Comprehensive model for the activation mechanism of Al-Zn alloys produced by indium

BESSONE J.B:; FLAMINI D.O.; SAIDMAN S.B.

CORROSION SCIENCE

Elsevier

Lugar: Cambridge, UK; Año: 2005 vol. 47 p. 95 - 105

0010-938X

Exploratory work on the electrochemical behaviour of the Al–4%Zn alloy in the presenceof In3þ in weakly acid chloride and acetic media is reported. It was found that in chloridesolutions, active dissolution takes place at very negative potentials ()1.5 VSCE). This significativeenhancement in the electrochemical activity of the alloy is described and discussed. Theaim of this paper is to explain the relationship between the operating potential ()1.1 VSCE)given by the commercial alloy (basically an Al–Zn–In alloy), its high efficiency, its quasiuniformattack observed and the enhanced activity found ()1.5 VSCE). An unified model thatexplains this findings and the activation process of pure Al by In3þ is proposed. It was foundthat two activation mechanism are operative on Al: (i) When sufficient amount of In at theinterface in quasi-liquid state is present, an In–Al amalgam is responsible for the activationprocess ()1.5 VSCE). This process is favoured by Zn reach zones that favours In enrichment atthe interface by displacement reaction. (ii) At higher anodic potentials (near )1.2 VSCE), thepresence of In at the interface facilitates a chloride adsorption process which depolarised theanodic reaction.