The Bolting of Magnesium Components in Car Engines

ii Declaration This dissertation is the result of my own work and does not include any work that is the outcome of collaboration. No part of this dissertation has been submitted at Cambridge or any other University for a degree, diploma or other qualification. The total length of this dissertation is 13150 words. Acknowledgements The author would like to thank the following: Professor Bhadeshia for his continual enthusiasm, support and cheerfulness and particularly for his comments on the first version of this report; Thomas Hermansson and Ingemar Bertilsson for providing the data; Ingemar Bertilsson for sending me numerous papers; Thomas Sourmail for providing the Models Manager software and providing technical assistance with the hardware and software; and to Oomps and Kerry for their help with the proof reading. Model 1 and Model 3 have been submitted to the Materials Algorithm Project for Abstract The automotive industry is striving to produce lighter vehicles. At present this is achieved through the use of ultralight steels, aluminium alloys and magnesium alloys for some body parts. Magnesium has the highest strength-to-weight ratio of any structural metal and so engineers are keen to use as much magnesium as possible in their vehicles. However, magnesium alloys creep, even at room temperature, restricting their use. This project focuses on the problem of bolting together magnesium alloys components at temperatures around 100 o C, such as those found in car engines. The bolted joints undergo stress relaxation even at such low temperatures. The problem of stress relaxation in magnesium alloy AZ91D is investigated using four physical and non-physical neural network models. These models have half the noise level of the experimental results used to make the networks and their predictive qualities are shown to be an improvement over standard empirical models. The networks were used to attempt to reproduce published results and to calculate the activation energy for self-diffusion in magnesium.