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Fabrication of Metal Matrix Composites by Friction Stir Processing Open Access


Other title
Mechanical Properties
Metal Matrix Composite
Friciton Stir Processing
Type of item
Degree grantor
University of Alberta
Author or creator
Izadi, Hossein
Supervisor and department
Mendez, Patricio (Chemical & Materials Engineering)
Gerlich, Adrian (Chemical & Materials Engineering)
Examining committee member and department
Nychka, John (Chemical & Materials Engineering)
Luth, Robert (Earth & Atmospheric Sciences)
Prasad, Vinay (Chemical & Materials Engineering)
Schneider, Judy (Mechanical Engineering, Mississippi State University)
Department of Chemical and Materials Engineering
Materials Engineering
Date accepted
Graduation date
Doctor of Philosophy
Degree level
This thesis focuses on fabrication of aluminum matrix composites using friction stir processing. Al 5059 alloy was selected as the matrix alloy, and the effect of processing parameters on microstructure and mechanical properties of this alloy was studied in detail. Friction stir processing was conducted using three different tools with different rotation speeds. Microstructural characterization was carried out by optical microscopy, SEM and TEM. It was shown that fine grains form in the stir zone as a result of dynamic recrystallization and these fine grains do not grow during the cooling cycle because of the effect of magnesium on reducing grain boundary mobility. TEM analysis also showed that the microstructure contained Al6(Mn,Fe) particles with two different morphologies. It was confirmed that refinement of these particles can more effectively pin the grain boundaries and suppress grain growth. Grain size measurement was performed on the samples to investigate the effect of process parameters on recrystallization and grain growth in the stir zone. Mechanical properties were also obtained by microhardness and tensile tests. A tool with 3 flats in combination with a rotation speed of 454 RPM provides slightly higher grain refinement and subsequent mechanical properties. It is shown that friction stir processing reduces the fraction of elongated precipitates that form on the grain boundaries of the base material, and this resulted in approximately a 10% improvement in elongation to failure in friction stir processed Al 5059 samples. Particle fragmentation also appeared to increase the rate of work hardening, which also likely contributed to enhanced ductility. A multi-pass multi-tool FSP technique using different processing parameters was proposed for fabrication of Al 5059/Al2O3 and Al 5059/CNT composites. A uniform distribution of reinforcing particles was achieved in both cases with a uniform hardness profile through the stir zone. The microhardness of the composites was significantly higher than the original aluminum alloy. However, it was noted that the thermo-mechanical cycles during processing of the Al/CNT composites have destroyed the tubular structure of the CNTs.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
H. Izadi, A. Nolting, C. Munro, A. Gerlich, Effect of Friction Stir Processing Parameters on Microstructure and Mechanical Properties of AL 5059, Proceedings of the 9th International Conference on Trends in Welding Research, 2012 ASM International.H. Izadi, A. Gerlich, Distribution and stability of carbon nanotubes during multi-pass friction stir processing of carbon nanotube/aluminum composites, Carbon 50 (2012) p 4744 –474 9.

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