Influence of conditions of crystallization and thermal processing on morphology of silicon phase in hypereutectic silumin АК18 is studied. It is shown that abnormal quasi-eutectoid structure on the basis of branched dendrites of the silicon phase, having dispersed structure is formed in the bottom of a pig at the concentrate of silicon more 15% in crystallization process. The given structure is capable to transformation of separate compact inclusions in baking process. Remelt of the pig and the subsequent crystallization lead to anomaly disappearance in morphology of silicon phase and to formation of usual hypereutectic structures with primary crystals (Si) in the form of polyhedrons. Basic possibility of realization of structure with a high volume fraction of silicon particles at their small sizes (2–4 microns) is shown.