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Paper Abstracts Contained in the Proceedings of the 10th International Conference on Semi-Solid Processing of Alloys and Composites, S2P2008

1. Semi-Solid Metal Processing - A Process Looking for a Market

Plato Kapranos

Abstract: The birth of Semi-Solid Metal Forming (SSM) or as it has

now come to be widely known, Thixoforming, is a typical case of

development of a technological innovation. Serendipity, stroke of

luck, call it what you may, the beginning of SSM is based on an

almost accidental discovery by a student carrying out a series of

meticulous experiments. On the one hand, some technological failures

have contributed to the lack of success across the board for SSM

technologies. On the other hand, the 'long childhood' of the resulting

technology or the process of moving from 'Innovative Idea to Market'

has been largely the result of difficult and in hindsight sometimes wrong

managerial decisions, occasional personality clashes, patent rights and

at times unavoidable all out business 'warfare'. Of course, hindsight is

beautiful but unfortunately it always comes after the event. However, if

one looks carefully at some of the notable successes of SSM forming

one can discern that the problems were more on the human scale;

people failures rather than technology failures.

This paper aims to bring out some of these points by outlining the

historical development of Thixoforming.

2. Theory and Technology of Semisolid Metal Molding

Frank Czerwinski

Abstract: Fundamentals of semisolid metal molding, including the

particulate feedstock, methods of its generation and features that

make it useful for processing, are outlined. Melting characteristics of

the feedstock under sole influence of heat are considered, covering a

wide range of microstructural and microchemical factors, believed to be

of importance at high temperatures. The generation of the thixotropic

slurry within the injection molding system and its solidification behaviour

are accompanied by detailed features of the molded structures and their

correlation with properties of net-shape components. In addition to

conventional techniques the novel processing concepts including near-

The S2P International Conferences are dedicated to science

and technology of semi-solid processing of metals. Since the

discovery of the specific flow behaviour of metals in semi-

slid state during the seventies of last century, this fascinating

technology has experienced a dynamic development history

which has led to a whole family of new production processes,

new equipment and industrial applications.

In order to fully exploit the technical and economical

potential of these new ideas, it is important to achieve a

better understanding of the microsturcture development,

flow behaviour, improved material and process modelling as

well as process control. The S2P International Conferences

have contributed to achieve this goal by providing a

forum for scientists from various disciplines as well as for

engineers and production specialists to learn from each

other, to share the common knowledge and to develop

a common sense on fundamental topics and industrial

requirements.

The 10th International Conference on Semi-Solid

Processing of Alloys and Composites, S2P2008, organized

by the RWTH Aachen University, Germany and the

University of Liège (Belgium) took place from September

16 to 18, 2008. The conference concentrates on the

advancement of fundamental knowledge and development

of materials and industrial processes for semi-solid

manufacturing of high performance metal components.

145 scholars from 33 countries attended the event, of

which 14 are Chinese continent's delegates from University

of Science and Technology Beijing, Harbin University

of Science and Technology, General Research Institute

Nonferrous Metals, and Huazhong University of Science and

Technology, etc. and 1 delegate from Hong Kong, China.

The conference collected 131 technical papers in total

including poster display 20, among these, 26 is from Chinese

continent's scholars (poster display 14). with the exception

of 5 plenary presentations, the rest 127 were presented at

three technical sessions, respectively. Their topics cover the

following four subjects: Process Development and Industrial

Application (45); Materials Development and Characterization

(49); Numerical Modeling and Simulation (16); Process and

Parts Assessment (17). Dr. Keung Wing Ching from Hong

Kong Foundry Association made his presentation on “Status

Quo of Semi-Solid Technology in China”.

The 11th International Conference on Semi-Solid

Processing of Alloys and Composites will be held in Beijing

of China in 2010. The biennial S2P Conference has its nine

highly successful predecessors held in:

• Sophia-Antipolis, France (1990)

• Cambridge, MA, USA (1992)

• Tokyo, Japan (1994)

• Sheffield, England (1996)

• Denver, CO, USA (1998)

• Torino, Italy (2000)

• Tsukuba, Japan (2002)

• Limassol, Cyprus (2004)

• Busan, Korea (2006)

The following is the paper abstracts contained in the

proceedings of the S2P2008.

