the 10th international conference on semi-solid … · · 2009-12-04abstract: semi-solid metal...
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CHINA FOUNDRY Vol.6 No.4
19. Microstructural Evolution of AZ91 Alloy Containing 3%Ca Prepared by Cooling Slope
A. ravani, H. Aashuri, P. Davami, A. Narimannezhad, A. Foroughi and M. Kiani
Abstract: Globulization of the grain refined AZ91 magnesium alloy with Ca
on a cooling slope was investigated. Dendritic morphology of the grains was
transferred into round and well distributed small particles as a result of grain-
refinement effect of Ca in the alloy. Semi-solid holding of the alloy was carried
out at different temperatures to improve the spherecity of the globules. Results
show that, remelting at 540 ℃ for 30 min provides the best shape factor for
the alloy. The study of coarsening kinetic in this alloy showed lower growth rate
alternative other research which used same condition for produce semi-solid
billet just in using Ca.
20. Comparison of Microstructural Changes in a SIMA Processed A356 Aluminum Alloy after Unidirectional Compression and Rolling: Effect of Pressure Depth
M. Hajian Heidary, M. Bigdeli, A. Mahdavi and F. Khomamizadeh
Abstract: In this study, in order to compare effect of unidirectional
compression and rolling on final microstructure of strain induced melt
activated (SIMA) A356 aluminum alloy, rectangular samples with dimensions
of 3 cm × 5 cm in area and l cm in thickness and cylindrical specimens
with 2.5 cm in diameter and 1cm in length, have been prepared for rolling
and compressing processes, respectively. Then, these samples were
plastically deformed at a same strain in ambient temperature. Afterward,
the strained samples were cut into equal quarters. In the next stage, to
produce globular microstructure, these specimens were partially remelted in
580 ℃ for different times. Results obtained from light microscopy showed
that specimen's thickness and so, its strain affected zones influence on
the globulization of dendrites. In addition, it was seen that at a given strain
and constant diameter, increase of H/D ratio led to increase of needed time
for reaching a certain sphericity in cylindrical samples. Also, it was showed
that microstructural evolutions during SIMA processing of both rolled and
unidirectional compressed samples were relatively identical. However, at a
same condition, ultimate size of globulized dendrites in the rolled samples
was smaller than those of compressed ones.
21. Processing of Al-45Sn-10Cu Based Immiscible Alloy by a Rheomixing Process
H. R. Kotadia, J. B. Patel, Z. Fan, E. Doernberg and R. Schmid-Fetzer
Abstract: The growing importance of Al-Sn based alloys for producing
self lubricating bearing materials in automotive industries necessitates
the development of new alloys for improved performance. The recent
thermodynamic work by Schmid-Fetzer at Clausthal University of Technology
predicted that the addition of Cu to the binary Al-Sn system makes the
miscibility gap stable. With the guidance of the calculated phase diagram,
experimental investigations were conducted on the ternary Al-Sn-Cu system
to understand the solidification behavior of this immiscible system under
intensive forced convection. The experimental focus was to investigate the
effects of shear rate, shearing temperature and cooling rate on the solidified
microstructure.
22. Analysis of Rheological Properties of Steel near Solidus Point using Gleeble (R) Simulator
Krzysztof P. Solek, Zbigniew Mitura,Miroslaw Karbowniczek, Plato Kapranos,
Roman Kuziak and Jan Dutkiewicz
Abstract: The main goal of this work is the analysis of rheological properties
of steel alloy at high temperatures, just below the solidus point, and in
the semi-solid state with low liquid phase content. Data obtained from
the analysis can form the basis of numerical simulation for designing and
optimizing the thixoforming processes. The rheological properties should
be known over a wide temperature range so that the simulations could also
predict defects such as incomplete die filling. The analysis concerned M2 tool
steel alloy. The paper also discusses development of globular microstructure
in partially melted steel.
23. Alloy Characterization to Adapt Steels to Thixoforming: Study of a High Chromium High Carbon Steel
B. Fraipont and J. Lecomte-Beckers
Abstract: This paper deals with the examination of the influence of alloying
elements on the thixoformability of a Cr steel. It focuses on the liquid
fraction curves of different Cr steels with modifications of composition. The
effect of composition modifications was observed. The solid fraction versus
temperature has been obtained by a thermodynamics software (MTData)
and by Differential Scanning Calorimetry (DSC), limited to low heating rates.
MTData permits to obtain information on the influence of alloying elements,
with the advantage of the possibility to change the chemical composition very
easily. The DSC tests determine the influence of the heating rate on these
curves.
