Stress relaxation of AZ31 alloy using high energy diffraction microscopy

AZ31 is a commercial Mg-3%Al-1%Zn ternary alloy with good specific strength, but relatively limited room temperature formability -- a consequence of marked difference in strength of slip systems in this hcp alloy. Tensile test is the traditional method to study the kinetics of individual slip/twin events and, in the present work, High Energy Diffraction Microscopy (HEDM) is used to explore the kinetics at the scale of individual grains by following diffraction spots during a loading increment and subsequent relaxation. The study was conducted at the Advanced Photon Source (APS) sector 1-ID-C at Argonne National Laboratory and loading steps and relaxation were set at different points within elasto-plastic transitions (118MPa, 135MPa, 153MPa and 168MPa). Two different aspects of diffraction pattern were studied in the thesis: individual peak dynamics and reflection-wise ellipse-fitting strain time series. Peaks of crystallographic planes having a normal roughly parallel to the tensile axis are tracked and the relative plane distances calculated from radial displacements. Generally speaking, grains not favorably oriented for basal slip showed a loading response followed by small (or no) relaxation. In contrast, grains with a pyramidal plane sharing a normal with the tensile axis demonstrate quite diverse response. As for ellipse fitting result, net peak strains relating to loading step for distinct plane families decreased linearly with dot product of loading-direction vector and corresponding basal plane normal vector. The thesis concludes the algorithm for analysis: image rotation, image combination, Gaussian filtering, peak isolation, trajectory generation, reciprocal space--detector space transformation, ellipse fitting and peak strain--orientation correlation.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Tang, Wenli

Contributors dc:contributor

• Beaudoin, Armand J.

• Magnesium
• X-Ray Diffraction
• Stress Relaxation
• Crystallography
• High Energy Diffraction Microscopy
• Deformation Mechanism

Statement dc:rights

• Copyright 2014 Wenli Tang

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/50636

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/50636