Influence of heat treatments and anodization on fatigue life of 2017A alloy

In order to investigate the coupled effects of heat treatments and anodizing processes on fatigue life of aluminium alloy 2017A, a series of fatigue tests were conducted at 25 Hz. The effect of different tempers, naturally and artificially ageing (T4 and T6) and overageing (T7) conditions before sulphuric anodization were studied. Additionally, information on the microstructure of the anodic films was acquired by Scanning Electron Microscopy (SEM) analyses. The image analysis yielded qualitative information on the evolution of the surface morphology as a function of the substrate microstructure. Hence measured mechanical properties were directly related to the corresponding microstructure, the result of fatigue tests showed a decrease in fatigue life of anodized specimens as compared to untreated ones. This phenomenon became more pronounced in the T6 and T7 states. The decrease in the fatigue life could mainly be attributed to the brittle nature of oxide layer and to the heterogeneous microstructure of the film.