Creep resistance in Mg-Al-Ca casting alloys

The automotive use of magnesium is relatively low-temperature components. Its use in elevated-temperature structural components such as automatic transmission and certain engine parts requires the development of cost-effective alloys that can meet the performance requirements of these components for elevated-temperature (150 degrees C) strength and creep resistance. This study is on the development of a Mg-Al-Ca alloy system that has good creep-resistanceat 150 degrees C. The increased creep resistance of the alloy is due to the existence of an Al2Ca intermetallic compound in the as-cast structure. Microstructural investigation of the alloy before and after creep loading shows the role of microstructure in creep resistance. The tensile yield strength and the ultimate tensile strength of the alloy at 150 degrees C in the diecast state are equivalent to the more expensive rare-earth containing magnesium alloys. Corrosion resistance of the diecast alloys at 0.11- 0.23 mg/cm(2)/day, as measured through the salt-spray corrosion test, falls in the range of high purity magnesium alloy AZ91D and the rare-earth containing AE42 alloy.