effect of heat treatment on filiform corrosion of aluminum alloy aa3005

Eect of heat treatment on ®liform corrosion of aluminium alloy AA3005 A. Afseth a,c, * , J.H. Nordlien b , G.M. Scamans c , K. Nisancioglu a a Department of Materials Technology and Electrochemistry, NTNU, N-7491 Trondheim, Norway b Department of Corrosion and Surface Technology, SINTEF, N-7465 Trondheim, Norway c Alcan International Limited, Banbury Laboratory, Southam Road, Banbury OX16 7SP, UK Received 14 July 2000; accepted 4 January 2001 Abstract The eect of heat treatment on the ®liform corrosion FFC) susceptibility of rolled aluminium alloy AA3005 at temperatures in the range 150±500°C is investigated. A drastic loss of corrosion resistance takes place as a result of annealing at temperatures in excess of 350°C. TEM investigations revealed a highly deformed near-surface region, approximately 1 lm 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 ®ne 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 identi®ed as the main cause of the observed loss of FFC resistance. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Aluminium; Filiform corrosion; Deformed surface layers,Thermo-mechanical processing 1. Introduction Recent work has brought to attention the detrimental eect of high tempera- ture heat treatment on the ®liform corrosion FFC) resistance of several wrought www.elsevier.com/locate/corsci Corrosion Science 43 2001) 2093±2109 * Corresponding author. Present address: Alcan International Limited, Banbury Laboratory, Southam Road, Banbury OX16 7SP, UK. Tel.: +44-1295-452888. E-mail address: [email protected] A. Afseth). 0010-938X/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII:S0010-938X01)00014-2

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The effect of heat treatment on the filiform corrosion (FFC) susceptibility of rolled aluminium alloy AA3005 at temperatures in the range 150–500°C is investigated. A drastic loss of corrosion resistance takes place as a result of annealing at temperatures in excess of 350°C. TEM investigations revealed a highly deformed near-surface region, approximately 1 μm 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.

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