Coarsening Kinetic of Aluminium-Scandium and Aluminium-Zirconium-Scandium Precipitates

Al-Sc-based alloys exhibit a unique combination of high strength and plasticity, corrosion resistance and weldability [1-4]. Mechanical properties of these alloys depend on their microstructure and their phase composition, so its knowledge provides an opportunity to improve material properties by thermal treatment. The addition of Sc to aluminium is a very effective mean to form small ordered L12 precipitates which increase the tensile strength and inhibit recrystallisation.. Recently it was demonstrated that these precipitates remain coherent up to sizes of. 40 nm in diameter [1]. To further improve the properties of Al-Sc alloys, the effects of ternary additions to Al-Sc alloys have been investigated [5]. Previous studies have shown that addition of Zr in Al-Sc alloys improve the stability these systems to coarsening [20-21]. It was determined that Zr segregates to the α-Al/Al3Sc heterophase interface and acts as a barrier for the diffusion of Sc across the interface, which leads to a lowering of the coarsening rate [22-23] as compared to binary Al-Sc alloys. Harada and Dunand [7] shown that zirconium addition reduces the lattice parameter of Al3Sc and concomitantly the inter- face free and elastic strain energies. The purpose of this work is to study the microstructural evolution in binary Al-Sc and in ternary Al-Sc-Zr alloys. Phase field approach based on the Cahn-Hilliard and Ginzburg-Landau equations [12-18] has been used. It is shown that L12 particles have a heterogeneous structure with the Al3Sc core surrounded by a Zr-rich shell .