Electrochemical behaviour and corrosion inhibition of Al, Al-6061 and Al-Cu in neutral aqueous solutions

The electrochemical behaviour of Al and two of its widely used alloys, Al-6 061 and Al-Cu, was investigated in neutral solutions at pH 7. The corrosion inhibition of these materials was studied in neutral solutions using sulph ates, molybdates and dichromates as passivators. The effectiveness of dichr omates as passivators for Al and its alloys in these solutions was discusse d. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to explain the role of the passivating anion in the corrosi on inhibition process. It was found that Cr and Mo are incorporated in the barrier film on Al or its alloys after immersion in neutral solutions conta ining these anions. Sulphate ions are adsorbed on the barrier film surface or present in the film in a very low concentration compared to dichromates and molybdates. The inhibition efficiency increases as the concentration of the passivating anion in the solution increases. Scanning electron microsc opy (SEM) has shown that the Al-Cu ahoy has remarkable flawed regions which are due to the presence of Cu on the alloy surface, as was confirmed by XP S. The flawed regions completely disappear after immersion in solutions con taining dichromates and partially disappear after immersion in solutions co ntaining molybdates. (C) 1999 Elsevier Science Ltd. All rights reserved.