Russian Journal of Non-Ferrous Metals最新文献

In this research, the effects of different stirring speeds on the molten pool flow and the internal flow field of the molten pool were studied by water simulation and numerical simulation. The software ANSYS ICEM, ANSYS FLUENT, and Tecplot 360 were used to model, compute, and post-process, respectively. A physical model made of plexiglass was used to conduct the water simulation experiment. The advantages of vortex smelting reduction were analyzed theoretically and verified by high-temperature experiments. At a stirring speed of approximately 150 rpm, vortex smelting reduction was not only beneficial to the uniform dispersion of the material particles in the molten pool, increasing the reduction reaction rate, but it was also beneficial to the separation of slag and metal. The experimental results confirmed the advantages of vortex smelting reduction, contributing to the recovery of iron in high-iron red mud.

Additive manufacturing, which includes a set of technologies for manufacturing complex-shaped products with the required set of properties, is currently being widely developed. Most additive technologies are associated with the manufacture of the product by melting and fusion of metal powder particles by means of laser radiation. Eutectic aluminum alloys of the Al–Ca, Al–Ce, Al–La, and Al–Ni systems, which have excellent casting properties, are supposedly promising for use in additive technologies. However, there is very little information in the literature on the effect of laser processing on such eutectic structures. In this regard, the work investigated the effect of laser radiation on the structure and mechanical properties of samples from eutectic compositions, namely, Al–8% Ca, Al–10% La, Al–10% Ce, and Al–6% Ni. To do this, the continuous laser modification of their surfaces was carried out. The level of hardening was evaluated by measuring the microhardness of the modified surface. The mechanisms of fracture of specimens under tensile testing have been established. It is shown that, in the structure of the modified surfaces of samples of four alloys, the distribution of the second component becomes more uniform compared to the structure of the base metal. In the Al–8% Ca alloy, the greatest hardening effect is observed, which, however, contributes to embrittlement under tensile stress. However, the modified Al–8% Ca alloy is of interest because of its increased hardness and therefore possibly increased wear resistance. On the contrary, laser modification of the surfaces of the Al–10% Ce, Al–10% La, and Al–6% Ni alloy samples provides a lower hardening effect, but increases their tensile strength with the formation of a ductile or mixed ductile and brittle fracture. The results obtained confirm the prospects of using alloys of the Al–Ca, Al–Ce, Al–La, and Al–Ni systems in additive manufacturing.

The paper is devoted to the study of the combustion kinetics and mechanisms of elemental mixtures in the Zr–Mo–Si–B system, as well as the analysis of phase and structural transformations in the combustion wave. A thermodynamic analysis of possible chemical reactions occurring in combustion wave is carried out. In the range of 298–2500 K, the reaction of ZrB₂ formation is preferred. Above 2200 K, the formation of MoB becomes more thermodynamically advantageous compared to MoSi₂. Estimates of the phase stability of synthesis products have shown that the phases ZrB₂, MoSi₂, and MoB are in equilibrium. The experimental dependences T_c(T₀) and U_c(T₀) are linear, which implies an unchanged combustion mechanism at T₀ = 298–800 K. Preheating leads to an increase in U_c. Similarly, the increase in the proportion of Zr and B in the mixture has a similar effect, which increases heat emission and T_c. With a minimum content of Zr and B, the interaction of Mo with Si with the formation of MoSi₂ by the mechanism of reaction diffusion is decisive. With an increase in the proportion of Zr and B, the rise of T₀ to 750 K does not affect the T_c. The E_eff values (50–196 kJ/mol) confirm the significant influence of liquid-phase processes on the combustion kinetics. The mechanism of structure formation has been studied. In the combustion front, a Si–Zr–Mo melt is formed. The primary grains of ZrB₂ and MoB crystallize from this melt as it is saturated with boron. At the same time, the melt spreads over the surface of Zr and Mo particles. This leads to formation of ZrSi_x and MoSi_x films. Core-shell structures are formed behind the combustion front, which disappear as they move towards the post-combustion zone. The phase composition of the products is formed in the combustion front in less than 0.25 s.

The effect of warm rolling and three aging treatments on microstructure and mechanical properties of 7075 alloy was investigated via optical microscopy, electron backscattered diffraction, transmission electron microscopy and tensile tests. 7075 alloy was warm rolled and then were solution treated followed by three different aging processes viz., one-step, two-step and three-step aging. Results show that the ductility of 7075 alloy is improved during warm rolling and the strength increases with increasing total warm-rolled reduction. The average grain size decreases after aging compared with that in the solution state. The microstructure of the one-stage aged sample consists of elongated grains and equiaxed grains while almost completely equiaxed microstructure is obtained in solutionized, two-stage and three-stage aged samples. The distributions of dislocations, precipitates and grain refinement influence mechanical properties together. The one-stage aged sample possesses a combination of acceptable strength and excellent ductility. Two-stage and three-stage aged samples have higher elongations but lower strengths.

