Namahoot, Jutatip
(2005).
Effects of deformations on corrosion of Al-Mn alloys.
University of Birmingham.
Ph.D.
Abstract
Wrought Al-Mn alloys can develop a thin deformed layer on the surface as a result of hot and cold rolling. Subsequent heat-treatment precipitates fine secondary intermetallic particles which effect corrosion susceptibility. This work focuses on the effect of surface preparation and deformation on the electrochemical behaviour of Al-Mn alloys. The first part of the work investigated the effect of surface preparation such as mechanical grinding and polishing, alkaline etching and desmutting, and nitric acid treatment on electrochemical behaviour of an Al-1Mn-0.4Fe-0.3Si model alloy. Different surface preparations of this alloy show different electrochemical behaviour. In the second part of the work, the electrochemical reactivity of the surface layers of commercial rolled AA3005 sheet was investigated by profiling through the surface with GDOES (glow discharge optical emission spectroscopy). The microstructure and electrochemical reactivity was examined at different depths in order to compare the behaviour of the surface layers with that of the bulk alloy. In order to understand the role of deformation on corrosion behaviour of Al-Mn alloy, an Al-1Mn-0.4Fe-0.3Si model alloy was deformed by uniaxial compression and equal channel angular extrusion (ECAE) and followed by annealing. It was found that deformation is likely to have two effects on the surface of Al-Mn alloy. One effect is to cause the precipitation of particles that act as local cathodes and pit initiation sites. The other effect is that formation of precipitates will deplete the adjacent matrix in solute, making it more susceptible to dissolution.
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