Multi-Modal Sensing of Sensitization and Stress Corrosion Cracking Susceptibility in AA5xxx Alloys

In order to travel faster, travel longer, and carry larger payloads, new Navy ships are being designed with light weight alloys and composite materials. High magnesium AA5xxx series alloys provide a high strength to weight ratio and excellent corrosion resistance, but suffer from sensitization as anodic ß precipitates (Al¬3Mg2) are form along grain boundaries due to a combination of elevated temperature and time. The result is an increased susceptibility to intergranular corrosion and stress-corrosion cracking. The rates of progression of sensitization and stress corrosion cracking are thought to be closely linked to alloy microstructure, which is affected by material handling, composition, and temper among other factors. While methods exist for determining the level of sensitization at specific points in time, their inability to account for microstructural variability make them unable to predict remaining life in service. To reduce the risk of the use of AA5xxx alloys in marine environments, Luna proposes to develop a multi-modal measurement system that combines electromagnetic, ultrasonic, and x-ray diffraction techniques to provide a rich data set on the material’s microstructure that can be used in predictive models to determine the rate of progression of sensitization and stress corrosion cracking processes.