Multiscale In-Situ Characterization of Crystal Orientation, Temperature, and Microstructure Effects on Creep Defromation of Pure Magnesium and Mg-Al-RE Alloys

Magnesium (Mg) and its alloys are the lightest structural metals, valued for their high strength-to-weight ratios in automotive and aerospace applications. Their broader use is restricted by limited creep resistance and pronounced anisotropy of plastic deformation, especially at elevated temperatures. This thesis examines how crystal orientation, temperature, and β-phase morphology govern creep behavior in pure Mg and AE44 alloys. Novel in-situ nanoindentation creep methods were developed using an indenter inside a SEM. Additional techniques included in-situ tensile creep testing, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and crystal plasticity finite element (CPFE) simulations. Together, these enabled orientation-sensitive analysis of creep behavior and links between microstructure and bulk creep response. The first part of the thesis investigates orientation effects in pure Mg via spherical indentation, showing strong anisotropy in lattice rotation and slip activity, with c-axis misorientation controlling basal slip and twinning. The second part develops in-situ Berkovich constant-load indentation creep tests at 25, 100, and 180 ˚C. Analysis of activation energy, activation volume, and athermal flow stress indicates that creep is dominated by obstacle-limited dislocation glide, while higher temperatures promote dynamic recovery. The final part studies high pressure die cast (HPDC) AE44 alloys (AE44-2 and AE44-4). Results reveal that β-phase morphology enhances creep resistance by obstructing dislocation glide and grain boundary sliding. A Hall-Petch-like relationship between β-phase spacing and creep displacement highlights microstructural refinement as a pathway to improved high-temperature performance. This work establishes advanced testing methodologies and provides new mechanistic insight into the creep behavior of Mg and AE44 alloys. The findings strengthen the understanding of orientation, temperature, and microstructural effects, offering guidance for alloy design to improve lightweight, high-temperature applications.

Name thesis:degree_name

Ph D

Discipline thesis:degree_discipline

Mechanical and Materials Engineering

Grantor dc:publisher

The University of Western Ontario

Year dc:date.issued

2025

Author dc:creator

• Fu, Bolin

Advisors dc:contributor.advisor

• Klassen, Robert J.
• Abdolvand, Hamidreza

• Magnesium
• AE44 alloy
• Creep behavior
• In-situ indentation creep
• In-situ tensile creep
• Crystal orientation
• β-phase morphology
• SEM
• EBSD
• CPFE
• Elevated-temperature deformation.

Statement dc:rights

• Attribution-NonCommercial-NoDerivatives 4.0 International

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/20.500.14721/39115

OAI identifier oai:identifier

oai:uwo.scholaris.ca:20.500.14721/39115