Abstract: Oscillation experiments, creep tests and shear stress ramps have been performed to analyze
the yield stress and its time dependency. It has to be distinguished between iso-structural, dynamic
and static yield stress. The iso-structural yield stress occurs immediately after shearing. Since the
slurry structure remains unchanged, it is equivalent to the structure during shearing. At rest an internal
structure builds up, this leads to an increase of the yield stress, which is referred to as the dynamic
yield stress. It increases until its maximum value, the static yield stress, is reached.
Abstract: High mechanical properties in combination with low density are key features for
lightweight constructions in automotive and aerospace applications. The combination between the
innovative thixoforging process and the potential of fibre or particle strengthened composites with
metallic matrices (MMCs) provides an efficient manufacturing process of structural components with
continuous or gradient reinforcements.
The scope of the Center of Competence for Casting and Thixoforging Stuttgart (CCT) contains new
semi-solid manufacturing methods for metal matrix composites which have been developed and
applied for patent pending. While previous research projects were focussed on fabrication of
continuous fibre reinforced metal matrix composites, the local reinforcement insertion, located in the
center of high force and torsion load zones, is going to be the next evolution step of the CCT research
team. Therefore it is essential to verify, to simulate and to reproduce the process during infiltration of
the semi-sold matrix metal into the textile layer experimentally.
This paper illustrates investigations regarding the infiltration process of the thixotropic cast-alloys
AlSi7Mg0.3 (A365) into laminated fibre woven fabrics by computational fluid dynamics and
fluid-structure interaction analysis, taking account into specific manufacturing technology, the
rheological behaviour of the alloy with special focus on infiltration behavior.
Abstract: Light-metal matrix composites with tailor-made fiber reinforcements offer a good balance between
weight saving and high strength, a key feature for lightweight design in structural applications for
the automotive and aerospace industry. Light-metal MMCs manufactured by thixoforging of
thermally sprayed prepregs additionally exhibit superior mechanical properties of the matrix
material as well as low fiber damage during infiltration of the reinforcement fabric. However, one
of the difficulties during manufacturing of these materials is the difference in the thermal expansion
coefficients (CTE) of matrix and fiber material. Different thermal expansions lead to the
development of residual stresses during the cooling process that can deform the reinforcement
fibers and hence, lead to a decrease of the mechanical properties of the reinforced component.
Modeling by means of finite elements and numerical simulation is used in order to study parameter
variations during the cooling procedure and to select an optimized process route. The modeling and
simulation was performed in a collaborative work between the Institute for Manufacturing
Technologies of Ceramic Components and Composites, University of Stuttgart, and the Polytechnic
University of Cartagena.
Abstract: The morphology of semi-solid alloy is one of the key influence factors on the rheological
behavior of slurry during die filling and the mechanical properties of formed parts. However, it is
difficult to study such effect due to hard controlling of morphology in semi-solid state. In this paper,
a self-developed Searle-type viscometer was used to determine the rheological behavior of A356
aluminum alloy in different morphology, which was refined with the salts mixture of K2TiF6 and
KBF4. The results indicated that the flow behavior of refined A356 alloy in the semi-solid state
possesses obviously thixotropic behavior under isothermal shearing condition with less time to
reach steady state and lower steady apparent viscosity as compared to that of the A356 alloy. During
continuous cooling at a constant shearing rate, the apparent viscosity of refined A356 slurry in the
same solid fraction decreased with the content of Ti. It is shown from quantitative image analysis
that the primary α-Al grain in the refined alloy evolves from dendrites to rosettes or sphericitys, and
then tends to be rounder and finer in higher Ti content. The mechanism of the influence of
morphology on rheological behavior was also discussed in this paper.
Abstract: The investigation of the flow behavior of semi-solid steel alloys poses a great challenge by
reason of high operation temperatures and the need of ceramic components for the measuring system.
A high-temperature Couette rheometer has been developed to analyze flow properties of semi-solid
alloys up to temperatures of 1500°C. In the present work the alloy under investigation is X210CrW12.
