Dilute Mg alloys are exclusively identified for wrought structural applications in automotive industry. Any improvement in mechanical properties of alloys is possible only by grain size refinement and by the development of suitable texture. The grain size, grain size anisotropy and texture in these alloys affect the compatibility stresses in a very complex manner. To launch a full scale study towards understanding the complex deformation mechanisms operating in these alloys, it is necessary to understand the effect of grain size and texture on the mechanical behavior of Mg alloys in a broad or semi-quantitative manner first. Current literature lacks such broad study. In this present study, the effect of grain size, grain size anisotropy and texture evolution on the mechanical properties are examined in order to develop an understanding of the deformation mechanism that control the mechanical properties of a dilute conventionally extruded Mg alloy, AZ21. The approach adopted was to first study the microstructure and texture evolution in this conventionally extruded alloy. Since the grain sizes in these alloys vary over a wide range, it is hence necessary to study the microstructure evolution in a highly quantitative manner. In understanding texture, the present study is only limited to qualitatively evaluating the evolution of fibre component of texture using X-Ray Diffraction spectra. For truly quantitative microstructure evolution results in materials were grains sizes are spread over a wide range, it is critical to study a statistically enough no. of grains. Hence to avoid any sampling error, large montages (about 0.3 sq. mm) were constructed out of a series of high resolution images captured using an optical microscope. The montages so constructed are subjected to extensive image enhancement and various other operations are performed to convert these coloured to binary montages. Information like grain size, diameter etc., can be easily extracted from these binary montages and used for further analysis. Fibre texture in these conventionally extruded dilute Mg alloys generally develops due to alignment of basal planes along the direction of extrusion. The Critical Resolved Shear Stress for basal slip is very low when compared to that of non-basal planes. And also since there are very limited primary slip systems in these dilute Mg alloys, the development of strong fibre texture drastically changes the compatibility stresses and hence the mechanical properties . To broadly study the effect of microstructure-texture on mechanical proerties, after post extrusion annealing, heat treatments representing typical microstructure-texture combinations were identified. Effect of each microstructure-texture combination on the tensile and completely reversed cyclic fatigue properties are studied and qualitatively interpreted. The fibre texture showed pronounced effect on tensile ductility but it hardly affected the yield strength. With just 10% reduction in BPI, the ductility reduced by about 50%. A small change in average grain size did not alter the yield strength. Unlike tensile ductility, fatigue endurance stress was not altered drastically by the change in grain size or texture. But there appeared to be a significant effect of residual stress. In ending, a small change in microstructure-texture combination in these conventionally extruded alloys has a pronounced effect on ductility or in other words plastic properties. But a it has minimal effect on yield strength and fatigue endurance stress.

Thesis (Ph. D.)--University of Queensland, 2001. / Includes bibliographical references.

Thesis (Ph. D.)--University of Michigan, 1946. / Reproduced from type-written copy. Bibliography: leaves 43-44.

In recent years, magnesium and magnesium alloys have received much attention as a new biomaterial in orthopaedic applications due to their biodegradability, biocompatibility, and their mechanical properties that are similar to natural bone tissue. The most common problem associated with magnesium as a biomaterial is low corrosion resistance in physiological solutions. This decreases the mechanical integrity of the implants in the early stages of healing and has a negative impact on the overall biocompatibility. The main goal of this study was to create a multi-layered coating consisting of a silica sol-gel under-layer to protect the substrate from corrosion in body fluids and a mesoporous silica top-layer to enhance the bioactivity of the coated implant material. The results indicate that the deposited multi-layered coating enhances both the bioactivity and the corrosion resistance of the material.

