On the origin of fatigue corrosion cracking in Al7075

The fatigue corrosion cracking of the Al7075 alloy has been investigated by Scanning Electron Microscopy (SEM) and Auger Electron Spectroscopy (AES). Specimen exposed to cyclic load at room temperature until crack initiation show a significant increase of magnesium within a distance of about 1 m around the crack, while almost no aluminum was left. This segregation effect has been investigated in detail, yielding that the diffusion should most likely be driven by the gradient of the chemical potential through the oxidation of magnesium at the surface, while the required mobility for the diffusion process was gained by the mechanical stress of the cyclic loading.