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Technical Paper

Mechanical Properties of High Performance Aluminum Castings

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.
Technical Paper

MADI™: Introducing a New, Machinable, Austempered Ductile Iron

A unique combination of metal chemistry and heat treatment has lead to the invention of MADI (machinable austempered ductile iron). Two MADI grades have been developed: chassis grade for fatigue critical applications and crankshaft grade for high strength applications. The mechanical properties, fatigue life of components and quantitative machinability data of MADI, regular ADI and pearlitic ductile iron are presented. Since the design strength of MADI is 50-100% higher than currently used as-cast ductile irons, significantly lighter weight components can now be produced. MADI may lead the way to the increased use of low cost, ductile iron castings since, for the first time, both improved mechanical properties (fatigue resistance or high strength) and improved machinability have been obtained.
Technical Paper

Lightweight Iron and Steel Castings for Automotive Applications

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.
Technical Paper

Lightweight Crankshafts

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.
Technical Paper

Induction Hardened Ductile Iron Camshafts

The General Motors L850 world engine uses an induction hardened, ductile iron, camshaft. Unlike most induction hardened camshafts that are machined first and then hardened, this camshaft is deep hardened first and then machined. Using this process, the beneficial compressive surface residual stresses are extremely high. During the development of the L850 camshaft, the casting process was optimized to produce material of sufficient quality to resist quench cracking during the hardening process and to resist mechanical cracking during the machining process. Retained austenite content, residual stress profiles, hardness, microstructure and chemical composition were all characterized and optimized. This paper reviews the material and process development for this unique automotive application.
Technical Paper

Evaluation of Structural and High-Temperature Magnesium Alloys

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.
Technical Paper

Evaluation of High Temperature, Cast Magnesium Alloy, Front Engine Covers

A variety of new magnesium casting alloys specifically designed for high temperature applications are currently available. However, there is little published data from component tests or from test specimens sectioned from component castings. In this study, the mechanical properties (tensile, bracket thread integrity, bracket distortion and fastener/attachment point acceptability) of front engine covers made from three magnesium alloys (AZ91D, AJ62x and MRI-153M) and from aluminum alloy 380 are presented.
Technical Paper

Evaluation of Direct Quenched and Conventionally Heat Treated SAE 1046 Steel Axle I-Beam Forgings

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.
Technical Paper

Effect of Bolt CTE on Bolt Load Retention for Mg Alloys

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.
Technical Paper

Bolt Load Compressive Stress Retention Testing of Magnesium Alloys

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.
Technical Paper

Austempered Ductile Iron Castings for Chassis Applications

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.
Journal Article

Advanced Lost Foam Casting Processes and Materials

The lost foam casting process (LFCP) is a near-net shape casting process. This process is the most energy efficient casting process available. “Foundry Management and Technology” magazine analyzed the lost foam process and reported a 27% energy savings, a 46% improvement in labor productivity and 7% less material usage compared to other casting processes. The LFCP produces high value parts by combining multiple components into single castings, improving energy efficiency by achieving better metal yields, reducing materials consumption by eliminating cores, providing minimal post casting processing and improving as-cast dimensional accuracy. All of these process features reduce the total energy consumed during manufacturing.