Is there an environmental advantage of using magnesium components for light-weighting cars?

Light-weighting of automobiles has been a key issue for reasons of meeting stringent requirements on greenhouse gas (GHG) emissions. Weight reduction in cars can be achieved by design optimisation and/or direct substitution of heavier steel components with lighter metals. In respect to direct substitution, aluminium alloys are widely used and accepted by the industry, though magnesium is lighter than aluminium and has superior casting properties that make it attractive. This apparent advantage of using magnesium has to be assessed in light of the environmental burden created in the entire life cycle of the magnesium component, including the fuel savings in the use stage. This study reports on such an assessment, using lifecycle assessment (LCA) of an engine block (EB) that can be substituted for light-weighting. At each stage of production, the impact of adopting more sustainable technologies (such as the use of low-impact cover gas for protecting magnesium melt from oxidation in place of high-impact sulphur hexafluoride) are taken into account. The environmental performance of the magnesium EB is compared with functionally equivalent blocks made from aluminium and conventional cast iron and the new compacted graphite iron (CGI).