Corrosion of an Al–Zn–In alloy in chloride media

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.