Early stages during localized corrosion of AA2024 TEM specimens in chloride environment


Correspondence to: Sairam Malladi, National Center for HREM, Kavli Institute of Nanoscience Delft, The Netherlands.

E-mail: S.R.K.Malladi@tudelft.nl


Localized corrosion in AA2024-T3 specimens was investigated by ex situ transmission electron microscopy (TEM) studies to determine an experimental window for real in situ TEM corrosion studies. In the as-prepared specimens, intermetallic phases leading to local galvanic couples were classified based on the size and composition. The corrosion behavior of the TEM specimens was investigated in two kinds of corrosive environments, 1 M NaCl and oxygen bubbled through aqueous HCl of pH = 3. In the specimens exposed to a NaCl environment for a duration of 30 min, remnant copper-rich particles as a result of de-alloying were observed and energy filtered TEM (EFTEM) oxygen maps revealed the pitting of the oxide film at grain boundaries. In addition, severe deposition of NaCl crystals on the specimen surface was detected, making NaCl environment unsuitable for in situ TEM studies. Exposure to oxygen bubbled through aqueous HCl for durations of 20, 40, and 60 min gave insights into different stages of localized corrosion in this alloy. EFTEM elemental maps confirmed that the remnants formed during the de-alloying were Cu rich, whereas most of the corroded regions had oxygen-rich corrosion products. The corrosion behavior of the AA2024-T3TEM samples showed to be in agreement with corrosion of bulk material reported in the literature. Thus, oxygen bubbled through aqueous HCl is considered a suitable environment for carrying out in situ corrosion experiments in the TEM. Copyright © 2012 John Wiley & Sons, Ltd.