Results are provided for a study of the structure and mechanical properties of alloy AK12 modified with tabletted ultra-finely dispersed modifier based on silicon carbide, introduced “beneath a metal stream” without additional mixing, and in a rotary device. It is established that the optimum method for introducing modifier is that of “beneath a metal stream.” In this case the ultimate breaking strength increases from 110 to 150 MPa, nominal yield strength from 85 to 94 MPa, and relative elongation from 2.3 to 6.2% (metal pouring temperature into a mold 750 °C). Metallographic examination is used to determine the reduction in macro-grain size in test pigs (ingots) by a factor of four compared with control alloys, absence of porosity, and an increase in ingot density from 2.59 to 2.66 g/cm3. Introduction of ultra-finely dispersed modifier based on silicon carbide increases the number of crystallization centers in a 1 kg ingot to 2·1011 units.

Technology for Modifying Aluminum Alloys with Ultrafine Silicon

There has been growing interest in studying the formation of the structure and properties of aluminum alloys in a solid-liquid state, which is practically not used in domestic metallurgy and mechanical engineering, those at temperatures slightly higher than the eutectic, which leads to a change in the eutectic structure of the acicular type to a more dispersed equiaxial one. Therefore, the purpose of this work is to study structure formation during thixotropic treatment of an aluminum-silicon alloy, which takes place with the participation of a liquid phase, the modes of which can be adapted for thixotropic casting, which will allow changing the shape and size of eutectic crystals, which ultimately affects the mechanical properties of products. In the course of the work, the Al-12%Si alloy was studied, which underwent heat treatment at temperatures from 572 to 600 °C. During heating, isothermal holding, and cooling at a temperature above the eutectic temperature, melting and recrystallization processes occur in parallel. It was found that since the change in the state of the system is determined by a decrease in the thermodynamic potential (Gibbs energy), it is necessary to take into account the change in the volumetric energy and the change in the surface energy associated with melting (the appearance of new melt/α-solid solution and melt/Si interfaces). But it is also important to take into account that during isothermal exposure, the total surface energy will change in such a way as to minimize the final surface energy.

Structure formation of cast aluminum-silicon alloy during thixotropic treatment

Investigation of the effect of the non-stick coating quality on the structure and properties of the surface of cast iron castings

The purpose of this work is to study the structure and mechanical properties of an aluminum – magnesium system alloy after various types of heat treatment (quenching and ageing). The microstructure of an alloy has been studied by means of Zeiss OBSERVER.D1m microscope combined with a camera and image display on a monitor screen. Micro X-ray spectral analysis was performed by means of Carl Zeiss EVO 50 scanning electron microscope. The micro-hardness of the samples has been measured on prepared metallographic sections by means of DM8 micro-hardness meter. In the course of the process it has been found that quenching the Al-12,78% Mg alloy from temperatures of 430–440 ° C does not lead to the formation of a single-phase solid solution. Ageing at 100 ° C enables the formation of secondary phases. It was noted that with an increase in the quenching temperature, the micro-hardness increases slightly. An increase in the exposure time doesn’t influence greatly the micro-hardness of the alloy, while the structure remains practically unchanged.

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Structural Changes in the Aluminum - Magnesium System Alloy

The influence of various methods of activation on the graphite particles average size and micro-relief of particles have been studied. It has been experimentally proved that the size of graphite particles decreases after the process of mechano-activation, however graphite particles don’t change significantly after being processed by chemical activation. It should be noted that in the course of chemical activation the state of particles surface varies on shearing cuts. Particles’ surface can be described as a poly stratified system, comprising separate complex-structured buildups of the “rosette” type, where the graphite petals are located around the reinforcing rod. Moreover, the graphite petals are placed at different angles to each other, and they are of different thickness. The empty space between these buildups is filled with graphite particles, their petals being orientated freely. The particles size decrease and the change in the particles surface state are followed by their porosity increase, which, in its turn, leads to the fact that graphite particles’ surface becomes “super-hydrophobic” and helps the capillary forces resist the filtration of the melt into the pores of graphite particles.

/pdf/perspective-methods-of-graphite-quality-improving-28s8iuesa4.pdf

Perspective Methods of Graphite Quality Improving

The structure of natural crystalline and cryptocrystalline graphites from deposits of Krasnoyarsk krai is investigated by means of X-ray structural analysis using a D8 Advance diffractometer (Bruker, Germany). The variations in types and parameters of the crystal lattice due to the mechanical activation or mechanical synthesis of the material are revealed and the optimal activation modes of graphite at which they occur are established. The influence of the treatment time on the structural parameters of both types of graphites is considered. It is shown that their physicochemical properties are improved at the optimal activation duration due to the variation in the type and lattice parameters as well as amorphization of the crystal structure.

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Influence of the activation time on parameters of a graphite structure

Cryptocrystalline graphite properties study following treatment by different methods

A solution of the ecological problem of processing waste from metallurgical production is proposed. The results of research on the extraction of sodium and potassium chlorides from foundry slags are shown. A technological scheme based on leaching in hot aqueous solutions with subsequent evaporation is presented.

S. I. Lytkina

Papers

Influence of the activation time on parameters of a graphite structure

Cryptocrystalline graphite properties study following treatment by different methods

Development of Hardware and Technological Scheme of Processing of Sodium and Potassium-Containing Waste Of Foundry Production

Investigation of the effect of the non-stick coating quality on the structure and properties of the surface of cast iron castings