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Austempered ductile iron (ADI) castings provide a unique combination of high strength and toughness coupled with excellent design flexibility for chassis applications. This paper describes the development of the upper control arm for the 1999 Ford Mustang Cobra as an austempered ductile iron casting. The full service development process used is described from initial design through finite element analysis (FEA), design verification, casting production, heat treatment, nondestructive evaluation and machining. To achieve significant weight savings, an austempered ductile iron casting was chosen for this application instead of an as-cast SAE J4341, Grade D4512 ductile iron casting or a steel forging. This is believed to be the first application of an austempered ductile iron casting for a safety critical, automotive chassis application.

Elevated temperature bolt load compressive stress retention testing of four high temperature magnesium alloys (AJ50X, AJ52X, AS21X and AE42), two structural magnesium alloys (AM50A and AM60B), one aluminum alloy (383) and one gray iron alloy were performed at the INTERMET Technical Center over a period of about one year. Artificial aging of some of these alloys during testing was observed. The effect of a heat treatment designed to thermally stabilize the microstructure was evaluated and determined to significantly improve magnesium performance and degrade aluminum performance. This paper documents the test procedure and the test results.

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.

SAE 1046 steel axle I-beam forgings produced by the direct quench method and the conventional reheat and quench method were examined. Impact and tensile specimens obtained from sections of two direct quench and one conventional reheat and quench axle I-beams were tested. These data were correlated with hardness and microstructure to determine the relationship between microstructure and properties. The microstructure of direct quenched beams is coarse grained with a martensite case and bainite core. In contrast, the microstructure of conventionally heat treated beams is fine grained with a martensite and/or bainite case and pearlite core. Tensile and impact properties indicate that direct quenching is an acceptable alternative to the conventional reheat and quench process. Fatigue testing of direct quenched beams is currently being performed.

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.

Squeeze casting and semi-solid metal forming produce aluminum castings with exceptional properties. This paper compares the mechanical properties and microstructures of a production component processed by a variety of casting processes and heat treatments. Note, in all cases, the current insert tool used for squeeze casting was adapted to be utilized in the various semi-solid metal forming processes. The results showed that semi-solid metal forming produced consistently better mechanical properties compared to squeeze casting. Defects, primarily oxide films, were determined to be responsible for the lower and less consistent properties of the squeeze cast material.