Effect of the Melt Cooling Rate on the Structural-Phase State of the Al–Si Alloy Doped with Metals

The paper presents the results of a study of the microstructure, elemental and phase compositions of the eutectic alloy (wt %): Al–12.5 Si–0.8 Mg–0.4 Mn–0.7 Fe–0.9 Ni–1.8 Cu. A comparison of the microstructure of the alloy obtained at melt cooling rates of 10² and 10⁵ K/s is made. It is shown that an increase in the melt cooling rate leads to the refinement of structural components, a decrease in the volume fraction of primary α-Al dendrites, an increase in the volume fraction of a mixture of eutectic silicon and aluminum, and a decrease in the silicon concentration in the interdendritic space from 23 to 13 wt %. Using energy-dispersive analysis and X-ray diffraction analysis, it was revealed that inclusions of intermetallic compounds Mg₅Si₆, Al₁₇(FeMn)Si₂, and Al₃(CuNi)₂ are formed at melt cooling rates of 10² and 10⁵ K/s. A mechanism of the formation of a layered microstructure of an eutectic alloy is proposed. An explanation for the formation of X-ray amorphous nanosized particles in the foil layer adjacent to the mold is given.