Hypereutectic Silumins Research Articles

Electron-ion-plasma surface modification of hypereutectic silumin

In this study, an integrated treatment approach was employed to modify hypereutectic silumin. This method involved electroexplosive alloying of the surface layer with yttrium oxide powder, followed by irradiation with a pulsed electron beam. The experimental data obtained demonstrate that this integrated treatment results in the formation of a submicron-nanocrystalline structure characterized by high-speed cellular crystallization of aluminum within the surface layer. This structure is composed of crystallization cells enriched with aluminum atoms, indicating the creation of a solid solution based on aluminum. The nanocrystalline layers, formed by silicon particles and yttrium oxide, are positioned at the cell boundaries. The study reveals that, as a consequence of integrated treatment with an electron beam energy density of 25 J/cm2 , the wear parameter of the modified samples increases by 7.9±0.6-fold, and the friction coefficient decreases by 1.7±0.15-fold compared to the initial state. Additionally, the microhardness of the modified silumin surface layer increases by 1.5±0.12-fold compared to the initial state. When the electron beam energy density is elevated to 35 J/cm2, the wear parameter of silumin is enhanced by 2.1±0.21-fold, while the friction coefficient increases by 1.13±0.1-fold. However, the microhardness decreases by 1.3±0.13-fold, while still surpassing the specified characteristics of untreated silumin. This investigation postulates that the substantial increase in the wear parameter during integrated treatment may be attributed to the presence of silicon inclusions in the surface layer that did not dissolve during the modification process. These inclusions are surrounded by the high-speed cellular crystallization structure mentioned earlier.

EFFECT OF REE ON THE SOLIDIFICATION OF НYPEREUTECTIC SILUMIN

The theories and mechanisms explaining the processes of primary silicon modification in hypereutectic silumins are considered. The processes of crystallization of hypereutectic silumin treated with rare-earth elements (REE): yttrium, ytterbium, samarium, erbium, lanthanum and neodymium have been studied. The temperatures of phase transformations and parameters taking into account the solid phase separation in the crystallization interval have been obtained. Differences in crystallization parameters and the nature of solid phase evolution in alloys modified with yttrium, ytterbium, samarium, erbium, cerium and neodymium are shown. It is concluded that further research is necessary to clarify the mechanism of modification of primary silicon in REE hypereutectic alloys.

Shungite — new generation modifi er for aluminum-silicon alloys

The issues of increasing in the homogeneity of the structure and properties of castings made of hypereutectic silumins are considered. It is shown that the use of natural shungite as a modifier makes it possible to solve this problem and provides an increase in the level of mechanical properties hypereutectic silumins by 10...15 %, which expands the possibilities of their application for engine building and makes it possible to abandon expensive nanocarbon modifiers.

Modification of the Surface Properties of Hypereutectic Silumin by Irradiation with a Modulated Electron Beam

Modification of the Surface Properties of Hypereutectic Silumin by Irradiation with a Modulated Electron Beam

Study of technological properties of new aluminum-calcium alloys for pistons of internal combustion engines

The results of studies of the casting properties of aluminum-calcium alloys in comparison with known silumins are presented. The alloys were prepared in a resistance electric furnace based on pure components and ligatures. The pouring was carried out at temperatures of 700 and 780 oC for silumins and aluminum-calcium alloys, respectively, obtaining flat ingots for subsequent remelting and casting of samples. All samples were poured with the same superheat above the liquidus temperature of 100 oC. It is shown that alloys with calcium (both eutectic and hypereutectic) are not inferior to widely used silumins in terms of fluidity, hot brittleness, and form fillability. For the first time, the parameters of difficult shrinkage were determined in a T-shaped sample of aluminum-calcium alloys in comparison with silumins. It is shown that eutectic alloys have comparable values of linear shrinkage with eutectic silumins, and the shrinkage of the hypereutectic alloy Al – 6% Ca – 3% Mn exceeds the shrinkage of the hypereutectic silumin AK18 by 1.5 times (1.5 and 1%, respectively). A high deformation plasticity during hot and cold rolling of the Al6Ca3Mn hypereutectic alloy has been established. The overall reduction ratio after applying both rolling methods exceeded 95%. The primary crystals retained their compact size and shape. It has been established that the strength properties of cold-rolled sheets from the Al6Ca3Mn hypereutectic alloy correspond to the strength values of the AD31 industrial aluminum alloy, which allows to consider it promising in those industries where a combination of high manufacturability with reduced thermal and electrical conductivity is required.

Production process automation of internal combustion engine (ICE) pistons from hypereutectic silumins by injection molding with crystallization under pressure, followed by isothermal forging

A technology for the production of ICE pistons from aluminum alloys with a silicon content of 18 % is proposed. A method for pressing a crystallizing metal by pressure on a horizontal hydraulic press in order to obtain piston blanks for subsequent isothermal forging is developed. The pressing process is controlled by a computer control system embodied through the use of the modern industrial logic controllers and software. An interface for program control is developed. It indicated that the use of modern process control systems makes it possible to control the formation of the final product properties in real time. Keywords automation, computer control system, internal combustion engine pistons, isothermal forging, crystallization, pressure, mechanical properties of metal products

MODIFICATION OF HYPEREUTECTIC SILUMIN BY A PULSED ELECTRON BEAM

MODIFICATION OF HYPEREUTECTIC SILUMIN BY A PULSED ELECTRON BEAM

Study of structure and mechanical properties of aluminum alloys modified by shungite after heat treatment

The results of the effect of heat treatment on the structure and mechanical characteristics of the hypereutectic silumin modified by natural fullerenes in shungite rock are presented. It is established that the modifier provides uniformity of the structure of hypereutectic silumins and improvement of mechanical properties. The structural components of the alloys return to their original unmodified state with subsequent drying of the mechanical properties after heat treatment.

Вплив МГД - плазмової обробки розплаву на структуру і властивості литого алюмінієвого сплаву А390

Growth of production of cast products and the desire of enterprises to reduce the cost of manufacturing metal products led to a significant increase in requirements for the structure and properties of aluminum alloys. Increasing of physical and mechanical properties of alloys is most effectively at the stages of their preparation in liquid state. At that, it is possible to affect effectively on the quality of cast metal by external actions on alloys, deep refining from gases and harmful impurities, active modifying of alloy, reducing or eliminating the negative impact of heredity of charge materials. The main disadvantage of the processes of structure refinement of alloys by using modifiers is instability of their results, which depends on various reasons. One of the most important reasons is providing conditions for the formation and preservation of active modifier particles in the melt volume. They are assimilating by liquid alloy and acting on crystal nucleus at crystallization. It is known that only ~10% particles are active of the total number of particles added with the ligature into the melt. Other particles dissolve in the melt, take away by the crystallization front, or push back on to intergranular boundaries. The considered methods of electromagnetic, MHD and plasma actions on liquid metal allow to refine and modify alloys without use of special reagents. The paper presents studying of the structure and properties of supereutectic silumin A390 after treatment in casting magnetodynamic installation (MDI) by submerged into melt the plasma argon jet and alternating electromagnetic field & magnetohydrodynamic (MHD) effects, including simultaneous combination. There are developed the scientific and technological bases of MHD-plasma processing of liquid hypereutectic silumin A390 and original equipment for their realization. It provides dispersed structure of solidified alloy. Thus, there is a significant decreasing of sizes both particles of primary silicon and dendrites of α-solid solution of aluminium. Also, strength characteristics of alloys increased to 10%, and elongation rises up in 1.5-2 times. Keywords: plasma jet, magnetodynamic installation (MDI), aluminum alloy, mechanical properties.

Comparative analysis of the effect of Ni, Mn, Fe and Si additives on the microstructure and phase composition of hypereutectic aluminum-calcium alloys

