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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

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

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.