Plenary Presentations

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InformationMay 2009

4. Thixoforming of Steel: A State of the Art from an Industrial Point of View

P. Cezard and T. Sourmail

Abstract: Since the first research works in the end of 1980s on the

semi-solid forming of steel, this process has presented a great interest

and a real industrial potential. Several research teams, all over the world,

have shown the feasibility of such a process. Working on the parameters

which have an influence on the process, they pointed out the "technical

locks" which must be overcome to allow industrialization of the process.

A first and perhaps most important difficulty is the reliability of the

forming tools in an industrial production context. Much work has

therefore been devoted to identify ways to increase tools life. A second

important point is the possibility to obtain sound microstructure and

satisfactory mechanical properties. This paper is a state of the art review

on the subject of the thixoforming of steel, restricted to forming of

semi-solid reheated steel. Semi-solid forming process carried out after

partial solidification are therefore not covered. The reader interested in

such processes may refer to the review recently published by Hirt et al. [1].

The present review considers, in turn, the different steps of an

hypothetical production line and their particular challenges, from the raw

material to the final product.

liquidus molding, semisolid extrusion molding as well as the alloy and

composite generation in a semisolid state are described. An update

on commercialization progress is completed by a characterization of

the modern equipment used for process implementation with broad

references to metal die casting and plastics injection molding.

3. On the Modeling of Semisolid Suspensions

Andreas N. Alexandrou

Abstract: Due to the distinct rheologic characteristic of semisolid slurries

the process has well established advantages over competing near-net-

shape manufacturing technologies. Despite the obvious advantages of

the process its adoption by the casting industry, however, has been

slow. This is primarily due to lack of confidence of how these slurries

flow in die cavities. The added cost associated with the specially

prepared slurry has also affected the process commercial success.

Nevertheless these problems attention to the semi-solid metal process

has indeed increased over the years. The main focus of this review is

the modeling of semisolid slurries. The objective here is to present an

overview of relevant aspects of modeling by focusing on the physics

of the slurry and by stressing consistent mathematical and analysis

methods to determine the material constants.

Process Development and Industrial Application 1. Investigations on Thermal Influences for Thixoforging and Thixojoining of Steel Components

René Baadjiu, Frederik Knauf and Gerhard Hirt

Abstract: At the Institute of Metal Forming (IBF) current investigations

within the framework of the Collaborative Research Centre 289 are

mainly concentrated on forming of semi-solid precursor material of the

steel grades X210CrW12 and 100Cr6. One important task is the precise

temperature for the composition of solid and liquid phase fraction in the

preheated billet. Experimental measurements and numerical simulations

show significant heat losses during transport of the billet and after its

insertion into the die. These developing temperature gradients influence

strongly the resulting temperature field in the formed component.

In case of the forming tools the critical increase of the temperature

depending on the tool material is shown. As fundamental research in

the field of thixojoining the temperature development of the inserts is

analysed and demonstrates the feasibility of joining higher and lower

melting materials into the semi-solid matrix.

2. Influence of Processing Route on the Properties of Magnesium Alloys

Hagen Frank, Norbert Hort, Hajo Dieringa and Karl Ulrich Kainer

Abstract: Magnesium alloys had gained an increasing interest in

recent years due to their promising property profile for light weight

constructions. They offer drastic advantages in weight reductions in

automotive industries compared to steel or even aluminium. Therefore

they can be used to decrease the emission of green house gases

as requested by the EU directive for the reduction of CO2 emissions

and moreover due to their recyclability they also help to fulfill the

requirements from the EU directive regarding the end of life of vehicles.

But still there are some limitations with regard to strength, mostly at

elevated temperatures above 130 oC. To overcome these limitations

alloy development as well as process optimization has to be done for

further enhancement of the range of magnesium applications. This paper

will show and discuss the property profiles of the standard magnesium

alloy AZ91D compared to the recently developed, heat resistant

magnesium alloy MR-1153. The alloys have been processed using

normal high pressure die casting (HPDC), New Rheocasting (NRC) and

Thixomolding (R) (TM). As methods of investigation tensile and creep

tests have been applied. The creep properties have been determined

in the temperature range of 135-150 oC and loads of 50-85 MPa. All

these trials have been accompanied by metallographic observations (light

optical metallograph, SEM) and density measurements to investigate

the influence of the processing routes on microstructure and the

porosity of the materials. It will be shown that the differences in the

property profile of the chosen alloys are dependent on their different

chemical compositions as well as on different microstructures that are

obtained by the different processing routes. While in the case of AZ91D,

TM is showing advantages compared to HPDC for room temperature

applications, the NRC in combination with the heat resistant alloy leads

to an improvement of creep rates by two orders of magnitudes.

