RHEO-PROCESSING OF SEMI-SOLID METAL ALLOYS- A NEW TECHNOLOGY FOR MANUFCTURING AUTOMOTIVE AND...
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Transcript of RHEO-PROCESSING OF SEMI-SOLID METAL ALLOYS- A NEW TECHNOLOGY FOR MANUFCTURING AUTOMOTIVE AND...
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.
Page 3 © CSIR 2006 www.csir.co.za
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
Page 4 © CSIR 2006 www.csir.co.za
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
Page 5 © CSIR 2006 www.csir.co.za
(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
Page 6 © CSIR 2006 www.csir.co.za
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.
Page 7 © CSIR 2006 www.csir.co.za
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
Page 8 © CSIR 2006 www.csir.co.za
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
Page 9 © CSIR 2006 www.csir.co.za
Fig.6. Assemblage of the experimental version of CSIR Semi Solid Metal slurry maker
Page 10 © CSIR 2006 www.csir.co.za
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.
Page 11 © CSIR 2006 www.csir.co.za
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.
Page 12 © CSIR 2006 www.csir.co.za
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.
Page 13 © CSIR 2006 www.csir.co.za
Fig.11. A cup assembled with an aluminium consumable washer as a bottom lead of the cup
Page 14 © CSIR 2006 www.csir.co.za
Fig.12. A cup, on the right, and an ejected billet of Al-7%Si alloy, on the left
Page 15 © CSIR 2006 www.csir.co.za
Fig.17. A rheo-processed and water quenched 15.5 kg billet,
122 mm diameter and 480 mm length. The alloy is A356,
Page 16 © CSIR 2006 www.csir.co.za
100 μm 100 μm
(a) Top surface (b) Bottom centre
Fig.19. Microstructure at two positions of the 15.5 kg billet
Page 17 © CSIR 2006 www.csir.co.za
(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
Page 18 © CSIR 2006 www.csir.co.za
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
Page 19 © CSIR 2006 www.csir.co.za
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
Page 20 © CSIR 2006 www.csir.co.za
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.
Page 21 © CSIR 2006 www.csir.co.za
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)
Page 22 © CSIR 2006 www.csir.co.za
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.