The possibility of replacing the piston eutectic alloy of the Al-Si-Cu system AK12M2MgN, which was produced at OJSC "Zaporizhsky Aluminum Combine" from primary aluminum, with AK12M2MgNZH with an increased iron content, which will allow expanding the raw material base of production due to the use of scrap and waste. It is proposed to solve this problem by introducing into the technological process of processing the melt with a unipolar pulsed electric current during pouring according to specially developed modes. To investigate this possibility, experiments were conducted on the effect of electric current on the microstructure, phase composition of AK12M2MgN and AK12M2MgNZH alloys and their mechanical properties at temperatures of 20 oC and 300 oC. The melt was treated with an electric current in the following modes: electric current density (j) 100 - 400 A/cm2, pulse frequency (ν) 50 - 2000 Hz. The phase composition of alloys is considered. It is shown that the main iron-containing phase of the AK12M2MgN alloy is (Fe,Mn)3Si2AI15 (α) in the form of branched eutectic crystals. The acicular β-FeSiAI5 phase is practically absent. Unlike AK12M2MgN, the composition of AK12M2MgNZH alloy includes β-FeSiAl5 intermetallic and primary coarse crystals of (Fe,Mn)3Si2AI15 phase. After treatment of alloys in the liquid state with pulsed electric current in different modes, their microstructure and phase composition change significantly. The degree of differentiation of eutectic components increases. In particular, the linear size of eutectic silicon crystals, depending on the density and frequency of the electric current, decreases by 2-3 times. Primary crystals of the intermetallic (Fe,Mn)3Si2Al15 are formed in the AK12M2MgN alloy, which in cross-section have the appearance of compact, close to globular crystals. X-ray spectral studies have shown that despite the same crystallographic structure, eutectic and primary crystals of the (Fe,Mn)3Si2Al15 phase differ in the higher concentration of iron, manganese, copper and nickel in the latter. In the composition of the AK12M2MgNZH alloy, there is practically no acicular intermetallic β-FeSiAl5, the formation of which is one of the main reasons for the decrease in mechanical properties. Similar to the AK12M2MgN alloy, compact crystals of the primary phase (Fe,Mn)3Si2Al15 and a significant amount of the π-FeMg3Si6Al8 phase appear. Such structural changes ensured an increase in the mechanical properties at 20 and 300 oC of both the AK12M2MgN alloy and AK12M2MgNZH. The highest properties of both alloys are achieved at j = 100 A/cm2; ν = 1000 ‒ 2000 Hz. The characteristics of mechanical properties increase from 25 % to 40 %. The structural and phase changes caused by the processing of the AK12M2MgNZH melt with an electric current according to experimentally established modes provide it with mechanical properties at the level of the AK12M2MgN alloy with several higher heat resistance indicators. In addition, treatment of the melt with electric current allows to reduce the consumption of sodium-potassium fluxes by 15-50%; time of heat treatment for T1 from 10-12 hours. up to 2-3 hours.

High-strength cast aluminum alloy AM4.5Kd (VAL10) belongs to the Al-Cu system and due to the combination of a high level of physical, mechanical and operational properties, is widely used in high-tech industries and technology: aviation, space, shipbuilding, transport. Products from the alloy AM4.5Kd (VAL10) are obtained by all known methods of casting (in sand molds, in a chill mold, under pressure), differing in cooling rates. This has a significant effect on the structure and properties of the alloy, not only in the as-cast, but also in the heat-treated state, which determines the relevance of scientific work in this direction. The article presents the results of a study of the microstructure of the AM4.5Kd (VAL10) alloy with a change in its cooling rate during the curing process (Vcool.) from 0.4 °C/s to ≥ 105 °C/s. The alloy was melted, refined and, at a temperature of 750°C, poured into molds with different heat sinks. It is shown that an increase in the cooling rate during the hardening process leads to a decrease in the size of structural components, in particular, aluminum (Alα) solid solution crystals and to an increase in their microhardness. At a cooling rate of 0.4 °C/s, corresponding to solidification in a sandy form, primary Alα crystals are formed in the form of coarsened dendrites with an average size slightly larger than 800 μm, along the boundaries of which a fine network of particles of Al3Ti, Al12Mn2Cu phases and Alα+СuАl2 eutectics is formed. With an increase in the cooling rate, the branching of the dendrites and the volume fraction of the finely differentiated eutectic increase, the cooperative growth of phases in which is maintained throughout the entire range of cooling rates studied. The value of the dendritic parameter of the solid solution of aluminum regularly decreases with a practically unchanged shape factor of its crystals, which is almost up to Vcool. ≈ 105 °C/s is from 1.45 to 3.15. A similar dependence of the change in the macrograin size on the cooling rate was not found. Its anomalous growth was recorded at a cooling rate of ≥ 120 °C/s, at which the macrograin size is commensurate with the alloy cooled at a rate of 0.4 °C/s. In the work, such a discrepancy is explained from the standpoint of the theory of the nucleus and growth of crystals. Keywords: cooling rate, microstructure, AM4.5Kd (VAL10), structure formation, macrograin size.

To management the structure, mechanical and operational properties of the high-strength cast aluminum alloy АМ4.5Кд (ВАЛ10), the work uses a modification method based on the principle of structural inheritance, using rapidly cooled (Vcool. ≥ 10^5 °С/s) fine-crystal ligatures AlTi5 and AlZr10, and as well as ligatures of the chemical composition of the base alloy with nanoscale size of intermetallics and Alα crystals. Studies have shown that the introduction of fine-crystalline additives into the melt leads to a transition from a dendritic to a non-dendritic structure, a significant decrease in the size of the crystals of the Alα solid solution, and an increase in its degree of supersaturation. The microstructure becomes more uniform - the difference between the maximum and minimum size of the grains decreases. The most effective reduction of the grain size and the transition from dendritic to non-dendritic structure of the aluminum solid solution at increased cooling rates occurs when alloying with fine-crystal AlTi5 ligature introduced into the melt in terms of pure titanium 0.05-0.15 wt. %. We must think that the main factor of modification by rapidly cooled ligatures is the introduction of a large number of additional crystallization centers into the melt. After T6 heat treatment, the highest strength of AM4.5Kd alloy (VAL10) is achieved when modified with AlZr10 ligature, in particular, with a mass fraction of zirconium of 0.25%. Probably, this is mainly due to the expansion of the region of the solid solution of copper and zirconium in aluminum during high-speed cooling and its subsequent disintegration during heat treatment with the release of strengthening nano-sized CuAl2 and Al3Zr phases. Tribological studies of AM4.5Kd alloy (VAL10) were carried out. The alloy modified with fine crystal ligature of the base alloy composition in the amount of 12 wt.% has the highest wear resistance. Keywords: fine crystal ligatures, AM4.5Kd (VAL10), modification, microstructure, strength, wear resistance.