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Title: The role of solute and transition elements in the superplastic behaviour of aluminium alloys.
Author: Stavros, Katsas
ISNI:       0000 0001 3478 4593
Awarding Body: Imperial College London (University of London)
Current Institution: Imperial College London
Date of Award: 2007
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This project fOllows on from work carried out at Imperial College London to develop aluminium alloys with enhanced superplastic properties for automotive applications. In this prior work it was found that AI-Mg-Zralloys exhibited superior superplastic properties to other 5xxx alloys including the widely used superplastic variant of5083. The aim of the current work was to fully characterise the AI-Mg-:Zr alloys at each stage of the production route in order to optimise the processing conditions and exploit alternative production routes. It is generally accepted that there are two main requirements for superplasticity in ..J aluminium alloys. The first is the addition of a solute element to reduce the high stacking fault energy associated with pure aluminium energy and hence favour recrystallisation over recovery during thermomechanical processing. The second is a homogeneous dispersion of fine, thermally stable second phase particles to control grain growth via Zener pinning. For this reason the characterisation of the AI-Mg-Zr alloys focussed on the individual roles of the solute (magnesium) and transition element (zirconium) additions. In order to' better understand the role of zirconium a binary AI-Zr alloy was also prepared and investigated. Furthermore, some preliminary casting trials' where zirconium was either partially or totally replaced by vanadium were conducted. The purpose of these experiments was to' produce a more economical and practical grain control methodology. The implication of the work presented in this thesis is that although it is well recognised that solute elements together with high amounts of stored energy (as a result of complex thermomechanical processing) are both necessary to achieve superplasticitY in aluminium alloys, under certain circumstances the presence of either may be sufficient Furthermore, useful conclusions about the pinning capability of the second phase particles were also drawn. The findings described in this thesis can have a significant impact on the design not of)ly of the processing route of the AIMg- Zr alloys but also of other established superplastic aluminium alloys.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available