Doctoral Dissertations

Abstract

"Al-7Si-0.6Mg is one of the most important cast aluminum alloys because of its attractive mechanical properties and high castability. Microstructurally, the alloy consists of primary aluminum dendrites with eutectic Si particles in the interdendritic region. This makes the alloy quasi-brittle in nature which affects the ductility of the alloy to a great extent. In order to improve the ductility, the eutectic Si particles need to be refined which so far has been achieved by chemical and/or thermal modification. Friction stir processing (FSP) on the other hand can achieve the same through plastic deformation, and therefore replace the cast structure with a wrought microstructure. The eutectic Si particles get refined by at least 50 percent and the aspect ratio also gets reduced. As a result, the FSPed alloy shows improved mechanical properties especially in terms of ductility. Moreover, FSP leads to closure of casting porosities. In the present study it has been observed that these microstructural changes get reflected on the improved fatigue performance by the FSPed alloy. The fatigue life enhances by a factor of five as a result of FSP, when tested using a completely reversed cycle of stress. The life enhancement is even higher at higher stress ratio. Further, FSP caused significant grain refinement inside the stir zone. However, the fine-grain microstructure was found to be unstable at elevated temperatures due to abnormal grain growth (AGG) inside the nugget. Current results indicate that the AGG can be controlled by using selective process parameters as well as run configuration"--Abstract, page iv.

Advisor(s)

Mishra, Rajiv S.

Committee Member(s)

Newkirk, Joseph William
Richards, Von
Miller, F. Scott, 1956-
Landers, Robert G.

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Metallurgical Engineering

Sponsor(s)

National Science Foundation (U.S.). Industry/University Cooperative Research Centers

Publisher

Missouri University of Science and Technology

Publication Date

Spring 2009

Journal article titles appearing in thesis/dissertation

  • Effect of friction stir processing on fatigue behavior of an investment cast Al-7Si-0.6Mg alloy
  • Effect of friction stir processing on microstructure and tensile properties of an investment cast Al-7Si-0.6Mg alloy
  • Effect of process parameters on abnormal grain growth during friction stir processing of a cast Al alloy
  • Effects of stress ration on the fatigue behavior of a friction stir processed cast Al-Si-Mg alloy

Pagination

xv, 126 pages

Note about bibliography

Includes bibliographical references.

Rights

© 2009 Saumyadeep Jana, All rights reserved.

Document Type

Dissertation - Restricted Access

File Type

text

Language

English

Library of Congress Subject Headings

Friction welding
Aluminum alloys -- Microstructure
Aluminum alloys -- Mechanical properties

Thesis Number

T 10242

Print OCLC #

862972707

Electronic OCLC #

905852177

Link to Catalog Record

Electronic access to the full-text of this document is restricted to Missouri S&T users. Otherwise, request this publication directly from Missouri S&T Library or contact your local library.

http://laurel.lso.missouri.edu:80/record=b10158014~S5

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