24. The Semi-Solid Forming of an Improved AA6061 Wrought Aluminum Alloy Composition
Joseph Langlais, Neivi Andrade, Alain Lemieux,X. G .Chen and Laurent Bucher
Abstract: The semi-solid forming (SSF) of aluminum alloys offers many
advantages over conventional casting processes. Nevertheless, the semi-
solid forming is still far from its full commercial potential and mainly used in
specific niche markets. The market positioning requires simple, low cost, and
versatile SSF processes that are capable of processing a wide range of alloy
composition including wrought alloy compositions. However, wrought alloys
must be adapted to obtain the desired semi-solid processing ability and
proper mechanical properties. The processing of these attractive alloys with
the SEED process offers the possibility to better target specific applications
and customers' needs. In the present paper, the alloy development of
AA-6061 aiming to minimize the hot tearing propensity during forming
process is reported. An overview of the industrial SEED process used to
produce the semi-solid AA-6061 feedstock is presented. The mechanical
properties of the cast parts subjected to a specific heat treatment were
evaluated. As part of the joint effort between Alcan International Limited and
the National Research Council of Canada (NRC), the fatigue results obtained
from the semi-solid AA-6061 die cast parts will be also reported.
25. A Novel Process for Fabrication of Globular Structure by Equal Channel Angular Pressing and Isothermal Treatment of Semisolid Metal
H. Meidani, S. Hossein Nedjad and M. Nili Ahmadabadi
Abstract: A new process for fabrication of semisolid billets is introduced,
which involves equal channel angular pressing and isothermal heating in the
semisolid state. The process leads to a relatively fine globular microstructure.
The microstructure evolution during isothermal treatment is studied and it is
shown that dendrites breaking up has happened during equal channel angular
pressing in semisolid state. The microstructural evolution during isothermal
heating and the mechanism for the formation of the globular structure is tried
to be understood and also modeled.
26. Fabrication of Semi-solid Slurry for Steels and Their Rheo-rolling Process
Renbo Song, Yonglin Kang and Aimin Zhao
Abstract: Semi-solid metal forming (SSM) has been recognized as a new
forming technology, which is different from the present metal forming
methods. Basic research on SSM has been put into operation and a number
of SSM techniques have been widely applied in industry. In the application
of SSM technique, at present, it is mainly used to produce the low melting
point alloys such as AI-base. Zn-base and Mg-base alloys, but the high
melting point alloys, for example steels as the most widely useful metal are
not extensively studied and applied. In the present work, the electromagnetic
stirring method was used to prepare semi-solid slurry of spring steel
60Si2Mn and stainless steel 1Cr18Ni9Ti. At the same time, spring steel
60Si2Mn and stainless steel 1Cr18Ni9Ti were directly rolled into thick strips in
the semi-solid state (Rheo-rolling). It is aimed at studying the microstructure
and properties of the strips to establish the feasibility of rheo-rolling for
the production of the steel strips. According to the present research work,
it has been shown that rheo-rolling process combines the casting and hot
Paper Abstracts Contained in the Proceedings of the 10th International Conference on Semi-Solid Processing of Alloys and Composites, S2P2008 (Part III)
379
InformationNovember 2009
rolling into a single step for near net-shape production, compared with the
conventional hot-rolled metallurgical process. Besides being such a cost-
effective process, rheo-rolling process possesses irregular crystal grains
such as rosette-type primary crystals in the microstructures because of
sufficient agitation during solidification. The overall homogenization of the
macrostructures in the whole part of steel ingot can be achieved.
27. Development of Non-dendritic Microstructure of Aluminum Alloy in Semi-solid State under Ultrasonic Vibration
Wu Shusen, Zhao Junwen, Zhang Liping, An Ping and Mao Youwu
Abstract: The effect of processing parameters on the semi-sol id
microstructure has been investigated in the course of semi-solid slurry,
preparation of A356 Al alloy by ultrasonic vibration method. The A356 melt in
temperature of 630-660℃ was poured into a special metal cup, and exposed
to ultrasonic vibration at 20 kHz or isothermal holding for a certain time after
vibration. The results show that the semi-solid slurry with primary alpha-Al
crystals smaller than 90 μm and an average shape coefficient (S) over bar
(F) (S-F was defined as S-F = 4 pi A/L-P(2)) above 0.5 could be prepared
by ultrasonic vibration for a time less than 144 s. In the isothermal holding
period after a short time of ultrasonic vibration, the average particle diameter
increased with the increase of holding time, but (S) over bar (F) decreased
at first, and then increased a little. It was discovered that ultrasonic vibration
is a good method to prepare semi-solid slurry with fine and relatively round
primary crystals due to cavitation and acoustic streaming effects.
28. Quick Semi-Solid Slurry Making Method Using Metallic Cup
F. Pahlevani,K. Anzai and E. Niyama
Abstract: The needs for high-strength and light weight structural materials
have increased in automotive and aerospace structure applications. The
semi-solid processed light alloys inherently offer the opportunity to produce
high integrity components for these requirements. Various processing
methods exist for applying agitation to a molten metal during solidification to
obtain metal slurries suitable for semi-solid metal processing. In this paper,
a new technique (Cup-Cast method) to achieve semi-solid metal structure
using agitation and direct spherical growth during solidification is reported.
Cup-Cast method is the most quick and simple semi-solid processing route
which semi-solid slurry would be prepared just by pouring molten metal into
a metallic cup. In this study Cup-Cast method was introduced and effect of
process parameters on micro-structural characterization of slurry prepared by
this method was investigated.
