Formation of the microstructure of rapidly solidified hypoeutectic Al-Si alloy

The authors present results on microstructure and component distribution of industrial hypoeutectic Al-Si alloy, obtained at cooling rates of 102 and 105 K/s. Bulk samples are characterized by a heterogeneous structure that represents the large dendrites of a solid solution based on aluminum, and a eutectic lamellar mixture of aluminum and silicon filling the interdendritic spacing. The rapidly solidified foils are characterized by more dispersive microstructure and chemical homogeneity; however, they have a microstructure layering in the form of a cross-section. It was established that crystallization proceeds according to the fundamentally different mechanisms: near-equilibrium crystallization for bulk samples, and chemically partitionless crystallization for rapidly solidified foils.