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The automobile and light truck industries are increasingly using more magnesium castings in structural and high-temperature applications. Unfortunately, the castability and mechanical behavior of the commonly used alloys have not been compared under similar conditions. Further, new alloys intended for high-temperature applications (Noranda AJ50X, Noranda AJ52X, Hydro AS21X, Dead Sea Magnesium MRI-153) are being promoted, but their casting and mechanical behavior are not well known. Therefore, five high temperature magnesium alloys (AJ50X, AJ52X, AS21X, MRI-153 and AE42), two magnesium alloys more commonly used for structural applications (AM50A and AM60B) and one aluminum alloy (383) were melted and cast at the INTERMET Monroe City Plant (a production high-pressure die casting facility). The castings were subsequently evaluated at the INTERMET Technical Center and outside testing laboratories.

The automobile and light truck industries are increasing considering the use of magnesium castings in structural and elevated-temperature applications. Unfortunately, the bolt load compressive stress retention behavior of magnesium alloys is unacceptable for most elevated temperature applications. In this investigation, the effects of bolt strength and the mis-match in the coefficient of thermal expansion (CTE) of magnesium alloy AZ91D and the bolt material has been determined for a wide range of materials (martensitic steel, austenitic stainless steel, ductile iron and aluminum alloys). Also, the effect of heat treating the magnesium alloy, the effect of re-tightening the bolts after the first thermal cycle and the maximum load carry capacity of numerous bolt materials were determined. Corrosion was not considered.

The automotive industry continues to look for opportunities to reduce weight and cost while simultaneously increasing performance and durability. Since the introduction of aluminum cylinder blocks and heads, very few “innovations” have been made in powertrain design and materials. Cast crankshafts have the potential to produce significant weight savings (3-18 kg) with little or no cost penalty. With the advent of new, high strength, cast ductile iron materials, such as MADI™ (machinable austempered ductile iron), which has the highly desirable combination of good strength, good toughness, good machinability and low cost, lightweight crankshafts are posed to become a high volume production reality. An extreme demonstration of a lightweight crankshaft is the current use of a cast MADI crankshaft in the 1100 HP Darrell Cox sub-compact drag race car.

The use of aluminum to produce lightweight automotive castings has gained wide acceptance despite significant cost penalties. Lightweight iron and steel casting designs have been largely ignored despite their obvious cost and property advantages. This paper reviews and discusses the following: 1) various processes for producing lightweight iron and steel castings, 2) examples of lightweight components in high-volume production, 3) examples of conversions from aluminum to iron, 4) material properties of interest to designers, 5) examples of concept components and 6) efforts to improve the design and manufacturing processes for lightweight iron and steel castings. In summary, the potential for low-cost, lightweight iron and steel castings to aid the automotive industry in achieving both cost and weight objectives has been demonstrated and continues to expand. In general, however, automotive designers and engineers have not yet fully taken advantage of these technologies.