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 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 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 LIQUID SEMI-SOLID SOLID HOT FORMING SEMI-SOLID METAL CASTING/FORMING Known since 3000 BC Known since 3500 BC Ambient temperature COLD FORMING Known since 4000 BC Known since 1973 AD THIXO RHEO Globular structure formation Liquidus temperature Solidus temperature CASTING Fig.1. The metal forming processes places in a “Time- Temperature” diagram

Page 5 © CSIR (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 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 Thixocasting (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 High Pressure Die Casting Liquid Metal Semi-solid metal with globular grain structure Cool and stir Transfer Rheocasting Fig.5. Diagram of the one-step Rheo route of SSM casting method

Page 9 © CSIR Fig.6. Assemblage of the experimental version of CSIR Semi Solid Metal slurry maker

Page 10 © CSIR 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 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 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 Fig.11. A cup assembled with an aluminium consumable washer as a bottom lead of the cup

Page 14 © CSIR Fig.12. A cup, on the right, and an ejected billet of Al-7%Si alloy, on the left

Page 15 © CSIR 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 μm (a) Top surface(b) Bottom centre Fig.19. Microstructure at two positions of the 15.5 kg billet

Page 17 © CSIR (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 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 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 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 4  C Production rate: one billet per minute.

Page 21 © CSIR 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 – – – – – 18 ( including CSIR process)

Page 22 © CSIR 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.