In situ atomic force microscopy was used in conjunction with microlithography and scanning Auger electron spectroscopy to monitor localized corrosion near iron-rich inclusions in Al-6061-T6 immersed in 0.6MNaCl and also sulfur-rich inclusions in 304 stainless steel (SS-304) in 0.5M NaCl. The local rate of aluminum corrosion was found to depend on the shape of the nearby iron-rich inclusion. At the corrosion potential, trenches were observed to form in the aluminum host matrix adjacent to the inclusions, and the corrosion sites gradually evolved into circular shapes owing to dissolution. During the dissolution process, the width of the dissolution area was an order of magnitude greater than the depth. Application of a 400 mV cathodic overpotential prevented corrosion initiation, while application of a 500 mV cathodic overpotential greatly accelerated the dissolution rate in comparison with that at the rest potential. On SS-304, exposure to 0.5M NaCl was accompanied by formation of deposits, which decorated the inclusion surface as well as the surrounding area up to four times the radius of the original inclusion.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry