Thesis--University of Florida. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 254-257).

For additive manufacturing, research has shown that the chemistry and microstructural properties of the feedstock powder can significantly affect the properties of the consolidated material. Thermal treatment and recycling parameters for powders used in both solid and liquid state processes can further affect the microstructure and properties of the consolidated parts. Understanding the powder microstructure and effects of powder pre-treatment can aid in optimizing the properties of the final consolidated part. This research proposes a method for the characterization and optimization of powder pre-processing thermal parameters using aluminum alloy powder as examples. Light microscopy, electron microscopy, and hardness were used to evaluate each condition.

No description available.

The purpose of this investigation was to determine the optimum conditions for explosion of a mixture of aluminum powder and liquid oxygen when fired without the use of a fixed detonator.

The objective of the thesis is to understand the particle/substrate interaction of micron-sized High Purity (HP) aluminum (Al) powder particles with varying surface oxide/hydroxide layers, during single particle impact and determine the critical impact velocity (CIV). Advancements in analytical techniques enable in-situ supersonic impact of individual metallic micro-particles on substrates with micro-scale and nanosecond-level resolution. This novel capability allowed direct observation and measurement of a material-dependent threshold velocity, above which the particle underwent impact-induced material ejection and adhered to the substrate, (critical impact velocity). The data was then compared to empirical, as well as predicted values of the CIV from published data that were based upon theoretical iso-entropic fluid dynamics models. A major emphasis of this research was to perform, in-depth characterization of the Al powder in the as-received, gas atomized state and subsequent to controlled temperature and humidity exposure (designed to form a prescribed oxide and/or hydroxide surface layer) and finally after single particle impact. Analytical techniques including XPS, ICP, IGF, TEM and SEM were performed to determine the species of oxide and/or hydroxide, bulk chemical composition, oxygen content and thickness of the surface oxide/hydroxide layer. Finally, bulk samples of material were produced by the cold spray process, from powder representing select test groups and subsequently characterized to determine tensile and hardness properties, chemistry, microstructure and conductivity. A fundamental understanding of the role of surface oxidization in relationship to particle deformation during impact and the bonding mechanism will be applicable toward the development of optimized parameters for the cold spray (CS) process. Results from this study will aid in the development of industrial practices for producing, packaging and storing Al powders.

No description available.

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.

No description available.

The implementation of technologies such as aluminum powder metallurgy (P/M) can be used in the automobile industry to have potential economic and environmental advantages. This technology to produce vehicle components can offer the combination of weight savings due to the low density of aluminum and material and machining savings via near net shape processing attributes. In an effort to expand the scope of application for aluminum P/M, considerable research has emphasized the development of new alloys and composites. One such alloy is P/M 2324, an aluminum-copper-magnesium alloy developed to have increased mechanical properties over the standard aluminum P/M alloys of the AC2014 type. The objective of this work was to undertake a comprehensive study on the effects of hot deformation on the emerging alloy P/M 2324 as well as the alloy with a SiC addition. Here, a forgeability study of these alloys and its wrought counterpart AA2024 was completed. To

Currently, there is a high demand for lightweight aerospace materials, driven by the desire to provide enhanced fuel efficiency by reducing vehicular weight. Aluminum alloys are attractive due to their excellent mechanical properties and high strength to weight ratios. Powder metallurgy (PM), which converts metal powder into a high performance product, presents an alternative to traditional forming techniques, which are often unable to provide adequate dimensional tolerances. The challenge is to determine if aluminum PM alloys and technologies can be successfully employed within aerospace applications. This research focuses on the PM processing technologies (die compaction, cold isostatic pressing (CIP), and spark plasma sintering (SPS)) of two alloys, PM2024 and PM7075. Processing parameters were assessed using attributes such as density, hardness, and tensile properties. Both powders showed comparable densities and tensile properties to their wrought equivalents. Ultimately, the groundwork was laid for future research into these alloys and their processing methods.