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Metal Casting Technologies : June 2007
TECHNICAL FEATURE www.metals.rala.com.au 26 Researchers with CSIRO's (Australia) Sustainable Ecosystems division, they have been looking at total GHG emissions or environmental load at 4 stages of manufacture. This is otherwise known as cradle-to-grave or the Life Cycle Analysis (LCA): production of ingots, manufacture and assembly of components, use in cars and recycling/disposal. They tracked these along with other factors or variants to derive a total of seven engine block (EB) 'product systems'. Focusing on engine block production, Tharumarajah and Koltun showed that use of sustainable technologies for magnesium EB production, as opposed to conventional methods, resulted in a GHG emissions decrease of approximately 55%. (See Table 4). Certainly good. But would this order of magnitude transfer when comparison was made of magnesium, aluminium and cast iron EBs? (See Figure 1). In terms of environmental load, magnesium provided better results than aluminium and certainly cast iron. However, this improvement is diminished or lost, even with the use of sustainable technologies, when the source and process utilised is considered. In this instance, China's magnesium production method, involving the use of thousands of low cost, coal-fired kilns (and previously examined in this magazine by this writer), provides increased GHG emissions that offset any advantages that magnesium might otherwise have had over the entire aluminum components production process. Given this, it appears that aluminium, as the 'metal of choice', will not have this general view changed about it any time soon. ● Table 4: Summary of total Cradle-to-Grave GHG Emissions of Magnesium Engine Block GHG Impact kg CO2-equ/EB Conventional Improved Mg supply* 599 400 Mg alloy making 1216 125 Manufacturing and assembly 633 49 Use 1677 1677 Total 4125 2251 * 70% primary, 30% secondary Mg Source: Tharumarajah, A. and Koltun, 2007. MAGNESIUM ENGINE BLOCK The engine block is the heaviest single component in a car and the block made from magnesium alloy represents an example of light-weighting heavier automobile components by direct substitution. It is also representative of advanced and specialised magnesium alloy making technologies that is competitive with both cast iron and aluminium engine blocks. While aluminium engine blocks have been slowly replacing case iron blocks and saving around 66% in weight, magnesium equivalents takes this reduction further to around 75%. Other benefits of using magnesium can be its high shock and dent resistance and its greater ability than aluminium to dampen noise and vibration. The magnesium EB for a V6 3.0 litre engine weighs 30kg compared to 39kg and 64.6kg respectively for an aluminium and cast iron block. Source: Tharumarajah, A. and Koltun, 2007. Figure 1: Comparison of Life Cycle GHG Impacts for Different Engine Blocks References: Tharumarajah, A. and Koltun, P. Is there an environmental advantage in using magnesium components for light-weighting cars? Special Issue: The Automobile Industry and Sustainability, Journal of Cleaner Production, Volume 15, Numbers 11-12, 2007. Email: firstname.lastname@example.org