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Title: Thermo-mechanical processing of advanced magnesium alloys
Author: Chatterton, Mark
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2015
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Through process modelling (TPM) is a powerful tool to help understand and optimise industrial metal processing routes to obtain the desired microstructure and properties in the final product. In this study, the development of a TPM to predict key microstructural parameters in extruded rare-earth (RE) containing wrought magnesium alloy is discussed. Such alloys have a complex microstructure after processing. Additions of RE elements to extruded magnesium alloys can lead to a weaker texture and the emergence of a new 'RE-texture' component. Understanding the formation of this component after extrusion is difficult because the final microstructure is often fully dynamically recrystallised. To produce such a model, it has been necessary to improve understanding of the microstructure development during processing and how these are influenced by process parameters. Laboratory simulations and microstructural analysis have been used to identify the key relationships between process parameters and microstructural evolution. These results have been used to guide the development of a TPM model that couples a finite element prediction of temperature, strain, and strain rate with simple microstructure models to estimate the fraction of recrystallisation, the grain size and the fraction and distribution of second phase particles. The model predictions have been compared against the experimental data and applications of the model are discussed. To investigate the emergence of the RE-texture, a Mg alloy with high RE content has been cold drawn into wire. This is an axis-symmetric process with a strain path somewhat similar to extrusion. Using this method has enabled both the deformation and static recrystallisation behaviours to be separated, providing insights into the essential conditions needed to form the RE texture in (hot) extrusion. The drawn microstructure was characterised by elongated grains with basal fibre texture. Tensile, compression and double twins were visible but shear bands were not. During annealing, new statically recrystallised grains formed at grain and twin boundaries and at particles, leading to weakening of the drawn texture but no emergence of the RE-texture occurred, which suggests that shear banding has a critical role in forming the RE texture.
Supervisor: Robson, Joseph ; Quinta Da Fonseca, Joao Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: magnesium texture ; extrusion modelling