In Situ Marine-Grade Aluminum Alloy Characterization for Sensitization Resistance and Stress Corrosion Cracking Prediction

The goal of this proposal is to develop a compact sensor package and monitoring protocol for detecting the degree of sensitization in 5xxx series alloys that accounts for lot-to-lot variability. 5xxx series aluminum alloys have been utilized in marine applications to reduce weight and lower the center of gravity of ships for many decades. While effective, they can become susceptible to intergranular corrosion damage and stress corrosion cracking through a process called sensitization. The extent of this vulnerability exhibits large variations between nominally identical materials, which are believed to stem from insufficiently constrained processing protocols within the defined standards. The U.S. Navy seeks to be able to quickly access the materials state and its susceptibility to sensitization. In this study, we will deploy an original approach requiring two non-destructive techniques (eddy current based conductivity and ultrasonic attenuation) to separate out two independent components believed to contribute to the total sensitization response, the microstructural configuration of high-angle grain boundaries in the material and the state of sensitization along these boundaries. From these parameters a sensitization measurement that accounts for lot-to-lot variation can be calculated using recently established models.