Russian Journal of Non-Ferrous Metals最新文献

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 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.

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.

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.