A comparative analysis of the phase composition and morphology of primary crystals in hypereutectic alloys of the Al–Ca–Ni–X system (where X is Fe, Si, Mn) was carried out by calculation and experimental methods, including the construction of liquidus surfaces. Additional alloying of the base Al–6%Ca–3%Ni alloy with iron and silicon leads to the formation of coarse elongated primary crystals up to 100 μm in length. It was found that the addition of manganese, on the contrary, leads to the formation of relatively small (average size about 20 μm) compact primary crystals of two four-component phases. Presumably, they are phases based on ternary compounds Al9CaNi and Al10CaMn2. The composition of eutectics in quaternary alloys has been determined. All aluminum-calcium eutectics are characterized by a higher proportion of the second phases, a thinner structure compared to the aluminum-silicon eutectic in AK18 silumin, and are also capable of spheroidization upon heating, starting from 500 °C. The combination of compact and spherical particle morphology after annealing in the 63-2Mn alloy appears to be favorable for deformation. Comparison of the manufacturability of the experimental alloy Al–8%Ca–1%Ni–2%Mn and the grade silumin AK18 showed the advantage of the former. In terms of the totality of its characteristics, the experimental alloy can be considered as the basis for the development of hypereutectic alloys of a new generation as an alternative to piston silumins of the AK18 type. The experimental alloy, the microstructure of which is characterized by a compact morphology and small size of primary crystals and a fine structure of the eutectic, in contrast to hypereutectic silumins, does not require special modification.

Surface modification of hypereutectic silumin subjected to a millisecond modulated electron beam treatment

In this work, using a unique feature of the “SOLO” electron source with a grid plasma cathode based on a low-pressure arc discharge, which consists in the possibility of controlled operation of the beam power during a pulse of submillisecond duration, and, accordingly, the rate of energy input into the sample surface, we investigated the modes irradiation of samples of hypereutectic silumin. The irradiation modes had the same energy density during the first 200 μs of the pulse, equal to 20 J/cm2 and differed in different durations of further maintaining the surface temperature at 600°C for a time of up to 1 ms. The results of tribological tests and methods of diffraction microscopy of the investigated defect structure, the elemental and phase composition, the morphology of the strengthening phases of the modified layer of the hypereutectic silumin samples are presented.

Structure and phase composition of hypereutectic silumin alloy Al – 20Si after compression plasma flows impact

The results of structure and phase composition investigation in hypereutectic silumin alloy with 25 at. % Si content after high-energy pulsed compression plasma flows impact are presented in the work. The compression plasma flows impact with an absorbed energy density 25 – 40 J/cm2 allows to modify the sub-surface layer with a thickness up to 30 – 32 µm due to its melting and high rate solidification. By means of X-ray diffraction method, it was found the formation of two silicon phases with different grain sizes. The high-dispersed structure of silicon is presented in the Al-Si eutectic while the silicon phase with coarse grains exists in the primary crystals. The obtained results are the basis for a new method development for nanostructuring of the surface layers of hypereutectic silumin alloys increasing its wear resistance.

Thermal stability of the hypereutectic silumin structure subjected to a pulsed electron beam treatment

Hypereutectic silumins have many positive properties - low density, high specific strength and corrosion resistance. They are non-magnetic, retain their strength at low, up to cryogenic temperatures, have a relatively low thermal expansion coefficient, high modulus of elasticity, increased wear resistance in friction pairs, etc. The structure of hypereutectic silumin is formed by a plastic eutectic matrix and brittle primary silicon crystals larger than 100 urn, and also contains crystals of aluminides of iron, copper, titanium and zirconium. Silumin of hypereutectic (18 wt% Si) composition was modified by irradiating the specimens by an intense pulsed electron beam. It was found that irradiation of hypereutectic silumin with an electron beam leads to a significant decrease in the number of micropores, the formation of a structure of high-speed cellular crystallization.

Effect of heat treatment on structure and mechanical properties of aluminum alloys modified by nanocarbon

The heat treatment of hypereutectic silumins modified by nanocarbon is considered. The structures and mechanical properties of the modified and unmodified heat treated hypereutectic silumins are studied. The regularity of changes in the structure and characteristics of hypereutectic modified silumins with various methods of heat treatment are established.

Модификация структуры заэвтектического силуминового сплава Al-44Si при воздействии компрессионных плазменных потоков

Effects of the high-energy compression plasma flows on the structure, elemental composition, and phase state of Al-44 at.% Si hypereutectic silumin alloy have been investigated. Using scanning electron and optical microscopy it was found decreasing in grain size of both primary silicon particles and Al-Si eutectic parts with increase of absorbed energy density of compression plasma flows. The primary silicon crystals were dispersed down to 300 nm in the result of high cooling rate of the melted layer after its homogenization by means of hydrodynamic mixing. It was found that increase in the absorbed energy density, homogenization of elemental composition in the modifies layer occurs due to increase in lifetime of the melted state and more efficiency mixing process.