29. Study on Semi-solid Continuous Roll-casting Strips of AZ91D Magnesium Alloy
Xie Shuisheng, He Youfeng,Huang Guojie, Geng Maopeng and Zhang Ying
Abstract: Semi-solid continuous roll-casting process applied to produce
the AZ91D magnesium strips and its microstructure was studied in this
paper. In order to examine further process ability and forming property of
the roll-casting strips, hot and cold rolling and punching experiments were
investigated. It was clarified that it is significant to combine the semi-solid
process techniques with roll-casting techniques, through which we can get
high quality magnesium alloy strips with non-dendritic structure and improve
the overall properties of the products. The largest deformation by cold rolling
and hot rolling can reach 18% and 21% respectively with one-pass roller.
30. X-Ray Microtomography Investigation of the Effect of Ba Additions on the Microstructure of Partially Remelted Al-4%Cu Alloys
Sofi ane Terzi, Nathalie Limodin, Elodie Boller, Luc Salvo and Michel Suery
Abstract: The aim of this work is to study by X-Ray microtomography carried
out at ESRF Grenoble the microstructure of an Al-4wt%Cu alloy which was
previously cold rolled to obtain globules of the solid phase upon heating in the
semi-solid range. Since this process produced entrapped liquid in the globules,
3D quantification of this liquid was performed. Moreover, the influence of
the addition to the alloy of a small amount of Ba, which has been shown to
decrease the contiguity between the solid globules as a consequence of the
decrease of the solid-liquid interfacial energy sigma(sl), was investigated.
It is in particular shown that the amount of entrapped liquid is much larger
in the Ba-containing alloy in agreement with the reduction of sigma(sl),
whereas the size of the liquid pockets is similar. In addition characterization of
the interglobular liquid shows that the interface area between this liquid and
the solid per unit volume is larger for the alloys containing Ba in agreement
with previous observations carried out on 2D sections. The influence of strain
during cold rolling is also reported but it is shown to have a quite limited
influence on the previous parameters.
31. Effect of Ultrasounds Treatment on Alloys for Semisolid Application
Annalisa Pola, Alberto Arrighini and Roberto Roberti
Abstract: Semisolid metallic alloys are commercially produced by means of
mechanical or electromagnetic stirring. Among the mechanical devices, the
rotating pin immersed in a solidifying alloy seems to be easier to manage in
industrial practice although it can induce some porosity, depending on the
shape of the pin.
As known; ultrasounds are mechanical waves which, when applied to liquid
metals, increase the number of solidification nuclei, so that the cast products
show superior mechanical performances, as a consequence of the finer grain
structure.
In this paper the use of ultrasound waves applied to different alloys during
solidification was studied in order to obtain feedstock for semisolid die-
casting application.
A dedicated ultrasound power unit, together with a proper sonicator pin,
was designed and manufactured by the authors and, subsequently, the effect
of the ultrasonic treatment on the microstructure of A356 aluminum alloy and
ZA27 zinc alloy was investigated.
All the produced samples were characterized by metallographic analyses to
measure the globule size and shape factor, which are main criteria for thixo-
microstructure assessment.
The results were compared to those obtained with traditional mechanical
stirring, showing the higher capability of ultrasound treatment in producing
better semisolid microstructure.
An optimized combination of process parameters seems to be necessary
to get a reasonable thixotropic structure in treating ZA27 alloy.
Less severe production conditions are needed in the case of aluminum
alloy, revealing the potentiality of ultrasounds as an alternative treatment to
traditional mechanical stirring, with the further advantage of alloy degassing
and grain refinement, without the use of expensive additions (TiB2). Trials
were finally performed on a continuous casting pilot plant in combination with
electromagnetic stirring to produce semisolid billets.
32. Effect of Reheating to the Semisolid State on the Microstructure of the A356 Aluminum Alloy Produced by Ultrasonic Melt-Treatment
W. Khalifa, Y. Tsunekawa and M. Okumiya
Abstract: The effect of reheating to the semisolid state (soaking treatment)
on the microstructure evolution of the A356 aluminum alloy prepared by
ultrasonic melt treatment was studied in this paper. The results showed that
in general the longer the soaking process the larger and the more round the
grains obtained. Higher roundness occurs at shorter soaking times in the
fine-grained as-cast samples, and at longer times in the inhomogeneous or
the coarser-grained as-cast structures. The optimum thixotropic condition
(high roundness 0.72, and small globule sizes < 90 μm) are achieved after 5
min,soaking in the samples treated by UST at 623 and 620℃, which is the
typical soaking time dictated by the industrial practice in SSM. The amount
of entrapped eutectic as observed after soaking treatments is uniquely very
small, suggesting that the UST-treated ingots will have better formability in
the semisolid state. The growth rate constants are substantially low: in the
order of 479-748 μm3/s. These growth rate constants are much lower than
those reported for MHD-cast A356 ingots. The growth rates of the samples
produced by UST in the liquid state (i.e., 626, 623 and 620℃. Note that
liquidus temperature is 619℃) are lower than those of the samples treated
in the semi-solid temperatures, i.e. 617 and 614℃. The Ostwald ripening
is most likely the dominant growth mechanism in the UST-treated samples
during the soaking treatments. These results reveal the feasibility and
competence of UST as a potential route for thixotropic feedstock production.
