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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.

It is shown that cooling of casting molds by water with water flow of 0,42 m3/h and internal surfaces of castings with thickness of a wall 12–14 mm with water quantity 2,5×10–4–5×10–4 m3 allows to receive procurements with completely modified microstructure without use of modifiers. External layers of the produced castings consist of the eutectic silumin with compact crystals of silicon, and internal layers – of hypereutectic silumin with crystals of high-disperse primary and compact eutectic silicon.

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.

The paper presents the results of the study of the phase composition of hypereutectic silumin Al – 16.0 at. % Si – 0.2 at. % Fe. A comparative analysis of the phase composition of samples obtained at an average melt cooling rate of 102 K/s and at an ultra-high melt cooling rate of 105 K /s was carried out. At an average rate, the samples solidified in a graphite mold, and the ultra-high melt cooling rate was provided during the production of foils by the method of ultrafast quenching from the melt. It was established by X-ray diffraction and micro X-ray spectral analysis that the rapidly solidified foils consist of an aluminum-based solid solution supersaturated by silicon, dispersed silicon particles and the AlFeSi2 ternary compound phase. Comparative analysis of the results of X-ray diffraction and X-ray spectral studies of samples obtained at different melt cooling rates indicate that, during rapid solidification, the aluminum-based supersaturated solid solution contains up to 2 at. % Si.

Показано, что охлаждение литейных форм водой с расходом 0,42 м³/ч и внутренних поверхностей отливок с толщиной стенки 12–14 мм водой в количествах 2,5.10⁻⁴–5.10⁻⁴ м³ позволяет получать заготовки с полностью модифицированной микроструктурой без применения модификаторов. Наружные слои полученных отливок состоят из эвтектического силумина с компактными кристаллами кремния, а внутренние – из заэвтектического силумина с кристаллами высокодисперсного первичного и компактного эвтектического кремния.

Hypereutectic silumin is aluminum-silicon alloy. It is widely used as the material for producing pistons and sliding bearings. The samples were obtained in Belorussian State University and in the Physical-Technical Institute of the National Academy of Sciences. The percentage of silicon is 18-20 wt.%. The structure has a large number of pores and cracks. The size of pores is 100 μm. The method of modification have been carried out in two steps. The first step is ion-plasma deposition ZrTiCu coating. The second step is melting the coating into the substrate. After modification microhardness is 3.2 GPa, wear resistance is 1.8 times less than in the untreated samples. The crystallites size is 0,2-0,4 μm. Thus, this method allows to obtain alloys in the near-surface layer, grinding the structure and increasing mechanical characteristics.

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.

Irradiation (“SOLO” setup, High-Current Electronics Institute SB RAS) of hypereutectic Al- (22–24) Si composition silumin samples with an intense pulsed electron beam was carried out. The formation of a multiphase submicron nanocrystalline structure is revealed. It was found that after modification, the hardness of silumin surface layer increases by more than 2 times. Tensile tests were carried out for flat proportional silumin samples in the initial and after irradiation states. An increase in the ductility of irradiated samples was demonstrated.

On the paper the influence of modifying micro additives on the refinement of primary silicon crystals in the hypereutectic AlSi21CuNi piston silumin have been examined. As the modifiers there were used micro additives of Phosphorus in the form of AlCu19P1.4 and CuP12 pre-alloys, sulfur in the form of CuS and iron in the powdered form. The modifying micro additives were used separately and together. Micro additions of iron were used together with phosphorus. Sulfur micro addition provided the fragmentation of the primary silicon crystals, but not as effective as the phosphorus micro additive. The best effect of fragmentation of the primary silicon crystals was ensured by the combined addition of phosphorus in the form of AlCu19P1,4 pre alloy with a micro additive of powdered iron which reduced the average size of the primary silicon crystals from 114 μm to 20 μm.

Показано, что плавление и литье заэвтектического силумина являются сложными физико-химическими наноструктурными процессами. В них главную роль играют центры кристаллизации первичных кристаллов кремния, нанокристаллы кремния, растворенный и адсорбированный кислород. Роль модифицирующих кристаллов Cu3P сводится к уменьшению концентрации адсорбированного кислорода и интенсификации процесса коагуляции нанокристаллов кремния в центры кристаллизации первичных кристаллов кремния.

