Keywords and Phrases
Friction stir processing; Thermal stability
"Friction stir processing (FSP) is an adapted version of friction stir welding (FSW), which was invented at The Welding Institute (TWI), 1991. It is a promising solid state processing tool for microstructural modification at localized scale. Dynamic recrystallization occurs during FSP resulting in fine grained microstructure. The main goal of this research was to establish microstructure/superplasticity relationships in FSP aluminum alloys.
Different aluminum alloys (5083 Al, 2024 Al, and Al-8.9Zn-2.6Mg-0.09Sc) were friction stir processed for investigating the effect of alloy chemistry on resulting superplasticity. Tool rotation rate and traverse speeds were controlled as the prime FSP parameters to produce different microstructures. In another study, lap-joints of 7475 Al plates were also studied to explore the possibility of developing FSW/superplastic forming route. Microstructures were evaluated using optical, scanning and transmission electron microscopy, orientation imaging microscopy and differential scanning calorimetry. Mechanical properties were evaluated using tensile testing.
FSP 2024 Al (3.9 µm grain size) exhibited an optimum ductility of 525% at a strain rate of 10-2 s-1 and 430°C. Grain boundary sliding mechanism was found to be the dominant mode of deformation in this alloy. In 5083 Al alloy, it was found that changing the process parameters, grain sizes in the range of 3.5-8.5 µm grain size could be obtained. Material processed with colder processing parameters showed a decrease in ductility due to microstructural instability, and followed solute drag dislocation glide mechanism. On the other hand, materials processed with hotter parameter combinations showed mode of deformation related to grain boundary sliding mechanism. FSP of as-cast Al-Zn-Mg-Sc alloy resulted in ultrafine grains (0.68 µm) with attractive combination of high strain rate and low temperature superplasticity. This also demonstrated that superplastic microstructures could be obtained directly from as-cast alloys via a single step of FSP.
All these showed that FSP has the potential of becoming an important grain refinement technique for producing fine grained aluminum alloys with superplastic properties. Microstructural instability of FSP aluminum alloys at higher temperatures can be limited or eliminated with proper control of process parameters and improved alloy design"--Synopsis, pages iv-v.
Mishra, Rajiv S.
Van Aken, David C.
Newkirk, Joseph William
Peaslee, Kent D., 1956-2013
Dharani, Lokeswarappa R.
Materials Science and Engineering
Ph. D. in Metallurgical Engineering
University of Missouri--Rolla
Journal article titles appearing in thesis/dissertation
- Multi-sheet structures in 7475 aluminum by friction stir welding in concert with post-weld superplastic forming
- High strain rate superplasticity in a commercial 2024 Al alloy via friction stir processing
- Evaluation of microstructure and superplasticity in friction stir processed 5083 Al alloy
- Low temperature superplasticity in a friction-stir-processed ultrafine grained Al-Zn-Mg-Sc alloy
xvii, 143 pages
© 2004 Indrajit Charit, All rights reserved.
Dissertation - Restricted Access
Aluminum alloys -- Microstructure
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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://merlin.lib.umsystem.edu/record=b5135041~S5
Charit, Indrajit, "Microstructural and superplastic characteristics of friction stir processed aluminum alloys" (2004). Doctoral Dissertations. 1525.
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