Date of Award

12-2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Hahn Choo

Committee Members

Yanfei Gao, Peter K. Liaw, Dayakar Penumadu

Abstract

The combined effects of texture and grain size on the yielding and hardening behavior in a hot-rolled AZ31B Mg alloy were studied by using synchrotron x-ray diffraction and visco-plastic self-consistent (VPSC) simulation methods.

First, the influence of texture on Hall-Petch relationships (namely, critical resolved shear stresses and hardening parameters) in a Mg alloy was investigated to establish a constitutive basis for the VPSC simulation.

Then, the changes in dominant deformation mechanisms (basal, prismatic, and pyramidal slip as well as extension twin) and their relative interactions were studied systematically as a function of the initial texture using a VPSC scheme. The simulation results provide basic understanding of the effect of texture on the hardening behaviors in terms of the interaction of various active deformation mechanisms.

Subsequently, the interplay between the texture and grain size effects on the activation of multiple deformation mechanisms and the plastic anisotropy was studied by incorporating the Hall-Petch Relationship in the VPSC modeling scheme.

Finally, the influence of {1012} extension twin on the texture and microstructure evolution was investigated to understand physical implications of the simulation results. Specifically, the hardening anisotropy introduced by extension twin was studied with a focus on dislocation-twin interactions in terms of texture hardening, size hardening, and glissile-to-sessile transition hardening.

The current study provides a basic micromechanical understanding of the effects of complex interactions among texture, loading path, and grain size on the yielding and hardening behavior of a wrought Mg alloy through plasticity simulations and diffraction measurements. The results would help improving the formability and advancing manufacturing techniques of wrought Mg alloy components for structural applications.

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