Semi-solid solidification of alloys is a complex multi-physics problem involving phenomena such as solid–liquid phase transformation, heat and solute transport, liquid flow, solid motion, solid–solid interaction, solidification shrinkage, solid deformation, and porosity formation. These phenomena have both negative and positive effects on the solidified products. Negative effects include introduction of solidification defects such as microsegregation, macrosegregation, porosity, and solidification cracking during solidification, while the plausible positive effects include microstructure refinement due dendrite fragmentation and semi-solid deformation. Although these phenomena have been experimentally observed during semi-solid solidification, numerical simulations are essential to elucidate their detailed mechanism and to control the solidification microstructures with high accuracy. Accordingly, we attempted to explain the semi-solid solidification using phase-field method as a major numerical model. In this talk, the multi-phase-field modeling and simulation of semi-solid solidification will be presented, with a particular focus on semi-solid deformation [1, 2]. Because such simulations are computationally expensive, we accelerated the simulations by parallel computing using multiple GPUs [3]. REFERENCES [1] N. Yamanaka, S. Sakane, T. Takaki, 2D multi-phase-field lattice Boltzmann simulations of semi-solid shear deformation, IOP Conference Series: Materials Science and Engineering 1274(1):012045, 2023. [2] N. Yamanaka, S. Sakane, T. Takaki, Multi-phase-field lattice Boltzmann model for polycrystalline equiaxed solidification with motion, Computational Materials Science 197:110658, 2021. [3] T. Takaki, Large-scale phase-field simulations for dendrite growth: A review on current status and future perspective, IOP Conference Series: Materials Science and Engineering 1274(1):012009, 2023.