Rheological research of partially-solidified dendritic Sn–14.8wt%Pb alloy by two backward extrusion methods

Abstract

Two different backward extrusion methods were compared to study the rheological behaviour of partially-solidified Sn–14.8wt%Pb alloy for strip casting. For this work, the partially-solidified alloys were dendritic, as opposed to globular semi-solid slurries which have been studied more intensively. The first method was a constant-velocity experiment operating at constant extrusion-velocity of 3.5 mm s−1 and four different extrusion ratios. The second method was a varying-velocity experiment with unchanged extrusion ratio and four different extrusion velocities.Both backward extrusion experiments were carried at different temperatures ranging from 183 to 208°C. The two experiments obtained quite different results, which are discussed accordingly. Moreover, an unreported abnormal shear thinning behaviour was the main characteristic of the rheological behaviour of the partially-solidified alloys. Finally, the applicability of these two different methods of measuring the viscosity of partially-solidified alloys at different solid fractions is compared and discussed.