Belinda Stening, Curve editor, spoke to Professor David StJohn, chief executive officer of CAST, the cooperative research centre (CRC) for light metals, based at the University of Queensland, and its industry partners to find out the latest on new metals.

CAST’s objective is to work with industry to improve processes, reduce costs and increase productivity, with a view to tapping the potentially lucrative global market for lightweight components, especially in the automotive sector. Its activities are underpinned by scientific capabilities that can be applied across all areas of metals manufacturing.

“Our industry participants span from metal producers, through to suppliers of equipment, to light metal producers, component manufacturers and finished product manufacturers,” StJohn explained.

“We focus on reducing maintenance requirements and downtime and look at process improvements to reduce scrap. We also create new business opportunities by developing new alloys. And we look at reducing greenhouse gas emissions from processing, as well as ways to save energy.”

Rethinking aluminium

The major focus of CAST’s work with aluminium is on ‘upstream’ activities. Continuous casting technologies that generate ingot for extrusions, and ingot that is remelted for casting, are being looked at with Rio Tinto Aluminium Technologies and o.d.t. Engineering, a manufacturer of casting equipment in Melbourne.

“There are three new casting technologies, all being commercialised by o.d.t.,” said StJohn. “Two of these relate to ingot casting and increasing the productivity of casting machines.

"One is a new ingot mould design, called CASTmould, which gives faster heat transfer, and the other, CASTfill, is a wheel that puts the hot metal into the ingots faster while producing the same quality as traditional methods. The third, AirCAST, is hot mould technology for the casting of extrusion billets.

"The advantage of this technology is that it gives a beautiful surface finish to the billet, so machining is reduced, and its appearance makes it more marketable.”

New Castalloy, the Adelaide manufacturer that produces finished aluminium wheels for Harley Davidson, has developed a strong relationship with CAST through the successful implementation of projects analysing defects, improving manufacturing lead times, and conducting market surveys on new technologies.

“All of the wheels are exported from South Australia to York, Pennsylvania, and Kansas City, for assembly,” said Russell Barnett, process engineer from New Castalloy.

“The manufacture of motorcycle wheels involves three main processes: casting, machining, and chromium electroplating to produce the ‘jewellery’ finish. Harley Davidson has stringent cosmetic quality requirements on all their products, so the technical support and state-of-the-art equipment that is available through CAST is invaluable.”

With the constant pressure of cheaper components from overseas manufacturers, the need to stay abreast of new and developing technologies is paramount to Australian companies if they are to compete.

Two projects focused on the heat-treatment process at New Castalloy were recently conducted to improve efficiencies. “The first involved the optimisation of the lengthy cycle times associated with the heat treatment of aluminium wheel castings,” said Barnett.

“The outcome of this project led to a twenty-five per cent reduction in cycle time, facilitating a cost saving of more than $300K for us. The second project involved an extensive survey of fluidised bed technology and its application to the manufacture of aluminium wheels. This in-depth report, which included a list of overseas contacts, has led us to negotiations with a US company.”

Aluminium alloys also promise future applications in the automotive industry. Suspension components needing high strength, high ductility and fatigue resistance may be one growth area.

According to StJohn, we need to develop casting processes that reduce the number of defects in the stress-critical areas and also produce very sound, high-quality castings with low porosity.

The CSIRO has developed a high-pressure die-casting process called ATM, which achieves a refinement of microstructure and reduction in porosity. It is also commercialising a heat treatment process for aluminium alloy high-pressure die-castings that doubles yield strength and improves ductility.

“These technologies have enormous potential due to the opportunities they create in terms of weight reduction, reduction in material waste and the lowering of costs,” said Barrie Finnin, from the CSIRO.

Riveting magnesium

Magnesium, too, is finding new applications. It is easily cast and many components can be integrated into one casting. It lends itself to complex parts and can also eliminate parts, which reduces manufacturing costs, noise and vibration, and the number of nuts and bolts that can come loose.

The use of magnesium in automotive applications has the potential to reduce the weight of the vehicle, thus improving fuel efficiency and vehicle agility, and cutting exhaust emissions.

The market penetration of magnesium in the automotive industry is currently low, though its use for steering wheels and instrument panel castings is well established in North America.

