A study of alloys based on the magnesium-lithium system
Das, Siddhartha
This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/23047
Description
Title
A study of alloys based on the magnesium-lithium system
Author(s)
Das, Siddhartha
Issue Date
1989
Department of Study
Engineering, Metallurgy
Discipline
Engineering, Metallurgy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Metallurgy
Language
eng
Abstract
A study has been made of the development of microstructure, mechanical properties and oxidation behavior of Mg-Li-Si alloys. In the first instance, an attempt has been made to determine the phase equilibria that occur under near-equilibrium conditions for the case of Mg rich alloys. This has involved the application of optical metallography, x-ray diffraction and differential scanning calorimetry. As a result, the ternary phase diagram for these Mg-rich alloys has been drawn semi-quantitatively. This diagram has been used together with optical and electron metallography to determine the effect of Li on the Mg-Si binary system, as well as understand the development of microstructure in rapidly solidified Mg-Li-Si alloys. Thus, Li is found to reduce the eutectic temperature and also cause the eutectic composition to occur at lower concentrations of Si. A coupled eutectic microstructure has been produced by rapid solidification processing for an hyper-eutectic composition given by Mg-xLi-3Si (where x = 5 to 12 wt.%), and the difference between the behavior of the binary Mg-Si and the ternary Mg-Li-Si alloys has been assessed. The mechanical properties of these alloys have been studied using various types of sample. Thus, rapidly solidified melt-spun ribbons containing coupled eutectic as well as cellular microstructures have been tested, and it has been found, contrary to expectation, that the dispersed phase Mg$\sb2$Si provides sites for crack initiation at the particle/matrix interfaces. In laser surface melted alloys, the effect of Li has been associated with a refinement of grain size. Decohesion along the particle (Mg$\sb2$Si)/matrix interfaces again limits the plastic properties of these alloys. The oxidation behavior of the as-cast Mg-Li and Mg-Li-Si alloys has also been studied. It appears that microstructure has a significant effect on the oxidation behavior of these alloys. It has been proposed that oxidation is taking place at the oxide-metal interface, requiring the diffusion of oxygen through the growing oxide layer.
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.
