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Metal solidification is the phase transformation in which a liquid metal or alloy cools below its liquidus temperature and crystallizes into a solid, involving the nucleation of stable solid grains from the undercooled liquid and their subsequent growth through the moving solid–liquid interface ^[1]. The process is governed by the coupling of heat flow, solute redistribution, and interface morphology: as the solid advances, latent heat must be removed to the surroundings, and rejected solute accumulates in the liquid ahead of the interface, producing constitutional undercooling that destabilizes a planar front into cellular or dendritic growth ^[2]. Solidification is distinguished from simple freezing of a pure substance by the fact that alloys solidify over a temperature interval between the liquidus and solidus, partition solute between the phases, and develop a microstructure—grain structure, dendrite arm spacing, and segregation—whose scale is set by the local thermal gradient and growth velocity ^[1]. The defining physics is the motion of a solid–liquid interface driven by heat extraction and the resulting morphological instability, which determines as-cast structure, segregation, and defect formation, rather than being a mere transition from liquid to solid at a single melting point ^[2]. It comprises nucleation and growth controlled by undercooling, heat transfer, and solute transport ^[3].