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The method of quenching-microstructural analysis, the so-called "stop-quenching", was used to study phase transformations during crystallization of the AK7 casting alloy of the Al-Si-Mg system. The alloy is smelted from scrap and waste, therefore it contains a large amount of impurities, including iron, copper. It was found that the formation of the structure of the AK7 alloy is carried out in the course of the following reactions: 1. Р → Аlα. 2. P → α-(Fe, Mn) 3Si2Al15 + Alα.3. P → β-FeSiAl5 + Alα. 4. P + β-FeSiAl5 → α-(Fe, Mn, Cu)3Si2Al15. 5. P →β-FeSiAl5 + Si + Alα. 6. P → β-FeSiAl5 + α-(Fe, Mn, Cu)3Si2Al15 + Si + Alα. At the last stages of crystallization, eutectics are formed, which include phases with magnesium and copper: Mg2Si, π-FeMg3Si6Al8, W-Cu2Mg8Si6Al andθ-CuAl2. The transformation P → β + Si + Alα is realized both by the mechanism of cooperative growth of the β, Si, and Alα phases, and by the formation of double eutectics: P → Si + Alα and P → β + Alα, which grow simultaneously in the same temperature range from various centers of crystallization. The four-phase eutectic transformation P → β + α + Si + Alα is carried out according to the type of double or triple eutectic reactions: P → Si + Alα; P → α + Alα; P → β + Alα; β + Si + Alα. The main iron-containing phase in the AK7 alloy is the needle-shaped intermetallic compound β-FeSiAl5 - a stress concentrator, which leads to a decrease in mechanical properties. In this work, the neutralization of the harmful effect of iron was carried out by treating the melt with a unipolar pulsed electric current, under the influence of which the cluster structure of the melt changes. During crystallization, instead of β, a branched phase α is formed. The ratio of intermetallic compounds β and α depends on the processing modes. With optimal parameters of density and current frequency, at which the volume fraction of the branched phase α is the largest, the strength of the AK7 alloy increases by 32.1%, the hardness by 16.7%, and the relative elongation by 2.5 times, bringing its mechanical properties closer to the primary alloy AK7h. Keywords: aluminum-silicon alloys, phase transformations, iron-containing intermetallic compounds, growth forms, treatment of the melt with an electric current.

metaloznavstvo ta obrobka metalìv

Phase transformations during the crystallization of the AK7 alloy, neutralization of the harmful effect of iron by treating the melt with a pulsed electric current