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The influence of grain refinement on the corrosion mechanism of 7475 aluminium alloy
|Ewa Ura-Bińczyk , Alicja Z. Bałkowiec , Malgorzata Lewandowska , Krzysztof J. Kurzydlowski
Warsaw University of Technology, Faculty of Materials Science and Engineering (InMat), Wołoska 141, Warszawa 02-507, Poland
The 7xxx series aluminium alloys are widely use in the aerospace industry due to their high strength. The grain refinement down to nanometre scale offers the possibility to further increase their mechanical properties which was already confirmed in a number of studies. However until now, there is a lack of comprehensive studies of the influence of grain size refinement on the corrosion mechanisms of aluminium alloys.
The aim of this study was to compare the electrochemical behaviour of polycrystalline and nanocrystalline 7475 aluminium alloy. The corrosion resistance and susceptibility to localized attack was investigated by means of potentiostatic and potentiodynamic polarization in solutions containing chloride ions of different pH (0.05M NaCl of pH2, pH8.4 and pH12). The extended microstructural characterization was carried out using SEM, TEM, EDS and EBSD techniques to determine the morphology of the corrosion attack.
The polarization tests showed that in strong alkaline environment, the electrochemical behaviour of poly- and nanocrystalline material was very similar. In strong acid solution, the nanostructured material was characterized by higher dissolution rate whereas in the solution of pH 8.4, the breakdown potential and the open circuit potential were shifted to more negative values which indicated poorer corrosion resistance of nanocrystalline material. The microscopic investigations indicated that in both cases the corrosion attack was strongly related with intermetallic particles, however, the morphology of this attack is different. In the case of polycrystalline material the peripherical pitting and intergranular corrosion along high angle grain boundaries was observed while in nanocrystalline material the corrosion damage was accumulated only in the region near the intermetallic particles.
This work was carried out within a NANOMET Project financed under the European Funds for Regional Development (Contract No. POIG.01.03.01-00-015/08). The processes of HE were carried at the Institute of High Pressure Physics of Polish Academy of Sciences.
Presentation: Poster at E-MRS Fall Meeting 2009, Symposium H, by Ewa Ura-Bińczyk
See On-line Journal of E-MRS Fall Meeting 2009
Submitted: 2009-05-19 13:47 Revised: 2009-06-07 00:48