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Deformation mechanisms in magnesium alloy Elektron™ 675.

Randman, David (2011) Deformation mechanisms in magnesium alloy Elektron™ 675. PhD thesis, University of Sheffield.

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Magnesium is a very lightweight and strong material and thus is of particular interest to industries such as aerospace and automotive. Elektron™ 675 is a new alloy developed by Magnesium Elektron Ltd. and based on the magnesium-gadolinium-yttrium system. This gives particularly high strength and high temperature stability but currently proves more difficult to process than conventional magnesium alloys. The objectives in the current work were to study the deformation behaviour with particular emphasis on the flow behaviour during rolling and the deformation mechanisms that are operating. To study the deformation behaviour over a wide range of conditions, plane strain compression (PSC) tests were carried out in a matrix between 380°C and 520°C and Is-1 and 10s-1 strain rates, similar conditions to those experienced in industrial rolling. The tests showed similar behaviour at all conditions with a rise to a peak stress followed by continuous softening and constitutive equations of flow stress were developed. Further PSC tests were used to study behaviour such as static recrystallisation during annealing and the effect of non-isothermal rolling with cold rolls. Following deformation, the microstructures were studied using various microscopy techniques, the most common being electron backscatter diffraction (EBSO). It was found that {loT 2} twinning was very prevalent in the early stages of deformation, particularly in the tests deformed at low temperatures or high strain rates. Slip occurred predominantly on the basal plane but was also observed on prismatic planes and there was strong evidence that <c+a> pyramidal slip was also active. Dynamic recrystallisation was observed in necklace formations around grain boundaries and is thought to have formed by the continuous dynamic rotation recrystallisation mechanism. This study has provided new information on the deformation mechanisms that operate in high strength magnesium alloys and has calculated a viable process window in which Elektron 675 can be rolled.

Item Type: Thesis (PhD)
Academic Units: The University of Sheffield > Faculty of Engineering (Sheffield) > Materials Science and Engineering (Sheffield)
Identification Number/EthosID: uk.bl.ethos.538018
Depositing User: EThOS Import Sheffield
Date Deposited: 01 Nov 2016 15:45
Last Modified: 01 Nov 2016 15:45
URI: http://etheses.whiterose.ac.uk/id/eprint/14692

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