Orientation dependence of dislocation structure evolution of aluminum alloys in 2-D and 3-D
by Colin Clarke Merriman, M. S.
Washington State University
Chair: David Field
A proper understanding of the relationships that connect deformation, microstructural
evolution and dislocation structure evolution is required to extend service lifetime of
components, reduce the manufacturing costs, and improve product quality. This requires
significant efforts in performing accurate analysis of undeformed and deformed microstructure
and identifying the microstructural response to an applied stress, be it in compression tension, or
fatigue. Current models are based on observed phenomenology of the process and therefore fail
to predict microstructural response of a material beyond a given set of known parameters.
Current research is aimed towards making contribution in the areas of (i) microstructural
characterization, (ii) understanding the influence of various microstructural parameters on the
evolution of dislocation structures and (iii) on relating the physically measurable microstructural
parameters to stress response.
In a continuing effort to improve characterization of the dislocation structures of
materials the local orientation gradient in deformed polycrystalline samples is examined by the
collection of electron back-scatter patterns. Along with the lower bound calculation of the excess
dislocation content (planar dataset), a 3-D excess dislocation density calculation is introduced,
for serial section datasets, to better understand the bulk microstructural response. In addition, the
excess dislocation density dependence on step size is examine to determine if there is proper step
size to be used to for the excess dislocation density calculation.
Microstructural evolution during small and large strain channel die deformation of
aluminum alloy (AA) 1050 and AA 7050 T7541 was investigated using SEM techniques. From
this the orientation dependence of dislocation structures was examined through the initial texture
of the material and the plotting of excess dislocation content and Taylor factor in orientation
space. It was observed that the Taylor factor and the initial texture has an influence on the
deformation behavior and dislocation evolution of aluminum. Neighboring grains (including
lattice orientation and dislocation content) and precipitate morphologies also were observed to
play a significant role in the microstructural and dislocation response. The observed difference in
the evolution of dislocation structures of AA 1050 and AA 7050 T7541 were attributed to their
varying manufacturing parameters and differing alloy content.
School:Washington State University
School Location:USA - Washington
Source Type:Master's Thesis
Keywords:structural analysis engineering aluminum alloys dislocations in metals
Date of Publication: