Thixoforming : Semi-solid Metal Processing

356j 9 Rheocasting of Aluminium Alloys and Thixocasting of Steels
Figure 9.41 The RCP (schematic).
aluminium can (container), ensuring wall contact during melt inflow. At first contact
with the room-temperature container wall, seed crystals are formed and subsequently,
because of the flow, are finely dispersed in the container. The heat capacity of the
container suffices to cool the melt below the liquidus temperature. Because of this,
and as a result of a high grain density, a globular microstructure forms (cf. cooling
channel process). Therefore, the container is placed directly after pouring into a
cooling device and covered immediately afterwards and filled with an argon atmosphere
to prevent combustion. To minimize the process time, the container is cooled
with pressurized air. At the aimed for process temperature, and at the aimed for solid
fraction, the container is transferred, together with the semi-solid billet, to the shot
chamber of the die-casting machine (Figure 9.42) and pressed into the die. The folded
container remains completely in the biscuit [48] (Figure 9.42).
The use of a non-returnable container, consisting of 99.5-aluminium, avoids
recycling [49]. Apart from this, the use of steel cans and so on is also possible and
Figure 9.42 RCP: (a) container with semi-solid slurry placed in the
shot sleeve; (b) folded container in the press biscuit.