3. Forming of Biocompatible Materials in the Semi-Solid State

Levente Kertesz and Mathias Liewald

Abstract: Semi-solid processing of materials provides advantages

of both forging and casting. Experiments with high-melting and

biocompatible al loys aiming at a "near-net-shape" production

technology recently have been conducted. Advanced trials showed, that

processing of such materials by means of semi-solid forming deliver

a huge potential for feasible workpiece shapes and drastically reduces

machining time and subsequent surface treatment efforts.

In contrast to semi-solid forming of aluminium alloys at relatively

low temperature levels any processing of high-melting point alloys in

the semi-solid state is much more challenging due to higher forming

temperature. Commonly used tool materials provoke high wear rates

due to wetting, bonding and melting processes which finally result in a

very short tool life time. Thus, more apt materials and composites for

forming tools and dies which can withstand corrosion, wear, tear and

extreme changes in temperatures have to be found. The development

of new design concepts for long-living close-to-production tools based

on such new materials will be a future goal.

4. A Comparison of Deep Drawing and Ironing of Metal Alloy Strip Produced Conventionally and Non- conventionally via Semi Solid Material Processing

Antonio de Pádua Lima Fiho, Márcio Iuji Yamasaki, Leandro Akita Ono,

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CHINA FOUNDRY Vol.6 No.2

Lourenco Nampo and Alcides Pa dilha

Abstract: A semi solid thin strip continuous casting process was used

to obtain 50%wt Pb/50%wtSn strip by single and twin roll processing

at speed of 15 m/min. A 50%wt Pb/50%wtSn plate ingot was also cast

for rolling conventionally into strips of 1.4 mm thickness and 45 mm

width for comparison with those achieved non-conventionally. This

hypoeutectic alloy has a solidification interval and fusion temperature

of approximately 31 oC and 215 oC respectively. The casting alloy

temperature was around 280 oC as measured by a type K immersion

thermocouple prior to pouring into a tundish designed to maintain a

constant melt flow on the cooling slope during semi solid material

production. A nozzle with a weir ensures that the semi solid material

is dragged smoothly by the lower roll, producing strip with minimum

contamination of slag/oxide. The temperatures of the cooling slope and

the lower roll were also monitored using K type thermocouples. The

coiled semi solid strip, which has a thickness of 1.5 mm and 45 mm

width, was rolled conventionally in order to obtain 1.2 mm thick strip.

The coiled thixorolled strip had a thickness of 1.2 mm and achieved

practically the same width as the conventional strips. Blanks of 40 mm

diameter were cut from the strips in a mechanical press, ready for

deep drawing and ironing for mechanical characterization. All the strips

achieved from non-conventional processing had the same mechanical

performance as those achieved conventionally. The limiting drawing

ratio (LDR) achieved was approximately 2.0 for all strips. Microscopy

examination was made in order to observe phase segregation during

processing.

5. Process Window Determination for Thixo- extrusion Processes Using a Steel Alloy

F. Knauf, R. Baadjou and G. Hirt

Abstract: A direct semi-solid bar extrusion process is characterized by

inserting a feed stock in a container and extruding through a forming

die with a punch. Compared to conventional bar extrusion the use of

semi-solid material complicates the process due to the requirement

of solidification of the material. To achieve the solidification of the

semi-solid bar, different basic tool concepts are presented. With a

combination of these concepts experiments were carried out using the

steel alloy X210CrW12 to detect the influence of the most influencing

parameters on press velocity, extrusion channel diameter, length and

geometry. Numerical simulations enable a better understanding of

the process mechanics like temperature development in the billet and

forming die as well as the material flow in the deformation zone.

