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Investigation of the Fe content effect and thermo-mechanical processes on oxide films of EN AW 8006 alloy with the EIS

Properties of anodic oxide films on EN AW 8006 alloy with different contents of Fe have been determined by the means of electrochemical impedance spectroscopy. The tested electrodes have been made of samples taken after industrial casting and cold rolling. In the passive potential range the system response in the Nyquist complex plane is a semicircle whose diameter increases with the increase of the potential. The capacitive semicircle describes the dielectric properties of the surface oxide film. When potential shifts to the anodic direction, oxide film formed on the surface of all samples have better protective properties. However, oxide film can form only at potentials that are more negative than the repassivation potential, Erp. When this threshold is overcome, and the active potential range entered, the surface oxide film is destroyed and the alloy dissolves intensively. These changes are accompanied by the appearance of an inductive loop in the impedance diagram and significant decrease of the total system impedance. The cold rolling of aluminium alloys generates the deformed layers on surface. These deformed layers have a high electrochemical reactivity which affects on corrosion resistance.

Aluminium alloys; Al-Fe-Mn alloy; EN AW 8006 alloy; rolling; EIS

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