Dependence of the corrosion behavior of aluminum alloy 7075 on the thin electrolyte layers

The corrosion behavior of aluminum alloy 7075-T6 dependent of the thin electrolyte layers in 1 M sodium sulfate solution has been investigated using cathodic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The oxygen reduction current is measured to be maximum at −1.1 V by cathodic polarization test when the thickness of the electrolyte layer is 110 μm. The EIS results show that the corrosion rate increases with the increase of the immersing time independent of thickness of the electrolyte layer although 110 μm thick electrolyte layer produces the largest corrosion rate over the immersing time between 0 h and 96 h. However, with the longer immersing time, corrosion rate of the sample in bulk solution becomes higher. This result can be explained that the diffusion of the corrosion product and the metal ions from the electrode in the case of the thicker layer is easier. SEM morphologies reveal that corrosion products on the surface of the samples are distributed unhomogenously, with their amount near edges being more than the center area. In addition, XPS analysis demonstrates that corrosion products are mainly composed of Al(OH)3 and Al2(SO4)3.