6. Investigation of Thin Wall Casting Made of Semi-Solid A356 Using Back Extrusion and Die Cast

M. Moradi, M. Nili-Ahmadabadi, B. Herdarian and S. Ashouri

Abstract: Semi-solid forming is a new technology in recent decades

that has a number of advantages over conventional casting routes. As a

result of these advantages, semi-solid processes are less limited in the

part geometry, mainly concerning the wall thickness. According to many

researches on aluminum alloys, the evaluation of flow and die filling

properties of alloys as well as their resulting mechanical properties which

are depended on various process parameters are being investigated

up to now. Semi-solid forming processes contain three main steps:

feedstock manufacturing, reheating and forming. Feedstock quality and

reheating have strong effect on success of forming procedure. In order

to understand and describe forming behavior in the semi-solid state,

two different tests have been studied in the same casting conditions.

In this study, back extrusion and die casting processes were used to

investigate the effect of section size and process on the mold filling. In

the case of back extrusion process a cup shaped specimen and in the

case of die casting process, a step die with different sections size were

used. Microstructures of different sections of specimens were studied

by optical microscopy to depict the effect of different variables on the

quality of products.

7. Basic Study on Thixo-Co-extrusion of Multi-layer Tube with Al/Mg Alloys

Wang Kaikun, Zhang Peng, Du Yanmei, Zeng Pan

Abstract: Thixo-forming is in the forefront of metal processing

technology in the 21st century. The research on thixo-co-extrusion

of multi-layer tube as extension and development of the semi-

solid forming technology is a completely new processing method for

the composite material forming and is of great significance, in which

different semi-solid billets (slurries) are extruded at the same time

to form multi-layer tubes. In this study, different sizes of column-

shaped and ring-shaped billets of Al/Mg alloys were firstly prepared by

using specially designed molds. Then they were reheated by electric-

resistance furnace, microstructures from different heating laws were

investigated. Lastly, FEM simulation on thixo-co-extrusion of double-

layer tube with A356/AZ91 was conducted.

8. Feasibility of Recycling Aluminum Alloy Scrap by Semisolid Extrusion

Sumio Sugiyama and Jun Yanagimoto

Abstract: The feasibility of recycling machining grindings of aluminum

alloys by semisolid process has been investigated. Machining grindings

of A2011 aluminum alloy produced experimentally by lathe machining

were used. The material is put into a metal mold and compressed

up to 90% of the true density at room temperature. The metal mold

with the compressed machining grindings is heated up to a specified

temperature. Afterwards, the metal mold is set into the extrusion

container, and extrusion in hot and semisolid range was carried out.

In this experimental study, extrusion load, internal structure of the

product and mechanical properties (tensile strength, elongation,

hardness) of the product are assessed. It was proven that semisolid

extrusion is about 40% less extrusion load compared with that of hot

extrusion, the shape of the machining grindings remained in the hot

extrusion and the semisolid extrusion products extrusion ratios higher

than 10 have excellent elongation property, which is comparable to the

commercialized product.

9. Thixo-extrusion of 5182 Aluminium Alloy

Plato Kapranos, Toshio Haga, Ermanno Bertoli, Annalisa Pola

Abstract: Extrusion is a well established technology for the production

of complex sections of aluminium alloys. Thixo-extrusion in comparison

to traditional hot-extrusion offers several advantages such as lower

extrusion and friction forces, higher material fluidity, longer tool life etc.

Aluminium alloy 5182 is an important commercial alloy characterized

by high strength and ductility, high corrosion resistance and good

formability; it is commonly used for the production of wrought

automotive components and it is also suitable for semi-solid applications

thanks to its wide solidification range. The aim of this paper is to attempt

the shaping of 5182 Al-Mg alloy through the thixo-extrusion process

using a ceramic tool and evaluating the effect of different routes of

making the feedstock on the semisolid microstructure. Particularly, two

different methods were investigated: Near-solidus casting and Roll-

casting using a cooling slope.

All the samples produced were characterized by metallographic

analysis in order to measure globule size and shape factor, as the main

criteria used for assessing thixo-formability.

10. Forging Process of Wrought Aluminum Alloy with Controlled Solid Fraction by Electromagnetic Stirring

J. W. Bae, S. M. Lee and C. G. Kang

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InformationMay 2009

Abstract: This study demonstrates the indirect rheoforging of wrought

aluminum alloys fabricated by electromagnetic stirring (EMS). EMS

was carried out by varying pouring temperature of theological material

and subsequently the rheo-material was forged into the sample which

consisted of the direct and indirect forging part, by varying the applied

forging pressure. The rheo-material completely filled the die cavity at

the applied forging pressure of 150 MPa. To transfer the densification

pressure to the end of the part, the applied forging pressure of over

170 MPa was necessary. To control liquid segregation, solid and liquid

phases distribute uniformly by deriving the laminar flow. When liquid

segregation occurred significantly during rheoforging, the strength

revealed as low as 268 MPa. Investigating relationship between

microstructural features and mechanical properties of the product,

the rheoforged material through EMS revealed the fine and globular

microstructure. Microstructure with uniform distribution of solid and

liquid phase (no segregation) showed good mechanical property of the

rheoforged material whose tensile strength was 341 for Al6061.

