Thixoforming : Semi-solid Metal Processing

192j 6 Modelling the Flow Behaviour of Semi-solid Metal Alloys
Figure 6.29 (a) Samples of the aluminium alloy
after solidification. Due to geometric boundary
conditions the ingate system consumes most of
the billet material, which limits the experimental
time for quasi-steady-state flow significantly.
(b, c) Material running in the overflow keeps the
shape of the capillary cross-section and exhibits
a specific flow characteristic at certain shear
rates. Examples are given for flow velocities of
(a) 2.1 and (b)3.6 m s 1 .
experimentally necessary steady-state conditions. The measurement time is shortened
to an analysable constant pressure level lasting for 0.04 s. Second, wall slip is
caused by hydrodynamically induced segregation due to pressure and shear velocity
gradients perpendicular to the flow direction (Figure 6.30). The above-mentioned
Figure 6.30 Capillary experiments are generally attended by
segregation phenomena. Phase distribution can be correlated
with the chemical distribution. For an AlSi7Mg0.3 alloy and an
initial fS ¼ 0.45 the silicone content increases perpendicular to the
flow direction.