The effect of microstructure and environment on fatigue crack growth in 7049 aluminium alloy at negative stress ratios

The EFS (Electrochemical Fatigue Sensor) is a device that is based on a study of electrochemical–mechanical interactions, providing information about the status of fatigue damage in a material, and promises to become a useful non-destructive, niche testing tool. The EFS has been shown to function for several commercial alloys, as well as in different environments. The present work is to confirm the feasibility of applying the EFS for assessing fatigue damage in duplex stainless steels. A second goal is to investigate the possibility of using an aggressive environment as an electrolyte within the EFS device. In doing so, corrosion-fatigue testing was conducted in EFS solutions at three different pH values: 8.4, 6 and 2. The results show that the fatigue life is longer at a pH value of 6. Such an unexpected environmental effect is discussed and related to the dissolution of the surface roughness generated by cyclic deformation, together with a higher repassivation rate.