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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.

The new patented high temperature alloy AJ52x has the potential to replace the aluminum alloy 380 in power-train applications. The creep properties of AJ52x are similar to the aluminum alloy A380 and overall mechanical performance is superior to other magnesium creep resistant alloys AS41 and AE42. These properties were presented in the SAE paper 2001-01-0424. The present paper reports on further evaluation of the properties of the AJ52x alloy. Thermal conductivity of AJ52x has been investigated in a range of temperatures from R.T. to 450°C; the thermal conductivity is higher than any die-cast magnesium alloy. So due to the high thermal conductivity, the AJ52x alloy is able to evacuate 75% of energy as the aluminum alloy currently used in the power-train components. These thermal properties have been compared with thermal properties calculated from electrical resistivity at room temperature.

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).