Economical and environmental factors in light alloys automotive applications

The effects of mass reduction through substitution of ferrous components by equivalent Al or Mg alloy components on the vehicle's cost and CO2 emissions are discussed using M.F. Ashby's penalty functions and exchange constants method. The viability of substitutions of At alloys by Mg alloys is also considered. Substitutions of cast components at equal volume and panels and beams at constant stiffness are considered. Substitutions of cast ferrous components are economically the only viable ones in terms of the CAFE (Corporate Average Fuel Economy) liability, although the cost penalty can be fully offset by the gasoline savings over the life of the car for most other forms of light alloy substitutions. When primary alloys are used, the gasoline savings over the lifetime of a lighter car offset the CO2 footprint of Al alloys in all cases. Because of their larger CO2 footprint, the environmental feasibility is somewhat restricted for electrolytic Mg, and more so for Mg produced by the Pidgeon process. Due to their high recyclability, Al casting alloys have a significant environmental advantage over all other light alloy applications. Viable substitutions of existing Al components by Mg components are largely restricted to castings of electrolytic Mg.