by Yeung Ching Chung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (leaves 69-71). / Text in English; abstract also in Chinese. / by Yeung Ching Chung. / Table of contents --- p.i / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- General overview --- p.1 / Chapter 1.2 --- The present study --- p.3 / Chapter Chapter 2 --- Sample preparation and characterization / Chapter 2.1 --- Sample preparation / Chapter A. --- General description --- p.5 / Chapter B. --- The thermal pulse furnace --- p.7 / Chapter C. --- The substrates --- p.9 / Chapter D. --- Sample preparation --- p.10 / Chapter 2.2 --- Sample characterization / Chapter A. --- Micro Raman system --- p.11 / Chapter B. --- Rutherford backscattering spectrometry (RBS) --- p.12 / Chapter C. --- X-ray powder diffraction --- p.13 / Chapter D. --- AFM. SEM and Surface Profiler --- p.13 / Chapter Chapter 3 --- Results and discussion / Chapter 3.1 --- The surface morphology / Chapter A. --- General description --- p.15 / Chapter B. --- The as-deposited amorphous film --- p.15 / Chapter C. --- The crystalline Ge film --- p.16 / Chapter D. --- The alloy film --- p.17 / Chapter E. --- The role of a-Si layer --- p.22 / Chapter 3.2 --- The depth profile (RBS) / Chapter A. --- General description --- p.24 / Chapter B. --- Peak temperature dependence --- p.27 / Chapter C. --- Heating rate dependence --- p.30 / Chapter 3.3 --- The near surface composition measured by Raman scattering / Chapter A. --- General description --- p.33 / Chapter B. --- Peak temperature dependence --- p.43 / Chapter C. --- Heating rate dependence --- p.45 / Chapter 3.4 --- Preferred growth direction / Chapter A. --- General description --- p.47 / Chapter B. --- Peak temperature dependence --- p.48 / Chapter C. --- Heating rate dependence --- p.51 / Chapter 3.5 --- Discussion / Chapter A. --- The particle size --- p.55 / Chapter B. --- The participation of Si substrate --- p.58 / Chapter C. --- The alloy formation --- p.58 / Chapter D. --- The abnormally fast interdiffusion --- p.63 / Chapter Chapter 4 --- Conclusion --- p.65 / Appendix --- p.67 / References --- p.69

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Gall, Kenneth; Committee Member: McDowell, David; Committee Member: Thadhani, Naresh. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Dissertation submitted in fulfilment of the requirements for the degree Master of Technology: Mechanical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology / Aluminium alloys has seen recent increase usage in the automotive industry. This is due to the global obligation towards carbon emission reduction and fuel efficiency in the transport sector. The good strength-to-weight ratio offered by Al-Si-Cu alloys showed promising results towards the compliance of these environmentally friendly criteria. The enhanced mechanical properties is obtained when the alloy is subjected to the T6 heat treatment process, which cause microstructural changes due to the evolution of intermetallic phases. The process involves solution heat treatment, for dissolving soluble Cu- and Mg-containing phases, the homogenization of alloying elements, and the spheroidisation of eutectic Silicon. It is followed by quenching, for maximum precipitation hardening particle retention in solution, and a further artificial ageing process with the aim to acquire a uniform distribution of small precipitates, for strength improvement. The heat treatment schedule applied in this study was conducted as follows: Solution heat treatment at a temperature of 525°C for 6h Quenching in water of temperature 50°C; Artificial ageing for 8h at a temperature of 175°C, and then after left inside furnace to cool down to room temperature. This is higher than the 520°C, but shorter than the 8-12h, observed in literature. Also, quenching is done at a lower temperature rather than 60°C, and artificial ageing at a higher temperature, rather than the 155°C. This was done to be able to draw a comparison between the MAGMASOFT® simulation, which has this non-adjustable schedule, and the experimental results. The simulated and experimental results were comparable and similar outcomes, but with some discrepancies. Such as the porosity was far more visible and intense in the experimental, than what was predicted by the software. The as-cast and heat treated microstructure revealed the expected evolution of intermetallic particles, such as dissolving of the Al2Cu and the spheroidisation of the eutectic Si phases. Another phase that was identified was the insoluble AlFeSi and other possible Fe-containing phases, which due to the higher solution heat treatment temperature, showed partial fragmentation and dissolution. The study provided practical data about the effect of heat treatment on microstructural evolution and how it affects the properties of the Al-Si-Cu alloy. It also brought to the attention and understanding of how critical pouring temperature is, as it affect the initial nucleation, and cooling rate, and therefore the micro and macro properties.

Aluminum-silicon-copper cast alloys of the 319-type have attained a commercially important status because of their widespread use. Artificial aging treatments are routinely applied to these alloys in order to obtain precipitation hardening and improve their mechanical properties. Standard treatments may not always yield the optimum achievable properties, thus Mg and Sr are commonly added to improve the response of the alloy to aging and to modify the eutectic Si morphology from acicular to fibrous, respectively. The present study was carried out to investigate aging behavior of four 319-type alloys in regard to such mechanical properties as their ultimate tensile strength, yield strength, microhardness, percent elongation and impact toughness. Non-conventional aging cycles were applied so as to evaluate the degree of the improvement in strength obtainable. These treatments, labeled in this study as T6- and T7-type multi-temperature and interrupted aging treatments, involve several heating stages at different temperatures, as opposed to the single stage at constant temperature specifications of the standard T6 or T7 heat treatment regimes. Scanning electron microscopy was used to examine the fracture surfaces of selected tensile-tested samples to compare the fracture behavior. Transmission electron microscopy was used to reveal and identify the tiny precipitates which appear in the microstructure as a result of the precipitation-hardening process due to artificial aging. It was found that the main strengthening phase is theta-Al2Cu in the form of needles; other phases were observed as minor constituents in this alloy, including the binary beta-Mg2Si, the ternary S-CuAlMg 2 and the quaternary Q-Al5Cu2Mg7Si 7. The results show that while Mg and Sr additions improve the properties of the alloy, the standard T6 treatment may not be the best available option to produce optimum properties. In fact, when the peak-aged (T6) condition is desired, the optimum treatment consists of a continuous artificial treatment at 170°C for 8 h; when the overaged (T7) condition is desired, a T7-type multi-temperature treatment consisting of underaging at 170°C for 1 h, then at 190°C for 1 h, and finally overaging at 240°C for 2 h is the best option.

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