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A specific objective of the European Mg-Engine project is to qualify at least two die cast Mg alloys with improved high temperature properties, in addition to satisfactory corrosion resistance, castability and costs. This paper discusses the selection criteria for high temperature alloys leading to four candidate alloys, AJ52A, AJ62A, AE44 and AE35. Tensile-, creep- and fatigue testing of standard die cast test specimens at different temperatures and conditions have led to a very large amount of material property data. Numerous examples are given to underline the potential for these alloys in high temperature automotive applications. The subsequent use of the basic property data in material models for design of automotive components is illustrated.

In addition to the creep properties, the fatigue properties are essential for the design of a power-train component in Mg which is operated at elevated temperatures. In case of the new BMW I6 composite Mg/Al crankcase using the AJ alloy system, material testing focused on both subjects. The basic mechanical properties were determined from separately die cast samples and also from samples machined out from high-pressure die cast components. Tensile, high cycle fatigue properties, low cycle fatigue and crack propagation properties were established and analyzed within the technical context for power-train applications reflected in the temperature and load levels. The aspects of mean stress influence, notch sensitivity and crack propagation are evaluated to estimate the performances of the AJ62A alloy system.

AJ alloy is used with a new Aluminum-Magnesium Composite Design, which is an innovative approach to lightweight crankcase technology. The component is manufactured using high pressure die cast process. A wide range of chemical compositions was used to develop a good understanding of the behavior of this alloy system (castability, thermophysical, mechanical, microstructure). The basic mechanical properties were determined from separately die cast samples and also from samples machined out from high pressure die cast components. Tensile, creep, bolt load retention/relaxation and high cycle fatigue properties were established and analyzed using multivariate analysis and statistical approach. This methodology was used to select the optimal chemical composition to match the requirements. The sensitivity of the alloy to heat exposure was investigated for both mechanical properties and microstructure.

Magnesium die casting alloys for elevated temperature applications are coming of age. Several research centers and companies have been working on alloy systems based on alkaline earth and rare earth alloying additions to push the limits for the creep performance of Mg-based die casting alloys. Noranda's Mg-Al-Sr based alloys have shown superior creep performance and high-temperature performance at temperatures as high as 150-175C and stress levels of 50MPa - 70MPa. The most recent alloy formulation AJ62x (Mg-6Al-2Sr) has in addition shown excellent castability, and superior hot-tear resistance. Based on these attributes AJ62x is positioned well for applications such as transmission cases and oil pans. In this paper, the mechanical properties (creep and tensile) of AJ62x are presented. The high ductility of the AJ62Lx version is an added advantage for this alloy.

For environmental reasons, automotive improved fuel efficiency is becoming increasingly important for OEM's. However, consumers are also demanding more in terms of added comfort and safety features. To meet these conflicting requirements, OEM's are turning to the increased usage of light-weight materials, such as magnesium alloys, for automotive components thus allowing for improved fuel efficiency while maintaining the ability to add extra comfort and safety features. Due to the presence of large castings in the power-train, as well as the significant mass in the front of a vehicle, high temperature magnesium alloys that can meet the service requirements of these components are under investigation. The types of mass reduction applications for these alloys include transmission cases, covers and other structural components. Diecasting, because of its high productivity, is the preferred manufacturing process for these types of components.

A new family of heat-resistant alloys has been developed by Noranda Inc. This new alloy system is based on the Mg-Al-Sr system. The three compositions evaluated in this system, namely (Mg-Al-Sr)1 (Mg-Al-Sr)2 and Mg-Al-Sr)3, hereafter referred A1, A2 and A3 demonstrate excellent creep and mechanical properties in the 150°C to 175°C temperature range. They possess excellent salt-spray corrosion resistance, comparable to AZ91D and AM type alloys and is superior to AS41 and the aluminum alloy A380. This combination of properties makes these alloys suitable for automatic transmission casing, crankcase, oil pump body, oil pan, belt pulley, cylinder cover, engine fan applications as well as other under-the-hood components. The present paper summarises the mechanical and corrosion properties and die casting of the alloys. The boit-load-retention test results are also discussed. Diecastability has been improved using a modified alloy composition (A4).