Design of Lightweight Magnesium Alloys: Processing, Microstructure and Properties
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Authors
Winner, Nicholas
Harvey, Cayla
Georgeson, Max
Dourte, Paul
Issue Date
2018
Type
Thesis
Language
en_US
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Abstract
Magnesium is the lightest structural metal. It is 78% lighter than steel and 35% lighter
than aluminum. Its high strength to weight ratio makes it an excellent material for applications
in automotive, aerospace, and structural applications. It also possesses an elastic modulus
and density comparable to human bone, which makes it an excellent alternative to other metals
for orthopedic implants. Unfortunately, magnesium shows di erent deformation depending
on the loading direction: its tensile deformation resembles typical metallic behavior while its
compression has a unique, twinning region of the stress-strain curve. This asymmetry is unreliable/
undesirable in practical applications. This twinning is caused by lack of slip systems in
magnesium that can accommodate deformation. Further limitations of magnesium include its
limited ductility, lower strength, and low corrosion resistance. Research mitigating or reversing
these weaknesses has largely focused on costly alloying elements. Elements such as thorium
and yttrium have provided excellent improvements to magnesium, but are prohibitively expensive
and not commercially viable. The objective of this work was to investigate the e ects
of commercially feasible alloying elements on the mechanical properties and microstructure of
magnesium. Using three aluminum-based commercial alloys (AZ31, AZ61, AZ80, and ZK60)
and a zinc-based commercial alloy (ZK60), these properties were investigated by mechanical
testing, electron backscatter di raction, and nanoindentation experiments. Through the use of
macro-scale tensile and compression experiments, di erent strengthening modes were identi ed
for di erent alloy chemistries. Evidence that alloyants can e ect the activation energy of twinning
was also observed. Electron backscatter di raction identi ed twin evolution with increased
compressive strain and also identi ed grains for nanoindentation. Nanoindentation con rmed
the presence of isotropy in magnesium's modulus with respect to texture and identi ed an
unexpected isotropy in hardness with respect to texture.
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