Thixoforming : Semi-solid Metal Processing

1970s [7]. Also, the quality of the components and the reproducibility of the whole
process have to be investigated thoroughly due to the narrow temperature interval in
which the material should be worked up [8].
The goal of this chapter is to give an overview of the technology and specific topics
related to the family of thixo- and rheoforging processes.
10.2
Forging in the Semi-solid State
10.2 Forging in the Semi-solid Statej371
Figure 10.2 Required forming steps for forging a wheel trunk. Material: C70S6. [5].
Based on first investigations on the thixotropic behaviour of semi-solid metal alloys
that were carried out by Spencer s group in the mid-1970s [9], different approaches to
forming processes were developed and investigated to benefit from the advantages of
the specific material properties. Investigations in research centres all around the
world concentrated on the forming of both light metal and high-melting alloys in the
semi-solid state and investigated elementary fundamentals for the production of
complex parts such as the rheology and material characterization, tooling and
forming strategies [10–18]. Whereas thixocasting and thixomoulding of aluminium
and magnesium alloys are applied on an industrial scale by several producers [19] (see
Chapter 9), thixoforging of aluminium is applied only for the production of rims by
SSR-Wheels as an industrial producer. The development of semi-solid forging of
high-melting alloys such as steel is still under way.
In the case of high-melting steel alloys, technological problems slow the development
of the process for implementation as an industrial application. This is mainly
caused by higher processing temperatures, which increase the thermal loads of the
tools, and the requirements on process control. Therefore, one basic part of the
investigations has concentrated on the development of adapted tool concepts by
using coatings and ceramic tools (see Chapter 8) and the automation of the
process [20–25]. Nevertheless, different components have already been produced
by the thixoforging process and show the feasibility of thin-walled and complex parts
(Figure 10.3) using steel alloys.