Modification of a thermomechanical model to predict constitutive behavior of Al-Mg-Si alloys

A previously developed constitutive model for quantification of the effect of the condition of Mg and Si in AA6xxx alloys was used for the prediction of the flow stresses measured by plane strain compression (PSC) tests. As an extension of earlier work, two AA6xxx alloys were subjected to different thermal pretreatments and were plane strain compression tested at temperatures and strain rates typical for hot extrusion. Heating rates to the test temperature were varied. Dissolution behavior of the beta precipitates, needed for the quantification, was experimentally validated using differential scanning calorimetry. Significant differences in flow stress during PSC testing were observed as a function of the heating rate to the deformation temperature and of the different conditions that resulted from the different thermal pretreatments. The model was also applied to the combined set of present data and data reported earlier. This combined set of data encompasses a wide range of alloy compositions and thermal histories. It is found that the model gives a fair prediction. Excellent agreement was obtained by assuming that the parameter describing the solution hardening behavior in the model is temperature dependent instead of constant.