The use of magnesium and its alloys, as the lightest structural materials, to decrease the weight, improve the fuel efficiency and reduce the greenhouse gas emissions has significantly increased in the automotive and aerospace industries in recent years. However, magnesium alloys are commonly used as die casting products. The current application of wrought magnesium alloy products is limited because of their poor ductility at room temperature due to the formation of a strong texture and restricted active deformation modes in wrought magnesium products. Moreover, to support the application of magnesium alloys in automobile and airplane components, their dynamic mechanical response must be determined to evaluate their behavior during impact events such as car crash and bird strike in airplanes. Therefore, in this research study, the dynamic mechanical behavior of magnesium alloys at high strain rates was investigated. The effects of initial texture, composition, strain rate and grain size on the deformation mechanism were also determined. Split Hopkinson Pressure Bar was used to investigate the dynamic mechanical behavior of the magnesium alloys. Texture analysis on the alloy prior and after shock loading was done using X-ray diffraction. Scanning electron microscopy was used to study the microstructural evolution in the alloys before and after shock loading. Chemical analysis and phase identification were done by energy dispersive spectroscopy and X-ray diffraction analysis, respectively. Additionally, twinning type and distribution was determined by means of orientation imaging microscopy whereas dislocation types and distribution was determined using transmission electron microscopy. A visco-plastic self-consistent simulation was used to corroborate the experimental textures and possible deformation mechanisms. The dynamic mechanical behavior of cast AZ and AE magnesium alloys with different chemistries was investigated at strain rates ranging between 800 to 1400 s-1 to determine the effects of composition on the response of the alloys to shock loading. It was found that an increase in the aluminum content of the AZ alloys increased the volume fraction of β-Mg17Al12 and Al4Mn phases, strength and strain hardening but, on the other hand, decreased the ductility and twinning fraction, particularly extension twinning fraction, for all the investigated strain rates. In addition, increasing the strain rate resulted in considerable increase in strength of the alloys. Texture measurements showed that shock loading of the AE alloys resulted in development of a stronger (00.2) basal texture in samples with higher content of yttrium at the investigated strain rates. Increasing the yttrium content of the cast AE alloys decreased twinning fraction but increased dislocation density and volume fraction of the Al2Y second phase. As a result, the tensile strength and ductility of the alloys increased which is an interesting result for high-strain rate applications of AE alloys in comparison to AZ alloys. The dynamic mechanical behavior of rolled AZ31B and WE43 magnesium alloys were also studied at strain rates ranging between 600 to 1400 s-1. A strong (00.2) basal texture was observed in all shock loaded AZ31B samples. It was also observed that increasing the strain rate led to an increase in strength and ductility, but to a decrease in twinning fraction. A high degree of mechanical anisotropy was found for all investigated strain rates so that the lowest strength was registered for the samples cut along the direction parallel to the rolling direction. Furthermore, it was found that at high strain rates, fine-grained AZ31B alloy exhibits better ductility and strength compared to coarse-grained alloy. However, the hardening rate of coarse-grained alloy was higher. In the case of rolled WE43 alloy, it was found that the strength and ductility increased and twinning fraction decreased with increase in strain rate. Furthermore, another effect of increase in strain rate was the higher activation of pyramidal <c+a> slip systems. In addition, degree of stress and strain anisotropy is low particularly at higher strain rates, which is mainly related to the weak initial texture of the samples due to the presence of rare earth elements. Furthermore, strength and ductility were found to decrease with increasing grain size, while twinning fraction, activity of double and contraction twins and strain hardening rate increase with increasing grain size. In both AZ31B and WE43 alloy, the presence of <c+a> dislocations was confirmed at high strain rates using ‘g.b’ analysis confirming activation of pyramidal <c+a> slip systems during dynamic shock loading.

Nanopowders and bulk nanostructred materials have gained large interest in recent years. Bulk nanostructured materials exhibit properties that are far superior in comparison to conventional micron grained alloys. The fabrication of large scale nano-grained materials has been achieved in a two step process: (1) the production of nanostructured aluminium alloy powders and (2) the consolidation of the powder using a electromagnetic shockwave process. / The first part consists of cryo-milling; the milling of powder in an attritor filled with liquid nitrogen. This causes successive welding and fracturing events as the powder is milled, thereby creating the nano-structure. The low temperature prevents the possibility of recrystallization and grain growth. The alloy used for this work was Al 5356 (Al-5%Mg). Two different types of raw source materials were investigated: pre-alloyed powders and a mixture of aluminum with pure magnesium or an Al12Mg17 intermetallic. Experiments have been conducted in order to determine the optimum milling parameters that will simultaneously give a grain size smaller than 100 nm; equiaxed milled particles and mechanically alloyed powder (in the case of the mixture). The optimum milling parameters were established at 15 hours of milling time with a rotational speed of 300 RPM and ball to powder weight ratio of 24:1 in the case of the pre-alloyed powders. For the mixture of pure aluminum with pure magnesium the parameters were 15 hours, 300RPM and 32:1. The parameters for the mixture with the intermetallic were 18 hours, 300RPM and 32:1. / The dynamic magnetic compaction technique was done with a peak pressure of 1.1 GPa. This ultra-high strain rate process minimizes the exposure of the powders to high temperature and therefore reduces the possibility of recrystallization and grain growth. Relative densities of compacted pieces obtained ranged from 86.39% to 97.97%. However consolidation characterized by particle to particle bonding with a melted layer was not accomplished.

Thesis (PhD) -- McMaster University, 1997. / Includes bibliographical references (leaves 178-179). Also available via World Wide Web.

Thesis(M.S.)--Auburn University, 2005. / Abstract. Vita. Includes bibliographic references.

Thesis (Ph.D.)--University of Wollongong, 2004. / Typescript. Includes bibliographical references: leaf 152-160.

Thesis (Ph.D.). / Written for the Dept. of of Mechanical Engineering. Title from title page of PDF (viewed 2009/06/11). Includes bibliographical references.