Thixoforming : Semi-solid Metal Processing

434j 11 Thixoextrusion
Figure 11.24 Extruded bars.
between the lowest press velocity possible (10 mm s 1 ) and 20 mm s 1 . For better
cooling conditions in the extrusion channel, the extrusion channel height was
increased to 100 mm. All experiments were carried out considering a fraction of
40% (T B 1270 C). The extrusion channel diameter was varied according to the first
experiments but no opening forming die geometry was considered. No coatings were
investigated in this series.
The installation of the cooling tube resulted in the production of bars. The
presented variations of the process parameters (here mainly the reduced press
velocity and the elongated extrusion channel length) showed no significant influence
on the process: the material exited the forming die in a semi-solid state and solidified
in the cooling tube.
Independently of the selected press velocity, extrusion channel height, diameter
and geometry, the maximum bar length was limited to 460 mm (Figure 11.24). The
weight of the extruded bar increased until the bar cracked due to its own weight. All
extruded bars showed such cracks. In Figure 11.25, two different kinds of cracks –
dripping cracks and cracks without contraction – are presented. Due to cooling of the
Figure 11.25 Different cracks that occurred.