Passivity Breakdown of Aluminium Alloys by Surface Enrichment of Group IIIA - VA Trace Elements

摘要

High temperature heat treatment of aluminium alloys gives rise to a curious anodic activation phenomenon, attributed to surface enrichment of the trace elements in Group IIIA -VA, specifically the low melting point elements Pb, Bi, In and Sn. The purpose of this paper is to investigate surface enrichment by heat treatment and anodic activation by electrochemical polarization, specifically of In in relation to Pb, by use of electrochemical, electron-optical and electron-spectroscopic techniques. Indium becomes easily segregated at the surface as a result of heat treatment, at much lower temperatures (300°C) than that required for Pb. Passivity breakdown occurs by further surface enrichment of any of these elements by selective anodic dissolution of the more active aluminium component in chloride solution.