The rheological behaviour of metallic suspensions

The knowledge of the rheological behaviour of metallic suspensions is an important issue when simulating die filling in thixoforming processes. Therefore rheological experiments like step-change in shear rate tests, shear stress ramps and oscillation experiments have been carried out to characterise the flow behaviour of semi-solid alloys exemplarily for A356 and Sn-15%Pb. The material exhibits a yield stress and shows shear-thinning and thixotropic flow behaviour, which is strongly influenced by the solid fraction, the particle shape and size and the degree of particle agglomeration. The instantaneous response on a change in shear rate was observed and pretends shear-thickening properties. All experiments were carried out in a Couette rheometer. The experimentally gained data are well fitted to a model approach, which consists of a modified Herschel-Bulkley law and accounts for the time-dependent effects by introducing a structural parameter kappa.