Thixoforming : Semi-solid Metal Processing

Table 11.2 Comparison of required forces and pressures for semi-solid extrusion of steels.
Steel grade
Container
diameter (mm)
Load range
(kN)
The steel billets are completely extruded to bars. The die cross-section is reproduced
well except for one arm not being filled (Figure 11.7). This is ascribed to scale
residues partly blocking the die inlet and might be prevented by inductive preheating
under flushing argon, as carried out in upscaled forming tests. The contour of the die
geometry of extruded bars is well defined, indicating smooth material flow during
extrusion. Although the bars maintain their shape after cooling and quenching in
water, solidification is incomplete after leaving the die, with the result that extruded
bars drip down due to their own weight.
However, the excellent formability of steel X210CrW12 observed during isothermal
thixoextrusion experiments is confirmed by optical and chemical analysis of
extruded bars according to the sampling scheme given in Figure 11.8.
Optical micrographs of different cross-sections along the bar length reveal only
small amounts of residual porosity and excellent homogeneity (Figure 11.9).
Figure 11.7 Cross-section of X210CrW12 bar thixoextruded using
self-heating alumina dies under isothermal conditions.
Pressure
(N mm 2 ) Source
AISI 304 30 n. s. n. s. 29 49 [5]
AISI 1080 30 40 140 56 a
198 a
[6]
carbon steel 40 147 196 117 a
156 a
[7]
AISI 1020 22 196 589 516 a
1549 a
[8]
AISI D6 (X210CrW12) 34 1 20 1 a
22 a
Experiments
a Values derived from force values.
11.4 Isothermal Thixoextrusionj421