UBC Theses and Dissertations
Co-deformation of an aluminum zinc alloy Breakey, J.W. Matthew
In some systems, including copper niobium, it has been found that as the scale of the two phases decreases, there is an anomalous increase in strength. Mechanisms of this strengthening have been postulated, but a general theory has yet to be developed. A model system to study the co-deformation of fine scale materials was developed and characterized. An aluminum 18.5at.% zinc alloy was selected and discontinuously precipitated to produce 100% transformation and an interlamellar spacing of 240nm.The material was tested using strain rate jump tests to determine the temperature sensitivity, tensile tested to determine work hardening and the temperature sensitivity, wire drawn to study the effect of large plastic deformation and finally tension compression tested to determine internal stresses. The bulk properties of the two phases are well known allowing for a detailed analysis of the composite properties when combined with the mechanical results. The material showed increased strength above the rule of mixture prediction from bulk properties due to a fine scale microstructure . Although the lamellar material had a much higher strength than the rule of mixtures would predict, the overall strength of the alloy did not approach that of more conventional high strength aluminum alloys. The material was found to be temperature and rate dependent, with an increased work hardening rate as the temperature was decreased. Temperature was found to play a key role in the stress partitioning between the two phases. Temperature dependent relaxation processes lowered the stress partitioning between the hard and soft phases as the temperature was increased. Therefore, stress relaxation must be minimized to maximize the strengthening found in fine scale materials.
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