Thixoforming : Semi-solid Metal Processing

364j 9 Rheocasting of Aluminium Alloys and Thixocasting of Steels
properties could be significantly improved. Using HT A, yield strengths of 410 MPa
could be obtained but the measured elongation to fractures were insufficient.
Treatment HT B, in contrast, results in very good ductility (up to 15%) in combination
with excellent mechanical properties at the same level as with HT A. In comparison
with sand casting and permanent mould casting, an increase in the mechanical
properties is achievable due to the fine microstructure caused by high-pressure die
casting and the suitability for heat treating. This demonstrates the high potential of
the cooling channel process.
9.5
Assessment and Outlook
9.5.1
Rheo Processes
The developed cooling channel process and rheo container process provide an
opportunity of industrial implementation. In addition to simple use, the processing
of highly reactive alloys such as aluminium–lithium and magnesium is feasible, due
to an optional enclosure. Furthermore, with the determined detailed process window,
the reproducible mechanical properties demonstrate the high potential of the
processes for industrial applications.
9.5.2
Thixocasting of Steels
Despite existing challenges regarding the tool concept, thixocasting of steels provides
a promising outlook for industrial application in the intermediate and long term, due
to the significantly lower temperatures and the high solid fractions. For a reproducible
feedstock material quality, the foundations were laid with the cartridge concept
and the energy-controlled reheating concept. The challenges that remain will be
approached in the coming years.
List of Symbols and Abbreviations
A area (of a grain)
A356 AlSi7Mg0.3
A357 AlSi7Mg0.6
AA1420 AlLi2.1Mg5.5
AA1420 AlLi2.1Mg5.5ScZr
AA2024 AlCuMg2
AA5086 AlMg4.5Mn
AA6012 AlMgSiPb
AA6082 AlSi1MgMn
AA7075 AlZn5.5MgCu