Corrosion of an Al–Zn–In alloy in chloride media A.G. Mu~ noz, S.B. Saidman, J.B. Bessone * Departamento de Qu  ımica e Ingenier  ıa Qu  ımica, Instituto de Ingenier  ıa Electroqu  ımica y Corrosi on (INIEC), Universidad Nacional del Sur, Av. Alem 1253, 8000 Bah  ıa Blanca, Argentina Received 14 November 2000; accepted 12 February 2002 Abstract In order to explain the electrochemical behaviour of Al–Zn–In based alloys in chloride media, a commercial Al–Zn–In–Si anode and a ternary alloy, Al–5%Zn–0.02%In prepared in our laboratory, were investigated using potentiodynamic techniques, complemented by SEM, EDX and TEM. The influence of alloy composition, agitation and previous cathodisation on the electrochemical response of the alloys was analysed. Results of previous investigations with pure metals (Zn and In) and with binary alloys (Al–In, In–Al, Zn–In) are also considered in this paper for the sake of comparison. The attack initiation on the Al–Zn–In alloy is related to In–Zn rich zones, segregated at grain boundaries. The presence of In in true electric contact with Al and Zn promotes Cl  adsorption at potentials more positive than 1.1 V. Then, the presence of Zn facilitates a surface enrichment of indium by a displacement reaction. This in turn, assures an accumulation of adsorbed Cl  , which maintains an active state of the Al matrix. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: A. Aluminium; Al–Zn–In alloy; Corrosion; Chloride; Sacrificial anode 1. Introduction The economic advantages of exploiting the high theoretical current capacity and the low active potential of Al as an anode have long been appreciated, although the spontaneous formation of oxide on Al exerts a strong passivation effect. Acti- vation of Al is obtained through a localized attack in the presence of aggressive anions, once a defined potential is exceeded in the anodic scan. The operating potential (pitting potential) makes Al unsuitable as a sacrificial anode. Therefore, www.elsevier.com/locate/corsci Corrosion Science 44 (2002) 2171–2182 * Corresponding author. Tel./fax: +54-291-4595182. E-mail address: jbessone@criba.edu.ar (J.B. Bessone). 0010-938X/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0010-938X(02)00042-2