Structure and mechanical properties of hypereutectic silumin irradiated by a pulsed electron beam

Structure and mechanical properties of hypereutectic silumin irradiated by a pulsed electron beam

Possibilities and prospects for producing silumins with different silicon contents using amorphous microsilica

Abstract The main objective of this work is to research complex physical−chemical processes of Al(l)−SiO2 interface and develop a new technology for producing foundry silumins based on amorphous microsilica obtained from silicon production waste. Effective methods for producing hypoeutectic, eutectic, and hypereutectic silumins using amorphous microsilica were developed. Alloys with a silicon content of 7 wt.% were obtained by blowing preheated amorphous microsilica into the aluminum melt (t=900 °C) along with the stream of argon followed by intense mixing. Alloys with a silicon content of 21 wt.% were manufactured by induction melting of a silicon-containing mixture (60% SiO2, 40%Al + 20%3NaF·2AlF3) subjected to the presintering when the amorphous microsilica was reduced to crystalline silicon. It is found that crystalline silicon, which is formed during the roasting of the tableted burden, is smoothly absorbed by the aluminum melt. Aluminum oxide, obtained during the redox reaction, dissolves in cryolite, after which aluminum and silicon are fused together and transferred to the melt. The calculation of the economic efficiency of producing silumins using amorphous microsilica demonstrates a quick project payback period, as well as a high level of its profitability.

Deformation, heat treatment and properties of piston hypereutectic silumins

A series of piston hypereutectic silumins based on Al – (15 ÷ 20) % Si alloyed with copper, magnesium, nickel, and chromium was studied. The alloys were modified with phosphorus and hydrogen-containing reagents to increase the deformability and mechanical properties. The experimental ingots, cast in the steel mold, had dimensions: diameter 190 mm, height 500-550 mm, weight 32-40 kg. The mechanical properties and temperature coefficient of linear expansion (TCLE) of the experimental ingots and forgings made from them are determined. Temporary tensile strength and relative elongation of deformed ingots from hypereutectic silumins were 227-306 MPa and 5.7-7.5%, respectively. The optimal heat treatment of deformed silumins was determined: quenching with step heating and aging, which allows the strength of forgings to be increased up to 370-470 MPa. Moreover, the ductility indicators remain at a high level, and the average TCLE of the alloys is (18.0 ÷ 19.2) ·10−6 К−1 in the range of 50 ÷ 200 °C.

STRENGTH CHARACTERISTICS OF HYPEREUTECTIC SILUMIN AFTER ELECTRON BEAM MODIFICATION

Irradiation (SOLO installation, Institute of High Current Electronics, Siberian Branch of the Russian Academy of Sciences) of hypereutectic silumin specimens of Al-(22-24)Si composition with an intense pulsed electron beam was carried out. The formation of the structure of highspeed cellular crystallization of aluminum (cell size 250-600 nm) was revealed. It was shown that the cell boundaries are strengthened by globular-shaped silicon particles (particles of size 50-70 nm). It was found that the hardness of the silumin specimen surface layer increases by more than 5 times after modification. Tensile tests of plane proportional samples showed an increase in the ductility of irradiated samples while maintaining the tensile strength.

The modification of hypereutectic high-alloy silumins — prospects for the development of technology for producing materials with a low linear expansion coefficient

This article discusses the possibilities of using hypereutectic silumins and the problems that impede their wider distribution. The known methods of manufacturing products from hypereutectic silumins of high quality are shown. A method for producing casting blocks from hypereutectic silumins by direct chill casting is considered. The possibility of milling primary silicon crystals by introducing modifiers and master alloys of Al-Si-P, Al-Cu-P systems, inorganic carbon and phosphorus compounds is shown. The tendency of copper-doped silumins to hot shortness is shown. The technology of impact on the melt of ultrasonic cavitation is considered together with the introduction of additional active modifiers made of master alloy rods to obtain casting blocks from hypereutectic high-alloy silumins using the method of direct chill casting with a primary silicon crystal size of no more than 10 µm. Technological principles for reducing the grain size of α-solid solution, uniformly distributed over the ingot cross-section, are proposed.