Effect of anodized coatings on fatigue strength in aluminum alloy

In order to investigate the effect of anodized film on fatigue strength of aluminum alloy, A2014-T6, repeated tensile fatigue test was conducted in laboratory air under the stress ratio, R, of 0.01 using smooth specimen with anodized film thickness of 3 mum. Fatigue strength of anodized specimen tested under R=0.01 decreased by 18-20 % as compared with that of the untreated one, even though the anodized film did not affect the fatigue behavior under the rotating-bending fatigue test of R = -1. The anodized film is fractured at an early stage of repeated tensile fatigue process, because it is too brittle to accommodate the substrate metal. Many cracks are induced to initiate at the substrate by flaws of the anodized film. It was pointed out through the study that the fatigue strength of anodized aluminum alloy is controlled by the crack initiation behavior in the substrate induced by the rupture of the anodized film, which is related to deformation of the substrate metal during fatigue process.