Characterization of electrochemically active surface layers on rolled commercial alloys AA8006 and AA5182 aluminum

Electrochemical properties of the as-processed surface layer on aluminum alloys can be significantly altered in relation to the properties of the underlying bulk material by thermomechanical processing, and this in turn affects the corrosion properties. A typical example is the large negative corrosion potentials obtained by heat-treatment of certain rolled commercial alloys. Two typical cases, as represented by the rolled aluminum alloys AA8006 and AA5182, were investigated in this work by electrochemical and surface-analytical characterization. Both materials exhibit unusually negative corrosion potentials in chloride solution, in as-received and annealed conditions. However, the former alloy is susceptible to filiform corrosion, while the latter is not. It was shown that the negative corrosion potential on alloy 8006 was a result of electrochemical activation, while that on alloy 5182 was due to passivation of the cathodic sites. An attempt was made to correlate the surface chemistry and structure specific to these alloys with their electrochemical and corrosion behavior. (C) 2001 The Electrochemical Society.