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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)

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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

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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