Modelling of the flow behaviour of wrought aluminium alloys at elevated temperatures by a new constitutive equation

The hot working behaviour of an Al–0.7%Mg–0.4%Si (wt.%) aluminium alloy has been investigated by tor- sion testing in the 450–575 C temperature range. The behaviour of the alloy, in terms of equivalent stress vs equivalent strain, was modelled by a modified form of the Hensel and Spittel constitutive equa- tion. In this new equation, the applied stress r was replaced by the sinh(ar) term, where a was a con- stant. The revised form of the Hensel–Spittel equation gave an excellent description of the flow curves and of the decrease in the strain rate sensitivity of the flow stress observed, at a given strain, with increas- ing strain rate. The model equation was then rewritten to explicitly include the Arrhenius term describing the temperature dependence of strain rate. The calculation indicated that the activation energy for hot working decreased from 218 to 198 kJ mol 1 in the considered range of strain.