IMPACTS OF PRECIPITATES AND ELECTROCHEMICAL ASPECTS OF LOCALISED CORROSION IN INDUSTRIAL ALLOYS

Abstract

The earliest stages of localised corrosion attack on AA5083 and AA2099 under chloride-contaminated thin-film electrolyte were investigated at ambient temperature over the humidity range 20%-85% RH. <i>In-situ</i> time-lapse Scanning Kelvin Probe Force Microscopy (SKPFM) elucidated, for the first time, silicide regions, which initially showed positive Volta potential (vs matrix), suffering from severe nobility loss due to ongoing physicochemical and electrochemical corrosion reactions. Transient events and the phenomenon of nobility adoption were also introduced, further demonstrating the new interpretation on the relationship between Volta potential and corrosion potential. Additionally, proper understanding and characterization of material breakdowns are equally important. Electrochemical breakdown response of the deleterious β-Al3Mg2 phase in AA5083 was investigated, while segregations of Si in the SS304L microstructure led to discoveries of anomalies in existing corrosion susceptibility test methods. Overall, this thesis represents a holistic study of the various precipitates in the industrial alloys’ microstructure and their correlation to corrosion.