Investigation of the microstructure and the rheology of semi-solid alloys by computer simulation

This paper is concerned with the simulation of the rheological behaviour of metallic alloys in the semi-solid state for low solid fractions (< 50%). This behaviour obviously depends strongly on the solid fraction but also on the shear rate and the influences of these two parameters are generally coupled. In order to decorrelate these influences, the concept of Effective Volume Fraction (EVF) is used. Indeed, at high shear rate the semi-solid slurry behaves as a suspension of hard spheres, whereas at lower shear rate, the aggregation of particles in clusters leads to liquid entrapment and thus, increases the EVF and the viscosity. A lattice model is used to simulate the aggregation / break-up processes which occur in a slurry under shear. When the steady state is reached, the model allows to calculate the fraction of entrapped liquid and therefore to estimate the viscosity. The results of the simulation concerning the 3D cluster structure and the viscosity are in good agreement with experimental results.