Direct Monitoring and Quantification of Deformation Twinning in Magnesium Alloys

Deformation twinning plays a dominant role in plastic deformation of hexagonal close-packed (hcp) polycrystalline materials. Furthermore, stain localizations were previously found to be related to twinning in Magnesium alloys. To date, experiments performed at the specimen level demonstrated the formation of strain localizations at locations with pronounced twin activity. The research work presented in this dissertation attempts to quantitatively identify correlations between strain localizations and twinning activity in magnesium. This is achieved by in-situ microstructure monitoring coupled with nondestructive evaluation techniques such as acoustic emission and digital image correlation. Characteristics of acoustic emission signals from twinning are identified through a combination of mechanical testing using a variety of specimens ranging from single to polycrystals in addition to testing both inside and outside the Scanning Electron Microscope as well as machine learning techniques. A novel approach to perform quasi in-situ cyclic loading was implemented allowing full field strain measurement as well as microstructure characterization at key stages of cyclic loading. Given this approach, the contribution of twinning in the measured plastic strain was possible to be directly calculated from microstructure information during cyclic loading conditions. In addition, such microstructure-related plastic strain was demonstrated to have strong correlation with macroscopic heterogeneous strain field measured by digital image correlation. The experimental findings in this dissertation can provide key inputs to models attempting to predict deformation behavior of magnesium alloys using microstructural information.