*********************************
There is now a CONTENT FREEZE for Mercury while we switch to a new platform. It began on Friday, March 10 at 6pm and will end on Wednesday, March 15 at noon. No new content can be created during this time, but all material in the system as of the beginning of the freeze will be migrated to the new platform, including users and groups. Functionally the new site is identical to the old one. webteam@gatech.edu
*********************************
Under the provisions of the regulations for the degree
DOCTOR OF PHILOSOPHY
on Tuesday, May 2, 2017
10:30 AM
in Love 210
will be held the
DISSERTATION DEFENSE
for
Judith M. Dickson
“DEVELOPMENT AND CONTROL OF STRENGTH ANISOTROPY AND CRYSTALLOGRAPHIC TEXTURE DURING EXTRUSION OF ALUMINUM 2195 AND 7075”
Committee Members:
Dr. Thomas H. Sanders, Jr., Advisor, MSE
Dr. Naresh Thadhani, MSE
Dr. Hamid Garmestani, MSE
Dr. Richard Neu, ME
Mr. Victor Dangerfield, Universal Alloy Corporation
Abstract:
The addition of lithium to high strength aluminum alloys significantly improves specific strength. Indeed, for aerospace applications, the third generation Al-Cu-Li alloy, Al 2195, is competitive with composite materials. However, unlike its non-lithium containing counterpart, Al 7075, it suffers from undesirable anisotropic mechanical properties in low aspect ratio extruded sections. To investigate the origins of this anisotropy, Al 2195 and Al 7075 were systematically extruded over a range of aspect ratios from 2-15 while maintaining a constant extrusion ratio. This study found that the interaction of high volume fractions of the Copper crystallographic texture with the strengthening precipitates in Al 2195 is responsible for the poor mechanical performance in low AR regions. Through a series of rolling studies, a higher initial billet temperature and a slower ram speed were hypothesized to minimize the Copper texture component in extruded Al 2195. As press trials are often cost prohibitive and lead to convoluted results due to imperfect press repeatability, the effects of extrusion press parameters on the final microstructure and properties would ideally be studied via simulations. However, it was found that the commercially available finite element software, HyperXtrude, was not able to predict the effects of press parameters on mechanical anisotropy. It is therefore recommended that the Barlat Method for prediction of anisotropic yield strengths be integrated into the HyperXtrude solver to allow for future computational parametric studies on the effects of extrusion variables on final strength anisotropy in extruded aluminum alloys.
