V. I. Nikitin

Melt treatment by pulsed magnetic fields aimed at controlling the structure and properties of industrial silumins

Computer modeling of main force factors when treating aluminum alloys by pulsed magnetic fields according to the radial and axial effect schemes is performed. It is established that, when using the radial scheme, the shock wave, which appears in the melt after a single pulse, affects its entire bulk for 40 μs; when using the axial scheme, this time is 416 μs. Experimental studies for industrial silumins AK6M2 and AK10M2N have confirmed the presence of a stable modifying effect under the magnetic pulsed treatment (MPT), notably, dendrite sizes of the α-Al phase and eutectic silicon crystals decrease, density and electrical conductivity increases, and alloy strength and plasticity in a cast state increase. Based on the experimental investigations, it is concluded that the MPT is most manufacturable for the axial effect scheme.

Theoretical and experimental substantiation of treatment of aluminum-based melts by pulsed magnetic fields

Factors causing the solid-phase dispersal of particles of alloying elements in the aluminum melt depending on their nature are considered. It is shown that the particles can be fragmented under the effect of uniform tensile stresses appearing due to the particles heating. The reasonability of using additional external effects (for example, magnetic-pulsed treatment of the foundry-alloy melt) to intensify the assimilation of silicon in liquid aluminum and provide the microcrystalline structure of the foundry alloy is substantiated theoretically and confirmed experimentally by the example of the Al–20 wt % Si foundry alloy.

Influence of treatment of melts by electromagnetic acoustic fields on the structure and properties of alloys of the Al–Si system

The influence of treating the melts by electromagnetic acoustic fields on the structure and properties of Al–12% Si and Al–20% Si binary alloys is investigated. In the course of experiments, the frequency of the electromagnetic field induced in the loop antenna varies as 500, 1000, and 2000 kHz. The melts are treated after their degassing and refining. It is established that this treatment method of the melts leads to a reduction of the total preparation time of alloy by 12% on average. The short-term treatment of the melts by electromagnetic acoustic fields promotes the refinement of the main phase components of alloys and an increase in their mechanical properties. When treating the Al–12% Si eutectic alloy with a frequency of 500 kHz, α-Al dendrites are refined from 30 to 22 μm and eutectic Si crystals are refined from 13 to 10 μm. When treating the Al–20%Si eutectic alloy with a frequency of 1000 kHz, eutectic Si crystals diminished from 8 to 5 μm and these of primary Si diminished from 90 to 62 μm. The ultimate tensile strength of the Al–12%Si eutectic alloy increases 13% under the mentioned treatment modes, while the relative elongation increases 17%; as for the Al–20% Si eutectic alloy, the same characteristics increases 9 and 65%, respectively. Based on these investigations, it is concluded that the selection of the treatment parameters of the melts of the Al–Si system by electromagnetic acoustic fields should be determined by the silicon content in the alloy. It is necessary to treat the melt by waves with a higher oscillation frequency with an increase in the silicon concentration. This treatment method makes it possible to form the modified fine-crystalline structure of alloy and, consequently, improves their mechanical properties. It can be successfully used when fabricating fine-crystalline foundry alloys and in the production of alloys of the Al–Si system. To determine the optimal treatment parameters depending on the structure of the initial charge and alloy nature, additional investigations are required.

Hereditary influence of the structure of charge materials on the density of aluminum alloys of the Al-Si system

The influence of dispersity of charge silicon and structure of initial charge alloys on the density of silumins of the Al-Si system is investigated using the improved express-method for determining the melt density. It is established that the structure of charge materials substantially and stably affects this characteristic, which should be taken into account in preparation technologies of alloys of the Al-Si system.

Application of Structural Inheritance Phenomenon at Producing the Al-Mg System Alloys

The prototype flat section ingots have been obtained by means of immersion casting from aluminum alloys of Al-Mg system. It is established that magnalium modification by ligature additives AlS 2.4 on the basis of introduction amount of 0.02% Sc in mass contributes to the strain degree increase at cold rolling without intermediate annealing.

