Federal State Unitary Enterprise All-Russian Scientific Research Institute of Aviation Materials of Kurchatov Institute (R&D Kurchatov Institute) (Moscow, Russia)¹ ; FSBEI HE Moscow Aviation Institute (National Research University) (Moscow, Russia)²

I. А. Petrov, Leading Researcher^{1, 2}, Candidate of Technical Sciences, Lumen-2007g@mail.ru

FSBEI HE Moscow Aviation Institute (National Research University) (Moscow, Russia)
А. D. Shlyaptseva, Associate Professor of the Educational Center of Institute No. 11 “New Materials and Production Technologies”, Candidate of Technical Sciences

Federal State Unitary Enterprise All-Russian Scientific Research Institute of Aviation Materials of Kurchatov Institute (R&D Kurchatov Institute) (Moscow, Russia)
А. V. Trapeznikov, Leading Engineer
К. А. Vlasova, Leading Engineer
V. А. Duyunova, Head of the Research Unit, Candidate of Technical Sciences

Baikov Institute of Metallurgy and Materials Science, RAS (Moscow, Russia)
D. I. Мayorov, Research Engineer

Modification of Al–Si system cast aluminum alloys is widely used in industry to improve their mechanical properties. Modification results in the refinement of the main structural constituents of silumins, namely the (α + Si) eutectic and α-Al dendrites. In addition to commonly used modifiers such as strontium and sodium, rare-earth elements are considered a promising alternative for the modification of eutectic silicon in silumins. Europium is regarded as an effective modifier for improving the microstructure of silumins. This paper reviews the theories and mechanisms explaining the modification of eutectic silicon in Al – Si system alloys. The mechanisms of eutectic silicon modification by europium are analyzed in the light of experimental data obtained using energy-dispersive X-ray spectroscopy, elemental mapping, and thermal analysis of Al–12 wt.% Si alloy. It has been found that several adsorption-based mechanisms are involved in the refinement of the structure and the alteration of eutectic silicon morphology. These include the twin plane re-entrant edge (TPRE) poisoning mechanism and the impurity-induced twinning (IIT) mechanism, both of which promote the formation of a high density of silicon twins. In addition, melt undercooling is observed, resulting in the formation of a larger number of eutectic silicon nuclei. The crystallization processes in the Al–12 wt.% Si alloy modified with europium have been investigated. The temperatures of phase transformations at different europium concentrations have been determined. Europium modification broadens the crystallization interval due to a decrease in the solidus temperature. The highest mechanical properties have been achieved at a europium content of 0.11 wt.% (UTS = 161.1 MPa and δ = 7.3%). The duration of the europium modification effect in the melt has been determined to be up to 300 min. The persistence of the modi fying effect is attributed to the physicochemical properties of europium and the thermodynamic processes governing its interaction with the melt. The influence of europium on porosity has also been studied. An increase in europium content in the Al–12 wt.% Si alloy leads to a slight increase in gas porosity.
This work was supported by the Common Use Center “Climatic Testing” of the Kurchatov Institute Research Center.

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