Papers by Author: S.R. MacEwen

Abstract: Superplasticity refers to a high temperature deformation process involving a marked sensitivity of the flow stress to the imposed strain rate, with resulting enhanced ductility. Although conventionally associated with fine-grained materials, superplasticity has recently been observed in coarse-grained alloys. The present research involves the deformation behavior of Al-Mg base alloys, where superpure Al-3%Mg and Al-5%Mg, and commercial Al 5056 were selected for study. The results for the Al-5%Mg and Al 5056 alloys are presented in this article. Flat sheet-type samples were tensile tested to 10% strain at increasing temperatures and at prescribed strain rates (0.001/s, 0.01/s, and 0.1/s). The dependence of flow stress on temperature was found to display some unusual characteristics. This behavior is interpreted as resulting from the occurrence of dynamic strain ageing (DSA). The aim of the overall study is to determine the relation between DSA and superplasticity in coarse-grained Al-Mg alloys. This will, in turn, lead to the control of the strain ageing behavior so as to produce the largest possible values of strain rate sensitivity (and, hence, elongation).

Abstract: Finite element modelling of sheet-forming operations, such as pressure-ram-forming, (PRF™) requires knowledge of forming limits under biaxial strain conditions. In this work, elliptical bulge tests have been used to evaluate the forming limits of an aluminum bodystock alloy, X309, that is used for PRF™ applications. Limiting dome heights have been determined as a function of pressure-rate and temperature. All tests have been done with the rolling direction, RD, of the sheet aligned with the major axis of the bulge.