33. Production of Semi-Solid Slurry through Heterogeneous Nucleation in Metal Matrix Nanocomposites (MMNC) Using Nano-scale Ultrasonically Dispersed Inoculants
Michael De Cicco, Lih-Sheng Turng, Xiaochun Li and John H. Perepezko
Abstract: Ever since copious nucleation was shown to be an efficient, cost
effective method for producing semi-solid slurry, many processes have been
developed to take advantage of the cost savings inherent in this method of
slurry production. Despite great advances in various aspects of semi-solid
processing, the cost competitive nature of the industry, most noticeably
the auto industry, has prevented a wider adoption of semi-solid casting
technology. This research aims to realize a more industrial appealing process
by combining the synergistic benefits of semi-solid casting technology with
metal matrix nanocomposite (MMNC) technology, thus creating higher value
products with superior properties cost-effectively. To do this, a process
that produces a semi-solid slurry though the nucleation catalysis induced
by nanoparticle additions as small as 1 wt. % to alloys is proposed and the
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CHINA FOUNDRY Vol.6 No.4
results are presented in this paper. Examination of the potential for nano-
scale inoculants to catalyze nucleation of solidification showed that despite
their small sizes, inoculants on the scale of tens of nanometers are capable
of catalyzing nucleation in the zinc and aluminum alloys studied. Employing
the differential scanning calorimetry (DSC), differential thermal analysis (DTA),
and droplet emulsion techniques with nanocomposite samples showed a
significant reduction in undercooling owing to the homogeneous distribution
of nanoparticles by ultrasonic mixing and the potency of those nanoparticles
to catalyze nucleation. Comparison of undercoolings between different
types of nanoparticles, such as silicon carbide (SiC), gamma and alpha
alumina (Al2O3), and titanium carbide (TiC), to relative potencies predicted by
minimum lattice disregistry showed a strong correlation. Results were also
examined in light of free growth and nucleation controlled grain initiation. For
nanoparticles predicted to be potent nucleation catalysts by lattice disregistry,
the undercoolings observed fell into the free growth controlled grain initiation
regime.
1. Numerical Simulation of Mould Filling in Rheocasting Process of Semisolid A356 Aluminum Alloy
Yuelong Bai, Jun Xu, Weimin Mao, Zhifeng Zhang and Hong Xu
Abstract: The apparent viscosity model of the semi-solid A356 aluminum
alloy, based on fitting of experimental data obtained by the Couette
type viscometer, was developed in the paper. The commercial package
CastSoft6.0 coupled with the model was used to simulate the mould filling
of the semi-solid A356 aluminum alloy in the key-shaped component with
iron cores. The simulation results showed that the position of the iron cores
has an important effect on the filling of the semisolid slurry, and it is easy
to obtain the completely filled key-shaped component when the iron cores
were near to the inlet. The filling tests verified that the simulation results
have good agreement with the experimental results. The fitting results
indicated that the developed apparent viscosity model is practical and feasible
and it can be used to simulate the mould filling process of the semisolid A356
aluminum alloy slurry. Also the parameters were optimized and the optimum
parameters are as follows: the inject pressure is more than 15 MPa, the inlet
velocity is more than 1.73 m/s and the forming temperature is over 585 ℃.
2. Study of the Precision Forging of an Impeller by Numerical Simulation and Test Forming
Weiwei Wang, Fei Han and Shoujing Luo
Abstract: In the present paper, the precision forging of an impeller was
studied by means of numerical simulation and test forming. Based on the
structure and dimension of the impeller, the combination structure was
used in the forging die to obtain the extrusion deformation. The forming
processes were simulated with DEFORM-3D for different billet dimensions
and processing parameters. The parameters, which could ensure the forming
quality of the impeller, were determined by the calculations and analysis.
The die structure and the billet dimensions were determined according to
the simulation results, and the forging die was designed and manufactured.
The billet with semi-solid microstructure was produced by means of the
direct heating-isothermal treatment. The forming was conduced in an
YX-315F hydraulic press, and the precision forgings of the impeller were
produced successfully. Both of the simulation and the forming test show that
the impeller forging can be formed with the combination structure die and
the extruding forming stale satisfactorily. The ideal parameters to produce
the precision forgings of the impeller are: billet temperature at 625℃, die
temperature at 450 ℃ and punch speed at 20 mm/s. Under these conditions,
forgings of the impeller can be produced with plump blades, smooth outer
surface, and good flow line. This can match the requirements of the precision
forging of impellers.
3. Numerical Modeling of Die Filling of Semi-Solid A356 Aluminum Alloy
A, Foroughi, H. Aashuri, A. Narimannezhad, A. Khosravani and M. Kiani
Abstract: Computer base simulation technique have been applied for
modeling the semi-solid die filling and part of the solidification process
of aluminum A356 alloy. A fairly simple one-phase theological model has
been implemented into a fluid flow finite element software Procast, to solve
the partial differential equations. This model is purely viscous nature and is
implemented in the power law cut-off model of Procast. The constitutive
parameters of this model were determined for a rheocast A356 alloy.
