RHEO-PROCESSING OF SEMI-SOLID METAL ALLOYS- A NEW TECHNOLOGY FOR MANUFCTURING AUTOMOTIVE AND AEROSPACE COMPONENTS Presented at the CSIR Research & Innovation.

RHEO-PROCESSING OF SEMI-SOLID METAL ALLOYS-

A NEW TECHNOLOGY FOR MANUFCTURING

AUTOMOTIVE AND AEROSPACE COMPONENTS

Presented at the CSIR Research & Innovation Conference

Unit: Metal & Metal Processes

L Ivanchev, D Wilkins, S Govender, W Du Preez, R Bean

Alloys and Processing

Date: 27.February, 2006

Page 2 © CSIR 2006 www.csir.co.za

THE EQUIPMENT

Machine for rheo casting of metal alloys

by controlled cooling and induction stirring

from liquid to semi solid state have been

designed. The machine has been tested for processing of

aluminium alloy A356 and continuous delivery of mush

billets 72 mm diameter and 200 mm length.

These dimensions are not the limits of the process

and billets up to 15.5 kg were successfully treated.


Molten metal at temperature close to the liquidus is pored

into stainless steel cups. They are moved in vertical

direction upwards and stepwise through three

conditioning units.

Each conditioning unit consists of an AC induction coil and few

air-cooling coils.

The induced electromagnetic field, supplied by the

induction coil, and the air blown from the air-cooling system

simultaneously tread the metal to the desired semi solid

temperature and structure.

The process was optimized to produce semi-solid billets

at a production rate of one billet per minute.

THE PROCESS


LIQUID

SEMI-SOLID

SOLID

•HOT FORMING

•SEMI-SOLID METAL

CASTING/FORMING

Known since 3000 BC

Known since 3500 BC

Ambient temperature

•COLD FORMINGKnown since 4000 BC

Known since 1973 AD

THIXO RHEO

Globular structureformation

Liquidus temperature

Solidus temperature

•CASTING

Fig.1. The metal forming processes places in a “Time- Temperature” diagram


(a) Dendrite structure (b) Globular structure

Fig.2. Typical microstructure of an Al-7%Si alloy after:

(a) liquid casting and (b) semi-solid casting


Fig.3. Plastic behavior of an Al-7%Si alloy treated to semi-solid state-globular structure and semi-solid temperature, during the technological “kitchen knife” test.


ThixocastingThixocasting

(a) (SSM feedstock manufacturing

(b) Thixo casting of the feed-stock into a component

Fig.4. The two steps of thixo route of SSM casting method


High Pressure Die Casting

Liquid Metal Semi-solid metal with globular grain structure

Cooland stir

Transfer

RheocastingRheocasting

Fig.5. Diagram of the one-step Rheo route of SSM casting method


Fig.6. Assemblage of the experimental version of CSIR Semi Solid Metal slurry maker


Fig.7. Assemblage of the semi-industrial version of CSIR Rheo Casting machine: the induction generator, the slurry maker, a 6-axis robot and the cup conditioning unit are visible.


Fig. 8. The three conditioning units slurry maker.

Each unit consists of an induction coil and an air spraying coil.

The induction coils provide induced magnetic field into the liguid metal to modify the metal structure from dendrite to globular.

The air spraying coil reduce the metal temperature form the liquid to the semi-solid value of the particular alloy.

A cup full with liquid metal is at the bottom waiting to be up-wards processed.


Fig.9. A ceramic lead above the top coil of the slurry maker.

The three thermocouples coming out of the lead are for controlling the final temperatures of metal at the top-, the middle and the bottom positions of the cup.


Fig.11. A cup assembled with an aluminium consumable washer as a bottom lead of the cup


Fig.12. A cup, on the right, and an ejected billet of Al-7%Si alloy, on the left


Fig.17. A rheo-processed and water quenched 15.5 kg billet,

122 mm diameter and 480 mm length. The alloy is A356,


100 μm 100 μm

(a) Top surface (b) Bottom centre

Fig.19. Microstructure at two positions of the 15.5 kg billet


(a) Top surface (b) Middle surface (c) Bottom surface

(d) Top centre (e) Middle centre (f) Bottom centre

Fig.18. Microstructure homogeneity in 6 positions of a 15.5 kg billet

300 μm


The main technological advantages of the SSM forming process are as follows: • Better mechanical properties, for example elongation

• Low gas porosity due to laminar filling and good airing

• Allows for casting of wide range of alloys inclusive of high strength wrought alloys. • Production of thin walled components

• Longer life of the dies

• Joining by LASER, MIG or TIG welding possible

• Heat treatment from T0 - T7 possible

• Near net-shape parts production

• Excellent surface finishing


APPLICATIONS OF SSM TECHNOLOGY

IN AUTOMOTIVE INDUSTRY

•BRAKE CALIPERS

•CLUTCH CYLINDERS

•SUSPENSION ARMS

•WHEELS

•PISTONS

•KNUCKELS

•ENGINE MOUNTS

•PULEYS

•ROCKER ARMS

•BELT COVERS

•MOTOR HOUSINGS

•SPACE FRAMES


The characteristics

of the A356 castings achieved in this work are: Grain size: less than 85 m Shape factor: less than 1.52

Mechanical properties in “T6” condition:

Yield Stress: 286 MPa, Ultimate Tensile Strength: 334 MPa, Elongation: 6.2 %

Maximum temperature variation in a single billet is 4C Production rate: one billet per minute.


THE PRESENT STATUS OF SSM TECHNOLOGY

Light Metal Components Market:The total SSM market in North America is estimated to grow from 0.6 million metric tons/year in 2002 to 2.4 million metric tons in 2012, or 400%.Structural castings: 20% in 2002 and 40% in 2012 growth / year;High integrity castings: 10% in 2002 and 40% in 2012 growth / year;Increasing Demand for Rheo Casting Technologies.

Number of Rheo Processes Reported:1996 – 11998 – 02000 – 32002 – 52004 – 18 ( including CSIR process)


Conclusions

• The general world trend is a shift to rheocasting processes.

• Increased interest from automotive and aero space industry to the CSIR technology.

• Although there are several new rheocasting processes, only one process and equipment is currently commercially available.

• We have a window of opportunity to enter world market in order to compete with the international consortiums.

RHEO-PROCESSING OF SEMI-SOLID METAL ALLOYS- A NEW TECHNOLOGY FOR MANUFCTURING AUTOMOTIVE AND AEROSPACE COMPONENTS Presented at the CSIR Research & Innovation.

Documents

metal structure

metal metal processes

semisolid temperature

semisolid metal alloys

b semisolid casting

solid metal slurry maker

semisolid billets

liquid semisolid solid