Equiaxed grains structure formation during solidification of thin plates of aluminum alloys: Insights from multiscale simulations

A multiscale framework combining macroscopic ProCAST and microscopic phase-field-lattice Boltzmann method was developed to investigate equiaxed grain formation and dendritic evolution during solidification of aluminum alloy thin plates. Predicted results show that Sc and Zr promote the formation of stable Al 3 (Sc,Zr) particles, which markedly increase the heterogeneous nucleation density, suppress sustained columnar growth, and favor a fine equiaxed structure. Microscopic simulations reveal that solutal convection can break the symmetric growth of dendrites. Upstream arms are accelerated by compression of the solute boundary layer, whereas downstream arms are suppressed by the solute enrichment. This effect is orientation dependent, and the dendrite with exhibits stronger flow splitting and downstream solute trapping. Dendritic growth in polycrystalline systems shows that a high nucleation density promotes earlier impingement, limits grain coarsening, and accelerates the formation of a compact equiaxed network. Significant pseudo binary solute segregation develops in the terminal solidification region, with Cu showing the strongest segregation and Zn the weakest. Increasing plate thickness reduces the cooling rate, resulting in the increase of the residence time of the residual liquid phase between dendrites. This inevitably exacerbates severe localized microsegregation and increases the susceptibility to terminal solidification defects, namely hot tearing and microporosity. These results provide a numerical basis for microstructure control and process optimization of microalloyed aluminum alloy thin plates.