Effect of Oxide Films on Fatigue Properties of Anodically Oxidized Aluminum Alloys

Aluminum alloys are widely used in our daily lives, from large structural parts such as automobiles to small items such as aluminum cans and aluminum foil, because of their light weight and high strength. However, aluminum alloys have the disadvantage of being soft and susceptible to surface damage, which is generally remedied by anodizing. In this study, fatigue tests were conducted with and without anodic oxidation treatment in order to evaluate the strength of anodic oxide. As a result, it was confirmed that anodic oxidation treatment reduced fatigue strength in a certain stress range. It was also inferred that cracks in the oxide film were the cause of the decrease in fatigue strength. Therefore, the condition of crack generation was also discussed by observing the surface condition during tensile and fatigue tests. From these tests, it was confirmed that the oxide film exhibits brittle fracture, and that these cracks lead to the notch effect, which results in the reduction of fatigue strength.