Comparing with experimental data the simulation results showed good
correlation with the model prediction. The designed die for rheocasting was
applied for the production of a small propeller with thin section.
4. FSI-Analysis of the MMC-Thixoforging Process Regarding the Rheology of the Aluminium Cast-alloy AlSi7Mg0,3
Peter Unseld and Mathias Liewald
Abstract: This paper illustrates investigations regarding the infiltration process
of the thixotropic cast-alloy AlSi7Mg0.3 into laminated fibre woven fabrics
by Fluid-Structure Interaction Analysis (FSI). As results of such FSI-Analysis,
on the one hand the kinematical behaviour of the reinforcement due to the
infiltration process on the macroscopic and microscopic level is obtained, and
on the other hand fluid dynamical effects of the regarded alloy is achieved.
Thus in the run-up to time-consuming and cost-intensive experiments,
informative bases like fluidic optimizing of the cavity or the configuration and
insertion of the reinforcement component can be numerically developed.
Furthermore a reliable prediction of transient permeability of the fibre fabric is
possible, which affects the infiltration process significantly.
Numerical input data such as rheological parameters characterizing the
behavior of partial solidified alloys have been conducted. Therefore basic
rheological tests of the aluminum cast-alloy AlSi7Mg0,3, like 'hysteresis
tests, 'shear rate jump tests' and detection of 'static' and dynamic yield
points and the differential structural parameter' have been conducted.
furthermore evolution of viscosity' has been correlated with thermodynamical
calculations using ThermoCalc (R). Finally the infiltration of a textile semi-
finished part (carbon fibre fabric / canvas bonding) by A356 is discussed as an
example to demonstrate the feasibility of FSI-Analysis, taking into account a
two-way coupling between the interacting CSM- and CFD-Codes.
5. A One Phase Thermomechanical Model For Semi-Solid Thixoforming
R. Koeune and J. P. Ponthot
Abstract: In order to model thixoforming processes, previous papers
presented a thermomechanical one-phase modeling. This first version
of constitutive model revealed several limitations: the model could not
degenerate properly to pure solid or liquid behavior neither to free solid
suspensions. The aim of this paper was to propose solutions to overcome
these limitations.
6. Use of Calphad Thermodynamics to Simulate Phase Formation during Semi-solid Processing
Bengt Hallstedt
Abstract: In this work we will explore the use of thermochemical simulation
methods (Calphad) to support alloy selection and processing in the semi-
solid state. Semi-solid processing has been investigated extensively for
aluminum alloys, in particular A356, but there is also an increasing interest
in using semi-solid processing for steels, in particular high carbon steels.
A key property for the semi-solid processing is the fraction of liquid phase
as function of temperature. It is necessary to know the fraction of liquid
phase in order to be able to control the process and in order to simulate the
viscous flow during various forming operations. The approach used here is
to calculate the fraction of liquid phase from thermodynamic (and diffusion)
data, using equilibrium calculations, Scheil-Gulliver calculations and diffusion
simulation. Normally only the solidification behavior is considered, but during
thixoforming also the melting behavior is of importance. However, there is
very little information on melting of alloys to be found in the literature. Here
an attempt will be made to discuss also melting as it cannot in all cases be
regarded as the reverse of solidification. In addition some further properties,
such as enthalpy, heat capacity and density as function of temperature will
be discussed. The materials treated are the aluminum alloy A356 and the tool
steel X210CrW12. Interestingly they show fairly similar solidification behavior.
7. Modeling of Inclined Cooling Plate Semisolid Processing by Model Alloy
H. Mehrara, M. Nili-Ahmadabadi, B. Heidarian, S. Ashouri and J. Ghiasinejad
Abstract: Continual improvement of product quality has been a long challenge
to Semi-Solid Metal (SSM) technology. By conventional semi-solid
processes, this might be attained at the expense of economical production.
The advent of Inclined Cooling Plate (ICP) process has already realized the
development of non-dendritic SSM while satisfying qualitative, quantitative
and economical requirements collectively. In spite of its potential advantages,
functional mechanisms of this process are not yet clearly understood that
makes its optimal utilization obscured. Basically, such understanding needs
Numerical Modeling and Simulation
381
InformationNovember 2009
a picture of the process. As the first step, this picture is pursued through
physical modeling of the ICP process i.e. direct observation of an analog
system by virtue of transparent character of a model alloy (succinonitrile-
acetone). Based on this phenomenological model, a picture of the process is
presented as follows: flowing molten alloy down ICP, multiple regions form
typically on the plate i.e. a chilled layer at the vicinity of the plate surface,
a two-phase mushy zone on the chilled layer and ambient liquid far from
the plate surface. In this process, interaction of the liquid forced-flow with
mushy zone separates solid particles from the stationary mush on the plate
resulting in a two-phase mixture which is responsible for the formation of
slurry i.e. SSM.
