In Situ Neutron Diffraction and Fluid Dynamics Modeling of Dynamic Recrystallization in Mg Alloys

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TECHNICAL SUMMARY:The objective of this project is to investigate the underlying physics of dynamic recrystallization in magnesium alloys during severe plastic deformation at elevated temperatures. Dynamic recrystallization involves the creation of new grains with low dislocation densities in a deformed microstructure during deformation. Dynamic recrystallization can strongly influence the mechanical properties in the variety of wrought metals and alloys used for structural applications. Friction-stir processing will be used to produce large plastic strains in specimens of commercial magnesium alloy AZ31. The transient nature of dynamic recrystallization and the critical role that twinning plays on grain refinement and crystallographic texture development in this magnesium alloy will be studied using in-situ, real-time neutron and synchrotron X-ray diffraction measurements and computational fluid dynamics (CFD) modeling. The research consists of three primary tasks: (1) develop a portable friction-stir-processing machine for use in in-situ diffraction studies; (2) in-situ, real-time diffraction measurements during plastic deformation to study the transient evolution of microstructure, namely texture, internal strain, dislocation density, subgrain size and twin density; and (3) computational fluid dynamics simulation of plastic deformation to study material flow rate and flow patterns in reference to temperature distribution and evolution. Simulation predictions will be correlated to microstructure evolution data to identify the dynamic recrystallization mechanisms responsible for microstructure development. Education, training and outreach activities will include high-school, undergraduate and graduate students. A new course on neutron diffraction will be developed.NON-TECHNICAL SUMMARY:Dynamic recrystallization is a complex phenomenon that occurs in metals and alloys while they are deformed, usually at elevated temperatures. It can significantly change the microstructure and properties of a material, either detrimentally or advantageously. The objective of this project is to investigate the mechanisms by which dynamic recrystallization occurs. This research will incorporate a magnesium alloy, AZ31, of interest for light-weighting vehicles. It will also use friction stir processing, which is of interest for advanced manufacturing. These will be combined with advanced diffraction experiments to study the underlying mechanisms of dynamic recrystallization. Education, training and outreach activities will include high-school, undergraduate and graduate students. A new course on neutron diffraction will be developed.