Effects of Stress on Localized Corrosion in Al and Al Alloys

摘要

In order to predict the development of corrosion, a fundamental understanding of the corrosion processes is required. In particular, the effects of mechanical stress on corrosion and their synergistic interactions must be understood. In this project, certain effects of stress on localized corrosion in AA2024-T3 were studied by a variety of techniques, including in situ microfocal x-ray radiography. Specifically oriented slices of material were taken from a wrought plate, stressed in tension either to a fixed displacement or a fixed load, exposed to special electrochemical cells, and imaged by radiography. These experiments image the full distribution of corrosion sites and allow for competition between seen to stop growing and be overtaken by another crack that had been shorter. Quantitative aspects of phase- contrast microfocus X-ray imaging of Al alloys have been developed. Phase- contrast X-ray imaging provides enhanced image contrast and improved edge definition and is important for further development toward NDE of structural materials. The effects of compressive stress and prior deformation on localized corrosion have also been studied. The first breakdown in AA7075-T6 has been shown to be caused by transient dissolution of a surface active layer created by deformation during sample preparation.