Journal
SURFACE AND INTERFACE ANALYSIS
Volume 42, Issue 4, Pages 185-188Publisher
WILEY
DOI: 10.1002/sia.3136
Keywords
AA7075 aluminium alloy; corrosion; near-surface deformed layer; grain boundary
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Funding
- EPSRC [EP/H020047/1] Funding Source: UKRI
- Engineering and Physical Sciences Research Council [EP/H020047/1] Funding Source: researchfish
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In the present study, the effects of mechanical polishing on the microstructure and corrosion behaviour of AA7075 aluminium alloy are investigated. It was found that a nano-grained, near-surface deformed layer, up to 400 nm thickness, is developed due to significant surface shear stress during mechanically polishing. Within the near-surface deformed layer, the alloying elements have been redistributed and the microstructure of the alloy is modified; in particular, the normal MgZn2 particles for T6 are absent. However, segregation bands, approximately 10-nm thick, containing mainly zinc, are found at the grain boundaries within the near-surface deformed layer. The presence of such segregation bands promoted localised corrosion along the grain boundaries within the near-surface deformed layer due to microgalvanic action. During anodic polarisation of mechanically polished alloy in sodium chloride solution, two breakdown potentials were observed at -750 mV and -700 mV, respectively. The first breakdown potential is associated with an increased electrochemical activity of the near-surface deformed layer, and the second breakdown potential is associated with typical pitting of the bulk alloy. Copyright (C) 2009 John Wiley & Sons, Ltd.
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