Author

Guozhen Zhu

Date of Award

2009

Degree Type

Thesis

Degree Name

Master of Applied Science (MASc)

Department

Materials Science and Engineering

Supervisor

David S. Wilkinson

Language

English

Abstract

AI-Mg sheets (5xxx series) for body-in-white (BIW) application are mostly
used for automotive structural parts due to their specific combination of
formability and strength. The limiting behavior for the wide application of AA5754
sheets is strain localization. The effect of microstructure inhomogeneties on
strain localization have recently been attracting a great deal of interest but not
fully understood. In this present work, the effect of grain-level microstructure
inhomogeneties in AA 5754 sheets is investigated.
Uniaxial tensile experiments combined with two 2-dimensional Digital
image correlation (DIG) techniques have been performed on coarse-grained
specimens to evaluate the deformations of individual grains. Grain orientations
and their evolution were measured by the electron backscattered diffraction
(EBSD) technique, and surface features such as slip traces were observed by
optical microscopy.
The regions of high local strain ('hot spots') within coarse-grained samples
nucleate at a very early stage of deformation and most of them continuously
grow throughout most deformation stages. 'Hot spots' are correlated with 'soft'
grains (i.e. grains with high Schmid factors) and soft-evolution grains (i.e. grains
with the <101> direction close to tensile axis).

McMaster University Library