8. Investigation of the Primary Phase Segregation during the Filling of an Industrial Mold with Semi-solid A357 Aluminum
Frederic Pineau and Genevieve Simard
Abstract: Casting metal alloys in the semi-solid state is now becoming a well
established manufacturing technique. But, the success of this technology
necessitates a good understanding of the feedstock material behavior.
To obtain high quality components with semi-solid metal processing, a
homogeneous distribution of phases must be maintained in the material
during the die filling stage. Many parameters affect the process such as
temperature, time and stress history, which influence the shape, size and
connectivity of the particles that make up the slurry. The subsequent phase
interaction mechanisms are quite complex and have direct effects on the
flow and final micro-structure distribution of the cast part and thus, without
any doubt, on its mechanical properties. Two-phase numerical models have
been developed to account for the liquid-solid phase separation. Several
two-phase models have been elaborated on the basis of soil mechanics and
consider that the phase interaction term is mainly due to the flow through a
porous medium. Because of the difficulties of making direct measurements
in an extremely hostile environment, there has been very little work done
to validate these models. In order to fill this gap, a better understanding
of the phase distribution and phase segregation mechanisms during the
filling step is required. In this work, the post-solidification primary alpha-
phase distribution inside an industrial semi-solid cast part has thus been
investigated. A thorough metallographic analysis has been performed using
an upright microscope coupled to a Clemex image-analysis software. The
results were then processed to produce a map of the final alpha-phase
distribution. Many different grain scales have been observed in the solidified
part and their distributions seem to be closely associated to the velocity field.
Contacts between moving particles seem to play an important role in the
phase distribution and show many similarities to granular materials. This latter
aspect should be considered in the development of new constitutive models
for semi-solid slurries.
9. Numerical Simulation of Semi-solid AZ91D Magnesium Alloy in Thixoforming Process
Ji Zesheng,Yan Honghua, Hu Maoliang and Zheng Xiaoping
Abstract: In the process of metal plastic forming severe plastic deformations
occur to the workpiece. As a result the constitutive relations between
material and geometry are nonlinear. One of the most common tools to solve
such problems is the finite element method. In thixoforming processes of
semi-solid metal many factors affect thixoforming fluidity. Therefore it is
important to simplify the problem and predict the metal flow properties. For
that reason the thixoforming process of semi-solid AZ91D magnesium alloy
was modeled with the theory of rigid viscoplastic finite element method using
the commercial finite element software DEFORM-3D (TM). The fluid and
effective stress-strain fields in the thixoforming process were obtained and
the relationships among stress, strain rate and temperature were analyzed.
10. On a Class of Thermo-visco-plastic Constitutive Equations for Semi-solid Alloys
S. Benke and G. Laschet
Abstract: The behavior of semi-solid alloys is quite different in tension,
compression and shear and depends strongly on the morphology of the
micro-structure. This article outlines a generalized viscoplastic material
model for semi-solid alloys which reflects this complex viscoplastic behavior.
From the generalized model a number of well known yield functions and
viscoplastic material models for semi-solid and solid materials can be
reproduced. The general model is applied to describe the behavior of the
semi-solid A356 alloy below the coherency temperature during equiaxed
solidification.
11. Thixoforming of Aluminium-silicon Alloys in a Mechanical Eccentric Press
Eugenio J. Zoqui, Luciano A. Lourencato and Davi M. Benati
Abstract: The semisolid processing technology is not widely used due to
the high cost of raw material and the equipment it requires. New low-
cost raw materials and processes could be the key to expand the use of
this technology. This paper describes an initial effort to develop new Al-Si-
Mg in terms of raw material production and processing. The morphological
evolution of all the alloys produced was characterized during their reheating
to the semisolid state at 45% and 60% solid fraction, as well as the
semisolid behavior in terms of viscosity versus shear rate. The adaptation
of the semisolid technology to the thixoforming process via eccentric
press was tested using equipment up to 25 tons. This type of equipment
is not commonly employed in this kind of processing. Results indicate that
alloys with low silicon content, e.g., 2 or 4wt%Si, behave similarly to alloys
with 7wt%Si, which are normally used in the thixoforming process, with
a viscosity of about 2 × 105 Pa.s. The semisolid behavior of low silicon
alloys indicates the potential expansion of the range of raw materials for this
application. Thixoforming of semisolid materials in an eccentric press appears
to be a very promising technology, yielding parts that, despite their simplicity
and restricted shape, display a very good final mechanical behavior.
12. Study on Thixo-extrusion of Semi-solid Aluminum
Adriana Neag, Veronique Favier, Regis Bigot and Dan Frunza
Abstract: Thixo-extrusion processing could become an important technique
to extend the range and complexity of extruded profiles. This work presents
the results of thixo-extrusion process applied on aluminum alloy and they
were carried out with both computer numerical simulation and experimental
methods. The thixo-extrusion set-up was made. Backward extrusion tests
were particularly studied and simulated using Forge 2005 software. The
constitutive equation used for these simulations is based on a micro-macro
model for the semi-solid evolution. The constitutive equation parameters
were identified due to comparisons of the simulated load-displacement
responses with experimental ones for backward extrusion tests on 7075
semi-solid aluminum alloy at different temperatures.
