Stress-strain computations of the DC casting process of aluminium alloy: A sensitivity study on material properties

摘要

Nowadays, numerical models aimed at predicting the ingot distortions and the stress build-up during direct chill (DC) casting of aluminium alloy slabs are available in different codes, commercial and "private" packages. A sensitivity analysis to the material properties used in these models has been carried out within the context of the Brite Euram research program EMPACT (European Modelling Project on Aluminium Casting Technology). The first sensitivity analysis is dedicated to the mechanical description of the "liquid elements", that is elements with temperatures higher than the coherency temperature of the alloy. A 2D transient model was run with Abaqus and with Alsim/Alspen in which "liquid elements" can be removed from the computation domain. By comparing the results, it is shown that the flow stress affected to the liquid should remain as low as possible provided convergence can still be reached. The second analysis is dedicated to the influence of the thermophysical properties of the alloy with special attention to the thermal conductivity. In that case, a 2D transient thermomechanical model of the DC casting process is used. The steady state temperature field inside the ingot and the associated ingot profile at the end of casting and after complete cooling are compared and it is concluded that the thermal conductivity of the alloy in the solid state is the most influencing property. The third analysis is dedicated to the influence of the description of the rheological behaviour of the solid phase. The results given by an elasto-plastic model with no hardening and no strain rate effects, an elasto-visco-plastic model including hardening and strain rate effects, an internal variable constitutive model and a truncated Garafalo type model are compared. It is shown that the deformation variables are mainly imposed by the thermal contraction and the continuity equations and that the stress field is little affected by hardening and strain rate effects. The goal of the present paper is to present the results of the different sensitivity cases and to determine which material properties should be paid more attention in order to better predict the main distortions and the stress build up undergone by an ingot during casting.