Development of a Novel Magnesium Alloy for Thixomolding of Automotive Components

Magnesium (Mg) alloy die-castings are increasingly used in the automobile industry to achieve cost-effective mass reduction, especially in systems where multiple components can be integrated into a single thin wall die casting. However, there are several component quality restrictions in thin-walled Mg die-castings, including variability in dimensional accuracy, part-to-part variation in mechanical properties, and porosity in the final part, which has limited the continued growth of die-cast components in the automobile industry. An alternative to die-casting is the process of thixomolding. While the die-casting process relies on filling a mold at high speeds with the alloy being in the completely molten state, the thixomolding process fills a mold with a thixotropic alloy in a semi-solid slurry state at a temperature between the liquidus and solidus temperatures. Ideally, the material should be ~30–65% solid rather than being completely liquid at the beginning of the injection process. Advantages of the thixomolding process over die-casting include a finer grain structure, lower porosity, improved dimensional accuracy, improved part-to-part consistency, improved mechanical properties (particularly ductility in the component), the ability to reduce wall thickness for mass savings, and longer tool life due to lower process temperatures. The objectives of this project which is a CRADA between Oak Ridge National Laboratory, FCA US LLC, and Leggera Technologies are to develop one or more novel Mg alloys more suitable for the thixomolding process with the potential improved room temperature strength and ductility when compared to current die-casting alloys while achieving components with low volume fraction of porosity. The team will develop the alloys, scale promising alloy/s and fabricate prototype component using the new alloy, and evaluate properties of the material when fabricated into the component.