Due to the wide industrial applications of aluminium and its alloys, extensive and intensive research concerning the electrochemical behaviour of these materials has been conducted. The electrochemical behaviour of Al and some of its widely used alloys was investigated in buffer solutions of different pH. The inhibition of corrosion of these materials in different solutions using known inorganic passivators like sulphates, molybdates and dichromates was studied. The effectiveness of dichromates as passivators for Al and its alloys in these solutions was discussed. X-ray photoelectron spectroscopy (XPS) was used to explain the role of the passivating anion in the corrosion inhibition process. It was found that Cr and Mo are incorporated in the barrier film on Al or its alloys after immersion in acidic or neutral solutions containing molybdates or dichromates. The inhibition efficiency is dependent on the concentration of the passivating anion in the solution. Scanning electron microscopy (SEM) has shown that the Al-Cu alloy has remarkable flawed regions which are due to the presence of Cu on the alloy surface as was confirmed by XPS. The flawed regions disappear completely after immersion in solutions containing the dichromates, and partially after immersion in solutions containing molybdates. The effectiveness of the dichromates as corrosion inhibitor for Al and its alloys is due to the powerful oxidizing properties of these anions which lead to the formation of a stable compact passive film.
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