11. Development of the Gas Induced Semi-Solid Metal Process for Aluminum Die Casting Applications

J. Wannasin, S. Junudom, T. Rattanochaikul and M.C Flemings

Abstract: A simple and efficient rheocasting process that has recently

been invented is being developed for aluminum die casting applications.

The process called Gas Induced Semi-Solid (GISS) uti l izes the

combination of local rapid heat extraction and agitation achieved by

the injection of fine gas bubbles through a graphite diffuser to create

semi-solid slurry. In the GISS process, the die casting machine and

the process cycle remain little changed from those of conventional die

casting. The GISS unit creates a low solid fraction of semi-solid slurry

in the ladle during the ladle transfer to the shot sleeve. The semi-solid

slurry is then poured directly into the shot sleeve. This paper presents

the detailed description of the process. The results of the semi-solid die

casting experiments with ADC10 alloy using the GISS process are also

reported and discussed.

12. Strategies for Re-heating Steel Billets for Thixoforming

Bernd-Arno Behrens, Dirk Fischer and Ahmed Rassili

Abstract: Inductive re-heating of billets is the state-of-the-art method

to enable the desired liquid fraction for thixoforming. In laboratory

experiments the temperature might be directly controlled since it is

usually possible to apply thermocouples for temperature measurements.

Due to technical restrictions temperature measurements especially in

the interior of a billet are difficult in industrial heating processes. For this

reason, thixoforming billets are heated without temperature monitoring

by using proven heating functions. Such functions are usually obtained

by trial-and-error or on the basis of FEA simulations. In both cases

exhaustive experimental work is usually necessary. Moreover, FEA

simulations require thermo-physical material data that is difficult to

obtain for industrial relevant heating processes.

In this paper an alternative method of experimentally obtaining

optimized heating functions by using a fuzzy logic controller is

introduced. Under steady-state environmental conditions this method

allows a quick and reproducible re-heating. The main advantages of the

fuzzy logic based approach are that no specific material data is required,

system specific properties such as the efficiency have not be explicitly

determined and that the practical implementation could be realized with

a minimum of experimental work.

13. Recent Developments within Semi-Solid Forming at the Institute for Metal Forming Technology, Stuttgart University

Mathias Liewald and Peter Unseld

Abstract: This paper illustrates several research activities being carried

out within the Center of Competence for Casting and Thixoforging

Stuttgart (CCT 'NOVUS').

A new method for manufacturing Metal Matrix Composites out of

the semi-solid state has been developed at the Institute for Metal

Forming Technology, Universitaet Stuttgart, and applied for patent

pending. Within this new manufacturing method for the production of

fibre and particle reinforced composites now disadvantages of liquid-

phase-techniques can be reduced in combination with decreased

manufacturing costs compared to conventional MMC-production

technologies due to short cycle times and the ability of near-net-shape

forming.

It is obvious that manufacturing process in the fabrication of

metal matrix composite materials will influence in some extent the

performance of these materials. A current research project at the

Institute for Metal Forming Technology (IFU), contributes implementing

specific boundary condition of the manufacturing process to numerical

analysis. Such boundary conditions exert direct influence on product

quality. For manufacturing of metal matrix composites limiting factors

are e.g. temperature, pressure, deformation, etc. Detecting input-

parameter for numerical analysis basic theological parameters, such as

static and dynamic yield points, hysteresis and shear rate jump tests,

detection of the differential structural parameter, evolution of apparent

viscosity of different cast-alloys are topics of current research project at

the Institue for Metal Forming Technology.

For reheating-process of semi-solid alloys new technologies have

been developed and applied for patent pending by the Institute for

Control Engineering of Machine Tools and Manufacturing Units (ISW).