The results of studies of interaction between titanium melts and silica-containing casting mold are presented. Pure silicon and compounds of titanium oxides and silicides have been detected by X-ray diffraction analysis in the contact zone. The problem of negative influence of the mold on the casting is solved by using thermochemically resistant monocorundic forms on an alumina sol binder and corundum filler. For casting according to meltable models, a composition of a refractory suspension with special additives has been developed, which will improve the wetting of models with suspension, as well as increase the strength of the mold. In the article, there are studies of sedimentation properties of suspension. A method has been developed for accelerated curing of sequentially applied layers of refractory suspension by drying in vacuum and subsequent chemical curing with a gaseous reagent. The formation time of one layer is reduced from 3–5 h to 20–30 min. Comparative studies of the kinetics of convective drying and dehydration in vacuum of alumina sol binder have been conducted. The process of removing moisture increases by 2–6 times once in a vacuum of 5–10 kPa. The method of X-ray phase analysis has made it possible to study the conversion of alumina sol during high-temperature heating. The stable phase α-Al₂O₃ in the mold shell is obtained when the calcination temperature rises to 1300–1350°C, and the strength of 9–12 MPa is also achieved when sintering additives are added to the suspension. Recommendations are given for additional protection of refractory ceramic layers after evacuation and drying: treatment of the last layer with gaseous hardeners and application of a polyvinyl acetal solution with a density of 1100–1200 kg/m³. The proposed technological solutions will make it possible to increase both the efficiency of the technological process of forming and casting of titanium alloys and the quality of castings.

Adequate heat input provided by the proper combination of friction stir welding (FSW) parameters is critical to sound welding. Optimum parameter setting requires exhaustive trials and extensive experiments, which require considerable time, resources, and cost. This study uses simulation and modelling approaches to generate three significant tool-work heat flux generating interfaces (tool shoulder, lateral and bottom surfaces of the pin). The temperature data was acquired by performing nine experiments on 4 mm thick AA6060-T5 sheets. The effects of significant FSW parameters (Tool Rotational Speed (TRS) and welding speed (WS)) on the heat input were modelled. The calculated heat input rates at the shoulder and pin surfaces (Q₁, Q₂, and Q₃) were numerically estimated. The experimental data was converted into a mathematical model using the response surface method to study the effect of welding parameters on heat input from each of the three surfaces. The analysis of the results showed that among three interfaces, the shoulder provides the most significant heat input due to the immense friction between this surface and the parts to be welded. The interaction between the main factors produced little heat on the three surfaces. The ANOVA test showed that the three models are a good approximation of the results of both experiments and theories.

The features of forms of occurrence of gold in technogenic raw materials—lying clinker of zinc production of the Belovsky Zinc Plant (Belovo, Kemerovo oblast)—are considered in the paper. The Belovsky plant operated from 1930 to 2003 using zinc concentrates from the Salair Mining and Concentration Plant. After the shutdown of the plant, the clinker dumps were stored at the plant’s industrial site and were repeatedly washed with acidic solutions to isolate copper. This form of storage and leaching has led to the transformation of the forms of noble metals found in clinker, which currently makes it difficult to extract gold. The gold content in clinker is at the level of 2–3 g/t, which makes gold recovery profitable. The presence of carbon in clinker complicates the known methods of both analytical detection of gold and its recovery. A method is proposed for determining the forms of occurrence and content of gold, taking into account the fact that gold may be present in the form of free fine gold and gold finely disseminated in iron and its oxides, in sulfide phases, in the quartz-silicate part of the clinker, and in the carbonaceous phase. It is shown that, depending on the storage conditions and the previous acid treatment, the forms of gold in the clinker change, which affects the choice of the technological scheme for processing the material. The share of gold available for leaching is at least 40%. The increased associativity of gold with the coal (flotation) phase and the sorption activity of coal brings significant interference into the study of the properties of gold forms in clinker, which requires preliminary carbon removal.

In order to improve the overall properties of cast Al–Cu–Mn alloy, the effect of Zr content on the microstructure and corrosion resistance of Al–Cu–Mn alloy was investigated. The microstructures of the alloy were analyzed by scanning electron microscopy and transmission electron microscopy, and the corrosion resistance of the alloy was tested by exfoliation corrosion (EXCO), intergranular corrosion (IGC) and electrochemical corrosion tests. The results show that the corrosion resistance of Al–Cu–Mn alloy with 0.2 wt % Zr is superior to other alloys. Specifically, the EXCO phenomenon of the alloy is lighter, and the rating of EXCO is EA. The IGC depth of the alloy can reach the lower value (56.3 μm). The electrochemical self-corrosion potential (E_corr), corrosion current (i_corr) and corrosion rate (R_corr) are –0.8046 V, 0.0028 mA m^–2 and 0.1558 mm a^–1, respectively. The improved corrosion resistance of the Al–Cu–Mn alloy with 0.2 wt % Zr resulted from the formation of the T phase and more uniform dispersive distribution of the Al₃Zr phase in the alloy.