Thixoforming : Semi-solid Metal Processing

426j 11 Thixoextrusion
Temperature (°C)
During extrusion, a load curve similar to those in laboratory-scale tests was
observed (Figure 11.14). The required extrusion forces were very low; peak forces
corresponded to an extrusion pressure of 9 N mm 2 .
The extruded bars showed that the complex shape of the die cross-section was
reproduced (Figure 11.15). However, along the bar length local distortions were
observed. Despite the cooling tube positioned beneath the die outlet, solidification of
the extruded bars was insufficient to prevent drip-like rupture of the thread.
Metallographic examination of as-extruded bars yielded no evidence of liquid-phase
separation but few pores.
Temperature (°C)
1600
1400
1200
1000
800
600
400
200
1400
1200
1000
800
600
400
200
0
0
T2
furnace control setpoint; Tc
container; T1
die inlet; T2
die land; T3
forging table surface; T4
heating rate
power
T1
0 1 2 3 4 5 6
TC 1
TC 2
Time (h)
Figure 11.12 Tool temperature evolution in industrial-scale
isothermal thixoextrusion experiments prior to forming.
0 50 100 150 200 250 300 350
Time (s)
heating rate
100
50
31
76
15
TC 1
TC 2
Figure 11.13 Heating strategy to realize a liquid fraction of approximately 40%.
Tc
T3
T4
70
60
50
40
30
20
10
0
8
7
6
5
4
3
2
1
0
Power (kW)
Heating rate (K min -1)