The two main advantages of this technique as compared with other

induction heating techniques are the direct online determination of

liquid-, solid fraction and heating-homogeneity as well as robustness

against variations of prematerial (chemical composition, billet-diameter,

etc.).

14. Flatness Based Control of Inductive Heating of X210CrW12 into the Semi-Solid State

Rainer Gasper, Alexander Schoenbohm, Manfred Enning and Dirk Abel

Abstract: The inductive heating of the feedstock material is a very

important step in the processing of semi-solid metals. On the one hand,

the billet has to be heated as fast as possible to the target temperature.

On the other hand, it must be guaranteed that the outer area does not

begin to melt prematurely. Also, at the end of the heating the billet

should have a uniform temperature distribution in order to obtain good

forming results. A flatness based control will be presented to calculate

the induced power over time trajectory from a desired trajectory for the

temperature in the middle of the billet. The temperature trajectory has

to be chosen so that the billet has the desired temperature behavior.

Experimental results will be shown for the flatness based inductive

heating of X210CrW12 just below the semi-solid state.

15. Numerical Simulation of Induction Heating of Aluminum Alloy Billets

N. Barman, J. Mukherjee and P. Dutta

Abstract: In this work, a numerical model for induction heating

is proposed. The heating process considers only interaction of

electromagnetic effects and heat transfer, and is represented by an

unsteady heat diffusion equation. The numerical simulation of the

process is performed using a finite volume method in which the

induction heating is represented by a volumetric heat source term. The

heat source term is evaluated analytically using principles based on

Faraday's and Biot-Savart laws. The technique is applied to the case of

induction heating of a cylindrical A356 aluminum alloy billet. The model

predicts magnetic flux density and temperature distribution during the

heating process. The effects of process parameters, such as frequency

and current density, on the temperature distribution are also studied.

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CHINA FOUNDRY Vol.6 No.2

The results show that nearly uniform distribution of temperature can be

achieved when the billet is heated slowly with low frequency and low

supply current density.

16. The Influence of Heat Treatments for Laser Welded Semi-Solid Metal Cast A356 Alloy on the Fracture Mode of Tensile Specimens

G. Kunene,G. Govender, L. Ivanchev, R. Knutsen and H. Burger

Abstract: The CSTR rheo-process was used to prepare the aluminium

A356 SSM slurries and thereafter plates (4mm x 80mm x 100 mm) were

cast using a 50-ton Edgewick HPDC machine. Plates were in the as

cast. T4 and T6 heat treatment conditions which had passed radiography

were then butt laser welded. It was found that the pre-weld as cast, T4

and post-weld T4 heat treated specimens fractured in the base metal.

However, the pre-weld T6 heat treated specimens were found to have

fractured in the heat affected zone (HAZ).

17. Semi-solid Casting of High-reactive Wrought Alloys by Means of the Alloy AlLi2.1Mg5.5ScZr (AA1420*)

Matthias Buenck, Fabian Kuethe，Andreas Buehrig-Polaczek, Alexander

Arnold，Bernd Friedrich and Roger Sauermann

Abstract: Semi-solid forming offers new potentials for processing of

high reactive and hot crack susceptible aluminium-lithium wrought

al loys. With the tai lored al loy AA1420* (AlLi2.1Mg5.5 +Sc+Zr) a

promising material for thixoforming with achievable high strength

of up to 500 MPa tensile strength and over 400 MPa yield strength

concomitant with its low density of 2.46 g/cm3 is achievable. Due to high

solid fractions the effect of solidification shrinkage could be sufficiently

decreased with the result of hot-tear-free casting.

Simulation supported a critical to cast automotive tie rod was

exemplarily manufactured via semi-solid-technology with promising

results.

Furthermore with an improved and advanced heat treatment

enhanced mechanical properties, comparable to those of rolled AA

1420, were achieved.

18. Effects of T5 and T6 Heat Treatments Applied to Rheocast A356 Parts for Automotive Applications

M. Rosso, I. Peter and R.Villa

Abstract: The correlation between the evaluation of the mechanical

and of the fatigue behaviour of the rheocast, T5 and T6 heat treated

SSM A356 aluminum alloy with respect to the microstructures of the

component has been investigated. The study has been carried out on

a suspension arm injected in a rheocasting 800-ton plant in Stampal

S.P.A. The new rheocasting is a process that allows obtaining the

alloys in a semisolid state directly from the liquid state, by controlled

cooling of the molten alloys. The resulting microstructures are very fine,

free from defects and homogeneous: these characteristics improve

the mechanical properties of the alloys and specially the response to

cyclic stress, an important issue for a suspension component. After

a preliminary tensile test analysis, axial high frequency fatigue tests

have been carried out at room temperature on specimen cut out from

the suspension arm to determine the Wohler curve and the number

of cycles to failure. The results of this work allow a comparison of the

effects of heat treatment process, T5 or T6, on semi-solid components

for industrial applications in the automotive field. On the basis of these

analyses the correlation between microstructure and mechanical

performances can be established.

