Morphology of dendritic bicrystals in hypereutectic aluminum-silicon alloys hardened in pressure casting

Hypereutectic silumins that possess a low coefficient of thermal expansion, high wear resistance and hightemperature strength, and excellent casting properties are an indispensable structural material for the production of cylinders, cylinder heads, pistons, and other parts of internal combustion engines. In pressure casting of hypereutectic alloys the structure formed is more complex than in hardening in metal or sand molds. In addition to excess silicon crystals and the eutectic such structures contain crystalline formations that are inadmissible in an equilibrium structure. The nonequilibrium components of the structure can transform during operational heatings due to redistribution of the alloying elements, which will inevitably affect the size precision of parts. However, the published data on the structure of hypereutectic silumins formed in pressure casting are quite scarce. The present paper is devoted to the special features of silumins manufactured by pressure casting.