Vol 60, No 3 (2019)

A review of publications on the interaction of salt melts of magnesium production with atmospheric air is presented. The measurement procedure of the weight of interaction products of salt melts with air is described. The results of investigating the emission intensity of hydrogen chloride and chlorine by salt melts of MgCl₂–KCl–NaCl, MgCl₂–NaCl–BaCl₂, and MgCl₂–KCl–NaCl–CaCl₂ systems, as well as the emission intensity of HCl + HBr and Cl₂ + Br₂ gases by salt melts of the MgCl₂–KCl–NaCl–NaBr system, are presented. The thermodynamic analysis of interaction reactions of magnesium salt solutions with atmospheric air is performed. It is revealed that magnesium chloride in the salt melt most intensely interacts with atmospheric air with the emission of chlorine and hydrogen chloride. The specific rates of formation of halogen-containing gases from the unit surface area of the MgCl₂–KCl–NaCl, MgCl₂–KCl–NaCl–BaCl₂, MgCl₂–KCl–NaCl–CaCl₂, and MgCl₂–KCl–NaCl–NaBr systems are measured. The influence of calcium chloride, sodium bromide, and magnesium fluoride on the emission intensity of halogen-containing gases by the surface of salt melts is measured. It is determined that the addition of magnesium fluoride into the composition of chloride melts reduces the emission intensity of chlorine and hydrogen chloride.

The results of a numerical investigation into the temperature–temporal dependences in continuous combined casting and pressing of the AK12 experimental aluminum alloy at a different overheating temperature from startup to the instant the steady-state thermal conditions are reached by the installation are reported. Calculations are performed based on a three-dimensional computer model of a complex heat exchange in an installation of a new design equipped by a horizontal rotary crystallizer. Theoretical investigations into the effect of overheating of the poured aluminum melt on the temperature-dependent heat exchange processes are performed. The influence of the character of the heat exchange in the transient thermal mode on the temperature field of the solidified melt for its different remoteness from the pouring point is determined. It is shown that the asymmetry of the temperature field in the control metal cross section near the pressing tool with the maximal temperature to the contacting crystallizer surface increases during crystallizer heating in the transient process. It is established that the duration of the transient process during the installation startup from the cold state until the steady-state thermal mode is attained depends on the temperature of the melt being poured. The maximal limit of overheating of the poured metal is determined, above which, when implementing the continuous combined casting–pressing technology, the aluminum melt does not solidify in the crystallizer and forced cooling of installation elements should be organized. The influence of melt overheating on the character of the temperature field along the crystallizer cross section is evaluated for the entire period of the transient thermal process. The design measures ensuring the rational temperature working conditions of bearings during the installation operation are given.

The compaction of powder of the Al–B–W in a copper shell is considered in this article. This material is supposed to fabricate, for example, grinding tool components or radiation protection elements. For this purpose, it is necessary to fabricate both short and long semifinished products, which requires the development and testing of various process flowsheets (methods) based on using static and dynamic loads, as well as their combinations. An analysis of experimental results shows the reality and possibility to implement the proposed flowsheets for fabricating tubular semifinished products of various sizes. The entire chain of their manufacture is considered from the production of powders to their compaction and sintering. To assess the quality of the sintered powder composition, metallographic investigations are performed. Their results show an almost complete absence of pores. Technology is developed that ensures the fabrication of new products, including long ones, from the Al–B–W powder composition.

