Electrodeposition and characterization of polypyrrole films on aluminium alloy 6061-T6

Polypyrrole films on aluminium alloy 6061-T6 were prepared by electropolymerization of pyrrole in sulphuric acid using two different processes – cyclic voltammetry and potentiostatic polarization – and assessed through SEM observation and voltammetry. The anticorrosive properties of these films were studied by polarization curves and electrochemical impedance spectroscopy.The polypyrrole films formed by both methods are homogeneous and present a globular structure. However, it was found that the films produced by cyclic voltammetry are thicker than those produced potentiostatically at a potential equal to the upper limit of the cyclic voltammetry (Eλa). It was also found that there is an optimum value for the formation potential (Eappl, in the case of the potentiostatic method or Eλa for cyclic voltammetry). Above this value, overoxidation of the polymer occurs, which is found to be deleterious to the coated system behaviour.From polarization curves no major differences were detected between the PPy-coated alloy and the bare material, indicating that no significant protection is achieved by the polymer coating. On the other hand, Bode diagrams are typical of a system undergoing pitting corrosion and show lower impedance values for the alloy covered with polypyrrole than for the bare metal. This can be attributed to the conductive character of the polypyrrole films.