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Accumulative Roll Bonding of AA 5083 toward Low Temperature Superplasticity.

紀錄類型:	書目-語言資料,印刷品 : Monograph/item
正題名/作者:	Accumulative Roll Bonding of AA 5083 toward Low Temperature Superplasticity./
作者:	McBride, Brady N. L.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2022,
面頁冊數:	143 p.
附註:	Source: Dissertations Abstracts International, Volume: 84-04, Section: B.
Contained By:	Dissertations Abstracts International84-04B.
標題:	Materials science. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28963462
ISBN:	9798352691076

Accumulative Roll Bonding of AA 5083 toward Low Temperature Superplasticity.
McBride, Brady N. L.

Accumulative Roll Bonding of AA 5083 toward Low Temperature Superplasticity. - Ann Arbor : ProQuest Dissertations & Theses, 2022 - 143 p.

Source: Dissertations Abstracts International, Volume: 84-04, Section: B.

Thesis (Ph.D.)--Colorado School of Mines, 2022.

This item must not be sold to any third party vendors.

Superplastic forming is a metal forming technique commonly used with aluminum alloys, such as AA 5083, to create intricate sheet components. There are numerous drawbacks with this process, including high forming temperatures (500 °C), low strain rates (5ⅹ10-4 s-1) and cavitation damage due to the nature of grain boundary sliding. Equations describing steady state creep behavior, which are used to model superplastic deformation, show a direct relationship between forming temperature and grain size. This work explores the use of accumulative roll bonding (ARB) as a grain refinement technique to create microstructures that are conducive for low temperature superplasticity. ARB consists of roll-bonding two sheets together. If a single 50 % rolling reduction is employed, the resultant sheet is twice as long and half as thick; the sheet can be sectioned in half and the process repeated multiple times to accumulate strain. ARB is notoriously difficult due to edge cracking. A procedure was developed to manipulate the strain states at the edge of the sheet during rolling to prevent defects. Sheets subject to 5 ARB cycles (ε = 4.0) were produced, characterized by large high angle grain boundary (HAGB) fractions around 80 % and grain sizes between 250 and 500 nm. The ARBed microstructure was determined to be resistant to discontinuous static recrystallization upon heating owing to the large fraction of HAGBs. This results in the microstructure retaining a sub-micron grain size for extended durations up to 250 °C. Superplastic deformation characterized by stable grain boundary sliding was found to be optimal for temperatures and strain rates between 225 to 250 °C and 5ⅹ10-4 to 1ⅹ10-3 s-1, respectively. This reduction in temperature is not only dependent on the sub-micron grain size, but also the presence of non-equilibrium grain boundaries which reduce the activation energy for grain boundary diffusion. Further reduction in temperature was limited by a transition from grain boundary sliding to solute drag creep.Biaxial bulge testing was conducted to simulate superplastic forming operations using the previously identified optimal parameters. Thinning ratios (to/tf) around 2.5 were achieved prior to failure with a cavitation void fraction below 2 %; this exceeds performance of current industrial superplastic forming operations in coarse grained AA 5083. Results suggest thinning ratios as high as 3.5 can be achieved while remaining under the 2 % void fraction limit established by the forming industry. Thus, sub-micron grained material produced by ARB has been shown to demonstrate low temperature superplasticity with a reduction in required forming loads, with the additional benefit of being able to sustain higher superplastic strains with less microstructural damage.

ISBN: 9798352691076Subjects--Topical Terms:

557839
Materials science.
Subjects--Index Terms:

Accumulative roll bonding

Accumulative Roll Bonding of AA 5083 toward Low Temperature Superplasticity.
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300 $a 143 p.
500 $a Source: Dissertations Abstracts International, Volume: 84-04, Section: B.
500 $a Advisor: Clarke, Kester D.
502 $a Thesis (Ph.D.)--Colorado School of Mines, 2022.
506 $a This item must not be sold to any third party vendors.
520 $a Superplastic forming is a metal forming technique commonly used with aluminum alloys, such as AA 5083, to create intricate sheet components. There are numerous drawbacks with this process, including high forming temperatures (500 °C), low strain rates (5ⅹ10-4 s-1) and cavitation damage due to the nature of grain boundary sliding. Equations describing steady state creep behavior, which are used to model superplastic deformation, show a direct relationship between forming temperature and grain size. This work explores the use of accumulative roll bonding (ARB) as a grain refinement technique to create microstructures that are conducive for low temperature superplasticity. ARB consists of roll-bonding two sheets together. If a single 50 % rolling reduction is employed, the resultant sheet is twice as long and half as thick; the sheet can be sectioned in half and the process repeated multiple times to accumulate strain. ARB is notoriously difficult due to edge cracking. A procedure was developed to manipulate the strain states at the edge of the sheet during rolling to prevent defects. Sheets subject to 5 ARB cycles (ε = 4.0) were produced, characterized by large high angle grain boundary (HAGB) fractions around 80 % and grain sizes between 250 and 500 nm. The ARBed microstructure was determined to be resistant to discontinuous static recrystallization upon heating owing to the large fraction of HAGBs. This results in the microstructure retaining a sub-micron grain size for extended durations up to 250 °C. Superplastic deformation characterized by stable grain boundary sliding was found to be optimal for temperatures and strain rates between 225 to 250 °C and 5ⅹ10-4 to 1ⅹ10-3 s-1, respectively. This reduction in temperature is not only dependent on the sub-micron grain size, but also the presence of non-equilibrium grain boundaries which reduce the activation energy for grain boundary diffusion. Further reduction in temperature was limited by a transition from grain boundary sliding to solute drag creep.Biaxial bulge testing was conducted to simulate superplastic forming operations using the previously identified optimal parameters. Thinning ratios (to/tf) around 2.5 were achieved prior to failure with a cavitation void fraction below 2 %; this exceeds performance of current industrial superplastic forming operations in coarse grained AA 5083. Results suggest thinning ratios as high as 3.5 can be achieved while remaining under the 2 % void fraction limit established by the forming industry. Thus, sub-micron grained material produced by ARB has been shown to demonstrate low temperature superplasticity with a reduction in required forming loads, with the additional benefit of being able to sustain higher superplastic strains with less microstructural damage.
590 $a School code: 0052.
650 4 $a Materials science. $3 557839
653 $a Accumulative roll bonding
653 $a Grain refinement
653 $a Superplasticity
653 $a Ultrafine grains
690 $a 0794
710 2 $a Colorado School of Mines. $b Metallurgical and Materials Engineering. $3 1182976
773 0 $t Dissertations Abstracts International $g 84-04B.
790 $a 0052
791 $a Ph.D.
792 $a 2022
793 $a English
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