This article is devoted to the topical problem of developing antifriction aluminum alloys economically alloyed with low-melting metals. It was found in earlier experiments that an alloy containing about 5% Si, 4% Cu, and 6% Sn (wt %) has a balanced complex of manufacturing and physicomechanical properties. The possibility of decreasing the tin concentration to 4% and its partial substitution by other low-melting metals such as bismuth and lead is considered because of the high cost of tin. The joint and separate influence of these elements on the phase composition of the Al–5% Si–4% Cu–4% Sn alloy is studied using thermodynamic calculations (in the Thermo-Calc program), including the construction of polythermal and isothermal sections. It is shown that additives of lead and bismuth cause the appearance of an extensive area of fluid stratification, so their total concentration should not exceed 1–2%. The phase composition and microstructure of the Al–5% Si–4% Cu–4% Sn–0.5% Pb–0.5% Bi alloy are studied using scanning electron microscopy and X-ray spectral microanalysis. It is revealed that low-melting metals are uniformly distributed in the structure of the alloy in the cast state and, in totality of properties, this material surpasses BrO4Ts4S17 antifriction bronze. Heat treatment according to the T6 mode leads to a significant increase in the hardness of the alloy under study. However, local fusion of the low-melting component occurs during heating for quenching at 500°C, which causes the deterioration of the microstructure during recrystallization and, consequently, causes alloy embrittlement.

The kinetics and mechanism of fatigue failure of the VT6 titanium alloy (composition, wt %: 5.95 V, 5.01 Al, 89.05 Ti) in the initial (hot-rolled) coarse-grained (CG) state and after equal-channel angular pressing (ECAP) in the ultrafine-grained state (UFG) are investigated. ECAP is performed using billets of the mentioned alloy 20 mm in diameter and 100 mm in length preliminarily subjected to homogenizing annealing. Then, quenching in water is performed from 960°C with holding for 1 h, tempering at 675°C for 4 h, and ECAP at 650°C (route B_с, φ = 120°, number of passes n = 6). The fine alloy structure after ECAP is investigated by transmission electron microscopy at an accelerating voltage of 200 kV. To determine alloy hardness, a Time Group TH 300 hardness meter is used. Static tensile tests are performed for round samples 5 mm in diameter using a Tinius Olsen H50KT universal testing machine. The extension velocity is 5 mm/min. Fatigue tests are performed using prismatic samples 10 mm in thickness at 20°C according to the three-point bending test using an Instron 8802 installation. It is shown that, under the same loading conditions, the fatigue life of alloy samples (the number of cycles before failure) in the initial CG state is higher than that of the alloy samples in the UFG state. It is shown that the number of cycles before fatigue-crack nucleation was at a level of 19–23% of the total sample longevity, regardless the alloy state. The straight-linear segment in kinetic diagrams of the alloy fatigue failure is approximated by the Paris equation. It is revealed that the propagation rate of the fatigue crack in the alloy with an UFG structure is somewhat higher than in the alloy with a CG structure. The microrelief of fatigue cleavages of the VT6 alloy both in the CG and UFG state can be characterized as scaly with fatigue grooves on the scale surface. A low-relief region 4–6 μm in length can be observed in the failure region of the samples with an UFG structure. The microrelief of the rupture region is pit, irrespective of the alloy state.

The results of model studies on the possibility of reducing energy costs and carbon dioxide emissions during the Waelz process of oxidized zinc-containing material are presented. Herewith, the METSIM specialized software product is used. It is well-known in the world practice of metallurgical processes and manufactures modeling and makes it possible to analyze the influence of the variation in the process modes on the final process results. Model calculations show that the largest decrease in consumption of energy carriers and CO₂ emissions are observed when using air blast heated to 200°C with an increase in its flow rate from 1000 to 7000 ncm/h and an accompanying decrease in atmospheric air suction. The calculated reduction of the specific carbon consumption and CO₂ emissions is 30.2–35.5%, and that of the total specific consumption of energy carriers is 28–32%. Herewith, blast heating to 200°C in the air heater of the waste-heat boiler does not require additional energy inputs in contrast with the variant of using the oxygen blast with electricity consumption for oxygen production. The intensification of the Waelz process with the application of the additional oxygen blast (or enrichment of the air blast with oxygen) and the heated air blast supply with an accompanying decrease in the atmospheric air suction leads not only to a decrease in the specific flow rate of the carbon energy carrier, but also to an increase in the degree of the carbon utilization. The maximal calculated increase in the degree of carbon utilization is 6.2 rel. %—from 60.3% when using cold air blast without oxygen to 66.5% using the air–oxygen blast heated to 200°C (7000 ncm/h of air and 185 ncm/h of oxygen) without atmospheric air suction. Maintaining the optimal redox and thermal process modes requires correctly controlling the kiln blow-out mode allowing for the atmospheric air suction in the kiln unloading head. Uncoordinated variations in specific consumptions of the charge, carbon, blast, and rarefaction in the dust chamber lead to an accompanying decrease in the zinc recovery into sublimates and an increase in its losses with clinker.

