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Microstructural characterisation and modelling of dilute magnesium-tin-aluminium alloys

Douglas, Gareth (2018)
Ph.D. thesis, University of Birmingham.

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Abstract

The ageing process of two magnesium alloys with compositions of Mg-1.75Sn-1.93Al and Mg-1.29Sn-2.85Al(at%) have been investigated. Three ageing times, 40, 72 and 160 hrs, were selected to correspond to the early growth, peak hardness and coarsened stage of the alloys and the hardness measured. Subsequently, the precipitates in the alloys have been classified by 4 morphologies, basal plates, 〈112 ̅0〉 laths, pyramidal laths and prismatic rods. and identified as Mg2Sn before the number density and size of the precipitates was measured. This has been achieved through a combination of X-ray Diffraction, Scanning Electron Microscopy and Transmission Electron Microscopy. Moreover, an Orientation Relationship of (0001)α//(111)β,[112 ̅0]α//[110]β was found to be common to three of the four morphologies with the pyramidal laths not conforming to a well-defined orientation relationship. This is then linked through observation to the lack of a common habit plane or growth direction for these pyramidal precipitates.
The obtained data has then been used to model the nucleation and growth of the precipitates using a Kampmann-Wagner Numerical framework, where key parameters such as the diffusion rate of Sn and the interfacial energy of the precipitates were fitted. This leads into a simulated strength against the ageing time which has been compared to the initial hardness measurements made. This has good agreement with not only the overall number density and precipitate sizes but also the size distribution of the precipitates
The effect of the two microstructures on the differing mechanical properties has been discussed, highlighting the importance of number density over the different precipitate morphologies observed, and future experiments outlined.

Type of Work:Ph.D. thesis.
Supervisor(s):Chiu, Yu-Lung and Jones, Ian P.
School/Faculty:Colleges (2008 onwards) > College of Engineering & Physical Sciences
Department:School of Metallurgy and Materials
Subjects:TN Mining engineering. Metallurgy
Institution:University of Birmingham
ID Code:8196
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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