Effect of heat treatment on filiform corrosion of aluminium alloy AA3005

The effect of heat treatment on the filiform corrosion (FFQ susceptibility of rolled aluminium alloy AA3005 at temperatures in the range 150-500 degreesC is investigated. A drastic loss of corrosion resistance takes place as a result of annealing at temperatures in excess of 350 degreesC. TEM investigations revealed a highly deformed near-surface region, approximately 1 mum thick, on the as-received material. The presence of this surface layer is caused by shear deformation of the surface region during rolling. The enhanced deformation undergone by the surface layer promotes secondary intermetallic precipitation in this region during subsequent heat treatment. The resulting microstructure, where the near-surface region contains a higher density of fine intermetallic particles and lower solid solution levels of the more noble alloying elements than the underlying bulk, results in preferential attack of this layer during corrosion processes and is identified as the main cause of the observed loss of FFC resistance. (C) 2001 Elsevier Science Ltd. All rights reserved.