Development of structural light-weight materials with necessary performance characteristics is an important task as they are used in mechanical engineering, aviation and space. It is known that macroproperties of a material depend on the structural-phase state at micro- and meso-level. One of the methods of transformation of the material structure is irradiation of the surface with an intense pulsed electron beam. The purpose of the paper is the analysis of the laws governing formation of a destruction surface structure of hypereutectic silumin AK10M2N in the as-cast state and in the state after exposure to a pulsed electron beam. Deformation of silumin samples was carried out using the strain to failure method. Electron beam irradiation was carried out in the high-speed melting mode of the surface layer of samples prepared for tensile testing. As a result of the studies, it has been found that irradiation leads to formation of multiphase structure with micro- and nanoscale inclusions in the treated surface layer with a thickness up to 70 µm. An increase in strength (in 2 times) and plastic (in 1.8 times) properties of silumin irradiated with an electron beam has been revealed.

Представлены результаты исследования фазового состава заэвтектического силумина Al – 16,0 ат. % Si – 0,2 ат. % Fe. Проведен сравнительный анализ фазового состава образцов, полученных при средней (102 К/с) и сверхвысокой (105 К/с) скорости охлаждения расплава. При средней скорости образцы затвердевали в графитовой изложнице, сверхвысокая скорость охлаждения расплава обеспечивалась при изготовлении фольг методом сверхбыстрой закалки из расплава. Методом рентгеноструктурного и микрорентгеноспектрального анализа установлено, что быстрозатвердевшие фольги состоят из пересыщенного кремнием твердого раствора на основе алюминия, дисперсных частиц кремния и фазы тройного соединения AlFeSi2. Сравнительный анализ результатов рентгеноструктурных и рентгеноспектральных исследований образцов, полученных при разных скоростях охлаждения расплава, позволил установить, что при высокоскоростном затвердевании пересыщенный твердый раствор на основе алюминия содержит до 2 ат. % Si. The paper presents the results of the study of the phase composition of hypereutectic silumin Al – 16.0 at. % Si – 0.2 at. % Fe. A comparative analysis of the phase composition of samples obtained at an average melt cooling rate of 102 K/s and at an ultra-high melt cooling rate of 105 K /s was carried out. At an average rate, the samples solidified in a graphite mold, and the ultra-high melt cooling rate was provided during the production of foils by the method of ultrafast quenching from the melt. It was established by X-ray diffraction and micro X-ray spectral analysis that the rapidly solidified foils consist of an aluminum-based solid solution supersaturated by silicon, dispersed silicon particles and the AlFeSi2 ternary compound phase. Comparative analysis of the results of X-ray diffraction and X-ray spectral studies of samples obtained at different melt cooling rates indicate that, during rapid solidification, the aluminum-based supersaturated solid solution contains up to 2 at. % Si.

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.

Treatment of hypereutectic structure silumin (18-24 wt% of Si) by an intense pulsed electron beam of submillisecond duration is carried out. Formation of submicro- and nanocrystalline structure in the surface layer is revealed, which is caused by ultrahigh (up to 108 K/s) cooling rates of the melted layer. It is established that the modification of the silumin surface layer by an electron beam increases its hardness by 5 times.

In this paper, hypereutectic silumin (22-24 wt/%) was used. The structure was studied before modification. It is represented by primary silicon grains with a size of about 100 μm. Intermetallic compounds are also non-uniform distributed. After modification by an electron beam, the crystallite size was 0.4-0.5 μm. There are several layers. The modification depth was 130 μm. Hardness increased in 1.7 times, wear resistance in 1.2 times. Also, in this paper, data was given on the variation of the elementary composition with respect to the depth of the sample. The film was melt into the surface of the sample by an electron beam after depositing. The hardness increased by 1.7 times, the wear resistance increased in 2.6 times in comparison with the untreated samples. The coefficient of friction was 0.39.

Silumin, aluminum with silicon alloy, is a promising material used for the manufacture of medium-loaded machine parts and mechanisms. High brittleness is one of the main drawbacks of hypereutectic silumin. Modification of a hypereutectic silumin (18-20 wt.% Si) was carried out by irradiating the samples with an intense pulsed electron beam. It was established that irradiation of cast hypoeutectic silumin by an electron beam leads to a significant reduction in the number of micropores, forming a high-speed cellular crystallization structure with a cell size of (0.4-0.6) [mu]m. An irradiation mode allowing to increase the silumin surface layer hardness by more than 4 times, wear resistance - by 1.2 times, to increase ductility by 1.2 times in relation to the initial material was detected (35 J/cm{2}; 200 [mu]s, 20 imp. 0.3 s{-1}).