In response to being underutilised, competitive research worldwide is searching for a cost-effective magnesium alloy that can be used for engine components, particularly the engine block, which comprises up to twenty-five per cent of the engine’s weight.

There is also considerable potential for the use of magnesium in powertrain applications (eg engines and gear boxes), given its lightweight nature.

Two alloys have been developed by CAST – one that can be precision sand-cast, and another for high-pressure die-casting – and these are being commercialised by Advanced Magnesium Technologies (AMT). These alloys have been specially developed to withstand the demanding temperature and pressure conditions of a modern car engine.

“We are marketing two powertrain alloys,” Gordon Dunlop, AMT’s chief technology officer said. “AM-SC1 has been developed for sand-casting and permanent mould casting. AM-HP2 is for high-pressure die-casting. AM-SC1 was initially developed in a project with the German casting company VAW (now part of Hydro Aluminium) and the Austrian engine-design company AVL.”

“This project resulted in the development of a new lightweight turbo-diesel engine that was road tested in a VW Lupo for two years,” said Dunlop. “AM-SC1 was the engine block material. The road trial had a very satisfactory outcome.”

“More recently a project with funding from the US Department of Energy and involving Ford, GM and DaimlerChrysler is using the alloy for the block of a lightweight V6 engine. This engine is currently being manufactured in preparation for an exhaustive testing program.

“AM-HP2 is a newer alloy with similar properties aimed at die-casting applications. This process is favoured by many car companies for production of engine castings. AM-HP2 is currently being evaluated by a number of European and Japanese automotive manufacturers.”

Another new magnesium alloy, called AM-lite, has also been licensed to AMT. “AM-lite is the product of an accidental discovery,” said StJohn.

“We noticed that alloys of this type had some exciting characteristics such as improved strength, and when cast the surface finish was much better than existing alloys. It showed great potential for auto trim and we then realised it could replace zinc die-castings.”

AMT involved MacDermid, a company specialising is electroplating technology, to develop an electroplate coating for Am-lite, and it is now being trialled in Asia as a casing material for mobile phones and laptop computers. Due to the recent hike in the price of zinc, AM-lite is now significantly cheaper for domestic products such as door handles and taps.

“We are currently working with customers to find applications for this alloy in electronics, hardware, sanitary ware, motorcycles and automotive,” said AMT’s Dunlop. “Because it competes with decoratively finished zinc, magnesium AZ91 and aluminium die-castings and plastics, it provides interesting opportunities to product designers.”

Future applications for magnesium are mooted for the body structures of cars, too. The lightweight aluminium car bodies made by BMW, Audi and Jaguar have set a trend for the use of new metals in the auto industry. “We are trying to anticipate the next wave in weight reduction, which is to introduce magnesium extrusions and castings as components on the body structure,” said StJohn.

Henrob, a Queensland company, is working with CAST to come up with a process technology that allows the use of self-pierce riveting (SPR) with magnesium castings.

“The problem with magnesium is that it is not very ductile, and therefore difficult to weld or join,” said Stuart Blacket, managing director of Henrob.

“SPR involves some forming of the metal, causing cracking. But by elevating its temperature, the metal can be formed without cracking. We are developing an elevated temperature joining process that will be used on a production line with robots.”

“The process of SPR involves the pressing of a self-pierce rivet into layers of material without a hole and forming a structural joint without the rivet penetrating the lower sheet. The process uses a reaction die mounted in a C frame to help form the joint under high force – typically 50kN.

" The process is ideally suited to joining similar or dissimilar materials in up to four layers with adhesive between the layers.”

SPR technology is now used by most of the major auto companies in some capacity, but it was Henrob and Audi who pioneered the use of the process with the aluminium-bodied A8 in 1993, by using SPR for the complete body structure in place of welding.

Henrob’s main involvement is in the design and manufacture of the tool assemblies. These need to be tailored for each application, so that the structure being riveted can be accessed. “SPR technology is applied by a riveting tool mounted onto a robot wrist or by manually held tools,” said Blacket.

“Henrob also designs the rivets and riveting process, and manufactures and supplies rivets to the tools in either continuous belt form or loose, for feeding in blow tubes.