Features of liquid-phase sintering compacts made of powders of the Al–10Zn alloy and tin of the PO 2 brand, as well as the influence of sintering modes on the structure and strength of forming antifriction composite of the (Al–10Zn)–40Sn composition, are studied. The porosity of the initial green compacts varies in a range of 5–18%. Compacts are sintered in a vacuum furnace under a residual gas pressure no higher than 10^–2 MPa. The sintering temperature varies in a range of 550–615°C and corresponds to the partial wetting of aluminum with liquid tin. The sample holding time at a specified temperature is from 30 to 180 min. Structural studies show that the particle size of the aluminum and tin phases increases with an increase in the sintering temperature and holding time. The mechanical properties of sintered composites are determined by their compression testing. The samples are cut from the middle of sintered compacts. It is established that samples made of the (Al–10Zn)–40Sn sintered alloy possess high ductility and exhibit higher strength when compared with the Al–40Sn sintered composite with a pure aluminum matrix due to the more intense strain hardening of a matrix at a high deformation. It is found that sintered composites prepared from high-density green compacts subjected to preliminary low-temperature holding possess the highest strength. Based on the results, it is concluded that the liquid-phase sintering in a specified temperature range makes it possible to prepare (Al–10Zn)–40Sn composites with a bound aluminum matrix effectively preventing the strain localization in soft tin-based phase interlayers. The optimal sintering temperature should not exceed 600°C.

Commercial F500 SiC powder and 6061Al powder were chosen to fabricate the mid-fraction SiC particles (SiCp)/6061Al composite of 30 vol % (volume fraction) SiC using a pressureless sintering technique. Decantation of the SiC powder and optimization of the sintering temperature were performed to improve the microstructure and properties of the composite. The results show that near full-densification of the 30 vol % SiCp/6061Al composite sintered at 680°C is achieved, and no SiCp/Al interfacial reaction occurs. The composite possess the following set of properties: relative density of 98.2%, bending strength of 425.6 MPa, thermal conductivity (TC) of 159 W/(m K) and coefficient of thermal expansion (CTE) of 12.5 × 10^–6/°C (20–100°C). The fracture of the composite occurs via cleavage of the SiC particles and ductile tearing of the Al alloy matrix, indicating a strong SiCp/Al interface bonding.

The effect of temperature fields of heating during continuous laser treatment on the performance of the T15K6 carbide insert plates is studied. A tool with T15K6 indexable carbide inserts is exposed to laser treatment by heating the working surface with continuous laser emission using an LK 3015ls07 industrial laser according to the KV_OSN program along the insert contours with a distance from the cutting edge of ~2 mm. The laser exposure time is 2–3 s using nitrogen as a shielding medium. The samples shaped as tetrahedral plates 12 × 12.70 × 4.76 mm in size (GOST (State Standard) 19050–80) are used for the investigation. The emission power density varies in the range q = 300 ± 100 W/cm² and laser-beam moving speed varies as V_L = 20 ± 10 mm/s. The hardness of the laser-hardened zone after laser exposure is H_μ = 15 500–21 500 N/mm². The laser impingement region was tested for cutting and abrasive wear, and microstructural analysis was performed. The cutting wear along the front and back surfaces of carbide inserts after laser treatment decreased fivefold. It is shown that a further increase in laser power density up to q = 400 W/cm² does not provide a positive trend. The diamond-abrasive wear with an increase in q is accompanied by wear reduction to 40 wt %. Microstructural analysis showed a decrease in the tungsten carbide grain size in a continuous laser treatment region from 5.6 to 4.3 μm.