Small additions of Sc to Al-based alloys have a profound effect on the grain size as well as the texture of the alloys cast in a chill mold. This implies that any macro-segregation during casting could result in significant variation in the microstructure of the component, with attendant variation in properties. Thus it is important to understand the mechanism of grain refinement and texture formation, for a proper design of the casting of the component. Inoculation is widely practiced in the Aluminum industry and very dramatic grain refinement achieved in many alloy systems. Based on this, one is tempted to claim that most of the grain refining effects of Sc additions are linked to the formation of Al3Sc from the melt, acting as nuclei for the fcc-Al solid solution leading to a grain refining action. However, it has been postulated that Sc works by changing the degree of anisotropy of the solid / liquid interfacial energy. It will be useful to determine which of these two mechanisms are dominant in these alloys. Neither the measurement nor the calculation of solid / liquid interfacial energy is trivial.

Under a recently awarded supplement, titled “Modeling Microstructural Evolution during Solidification in Al-Sc Alloys”, to the contract from Air Force Research Laboratory (# FA8650-04-D-5233), UES will construct analytical and phase-field models to examine the role of heterogeneous nucleation and solid/liquid interfacial energy anisotropy on the grain size and texture formation of Al-Sc alloys to help accelerate the development of these alloys for cryogenic and some other applications.

Additional details of this program can be obtained from Dr. "Tap" Triplicane Parthasarthy
(937-255-9809, E-Mail: Triplicane.Parthasarathy@wpafb.af.mil).