔKI relation for TL specimen and the da/dN-ΔKIeff relations for LT and TL specimens. Intergranular fracture and secondary cracking of intergranular type were observed quite often in the LT and TL specimens fatigued under free corrosion.