5th International Conference on Advances in Solidification Processes (ICASP-5) 5th International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining (CSSCR-5)

During the solidification of ternary eutectics, three solid phases form simultaneously from the melt. One system often employed to study this complex multi-phase solidification behavior is ternary eutectic $Al$-$Al_2Cu$-$Ag_2Al$. In this system the solubility of silver in the α-Al phase decreases by approximately 50% in a range of less than 20 K below the ternary eutectic temperature. This diffusion-controlled solubility shift is obvious from a comparison of microstructure in a normally processed sample with microstructure from directly behind a quenched interface, in which the solubility shift did not have time to occur. There are differences not only in the phase fractions of the three solid phases, but also in the shape of the phase regions and the pattern itself. In order to study the evolution of the microstructure caused by this solubility shift, quenched samples of directionally solidified ternary eutectic $Al$-$Al_2Cu$-$Ag_2Al$ were systematically annealed and the resulting post-solidification effects were studied with scanning electron microscopy for two different solidification patterns. The results show that the adjustment of the phase fractions takes place much faster than the rearrangement of the shape of the phases. This shape evolution is strongly influenced by the anisotropic interface energies, resulting in more straight solid-solid interface boundaries instead of the the competing curvature reduction. The outcomes of this work demonstrate that in order to obtain a more complete understanding of directionally solidified ternary eutectic $Al$-$Al_2Cu$-$Ag_2Al$, both the solidification and the subsequent post-solidification processes must be considered.