Differently performed experiments clearly show its shear-thinning and time-dependent flow
properties with a yield stress. This flow behavior is modeled using a Herschel-Bulkley approach
where the experimental results achieved serve to identify model parameters.
Abstract: Alloys of a specific microstructure exhibit a shear-rate history-dependent flow behaviour in the
semi-solid state. Rheological studies have been carried out using various experimental techniques
such as concentric cylinder rheometers of Couette or Searle type as well as capillary rheometers and
parallel plate compression tests. With the Searle type rheometer and the capillary rheometer two
different approaches of rheological measurement techniques are discussed and compared regarding
advantages, potentials and its distinct characteristics.
Experiments using the Searle type rheometer have been conducted under steady-state or oscillating
conditions and have been used to verify time-dependency of step responses due to discontinuous or
linear variances of the shear rate. These experiments provide all types of flow curve parameters as
implemented in the numerical simulation. However the variances of the commonly used Couette and
Searle type rheometers are limited to shear-rates which are significantly lower than that appearing in
the technical thixo- or rheocasting processes. For that reason an additional experimental set-up with a
horizontal slot capillary integrated in a shot-controlled high-pressure die-casting machine is used in
order to examine flow properties at shear rate conditions similar to those in real thixocasting
After an initial examination of low temperature model alloys, such as PbSn15, the experimental
set-up is then adjusted in order to obtain rheological data for light metal alloys such as Aluminium
AlSi7Mg0.3. The Aluminium alloy is processed within each rheometer either as partially solidified or
partially remelted in order to represent conditions of both, the conventional thixocasting and the lately
introduced rheocasting process. Finally the appearance of physical phenomena which affects the
accuracy of rheological experiments such as wall slip is considered for both types of rheometers.
Abstract: Computer simulation of semisolid structure formation is of significance in both
understanding the mechanisms of the formation of such structure and optimization the solidification
conditions for the required structure. A modified cellular automaton (mCA) model has been
developed, which is coupled with macroscopic models for heat transfer calculation and microscopic
models for nucleation and grain growth. The mCA model is applied to Al-Si alloys, one of the most
widely used semisolid alloys. It predicts microstructure morphology and grain size during semi-solid
solidification, and determines the effects of poring temperature and mould temperature on the final
microstructure. The simulated results are compared with those obtained experimentally. The resulting
simulations give some insight into the mechanisms about the semisolid structure formation in
Controlled Nucleation process.
Abstract: The behaviour of the semi-solid material is complex to simulate and many approaches
are proposed in the literature to represent it. In this work, different constitutive equations are
studied: the classical Northon-Hoff law, Joly and Merhabian’s one  and an innovative
micromechanical model using homogenisation technique . These constitutive equations have
been implemented in the FE code Forge2® to simulate simple forming tests, such as compression
and direct extrusion. The load-displacement curves using the three constitutive equations are
compared in order to estimate their capabilities.
Abstract: The flow behavior of a semi-solid A356 alloy at high solid fraction was studied. The
mushy zone was considered as an effective two-phase, so that the solid continuum can be
compressible porous media, and the liquid phase interaction with the solid skeleton was of Darcy
type. The semi-solid flow through the upsetting test was modeled in ABAQUS finite element
method software. The Gurson yield criterion has been developed for the modeling process of the
flow behavior of solid porous medium. Specimens were globulized by a thermomechanical process
and then were tested for various percentages of upsetting. The distribution of solid fraction along
the radius of the specimens at different height reduction showed a good correlation with model
Abstract: The main purpose of work was to develop a methodology of physical and numerical
simulation of the thixocasting processes. For the purpose of the studies an experiment was conducted
using a GLEEBLE 3800 simulator. In this work, the GLEEBLE 3800 system was adapted for physical
simulation of the processes of light metal alloy forming in the solid-liquid state. The physical
simulations of thixoforming processes and characterization of thixotropic materials were supported
by computer simulations using ADINA software. The numerical model of thixoforming processes
was developed in order to estimate values of the rheological model parameters.