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Design of Lightweight Magnesium Alloys: Processing, Microstructure and Properties
Chemical and Materials Engineering
Materials Science and Engineering
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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.