Integrated Thermo-mechanical Processing, Microstructure and Property Simulation System for Aluminum Alloys

The in-service lifetime of modern marine alloys (such as AA5083) has recently surpassed strength issues as the most significant interest of the US Navy concerning these materials. The principle factors limiting lifetime for these alloys are mass-loss due to corrosion, stress-corrosion cracking (SCC), toughness, and fatigue. Of these, corrosion is the most significant, mainly occurring due to preferential attack on beta phase precipitates at grain boundaries. Alloy design can mitigate this effect; for example, by increasing Zn content. However, this tends to relocate corrosion to the weld regions. Thus, more than alloy design, the most significant method to reduce this corrosion is to attract beta phase precipitates to nucleate on deformation substructure within the bodies of grains, rather than at the grain boundaries. To do this requires maximizing the in-grain substructure while still achieving desirable temper conditions. A tool to help predict the effect of processing (deformation + temper) on in-grain deformation structure, and hence nucleation sites, will provide engineers with the ability to design their processes for optimum lifetime performance. This proposal details the planned Phase II efforts to implement the proof-of-concept model demonstrated in Phase I, in order to provide an integrated process > microstructure > property simulation system for aluminum alloys. The result will be a suite of testing and characterization studies, as well as computer model development to study corrosion, strength, and stress corrosion cracking. This specifically will involve a). testing and characterization of various tempers (H321, H116) b). testing and characterization of variation on homogenization process c). developing and implementing microstructure evolution and property prediction models (grain boundary evolution, precipitation, strength prediction, corrosion prediction, stress corrosion cracking) and d). validating the modeling results against a selected industrial practice