Thixoforming : Semi-solid Metal Processing

318j 9 Rheocasting of Aluminium Alloys and Thixocasting of Steels
than light metal materials (aluminium/magnesium) or synthetic materials due to
their outstanding mechanical qualities despite the high specific gravity of between
7.6 and 8.2 g cm 3 . The exploitation of this potential by the continuing development
of innovative production technologies for the production of complex, highperformance
and weight-optimized steel components could lead to an expansion
of their competitiveness of the foundry industry.
The thixocasting process with steel materials offers unusual possibilities due to its
great design flexibility and the net-shaped qualities of the components in combination
with the productivity of a pressure die-casting method.
At the beginning of the 1980s, examinations of the pressure die casting of alloyed
steels were subject to different basis tests. In addition to the complex warming of
suitable pre-materials, the processing of the steel materials at modified presses or in
die-casting machines showed a variety of difficulties.
Major emphasis was put on austenitic and other high-alloyed steels (X5CrNi18-
10/X2CrNil9-11/HS6-5-2) because these showed a globulitic formation of the solid
phase due to the conventional production route [stress-induced and melt-activated
(SIMA) route, powder metallurgy] during reheating [32]. The extensive examinations
for the pre-material, its reheating and the subsequent design to model parts clarified
that the steel materials are in principle usable for thixocasting. The complex
remelting behaviour of carbon steels led to considerable problems with respect to
reproducible warming, although high-speed steels due to their content of eutectic
phase (HS 6-5-2-1, HS 12-1-4-5) were consequently often examined. In the course of
the examinations, it became clear that even commercially available semi-finished
material showed globulitic formation of solid particles during reheating [33].
The first components of more complex geometry showed satisfactory mechanical
qualities in addition to a good illustration precision and contour acuity (Figure 9.6). In
1999, a practically relevant project at the Studiengesellschaft f€ur Stahlanwendung
started with the aim of producing a motorcar connecting rod by thixo lateral extrusion
with the use of a modified multi-piston press. The mechanical quality demanded
could not, however, be achieved, which could be explained by the rapid failure of the
tool materials and also method-specific difficulties.
Figure 9.6 Components of projects P322 and P443.