Stress relaxation of AZ31 alloy using high energy diffraction microscopy

Tang, Wenli

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https://hdl.handle.net/2142/50636 Copy

Description

Title

Stress relaxation of AZ31 alloy using high energy diffraction microscopy

Author(s)

Tang, Wenli

Issue Date

2014-09-16

Director of Research (if dissertation) or Advisor (if thesis)

Beaudoin, Armand J.

Department of Study

Mechanical Sci & Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

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

Abstract

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.

Graduation Semester

2014-08

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

Copyright and License Information

Copyright 2014 Wenli Tang

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