Thixoforming : Semi-solid Metal Processing

Table 3.1 Summary of relevant temperatures and characteristics
for aluminium alloys and steels [18]. The values for the
temperature sensitivity of the enthalpy L are averaged values for
the interval 0.4 < f s < 0.6 [17].
Alloy
Ts
( C)
TL
( C)
T50
( C) df L 50 /dT
40 60
DT
( C)
T30
( C)
dfL 30 /dT
( C)
20 40
DT
( C)
L
(J g 1 K 1 )
A356 557 614 574 0.0083 17 572 0.092 3 11.5
AA6082 557 647 637 0.027 7 627 0.015 14 13.0
A319 500 603 562 0.039 10 554 0.015 14 10.4
100Cr6 1348 1461 1427 0.011 19 1405 0.007 27 3.2
HS6-5-2 1175 1432 1360 0.006 35 1308 0.002 59 2.0
X210CrW12 1221 1366 1291 0.004 50 1254 0.028 13 1.6
A356 with a 40% liquid phase and 4.6 for a 60% liquid phase. Special attention has to
be paid to the particular observed interval.
Especially steels with a complex casting behaviour and a resulting distinctive solidification
interval are suitable for thixoforming, because of their multiphase microstructure
and their advantageous liquid-phase interval size. The curve progression of
the solid-phase fraction fs as a function of the temperature [fs ¼ f(T )] is of technical
relevance for thixoforming processes, because the temperature sensitivity of the phase
fractions increases strongly with an increasingly steep curve progression and accurate
adjustments become more difficult [17]. Figure 3.4 shows the development of the
liquid-phase concentrations of different steels [19]. It is advantageous for the intervalsize
if the liquid-phase development overlaps with the disaggregation of carbides.
Figure 3.4 Particular liquid phase developments of different
steels at a heating rate of 10 K min 1 determined using DTA [19].
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