Numerical and experimental investigation of solidification structure in horizontal directional solidification process of Al-Cu alloy

The temperature field and the grain structure of Al-4.5%Cu (mass fraction) alloy in horizontal directional solidification process were predicted using a cellular automaton (CA) coupled with finite-element (FE) model. The Rappaz model was adopted to calculate the nucleation. And the Kurz-Giovanola-Trivedi (KGT) model was used to describe the growth kinetics of dendritic tips. The growth parameters of Al-4.5%Cu alloy were calculated using simplified KGT formula, which was derived based on the pure diffusion condition. The results show that the position of the columnar to equiaxed transition (CET) and the size of equiaxed grains can be simulated reasonably. However, large deviation of the simulated result exists in the chill zone as the movement of nucleus is not considered. The simulated and experimental results prove that the superheat greatly influences the solidification microstructures of Al-Cu alloy. Full equiaxed grains can be obtained if superheat is lower than 20°C, otherwise columnar grains will be observed. When the superheat is above 50°C, the positions of CET are no longer changed.