Process and Parts Assessment1. Infl uence of the Pre and Post Treatment Operations on the Properties of the Thixoformed Steel Parts
A. Rassili, J.C. Pierret, G. Vaneetveld, P. Cezard, R. Bigot and M. Robelet
Abstract: The pre and post treatment of the thixoformed parts in terms of
heating conditions and controlled cooling has a great influence on the final
microstructure and the properties of the parts and their homogenization. The
paper presents recent investigations on metallographic analysis and hardness
measurements on as thixoformed parts and post treated ones. For these
tests, different steel grades are investigated and the liquid fraction of the slug
before deformation is evaluated to 30 %.
2. Development of Adapted Heat Treatments for Steels out of the Semi-solid State after Thixoforming
S. Dziallach, W. Puettgen and W. Bleck
Abstract: The process of thixoforming incorporates a series of forming
processes in the semi-solid state, which can be categorized between the
conventional processes of forging and casting and combines the advantages
of these processes. Thixoforming of steels in the semi-solid state, requires
round, solid particles (globulites) in a liquid matrix which is deformed with
low forming forces. In order to achieve laminar material flow and to produce
segregation-free components, the material must fulfill diverse criteria. First,
the melting interval should be as large as possible for an easy temperature
regulation. Next, low solidus and liquidus temperatures are advantageous
regarding tool loading. Additionally, thixoformable steels should show a
melting behavior that is fine-grained and globular. Furthermore, these steels
should possess low contents of intraglobular liquid phase fractions.
This paper gives a survey of the current state of steel thixoforming
and deals with the development of adaptive heat treatment strategies.
Regarding the structure formation and the development of suitable heat
treatment strategies, the once semi-solid state yields new structures that
can be applied in ways not previously possible with conventional hardening
processes. New microstructures and up to date unknown better mechanical
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properties can be adjusted with an optimised heat treatment strategy.
By this, new fields of application for thixo-materials can be entered and
also advanced procedures for special applications can be established. For
example the steel X210CrW12 leads to a very hard material with high wear-
resistance, which can be used at higher temperatures than the conventional
hardened material. In general, new generic microstructures after thixoforming
results in unexpected favorable mechanical properties. Problems arise with
respect to segregation and pores which resulting in inhomogeneous property
distributions.
3. Steel Thixoforging: Heat Exchange Impact on the Mechanical and Metallurgical Features of Thixoforged Samples
Eric Becker, Pierre Cezard, Regis Bigot, Laurent Langlois, Veronique Favier and
Jean Christophe Pierret
Abstract: Steel thixoforging process combines the advantages of performing
parts having highly complex shapes and good mechanical properties. These
advantages result from the shear thinning flow behavior of semi-solids due
to microstructure changes during the material deformation. Many parameters
such as steel grade, raw speed, slug temperature, tool temperature influence
the steel thixoforging process. In this work, we are interested in analyzing
the influence of thermal conditions as well as ram speed on the flow behavior
and the microstructure of the final parts. To do so, thixo-extrusion tests on
a high speed hydraulic press were performed on C38 steels using different
ram speeds and different temperatures for the tools. The temperature is
measured in the die close to the tool-material interface during the whole
process. Correlations between the temperature measurements, the flow
profile and the microstructure are discussed. Using the Finite Element code
Forge 2005, these thixo-extrusion tests are simulated. Using an inverse
method, some parameters used in the thermal exchange modeling are
identified by successive comparisons between calculated and measured
temperatures within the die.
4. Improvement in Thixoforging of 7075 Aluminum Alloys at High Solid Fraction
G. Vaneetveld, A. Rassili, J. -C. Pierret and J. Lecomte-Beckers
Abstract: Thixoforging is a type of semi-solid metal processing at high solid
fraction (0.5<f(s)<1). 7075 aluminum alloys have been used as a feedstock
for thixoforging in order to investigate thixoformability of a high performance
aluminum alloy at high solid fraction. Higher solid fraction of 7075 alloy is
less sensitive to temperature, avoids metal splash at high speed and allows
laminar flow at high speed. Hot tool combined with lubricant tool coating
are used to slow down the solidification rate of the high solid fraction metal
by decreasing thermal exchanges with the tool. Improved thermal and
forming parameters will be applied to produce an automotive component by
thixoforging and mechanical properties have been measured from tensile
samples. High mechanical properties are obtained after T6 thermal treatment.
5. Microstructure and Mechanical Properties of Rheo-Extruded AZ31 Mg-alloy
Jun Xu, Shaoming Zhang, Bicheng Yang, Likai Shi and Z. Fan
Abstract: A new rheo-extrusion technique has been developed to produce
extruded profiles. The AZ31 slurry is fabricated by a twin-screw mechanism,
and has spheroidal solid particles with a grain size of about 50 to 80 μm.
