Anomalous rheological behaviour of semi-solid alloy slurries at low shear rates

A rheological investigation has been conducted using a concentric cylinder rheometer on a semi-solid sn-15% Pb alloy at solid fractions between 0.2 and 0.5. The results show anomalous flow behaviour in that, at low shear rates, the shear stress falls with increasing shear rate up to 250 s−1 under steady-state conditions. Possible explanations of this anomalous behaviour are discussed and it is concluded that it is a genuine feature of the bulk slurry and not an experimental artefact. It is further suggested to be a consequence of the rapid breakdown of the internal structure of solid particle clusters within the slurry which occurs at low shear rates.