Based on the studies of its structure, as well as technological and mechanical properties, the composition and application prospects are substantiated for a high-strength aluminum Al–Zn–Mg–Ca–Fe casting alloy with no heat treatment. As the subjects of study, we have obtained alloys based on a composition of Al–5.5% Zn–1.5% Mg (wt %) jointly and separately alloyed with 0.5–1.0% Ca, and 0.5% Fe. As the reference, we used standard AK12M2, AMg6lch, and AM4.5Kd casting alloys corresponding to GOST (State Standard) 1583–93: by means of pencil sample casting, the alloy has been tested for the tendency to form hot cracks owing to hindered shrinkage. It is shown that separate alloying with calcium and iron does not promote any improvement of crack resistance and adversely affects mechanical properties. The combined alloying with 1% Ca and 0.5% Fe makes it possible to improve the parameter of hot tearing susceptibility to the level inherent in the AMg6lch alloy. This effect is caused by the formation of eutectic calcium-containing phases, and the formation of a favorable grain structure in which there are no columnar grains. Iron in the structure of the alloy is bound in compact particles, representing a Al10CaFe2 phase, which is a consequence of a nonequilibrium crystallization process occurring in the course of chill-mold casting. The formation of this phase makes it possible to reduce the amount of zinc in the (Al, Zn)4Ca phase and mostly to conserve the composition of the (Al) solid solution, as is indicated by similar hardness values of the base Al–5.5% Zn–1.5% Mg alloy and Al–5.5% Zn–1.5% Mg–1% Ca–0.5%–Fe alloy, as well as the superiority of these values over the hardness values of alloys separately alloyed with calcium and iron. In addition, the hardness of the promising alloy in the as-cast state is more than 20 HV higher than the hardness of branded cast alloys in the same condition. The novel alloy in the as-cast state has shown the following competitive mechanical tensile properties: σUTS ~ 310 MPa, σ0.2 ~ 210 MPa, and δ ~ 4%.

Novel High-Strength Casting Al−Zn−Mg−Ca−Fe Aluminum Alloy without Heat Treatment

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

Aspects of effective use of “secondary” silumins in machine building and other brunches of industry are considered. Specific examples are used to show the possibility of raising the quality of cast articles from silumins and simultaneously decreasing their cost. The necessity to create competence centers in the field of aluminum casting from secondary silumins by attracting scientists from higher educational institutions and newly created national research technological universities is substantiated.

About some aspects of production of cast shapes from “secondary” silumins in Russia

Electrochemical behavior of 6xxx series aluminium alloys in electrolytes containing chloride ions

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

The effect of manganese and iron on the structure of AK12 silumin is studied by microscopic x-ray diffraction and spectrum analyses. Experimental alloys with Fe : Mn = 1 : 0, 1 : 0.5, 1 : 0.7 and 1 : 1 are investigated. Quantitative analysis of the microstructure is performed. The hub zone is studied for two models of car wheels. Recommendations for alloying AK12 silumin with manganese and iron for raising its mechanical characteristics are given.

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Effect of Iron and Manganese Content on the Structure of Cast Article from Aluminum Alloy AK12

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

Destruction mechanism of casting graphite in mechanical activation

The importance of a reasonable choice of effective technological solutions in the use of man-made resources is determined by such factors as the presence of large-scale man-madeformations in the region, which&nbsp; makes them a promising raw material for the development of hightech industries with a reduced negative impact on the environment. Therefore, in this work, we studied the possibility of using graphite-containing sludge from the aspiration system for cleaning gases in the production of cryptocrystalline graphite as part of a self-drying non-stick coating. The elemental composition of graphite-containing sludge is represented by carbon (up to 45 %), sulfur (up to 1.95 %), silicon (up to 13.0 %); phase composition - graphite (up to 44 %), calcite (up to 12.7 %), crystallobalite (up to 1.5 %), pyrite (up to 3.65 %), quartz (up to 19.23 %), clinochlore (up to 17,1 %) and halite (up to 1.56 %). The sludge particle size is 3.64 microns, the total surface is 36 506 cm2/cm3. Replacing graphite with sludge in the coating composition leads to an increase in its density from 1220 to 1750 kg/m3; viscosity from 34 to 105 s; abrasion resistance from 175 to 245 g of sand. The sludge-based coating does not form a casing layer, while the depth of the penetrating layer can reach 6.0&ndash;6.5 mm. The results of the study of the value of burn-on on the surface of a gray iron casting showed that replacing graphite with sludge leads to a decrease in the thickness of burn-on on the surface of the casting by 1.5&ndash;3.0 times, depending on the thickness of the casting wall. 

T. R. Gilmanshina

Papers

Effect of Iron and Manganese Content on the Structure of Cast Article from Aluminum Alloy AK12

Influence of the activation time on parameters of a graphite structure

Technology for Modifying Aluminum Alloys with Ultrafine Silicon

Destruction mechanism of casting graphite in mechanical activation

Use of graphite-containing sludge in the composition of non-stick coatings