  We propose a methodology for the rheological characterization of a semisolid
metal slurry using experimental squeeze flow data. The slurry is modeled as a
structural thixotropic viscoplastic material, obeying the regularized
Herschel-Bulkley constitutive equation. All rheological parameters are assumed
to vary with the structure parameter that is governed by a first-order kinetics
accounting for the material structure breakdown and build-up. The squeeze flow
is simulated using finite elements in a Lagrangian framework. The evolution of
the sample height has been studied for wide ranges of the Bingham and Reynolds
numbers, the power-law exponent as well as the kinetics parameters of the
structure parameter. Systematic comparisons have been carried out with
available experimental data on a semisolid aluminium alloy (A356), where the
sample is compressed from its topside under a specified strain of 80% at a
temperature of 582 oC while the bottom side remains fixed. Excellent agreement
with the experimental data could be achieved provided that at the initial
instances (up to 0.01s) of the experiment the applied load is much higher than
the nominal experimental load and that the yield stress and the power-law
exponent vary linearly with the structure parameter. The first assumption
implies that a different model, such as an elastoviscoplastic one, needs to be
employed during the initial stages of the experiment. As for the second one,
the evolution of the sample height can be reproduced allowing the yield stress
to vary from 0 (no structure) to a maximum nominal value (full structure) and
the power-law exponent from 0.2 to 1.4, i.e., from the shear-thinning to the
shear-thickening regime. These variations are consistent with the internal
microstructure variation pattern known to be exhibited by semisolid slurries.