The slurry was introduced into an extrusion container with an inner diameter
of 95mm, and then squeezed to a billet before extruding into a round bar
with a diameter of 22 mm using a 500 kN extrusion machine. It is found
that the new technique has a lower deformation resistance than that of the
conventionally hot extrusion technique in the same extrusion velocity. The
microstructure and mechanical properties of the rheo-extruded bars were
examined in detail. The results illustrated that grains of the bar were very fine
with the average grain size about 2.3 μm, and the mechanical properties
were improved substantially compared with those of the same alloy produced
by the conventional hot extrusion.
6. Influence of Parameters during Induction Heating Cycle of 7075 Aluminum Alloys with RAP Process
G. Vaneetveld, A. Rassili and H.V. Atkinson
Abstract: Thixoforging involves shaping alloys with a globular microstructure in
the semi-solid state. To reach this kind of material, the Recrystallisation and
Partial Melting (RAP) process can be used to obtain a globular microstructure
from extruded material with liquid penetrating the recrystallised boundaries.
Induction heating is used to apply the RAP process to slugs. One of the
benefits of this method of heating is the fast heating rate (20 ℃/s). This
paper will help to improve heating parameters by showing their influence on
7075 aluminum alloy recrystallisation. These parameters are the heating rate;
heating frequencies-power; presence or not of protective gas: position of
the slug in the inductor; energy stored inside the slug; oxide layer on the slug
side: chamfer of the slug upper corner.
7. Fatigue Behavior of Semi-Solid Cast Aluminum: A Critical Review
Myriam Brochu, Yves Verreman, Frank Ajersch and Laurent Bucher
Abstract: Aluminum alloys are increasingly used in automotive and aeronautic
applications to produce high performance, lightweight parts. Among the
reasons for this, is the emergence of high integrity processes (HIP), which
widens the field of application for cast aluminum alloys. In fact, metallurgical
quality and consistency that characterize components produced by HIP are
necessary for critical safety components. In addition to attaining maximum
strength, critical safety components need to be ductile and resistant to cyclic
loading. According to the North American Die Casting Association, rheocasting
is a high integrity process capable of producing parts with fewer defects
than conventional casting process. Rheocast components are known to have
better mechanical properties than permanent mold castings. Moreover, they
can be heat-treated which is impractical in the case of classical die cast
components. However, the fatigue behavior of rheocast aluminum alloys has
been investigated since about 2000 and few results have been published on
this subject. This paper reviews the studies of fatigue behavior of aluminum
semi-solid cast components. Published experimental results on high cycle
fatigue resistance (S-N diagrams), long crack propagation, crack closure
effects and short crack particularities are presented.
8. The Natural and Artificial Aging Response of Semi-solid Metal Processed Alloy A356
H. Moeller, G. Govender and W. E. Stumpf
Abstract: The heat treatment cycles that are currently applied to semi-solid
processed components are mostly those that are in use for dendritic casting
alloys. These heat treatments are not necessarily the optimum treatments
for non-dendritic microstructures. For rheocast alloy A356, it is shown that
natural aging prior to artificial aging causes the time-to-peak-hardness to be
longer compared to the time when only artificial aging is used. Furthermore,
a hardness plateau is maintained during artificial aging at 180 ℃ between 1
and 5 hours without any prior natural aging. A natural aging period as short as
1 hour results in a hardness peak (rather than a plateau) to be reached during
artificial aging after 4 hours at 180 ℃.
9. Effects of Thixoforming Defects on the Stress-Strain Curves of Aluminum Structural Parts for Automobile
Sang Yong Lee and Byung Hyun Choi
Abstract: The effects of thixoforming defects on the stress-strain curves of
aluminum structural part were quantitatively investigated. The A357-MHD
billet was thixoformed to manufacture a shock tower part of a small electric
vehicle. All tensile specimens were machined from only a shock tower
product to minimize the effects of different processing conditions. Tensile
tests were performed under the almost same conditions. The fraction of solid
and liquid phase, the sizes and area fractions of defects in the specimens
were measured and analyzed by an image analyzing program using OM and
SEM micrograph. The fracture strain values of the stress-strain curves were
greatly affected by amount of defects. However, the analyses with defects
existed in the area of gauge length did not show a clear explanation about the
relation with the fracture strain values. The measurements of defects in the
fractured surface represented more plausible results about the correlation of
forming defects and fracture strains.
10. Fabrication of Rheological Material of A356 Aluminum Alloy by Electromagnetic Stirring through Vacuum Pump
H. H. Kim, S.M. Lee and C.G. Kang
Abstract: This study demonstrates fabricating rheological material by EMS
system attached vacuum pump, in order to improve mechanical properties of
rheoforged products by removing defects such as porosity and oxides arising
from rheological forging process. The billet fabricated by ELMS in vacuum
pressure reduced formation of oxides and porosities of the inner material.
The billet fabricated by EMS in vacuum pressure below 56 cm/Hg remarkably
reduced porosities, comparing to the EMS in atmospheric pressure.
Note: 25 Poster are not contained