Strength and ductility of Mg alloys from first-principles

Magnesium alloys are of great interest in the transportation sector for vehicle weight reduction and improved energy efficiency due to their high specific strength. However, Mg has limited ductility at room temperature due to a high strength anisotropy (~100:1). Thus, forming is performed at ~300°C where the anisotropy is reduced to 4:1. In this work, we investigate the effects of 63 substitutional solutes on basal and prismatic slip in Mg. Using DFT and a flexible boundary condition method, we compute a-type basal and prismatic dislocation core structures and use these geometries to efficiently model the interaction of solutes with these cores based on solute interactions with stacking faults and strain. We show that the calculated misfit parameters are highly correlated so that only a few parameters are necessary to describe solute interactions in the dislocation cores. The geometric solute interaction models are validated against calculation with direct substitution of solutes in the cores. We predict basal solid-solution strengthening and prismatic solid-solution softening parameters for all 63 solutes. We show that 25 of these solutes (alkali, alkaline earth, rare earth metals, Zr and Hf) have the potential to increase prismatic slip and lower forming temperatures of Mg. Optimal concentrations and reduced forming temperatures are shown for these 25 solutes. Additionally, we study solute stacking fault misfits for the pyramidal (1-101) plane as a secondary slip system.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2013

Author dc:creator

• Yasi, Joseph

Contributors dc:contributor

• Trinkle, Dallas R.
• Ceperley, David M.
• Bellon, Pascal
• Errede, Steven M.

• Magnesium
• Density Functional Theory
• Dislocations
• Metallurgy
• Ductility
• Formability

Statement dc:rights

• Copyright 2012 Joseph Yasi

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/42144

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/42144