Development of Ultra-Refined Microstructure in Friction Stir Processed 7xxx Aluminum using Microstructural and Thermomechanical Modeling

Applied Optimization, Inc., in working with EWI, Inc., Ohio State University, and Boeing Phantom Works, proposes to demonstrate feasibility of using microstructural models to predict the required processing conditions that can produce nanostructured grain sizes in the thermo-mechanical affected zone in friction stir processing [FSP] of 7075-T6 aluminum. First step will be an FSP trial using the processing conditions reported in the literature. The data from this trial will be used as input for models. Microstructure modeling will be physically-based on state variables and mechanisms, the basic inputs to which will be initial microstructure and evolution of temperature, strain and strain-rate versus time during the FSP. Additional microstructure model will be direct morphological simulation of microstructure using the phase field method. Thermo-mechanics evolution during FSP will be modeled using analytical solutions for material flow and temperature field. This will be supplemented with 3-D finite element simulation as needed. The microstructure models and the thermo-mechanics model will be used in tandem to predict processing conditions that will improve upon the results of the FSP trial performed at the start. These new conditions will be used to perform a second FSP trial to demonstrate feasibility of the using the models to optimize FSP to produce nanostructured grain sizes.