An Investigation of the Fatigue Corrosion Behavior of Al 6063-T6 Alloy under Seawater Influence

The purpose of the present study was to investigate the fatigue behavior of Al-6063 alloy using standard rotating-bending test. Corrosion-fatigue test on similar samples was also performed at stress levels corresponding to fatigue test. The samples obtained from fatigue tests were considered as control samples and the results obtained from fatigue test in air were compared to the results obtained from corrosion-fatigue test in liquid seawater. Scanning Electron Microscopy (SEM) and Optical Microscopy (OM) were used to investigate the micro-structural features and crack characteristics of the specimens. The results obtained from fatigue and corrosion-fatigue test revealed that the presence of corrosion environment decreases the fatigue life. Additionally,  microstructure studies on the fracture surface due to corrosion-fatigue revealed that initiation of fatigue crack starts from the depth of corrosion steps and proliferate towards the sample center simultaneous with the penetration of liquid into the crack. Moreover, the appearance, size and propagation way of fatigue crack in corrosion-fatigue test was completely different from the cracks created in a fatigue test. The fracture surface due to corrosion-fatigue test was also different from the fatigue fracture surface. Further studies on failure levels revealed that the ratio of region area due to fatigue to the region area due to final failure was strongly decreased in the corrosion-fatigue test.