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

Electrochemical properties of the as-processed surface layer on aluminum al loys can be significantly altered in relation to the properties of the unde rlying bulk material by thermomechanical processing, and this in turn affec ts the corrosion properties. A typical example is the large negative corros ion potentials obtained by heat-treatment of certain rolled commercial allo ys. Two typical cases, as represented by the rolled aluminum alloys AA8006 and AA5182, were investigated in this work by electrochemical and surface-a nalytical characterization. Both materials exhibit unusually negative corro sion potentials in chloride solution, in as-received and annealed condition s. However, the former alloy is susceptible to filiform corrosion, while th e latter is not. It was shown that the negative corrosion potential on allo y 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 corre late the surface chemistry and structure specific to these alloys with thei r electrochemical and corrosion behavior. (C) 2001 The Electrochemical Soci ety.