Thixoforming : Semi-solid Metal Processing

Table 11.5 Tool characteristics of self-heating thixoextrusion tool.
Container
Material Al2O3, 99.7%
Inner diameter [mm] 85
Outer diameter [mm] 125
Cross-sectional area [mm 2 ] 5674.5
Wall thickness [mm] 20
Height [mm] 250
Die
Material Si 3N 4
Cross-sectional area [mm 2 ] 301.8
Extrusion channel length [mm] 300
Feeding angle [ ] 11.3
Extrusion ratio 18.8
required. With an inductive heating device, the billets were heated with time–power
strategies into the semi-solid state with maximum power first, followed by homogenization
phases to ensure a homogeneous temperature distribution in the billet
(Figure 11.13). During heating, the billet was prevented from oxidation by the inert
gas argon. Thermocouples measured the temperature development in the billet.
With the three-stage strategy, a final temperature of 1270 C was realized. This
corresponds to a liquid fraction of approximately 40%, according to differential
thermal analysis as described in Chapter 3. With this strategy, the billets were
homogeneously semi-solid but still dimensionally stable and subsequently extruded.
After the heating procedure, the billets were manipulated within 7 s to the
extrusion tool and subsequently extruded by the 6.3 MN SMS Meer open die forging
press.
Figure 11.11 Si3N4 thixoextrusion die for upscaled extrusion tests.
11.4 Isothermal Thixoextrusionj425