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| CSIRO | SOLVE | Issue 5 Nov 05 | |
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ARTICLE
LIGHT METALS: Travel Light
Graeme O'Neill reports on T-MagTM, an Australian light metals development that is leading towards increased use of magnesium in motor vehicle components. With oil prices imposing new pressures on vehicle manufacturers to find further weight savings, magnesium alloy components – even engine blocks – appear set to find an economically viable niche as an alternative to steel, iron and aluminium. A team of research engineers headed by Dr Thang Nguyen, from CSIRO Manufacturing and Infrastructure Technology (CMIT), has developed a new permanent-mould magnesium casting technology that promises to tame the featherweight but highly reactive metal for mass-production of vehicle components.
Barrie Finnin, leader of CMIT’s Manufacturing Technologies for Transport Theme, says T-Mag can cast lightweight magnesium-alloy engine blocks that will be only two-thirds the weight of current aluminium alloy blocks – a prospect that is already arousing the interest of high-performance car manufacturers in Europe. It will also be possible to cast high-integrity magnesium alloy wheels. Current casting technology cannot produce wheels of sufficient integrity to be safe and practical at an acceptable cost. T-Mag was developed through CSIRO’s Light Metals Flagship. A pilot-scale unit built for research and development has already produced successful demonstration castings, including alloy wheels, and magnesium alloy blocks for a 750cc, water-cooled, motorcycle engine will be cast shortly. Oil price rises are forcing vehicle manufacturers to pursue further weight savings through use of strong, lightweight magnesium alloy components for powertrain and load-critical applications. But such applications are not economically viable with current casting technologies, Mr Finnin says. HP casting is plagued by low as-cast yields: typically, it takes 6–7 kg of metal to produce a 3.5 kg casting. The unused metal cannot simply be recycled because remelting creates oxides and intermetallic compounds, and both the initial melting process and remelting the scrap consume large amounts of energy. “T-Mag requires only 3.7 kg of alloy for a 3.5 kg casting. This reduces recycling and energy use, and saves a lot of melt cost,” Mr Finnin says. T-Mag is a permanent-mould casting process that requires neither high pressure nor a vacuum to fill the die. The die fills smoothly from the bottom, minimising air entrapment and oxidation, and produces ‘X-ray’-quality castings that are virtually free of defects. The T-Mag casting machine successfully combines melting and casting in a single compact unit. The unit is hermetically sealed, making it easy to maintain the cover gas, which protects the magnesium from oxidation and minimises gas usage.
Due to highly effective cover gas protection, T-Mag castings have a natural surface lustre, making them visually attractive. The castings can be heat treated and welded. The traditional processes, gravity and low-pressure casting, deliver either low yields or have a problem maintaining the expensive and greenhouse-intensive cover gas without excessive consumption. Mr Finnin says CSIRO will now seek industry partners to commercialise T-Mag: “We’ve only just started to talk to the market about the technology, which is so new that the patents aren’t even published yet.” The simplicity of T-Mag’s design keeps tooling and operating costs in the low to medium range, comparable with those for gravity and low-pressure die casting of equivalent components. A single operator could supervise up to four machines operating continuously. CSIRO believes that T-Mag’s technical and economic attributes will give it a competitive advantage over current casting technologies, and remove many obstacles to the economic production of high integrity magnesium parts. T-Mag could be used with a new magnesium alloy called AM-SC1 for engine blocks. Current magnesium alloys lack the mechanical properties required to operate for long times at high temperatures. However, the new AM-SC1, developed in Australia by a team including researchers from CSIRO, University of Queensland, Monash University and Australian Magnesium Corporation (now Advanced Magnesium Technologies – AMT) under the Cooperative Research Centre for Cast Metals Manufacturing (CAST), is sufficiently robust for engine blocks. Powertrain systems developer AVL in Europe has successfully trialled an engine made from the Australian alloy in a Volkswagen Lupo sedan. The alloy is being commercialised through AMT. APPLICATION A permanent-mould technology has been developed that produces magnesium casts free of the porosity and other defects that have hindered the metal’s use in the past For further information contact: |
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The
technology, called T-MagTM, consistently produces high-integrity
magnesium alloy castings from permanent moulds, free of the porosity and other
defects that have hindered use of magnesium in the past.
In permanent-mould casting, disposable sand cores are used to produce complex hollow features inside castings, for example the cooling water passages in engine blocks. The high injection pressure and velocities in HP die casting make sand cores unusable, and consequently it is difficult to produce these features. T-Mag, however, can easily incorporate sand cores to produce them.
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