19. Semi-solid Extrusion of Complex-shaped Steel Rods Using Ceramic Dies

S. Muenstermann, R. Telle, F. Knauf and G. Hirt

Abstract: Isothermal semi-solid extrusion experiments using steel grade

X210CrW12 as work material were performed on an industrial forging

machine. An improved and tip-scaled tool design was applied, based on

the concept of self-heating ceramic dies tested in previous laboratory-scale

studies and allowing for die preheating temperatures of up to 1,400 ℃.

Steel rods of complex cross sectional geometry were formed at low

extrusion forces. Shape accuracy of as-formed rods is accurate and

metallurgical examination yields no evidence of liquid phase separation.

With a view on the intended industrial implementation construction of

ceramic tools has to be improved in order to avoid rupture of ceramic

parts due to thermo-mechanically induced stresses and to benefit from

the advantages inherent to ceramics in metal forming.

20. Laser Surface Modification of Tool Steel for Semi-Solid Steel Forming

Dermot Brabazon, Sumsun Naher and Patrick Biggs

Abstract: This paper presents an analysis of the effect of CO2 laser

processing parameters on the surface modification and heat treatment

of steels. The CO2 laser and sample movement process parameters

are presented. The controlled operation of these in conjunction with

each other is required to obtain better surface hardness and structure.

H13 tool steel samples were rotated at high speeds to keep exposure

times below 0.3 s. Laser processed samples were analyzed using

EDX spectroscopy, optical microscopy, Vickers and Martens micro-

hardness testing, and X-ray diffraction (XRD). Results show how the

hardness profile through the surface is related to the laser treatment

and resultant microstructures. Increased surface hardness was noted

due to a complete microstructural transformation to an amorphous state

in the glazed samples. The usefulness of such coatings on tool steels,

in conjunction with other thermal barriers, for the forming of semi-solid

steel alloys is presented.

21. Deposition of Oxides as Tool Protection for Large Thixoforming Dies by Using the Pulsed MSIP-PVD Process

Kirsten Bobzin, Nazlim Bagcivan and Philipp Immich

Abstract: Oxide coatings offer great potential for their use in forming

operations in the semi-solid state. Advantages of these types of

coatings are high resistance against abrasive wear, high hot hardness

and low thermal conductivity. Nevertheless deposition by pulsed

Magnetron Sputter Ion Plating-PVD for oxide coatings is quite

challenging: deposition rates are low and insulating layers on the target

surface can cause arcing. On laboratory scale it was possible to deposit

gamma-alumina using PVD in a temperature range, where hot working

steel can be utilized. The next important step in the development

towards an industrial application for larger forming tools is the upscaling

process to larger coating units. In this work the process development of

oxide coatings on an industrial coating unit for large tools was described.

To increase adhesion of oxide top-layer additional bond coats were

applied. Different process parameters like oxygen content, total pressure

and substrate bias were varied, to improve the performance. The

relationship between coating properties and process parameters of the

deposited films were characterized by X-ray-diffraction, Nanoindentation

and Scanning Electron Microscopy (SEM). By using reactive pulsed

PVD-process it was possible to deposit gamma-Al2O3 on large steel

tools for semi-solid melt protection. The developed coatings showed

for thixoforging processes of X210CrW12 an extraordinary stability in

field tests. The lifetime of the permanent moulds was increased by

using PVD thin film coatings as a tool protection.

22. Servomechanical Press: A New Press Concept for Semisolid Forging

Z. Azpilgain, R. Ortubay, A. Blanco and I. Hurtado

Abstract: Semisolid forging process requires special movement of

the ram, until now only achievable with hydraulic presses. The upper

die, placed on the press ram, must move fast during forming of the

component in order to reduce segregation phenomena, and, once the