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The theories and mechanisms that explain the processes of modification of primary silicon in hypereutectic silumins are considered. The solidification of a hypereutectic silumin containing a rare earth element (REE), namely, yttrium, ytterbium, samarium, erbium, lanthanum, or neodymium, is studied. The phase transformation temperatures and the parameters that take into account the precipitation of a solid phase in the solidification temperature range are determined. Differences in the solidification parameters and the character of solid-phase precipitation in alloys modified by yttrium, ytterbium, samarium, erbium, cerium, or neodymium are revealed. Further investigations should be performed to clarify the mechanism of the REM modification of primary silicon in hypereutectic silumins. [ABSTRACT FROM AUTHOR]

This work is a continuation of study [1] devoted to the effect of a submillisecond pulsed electron beam on the surface of hypereutectic silumin (AlSi20). Experiments are performed using a SOLO electron source with a plasma cathode in which the generated pulse power can be controllably changed during the pulse, which allows control of the energy-input rate to the target surface. The application of such a unique electron source enables consideration of the effect of maintaining the surface temperature of the irradiated sample (at a level close to the silumin melting point) at a pulse duration of less than 1 ms on modification of the properties of this surface. An increase in the time of maintaining the sample-surface temperature is shown to improve its microhardness and wear resistance. The modified layer has a cell structure similar to that formed during high-speed crystallization. The modified-layer depth reaches 60 μm. [ABSTRACT FROM AUTHOR]

The effect of melt hydrogen treatment on structure, morphology, and on physical and mechanical properties of hypereutectic alloy Al – 15% Si in cast and deformed conditions is studied. A melt is treated with hydrogen by different methods, i.e., with wet asbestos, in a steam atmosphere, and flushing with hydrogen prepared by alkali decomposition with aluminum. Ingots are deformed plastically by open forging and rolling. Alloy microstructure is studied by metallographic, electron microscopic, x-ray diffraction, and dilatometric analyses. Alloy density and microhardness are measured. Alloy atomic hydrogen content is studied by vacuum heating. It is shown that hydrogen treatment improves cast alloy structural parameters and deformability, raises post-deformation strength by a factor of 1.3 – 1.4, and lowers linear expansion coefficient. [ABSTRACT FROM AUTHOR]

Silumin (an alloy of aluminum with silicon) is a cheap industrial alloy with good corrosion resistance, high specific mechanical properties and good casting properties. As a result it has found wide applications in modern industry (aircraft and mechanical engineering, instrument making, shipbuilding, etc.). The aim of this work is to analyze the regularities of transformation of the structure and phase composition of the surface layer of a hypereutectic silumin ( Al - 22 wt % Si ), subjected to irradiation with an intense pulsed electron beam. It was found that irradiation of silumin with a pulsed electron beam ( 18 keV, 25 J / cm^2, 200 μs, 3 pulses, 0,3 s^(-1)) leads to melting of the surface layer up to 60 μm thick, the high-speed crystallization of which is accompanied by the formation of a submicro-nanocrystalline multiphase structure. It is shown that aluminum (a solid solution based on fcc crystal lattice) forms cells of high-speed crystallization; nanoscale particles of the second phases are located at the cell boundaries. Analysis of three-component state diagrams of the Al - Si - Fe - Cu system (the main elements of the studied silumin) demonstrated the possibility of forming a large number of two- and three-element compounds in the alloy under equilibrium conditions. It has been shown by diffraction electron microscopy that, along with three-element phases, phases based on four and, possibly, more elements are formed in silumin.

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.

It is shown that melting and molding of hypereutectic silumin are complicated physical and chemical nanostructural processes. The major part at these processes is played by the centers of crystallization of primary crystals of silicon, silicon nanocrystals, the dissolved and adsorbed oxygen. The part of the modifying crystals of Cu3P is reduced to decreasing of concentration of the adsorbed oxygen and an intensification of process of coagulation of nanocrystals of silicon in the centers of crystallization of primary crystals of silicon.

The work is a continuation of research concerning the influence of intensive cooling of permanent mold in order to increase the casting efficiency of aluminium alloys using the multipoint water mist cooling system. The paper presents results of investigation of crystallization process and microstructure of synthetic hypereutectic alloys: AlSi15 and AlSi19. Casts were made in permanent mold cooled with water mist stream. The study was conducted for unmodified silumins on the research station allowing the cooling of the special permanent probe using a program of computer control. Furthermore the study used a thermal imaging camera to analyze the solidification process of hypereutectic silumins. The study demonstrated that the use of mold cooled with water mist stream allows in wide range the formation of the microstructure of hypereutectic silumins. It leads to higher homogeneity of microstructure and refinement of crystallizing phases and also it increases subsequently the mechanical properties of casting.

The work is a continuation of research on the use of water mist cooling in order to increase efficiency of die-casting aluminum alloys using multipoint water mist cooling system. The paper presents results of investigation on crystallization process and microstructure of synthetic hypereutectic AlSi20 alloy. Casts were made in permanent mold cooled a with water mist stream. The study was conducted for unmodified AlSi20 alloy and a modified one with phosphorus, titanium and boron on the research station allowing sequential multipoint cooling using a dedicated program of computer control. The study demonstrated that the use of mold cooled with water mist stream and solution heat treatment allows in wide range for the formation of the microstructure of hypereutectic silumins. It leads to the growth of microstructure refinement and spheroidizing of phases in the casting.

The work is a continuation of research on the use water mist cooling in order to increase efficiency of die-casting aluminum alloys using multipoint water mist cooling system. The paper presents results of investigation of crystallization process and microstructure of synthetic hypereutectic AlSi20 alloy. Casts were made in permanent mold cooled with water mist stream. The study was conducted for unmodified AlSi20 alloy and modified with phosphorus, titanium and boron on the research station allowing sequential multipoint cooling using a dedicated program of computer control. The study demonstrated that the use of mold cooled with water mist stream allows the formation of the microstructure of hypereutectic silumins. A wide range of solidification temperature of hypereutectic silumins increases the potential impact of changes in the cooling rate on a size, a number and a morphology of preeutectic silicon and eutectic α+β (Al+Si).