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%). T his behaviour obviously depends strongly on the solid fraction but also oil the shear rate and tile influences of these two parameters are generally c oupled. In order to decorrelate these influences, the concept of Effective Volume Fraction (EVF) is used. Indeed, at high shear rate the semi-solid sl urry behaves as a suspension of hard spheres, whereas at lower shear rate, the aggregation of particles in clusters leads to liquid entrapment and thu s, increases the EVF and the viscosity. A lattice model is used to simulate the aggregation / break-up processes which occur in a slurry tinder shear. When the steady state is reached, the model allows to calculate the fracti on of entrapped liquid and therefore to estimate the viscosity. The results of the simulation concerning the 3D cluster structure and tile viscosity a re in good agreement with experimental results.