Constitutive behavior of as-cast aluminum alloys AA3104, AA5182 and AA6111 at below solidus temperatures

Abstract

Over the past decade thermomechanical models of the direct chill (DC) casting process have been developed in an effort to mitigate casting defects such as hot tearing as well as to develop a more scientific understanding of the thermal stress and strains which develop during the casting process. A key input to these models is the constitutive behavior of the material in the solid state under thermomechanical conditions that are typical of those experienced during DC casting (strain rates from 1 × 10 −1 s −1 to 1 × 10 −5 s −1 and temperatures from solidus down to room temperature). This research work presents use of an empirical model (the extended Ludwik equation) to predict the high and low temperature constitutive behavior of aluminum alloys in the solid state under deformation conditions relevant for DC casting. The effect of temperature, strain and strain rate has been studied for three commercially important alloys, namely: AA3104, AA5182 and AA6111. Material parameters used in the constitutive equation were calculated based on experimental measurements using a Gleeble 3500. To validate the constitutive equations developed, complex thermomechanical history tests were performed using the Gleeble 3500 that more closely resemble those experienced by the material during industrial DC casting. These measurements were then compared to the material response based on an ABAQUS finite element (FE) simulation of the test which modeled the material behavior using tabular data and included the effects of temperature, strain and strain rate. When using a commercial FE package such as ABAQUS, it was found that strain softening needs to be considered in situations where the temperature is changing during the simulation. An empirical model was developed to account for strain softening which occurs during continuous cooling tests based on the measured work hardening parameter “ n”.