"As reliability and up time are critical on a production line, a great deal of effort has been applied to the design of the rivet feeders, ensuring the tools can function effectively when a robot swings it around in any plane.”

Blacket cited the joining of mixed-material combinations as another growth area. “These can be either different metals or plastics or composite matrix materials”, he said.

“High-strength steel (HSS) is also growing in popularity in the general effort to reduce the weight of vehicles. It is more difficult to weld than normal steel and more susceptible to fatigue cracking. SPR is a viable alternative to welding for this new material.”

The process of extruding magnesium is slower than aluminium extrusion, so CAST is looking at ways to make it faster. “We are trying to speed up the process, and have a provisional patent on it. We are looking for market interest here but are ahead of demand with this technology – so this may take some time,” said StJohn.

In sheet-metal forming, the CSIRO is working on magnesium strip casting technology. “The Twin Roll Casting (TRC) process for magnesium alloy sheet has been in development now for about five years,” said the CSIRO’s Barrie Finnin.

“The process casts thin sheet directly from molten metal in coil or straight length form. The CSIRO’s TRC process can produce sheet up to about 600 mm wide and down to slightly less than 3 mm in thickness.”

This is a very competitive area, and the Koreans and Germans have developed similar technology.

“Magnesium sheet is currently used in the 3C (computers, cameras, CD players) market where its light weight and relative frequency (rf) shielding attributes and durability are advantageous to users of portable electronic products,” said Finnin.

“It is used in a fairly small way in the automotive sector, but that is likely to increase dramatically in coming years. Other applications include battery plates, photo engraving plates and leisure goods.”

Titanic titanium

Titanium is very strong, with the highest strength-to-weight ratio of any metal, but it is also expensive. In Australia, it’s popular use is in medical implants for teeth and the body, though this is set to change.

“Currently there is particular interest in titanium because of Australia’s involvement in the Joint Strike Fighter project,” said StJohn. “This means we can look towards manufacturing large components for aerospace.”

The cost of titanium is an obvious impediment to developing applications. At the moment Australia mines the minerals, ships them away and buys back the processed raw material.

In response, the CSIRO is looking at cheaper production technologies for titanium, such as powdered titanium and titanium alloy, and has developed technologies for bulk form products such as thin sheet and rod. For specialised applications, the CSIRO can also directly form 3D objects using Cold Spray technology, where particles impact into the product surface at supersonic speeds.

CAST, meanwhile, is focusing on reducing the cost of machining and manufacturing. “This will allow our manufacturing industries to be more competitive and gain a share of the global market,” said StJohn.

Going greener

CAST also does research into the ecological impact of metals, especially in relation to processing. “A cover gas is used when melting magnesium to stop it burning,” StJohn explained.

“This gas contains SF6, which is about the worst greenhouse gas around. Nobody knew how this chemical worked, but a PhD student working with us found that fluorine was the key element in the process. We looked for lower emission gases and found HFC134A, which is used in standard air-conditioning units. It has a much lower greenhouse impact and works better anyway.”

The new patented process using HFC134A is being marketed by AMT as AM-cover. Die-casting companies in the US and UK are using it and, according to AMT’s Gordon Dunlop, testing under the auspices of the US Environmental Protection Agency has shown that AM-cover reduces global warming emissions from this process by around ninety-eight per cent.

In the aluminium industry a lot of waste is melted again and recycled. Even so, there is work to be done. “We are looking at ways to reduce waste, increase yield and decrease the energy consumption used to make components,” said StJohn.

The CSIRO’s work in this area includes the development of a new eco-friendly permanent mould casting process for magnesium alloys called T-Mag, which it is commercialising in a joint venture with three Australian companies.

“In the lab we have demonstrated that we can make complex product geometries such as wheels and engine blocks, even using sand cores as needed,” said Barry Finnin.

“The technology is attractive because melting and casting are all enclosed under a cover gas and there is very little waste – as low as two per cent process scrap on the castings. T-Mag complements some of the magnesium alloy technology offered by AMT, too.”

The CSIRO is also helping CAST come up with a methodology for product lifecycle assessments and analysis, as part of its project review process. “It’s going to help companies target where they can get a cost benefit along with environmental improvements. It will be interesting to see from a cultural point of view, in a few years time, what impact this has had on our researchers,” said StJohn.

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