Thixoforming : Semi-solid Metal Processing

Figure 11.28 Model for extrusion process simulation.
channel, the already solidified material came in contact with the extrusion channel
wall and shell formation, as observed in the experiments and mentioned in the
literature several times, could be observed. In the experiments, the already solid billet
material stuck on the channel wall and the following material flowed by. This resulted
in a reduced bar diameter compared with the extrusion channel diameter using a
tempered forming die.
When observing the material flow, the development of a dead zone as in the
conventional extrusion processes could be detected (Figure 11.30). The material
flowed from the generated surface into the forming zone. There, the velocity of the
material increased to 300 mm s 1 .
With an extrusion channel length of 50 mm and a press velocity of 0.5 mm s 1 ,
solidification in the channel was realized. As shown in Figure 11.31, the bottom of the
Figure 11.29 Temperature development of the extrusion process.
11.5 Non-isothermal Thixoextrusionj437