Computer simulation of the microstructure and rheology of semi-solid alloys under shear

The rheological behavior of metallic alloys containing. both solid and liqu id phases is investigated in the low solid fraction range (<50%). This beha vior depends on both the solid fraction and the shear rate. The concept of effective volume fraction (EVF) is used to decorrelate the influence of the se two parameters. At high shear rate the slurry behaves like a suspension of hard spheres, whereas at lower shear rate particles tend to aggregate in clusters, entrapping liquid and thus increasing the EVF and the viscosity. A lattice model is introduced to simulate the aggregation/break-up process es within a slurry under shear. When the steady state is reached, the entra pped liquid fraction is calculated, leading to a viscosity estimation. Simu lation results for the viscosity and structure of the three-dimensional clu ster are in good agreement with experimental results. (C) 2000 Acta Metallu rgica Inc. Published by Elsevier Science Ltd. All rights reserved.