Thixoforming : Semi-solid Metal Processing

190j 6 Modelling the Flow Behaviour of Semi-solid Metal Alloys
Figure 6.25 Sn–15%Pb alloy: temperature–time curve and
heating rate during convection heating of a 75 mm billet of
160 mm length.
Figure 6.26 Experimental results using the Sn–15%Pb alloy.
Apparent viscosity as a function of the apparent shear rate. The
regression follows the Herschel–Bulkley model.
cylindrical billets 75 mm in diameter and 160 mm in length, was heated to the desired
experimental temperature using a horizontal inductive heating system. While
heating the billet, the core temperature was recorded using a type K thermocouple
and the heating rate was derived from the time–temperature curve as shown in
Figure 6.27. First rheological experiments were carried out using an MHD aluminium–silicon
alloy of A356 standard composition (AlSi7Mg0.3). The experiments
were performed for two different solid fractions, 0.4 and 0.35. The flow velocity of the
slurry u was changed from 1.4 to 3.55 m s 1 , which corresponds to a variance in the
true shear rate between 1300 and 3200 s 1 (Figure 6.28).
In addition to the determined flow curves, the samples which had been removed
from the capillary tool after solidification completely demonstrate the flow characteristics
of the semi-solid material under the specific experimental conditions