Dynamic Recrystallization of a Mg alloy during Friction Stir Processing: Grain Size Refinement and Texture Evolution

In order to manipulate the texture of friction stir processed Mg alloy, it is necessary to understand the dynamic recrystallization (DRX) and texture change during friction stir processing (FSP). In this study, both in-situ and ex-situ study were carried out on the mechanisms of dynamic recrystallization and texture evolution during friction stir processing of a Mg alloy.First, in order to understand the effect of temperature, strain rate, strain, and Zener-Hollomon parameter (Z) on the grain size refinement and texture development, a constitutive study was carried out by conducting a series of hot compression tests using a Gleeble system. The changes in dominant deformation mechanisms (slip to twinning transition) yielded significant alterations in texture and dynamic recrystallization behavior. The combined effect of texture and grain size refinement on mechanical properties was also examined by a series of tension tests on the DRXed samples.And, then to further unravel the texture evolutions during FSP, we measured in-situ texture development in AZ31 Mg alloy plates during the FSP at two different thermo-mechanical input, namely, low Z (LZ) and high Z (HZ) conditions using neutron diffraction as a function of position using a portable FSP machine. The in-situ neutron diffraction result provided unique insights to a transient texture development during the FSP.The present study provides basic understanding of the grain size refinement and texture development of a wrought Mg alloy during the friction stir processing and can help guide the manufacturing process to manipulate grain size and texture of Mg alloy for enhanced formability. In addition, the present study can be used to validate computational fluid dynamic modeling for FSP of Mg alloys.