Influence of modifiers on the change of mechanical properties of silumins

An increase in the sum of alloying elements in industrial silumins causes the formation of excess intermetallic phases in their structure. When introducing modifiers in such alloys above a certain amount, structural components are coarsened because of overmodification, which can cause a decrease in the mechanical properties of cast alloys. The optimal consumption of the modifying microcrystalline remelt decreases from 0.6 to 0.3 wt % with an increase in the sum of alloying elements in alloys from 7.35% (AK7ch) to 14.3% (AK10M2N). When using the AlTi5 master alloy, the optimal amount of introduced titanium decreases from 0.05 to 0.01% and, in the case of the AlTi5B1 master alloy, from 0.02 to 0.01%. The modifying effect of the AlSr10 master alloy enhances with an increase in the silicon content with smaller amounts of strontium introduced into alloys. It is shown that the consumption of the metallic modifier depends on its modifying ability, as well as the sum of alloying elements in the modified silumin.

Influence of various types of treatment on the structure, density, and electrical conductivity of deformed alloys of the Al–Mg system

A comparative investigation on the influence of AlZr4, AlZr10, and AlSc2 modifying master alloys, as well as magnetic-pulsed treatment (MPT) on density (in the liquid and solid states), electrical conductivity (in a solid state), and macrostructure of AMg5 and AMg6 alloys is performed. Mater melts are poured into special facilities providing cooling rates during the crystallization of ~102, ~103, and ~106C/s. Master alloys are introduced into the melts in an amount of 0.01% by the modifier element. It is shown that the modifying treatment of the melts by additives of nucleating master alloys promotes an increase in alloy densities in liquid and solid states. The electrical conductivity of alloys with additives of AlZr4 and AlZr10 master alloys lowers. The introduction of the AlSc2 master alloy increases in electrical conductivity of AMg5 and AMg6 alloys. This effect is established for the first time and requires additional investigations. It is established that, when compared with AlZr4 and AlZr10 master alloys, the AlSc2 master alloy prepared by crystallization in a water-cooled roll crystallizer most strongly affects the physical properties of alloys. It also provides the maximal macrograin refinement. MPT of alloys according to the axial effect scheme, similarly to the introduction of modifying master alloys, promotes an increase in the density of alloys in liquid and solid states. Electrical conductivity increases after MPT like after the addition of the AlSc2 master alloy into the melts. Alloy macrograin refining during MPT is comparable with the modification with the AlZr4 master alloy. Based on comparative investigations, it is concluded that MPT can be attributed to physical modification methods. It is proposed to use the determination procedures of density and electrical conductivity for the express evaluation of the modifying efficiency of studied effects.

Shortening the Time of Heat Treatment of Silumins of the Al – Si – Cu System by Modifying their Structure

The possibility of shortening the heat treatment hold of silumins of the Al – Si – Cu system by changing the parameters of the structure under chill casting is considered and a criterion for their evaluation is suggested. Alloys AK6M2 and AK8M3ch are used to demonstrate experimentally that decrease in the sizes of the crystals of primary silicon and in the transverse size of the α-Al secondary dendrite arms can halve the time of holding for quenching and aging at a guaranteed margin of the strength properties.

Effect of Crystal Structure Fineness for Charge Alloy AK6M2 on Its Flux Treatment Efficiency

The effect of charge billet structure and form of fluxes on structure, density, and gas content of alloy AK6M2 (Al – Si – Cu system) is studied. Alloys prepared from finely crystalline charge billet have smaller phase component sizes, lower gas content, and increased solid state density, and use of coarsely crystalline charge billets for alloy preparation necessitates an increase in flux preparation consumption in the stage of alloy preparation for casting.

Influence of the structure of charge billets, overheating, and holding time of melts on the properties of Al-5 wt % Cu alloys in liquid and solid states

The influence of the structure of charge bars, overheating temperatures, and isothermal holding time of Al-5 wt % Cu melts on their properties in solid and liquid states is investigated. It is revealed using the express method that the density of melts prepared from fine-crystalline charge bars (F-c charge) has reduced values compared with the melts prepared from coarse-crystalline charge bars (C-c charge). This peculiarity is retained over the entire studied range of overheating temperatures (760–1060°C). The influence of the structure of initial charge bars manifests itself in the second generation (after melting and crystallization from the corresponding overheating temperatures): alloys fabricated from the F-c charge have a smaller dendritic parameter α-Al and increased density and electrical conductivity compared with the alloys made from the C-c charge. It is shown that the involvement of deformed aluminum and copper waste into the charge composition provides a finely dispersed structure and increased density of Al-5 wt % Cu alloys in the solid and liquid states.