Simple constitutive description of Al–5·5Mg alloy deformed at elevated temperatures and strain rates

Abstract

The constitutive description of a commercial Al–5·5Mg alloy is analysed on the basis of a zero internal state variable approach known as the Sellars–Tegart–Garofalo (STG) model, employing for this purpose a number of stress–strain curves obtained from tests conducted at almost constant deformation temperature and strain rate. It is shown that such a model provides a satisfactory description of the flow stress data of the material as a function of the deformation conditions and that its formulation requires the determination of a relatively small number of material constants from the experimental data. It is also shown that the constitutive analysis can be conducted from the actual stress, strain, temperature and strain rate data without the need of performing any previous temperature and/or strain rate correction of the flow stress. These findings have important implications, in the sense that the constitutive analysis of the materials that undergo dynamic recovery during hot deformation can be conducted from data obtained under variable deformation temperature and/or strain rate, and including tests carried out at constant crosshead speeds. The present work also shows that more accurate results are obtained if the definition of the Zener–Hollomon parameter is slightly modified in order to eliminate the trivial temperature dependence of the activation energy for deformation by normalising its value by the factor μb³.