Russian Journal of Non-Ferrous Metals最新文献

The effect of the welding arc current (47, 57, and 67 A) on the structure and properties of the deposited samples obtained by electric arc robotic deposition has been studied. Welding wire Sv-AK5 (ER4043) of the Al-Si system was used as a filler material. The weld deposition was carried out on a substrate in the form of a plate 6 mm thick made of AMg6 alloy (Al–Mg system). In the process of surfacing, a typical two-phase structure of a hypoeutectic composition is formed in the samples, which is characteristic of alloys of the Al‒Si system with a silicon content of 5%. A trend to the enlargement of the structure in the direction from the substrate is observed along height of the deposited layers, which is associated with the accumulation of heat in the layers deposited along the height. With an increase in the welding arc current, dendrites based on α-Al and eutectic Si crystals are refined, while their density increases and microhardness decreases. The increase in density is due to a decrease in the proportion and size of gas pores and the refinement of structural components. The decrease in microhardness is associated with an increase in the proportion of the soft phase (α-Al dendrites) and a decrease in the number hard eutectic silicon crystals. The average content of silicon in the samples deposited in three modes is in the range of 5.46–5.91%, which corresponds to the chemical composition of the welding wire Sv-AK5 (ER4043). An increase in the welding arc current facilitates a growth of tensile strength and a slight decrease in the conditional yield strength and relative elongation. The patterns of the change in the mechanical properties of the deposited samples are due to the specifics of the formation of the cast structure of the deposited layers under conditions of directional solidification in the direction away from the substrate.

Different types of materials with unique performance are used together in the industry, and soluble and/or insoluble joining methods are applied to join these materials. However, the joining process is quite problematic due to the technological drawbacks that arise during the joining of materials with distinctive characteristics. For this reason, mechanical locking (frictional) joining method is recommended to reduce some of the problems emerging during the joining of different materials. Various material groups such as ferrous and non-ferrous metals could be able joined by the mechanical locking method (MLM). In this study, to the main aim is to determine the effect of rotation speed, which is one of the influential process parameters, on the process of joining CuZn30 (brass) and AA6063 aluminum alloy materials using MLM. The mechanical properties and microstructures of the specimens joined by applying different rotation speeds were examined. Consequentially CuZn30 and AA6063 materials were successfully joined using the MLM and the number of rotation speeds applied during joining had a significant effect on the joining process.

A solid waste from zinc production, zinc plant residue (ZPR) is a valuable resource for the recovery of zinc (Zn), lead (Pb), and silver (Ag). However, the ferritic structure of ZPR makes it difficult to leach these metals. Here, in order to increase the reactivity of the ZPR, mechanical activation using a high-energy ball mill was used. The sample mechanically activated for 15 min was subjected to two-stage leaching with the hydrochloric acid (HCl) solution. At the 1st stage, 74% of Zn was recovered from mechanically activated ZPR sample into the solution under the following conditions: 1 M HCl, 120 min leaching duration, liquid-to-solid ratio (L : S) of 4, the temperature of 25°C, and a rotation speed of 600 rpm. At the 2nd stage, 56% of Pb and 53% of Ag were recovered from the leaching residue, under the following optimized conditions: 8 M HCl, 120 min leaching duration, liquid-to-solid ratio (L : S) of 20, the temperature of 25°C, and a rotation speed of 600 rpm. Сonceptual flow-diagram of the zinc, lead and silver selective recovery from ZPR is proposed herein.

At the present time, aluminum alloys with silicon are the most widespread construction materials. In order to increase the mechanical properties of aluminum alloys, modifying with Sr, Ti, and B is used. However, in the foundries, when using scrap and secondary aluminum alloys, the modifying elements are accumulated in alloys in the form of intermetallic particles, which can lead to a decrease in the level of castability. This is connected with the fact that the used modifiers exert a short-term effect and cannot be activated upon remelting. Hence it is necessary to add the modifiers without taking into account the intermetallic particles already contained in the melt. This paper is devoted to studies on the effect of additions of Sr, Ti, and B on the fluidity of an A356.2 grade aluminum alloy determined by means of vacuum fluidity testing. It is shown that, when AlSr10 and AlTi5B1 commercial master alloys are used (containing up to 0.3 wt % Sr and 0.5 wt % Ti), no decrease in fluidity is observed. However, adding the same amount of Ti with the use of a homemade AlTi4 master alloy leads to a considerable decrease in the fluidity. With the help of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), the microstructure and phase composition of master alloys and of an A356.2 grade alloy after adding the mentioned master alloys have been investigated. Additionally, the Thermo-Calc software package has been used to evaluate the effect of modifier addition exerted on the phase composition and phase transition temperature of the alloy. It has been established that the effect of the modifier addition on the fluidity of the A356.2 grade alloy is connected with the shape and size of crystals containing the modifying elements in the master alloy structure. When there are coarse crystals formed by such phases, it is quite possible that the crystals are dissolved incompletely, which could hinder the free flow of melt.

This paper presents the results of theoretical calculations of the reactivity of gold, molybdenite, stibnite, galena, chalcopyrite, arsenopyrite, and pyrite in comparison with experimental data on the floatability of monomineral fractions with butyl xanthate, measured contact angles, and variation in the kinetics of the potential of mineral electrodes. The calculation method establishes the following series of the reactivity and oxidation ability: Au < Sb₂S₃ < MoS₂ < PbS < CuFeS₂ < FeAsS < FeS₂. During flotation in the Hallimond tube, natural gold grains demonstrate the highest recovery (70%) in the range of pH 5–7 as compared to all the sulfides; molybdenite and stibnite are recovered under the same conditions at the level of 50%. With an increase in pH in an alkaline environment to pH 12, the floatability of all the sulfides decreases with the exception of chalcopyrite. It is found that the duration of conditioning with the collector required for the highest recovery is inverse to the reactivity value. The measured contact angle of a drop of water on an untreated surface is the highest for a gold plate (78°) and the lowest for pyrite (67°), but the greatest increase in the contact angle (by 15°) for pyrite is noted after treatment with butyl xanthate at a concentration of 10^–4 mol/L and pH 6; for molybdenite, treatment with butyl xanthate has almost no effect on the measured value of the contact angle. According to the value of the electrode potential in the region of pH 2.0–5.6, the following series is determined: Sb₂S₃ < PbS < CuFeS₂ < FeAsS < FeS₂. Theoretical calculations and experimental data of the study of monofractions of sulfides and gold establish that the conditions of the experiment (pH, duration of conditioning, concentration of the collector) significantly affect the floatability. The calculated data on the reactivity of chemical sulfide compounds and gold in comparison with experimental results show the importance of maintaining certain flotation conditions to create contrast in the floatability of minerals.

In this study, the effects of different treatments (annealing, solid solution and Solution + aging) on the bending and thermal conductivity of SiC_p/Al composites fabricated by the pressure infiltration method were investigated. The fracture form of the composites was indicated to be characteristic brittle fracture with local ductile fracture. The bending strength of the composites was 674 MPa with Solution + aging, which is 57% higher than that in the as-cast condition. The microhardnesses of the composites increased after heat treatment, resulting in the maximum microhardness 276 HV with Solution + aging. By calculating the thermal conductivity of the composites, the order was determined to be cast < annealed < solid solution < solution + aging, and the thermal conductivity with solution + aging treatment reached 182 m^–1 K^–1, which is higher than 153 m^–1 K^–1 in the as-cast condition.