A positron annihilation study of corrosion of aluminum and aluminum alloy by NaOH

Reference:

Wu, Y. C., Zhai, T. and Coleman, P. G., 2012. A positron annihilation study of corrosion of aluminum and aluminum alloy by NaOH. Metallurgical and Materials Transactions A, 43 (8), pp. 2823-2831.

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Official URL:

http://dx.doi.org/10.1007/s11661-011-0806-9

Abstract

Corrosion of fully-annealed pure aluminum and a continuous-cast AA2037 aluminum alloy (solutionized and water quenched) in a 1M NaOH solution for various periods of time were analyzed with positron beam-based Doppler broadening spectroscopy. By varying the energy of the incident positron beam, corrosion-induced defects at different depths from the surface were detected. It was found that the Doppler-broadened annihilation line-width parameter was significantly increased near the surface of pure aluminum after corrosion, probably due to the interaction between positrons and nanometer-sized voids formed near the aluminum surface during corrosion. Examination by atomic force microscopy indicated that many pits were formed on the aluminum surface after corrosion. In contrast, a significant decrease in the line-width parameter was observed in AA2037 alloy after corrosion and interpreted as being caused by copper enrichment at the metal-oxide interface during corrosion; such enrichment at large cavity sites was confirmed by energy dispersion spectrometry.

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