The Department of Energy has aggressive targets to reduce vehicle weight in order to improve fuel economy which requires addressing all components including castings while maintaining affordability. Casting imperfections are a limitation to achieving this. Our proposal is to provide a method to reduce casting imperfections in ductile iron using the lost foam casting process such that it can be used in thinner sections and enable casting redesigns. The objective of the Phase I project is to show that ductile iron can be cast at 3 mm or less thickness while eliminating defects that currently prevent this. The imperfections addressed include massive carbides, porosity, high nodularity, and surface defects. The imperfections are prevented through the use of the lost foam casting process and optimizing process parameters. In Phase I, a variety of casting trials will be conducted to determine the necessary ranges for pour temperature and chemistry and compare them to when massive carbides, porosity, high nodularity, and surface defects form. Trials will be used to determine the range of feasible pour temperatures and chemistry. Methods of smoothing the lost foam surface to prevent surface defects that negativity affect strength and fatigue also will be investigated.Finally, the fluidity of the molten iron at thinner section sizes will be measured to determine the necessary gating design and maximum process capabilities. The public benefits are cost savings as fuel efficiency targets are achieved by having lighter weight casting designs. In Phase II, the heat-treated variation, austempered ductile iron will be studied. Austempered ductile iron has a superior combination of cost, density, and strength but its use is limited due to the current defects that occur at thin sections. If thinner ductile iron and austempered ductile iron can be achieved, they can be used to replace existing iron, steel, and aluminum castings. Since ductile iron is a more affordable material compared to aluminum and steel, it has a low or even negative $/lb-saved which saves the public money while helping meet fuel efficiency standards.
