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PROCESSING OF MAGNESIUM ALLOYS WITH
ULTRAFINE GRAIN STRUCTURE
by
Roberto Braga Figueiredo
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(MECHANICAL ENGINEERING)
August 2009
Copyright 2009 Roberto Braga Figueiredo
Object Description
| Title | Processing of magnesium alloys with ultrafine grain structure |
| Author | Figueiredo, Roberto Braga |
| Author email | figueire@usc.edu; figueiredo.rb@gmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Aerospace & Mechanical Engineering (Computational Fluid & Solid Mechanics) |
| School | Viterbi School of Engineering |
| Date defended/completed | 2009-06-15 |
| Date submitted | 2009 |
| Restricted until | Unrestricted |
| Date published | 2009-07-16 |
| Advisor (committee chair) | Langdon, T. G. |
| Advisor (committee member) |
Kassner, Michael Goo, E. K. |
| Abstract | The relationship between processing, structure and properties is analyzed in magnesium alloys subjected to equal-channel angular pressing.; Finite element modeling is used to show that the flow softening behavior associated with grain refinement might cause shear localization and billet failure in magnesium alloys processed by ECAP. It also shows that increasing the angle between the channels of the die reduces the accumulated damage in the billets and increasing the material strain rate sensitivity reduces the tendency for shear localization. Both procedures reduce the tendency for billet cracking.; The mechanism of grain refinement in magnesium alloys deformed at moderate temperatures differs from that observed in other metals such as copper and aluminum. Fine grains nucleate along pre-existing grain boundaries in a necklace pattern in coarse-grained magnesium while homogeneous nucleation of fine grains is observed in fine-grained. A bimodal grain size distribution is observed after processing alloys from an initial coarse structure and a homogeneous distribution of ultrafine grains is the outcome of a starting fine one.; Experiments and simulations are used to analyze the evolution of texture. It is shown that different components are formed depending on the activity ratio of non-basal slip and processing route. The measured pole figures exhibit features characteristic of high activity of non-basal slip. It is also shown that the development of some texture components and their orientation depends on the initial texture and the die angle which provide the basis for future texture engineering.; Excellent superplastic properties, including a record elongation for a magnesium alloy, were observed after ECAP. Systematic research showed that the structure characteristics prior and after ECAP play significant role on these properties. Grain growth during superplastic deformation causes a strain hardening effect. The experimental results showed good agreement with the theoretical model for grain boundary sliding. |
| Keyword | magnesium alloys; superplasticity; equal-channel angular pressing; texture |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m2370 |
| Rights | Figueiredo, Roberto Braga |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | http://www.usc.edu/isd/libraries/services/ask_a_librarian/email/ |
| Filename | etd-Figueiredo-3064 |
| Archival file | uscthesesreloadpub_Volume29/etd-Figueiredo-3064.pdf |
Description
| Title | Page 1 |
| Full text | PROCESSING OF MAGNESIUM ALLOYS WITH ULTRAFINE GRAIN STRUCTURE by Roberto Braga Figueiredo A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (MECHANICAL ENGINEERING) August 2009 Copyright 2009 Roberto Braga Figueiredo |
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