Semisolid metal processing is gaining interest very rapidly in the casting
industry. It offers distinct advantages over other near-net-shape technolog
ies, such as a more homogeneous microstructure, less porosity and thus impr
oved mechanical properties. A perfect control of die filling during process
ing is however necessary, especially in the case of semisolid forming of al
uminum, where a non-controlled die filling can lead to oxide inclusions.
Numerical simulation can be used to predict die filling, and hence to optim
ize the die design. However, the constitutive behavior of semisolid metals
is quite complex. Their non-Newtonian behavior depends not only on the volu
me fraction of liquid, but also on the metal's history prior to processing,
and the processing conditions.
In this study, a "Bingham type", or Herschel-Bulkley constitutive relation
is introduced, capable of describing correctly the bulk behavior of the sem
isolid slurry. This constitutive equation is implemented in a modified vers
ion of the casting simulation package PAM CAST SIMULOR. Simulations for the
filling of 2-D and 3-D cavities using different injection speeds and mater
ial parameters are presented. The results are in good agreement with experi
mental evidences featuring similar geometric characteristics. Optimization
of die design using numerical simulation is also introduced. (C) 1999 Publi
shed by Elsevier Science S.A. All rights reserved.