Russian Journal of Non-Ferrous Metals最新文献

Hot compression tests were conducted on an ultrahigh-alloyed Al–Zn–Mg–Cu alloy within a temperature range of 250 to 450°C and a strain rate range of 0.001 to 1 s^–1. The effects of strain rate and temperature on the flow curves were analyzed, along with the relationship between flow stress and microstructural evolution. The results indicate that, except for a strain rate of 1 s^–1 across all temperatures, the flow curves following the peak stress do not exhibit monotonic work hardening or dynamic softening. In contrast, continuous work hardening is observed at this strain rate. The diverse shapes of the flow curves are attributed to the various precipitates formed due to the high alloying element content. Dynamic recovery (DRV) is identified as the main flow softening mechanism for the ultrahigh-alloyed Al–Zn–Mg–Cu alloy. While dynamic recrystallization (DRX) contributes to flow softening at a strain rate of 0.001 s^–1, the deformed microstructure becomes the predominant softening mechanism at lower temperatures and higher strain rates. Additionally, the low intensity of isotropic texture at higher temperatures and strain rates facilitates DRX, resulting in a decrease in peak stress.

The aim is to conduct research in the field of hydrometallurgical refining of metallurgical silicon. The object of research was metallurgical silicon after oxidative refining from AO Kremnii, part of the United Company RUSAL (Shelekhov, Irkutsk oblast, Russia). The chemical composition of the obtained samples was studied by X-ray fluorescence analysis and X-ray spectral microanalysis. According to elemental analysis, metallurgical silicon contains (wt %) 0.53Al, 0.6094Fe, 0.0491Ti, 0.0628Ca, 0.0066V, 0.002Cr, 0.014Mn, 0.003Cu, 0.010P, 0.007Ba, 0.007Ni, 0.002Zn. It is shown that intermetallic compounds of the following composition were recorded in the studied samples: AlFeSi₂ (with an admixture of Ca), FeSi₂ (with an admixture of Al), FeSi₂Ti (with an admixture of Zr). To reduce the content of impurities in silicon, we selected the following acids as solvents: 10% H₂SO₄, HCl, and HNO₃, as well as 4% HF in various ratios. To study the possibility of reactions of interaction of intermetallic compounds with selected solvents, the values of the Gibbs energy change, which had negative values, were calculated. Experimental leaching of impurities was conducted on silicon samples with particle sizes of –200 μm under constant stirring using a magnetic stirrer. The process parameters included a temperature of 60°C, a liquid-to-solid ratio of 5 : 1, and a purification duration of 60 min. It was found that using a solvent mixture of sulfuric and hydrofluoric acids in a 1 : 1 ratio achieved the highest degree of silicon purification, with an impurity removal rate of 86.85%. It is shown that when using a mixture of sulfuric and hydrochloric acids in a ratio of 1 : 3, the degree of purification of metallurgical silicon was 41.48%. In this way, solvents that enable maximum purification of silicon from impurity elements were identified.

Insufficient corrosion resistance of magnesium alloys limits their technical and medical applications. It is known that the corrosion rate of these materials depends, among other things, on the orientation of the samples relative to the workpieces, for example, rods or sheets obtained by thermomechanical processing. There is an opinion in the literature that this is primarily due to the influence of crystallographic texture. In this work, the corrosion resistance of samples cut from extruded rods of industrial alloys ZK60 and AZ31 along and across the extrusion direction was investigated. The corrosion rate was determined by the loss of weight and volume of the samples, as well as by the volume of hydrogen released when they were dissolved in a 0.9% NaCl solution. The microstructure and surface of the samples after corrosion tests were investigated using scanning electron microscopy, energy-dispersive X-ray microanalysis, and electron backscatter diffraction. It is shown that the rod has a pronounced basal texture, and therefore the crystallographic orientation of the grains to the lateral surface of the transverse and longitudinal samples is very different. It was found that samples of both alloys cut across the rod had higher corrosion resistance than longitudinal samples. According to published data, if the anisotropy of corrosion properties were caused by crystallographic texture, then longitudinal samples, on the contrary, should have a lower corrosion rate than transverse ones. Therefore, it is concluded that, in the case of medium- and high-alloy magnesium alloys, the anisotropy of corrosion properties is associated mainly with the nature of the volume distribution of second-phase particles, and not with the crystallographic texture. It is shown that the row arrangement of particles on the surface of longitudinal samples leads to deterioration of corrosion resistance.

Aluminium closed-cell foams are valued for their low density, high stiffness, corrosion resistance, and recyclability, making them suitable for aerospace, marine, and automotive applications. The quality of these foams depends on raw materials and processing methods. Therefore, employing an efficient and cost-effective processing method and raw materials is vital for ensuring that the foam’s properties are not compromised. This work investigates the use of bio-waste chicken eggshell powder and recycled aluminium alloy as a foaming agent for closed-cell aluminium/SiC_p composite foams. The foams produced are examined for micro & macrostructure and its characteristic mechanical behavior. The influence of SiC_p concentration on foam expansion and stability are investigated. Eggshell powder enabled the aluminium alloy to expand and form foam, further adding SiC_p resulted in the homogeneous distribution of pores with negligible metal drainage.

To obtain products made of aluminum-matrix composite materials (AMCM) with the required level of mechanical properties, processing by means of intense deformation is necessary. To model the deformation behavior in nonstationary conditions of thermal deformation treatment, the identification of the AMCM model remains an urgent task. One of the approaches to the description of material fluidity is the use of the Johnson–Cook plasticity model. In the proposed work, the object of research is an AMCM made of granulated high-strength aluminum alloy V95 of the Al–Zn–Mg–Cu system, reinforced with 10 wt % SiC particles. The aim of the work is to determine the influence of nonstationary thermomechanical (pressure on the workpiece and heating temperature) deformation conditions on the true deformation and deformation rate of the composite material, as well as to identify the material model and verify its application to study the processes of shape change in the studied pressure and temperature range. An experimental study of the precipitation process under uniaxial compression of sintered cylindrical samples of AMCM in the range of initial pressures of 5.65–7.81 MPa when heated to 510, 530, and 550°C is conducted. In this range, the dependences of the degree of deformation and the average deformation rate for the process are obtained. Identification of the rheological model of the material was carried out. A mode of preliminary thermomechanical processing is proposed and a prototype is manufactured at an initial pressure of 6.7 MPa on the workpiece and heated to 550°C in 84 min. The above mode provided relatively uniform filling of the stamp cavities with composite material. To confirm the possibility of applying the results of parametric identification of the material model, simulation modeling of the technological process of manufacturing a prototype was carried out.

The concentrated sulfuric acid roasting method and caustic soda method, as the main processes for treating Bayan Obo mixed rare earth concentrate, have been operating normally for decades. However, due to their serious pollution, high cost, and waste of accompanying resources, relevant rare earth enterprises are facing severe environmental and cost pressures. The sodium carbonate roasting method is a clean method for treating rare earth minerals, but due to the phenomenon of “ring formation” in the rotary kiln during the reaction process, this process has not been widely promoted. Based on the above facts, this article proposes a decomposition method for sodium pelletizing to decompose monazite, which effectively alleviates the related technical problems caused by the “ring formation” problem. Moreover, the rare earth leaching rate is 86.87%, and the recovery rates of F, P, and Th are 98.64, 13.87, and 88.96%. It is a potential rare earth mineral cleaning production process and can provide certain technical references for relevant rare earth enterprises.

The paper presents the results of an experimental study into the possibility of producing ultrahigh temperature ceramics constituting solid solutions of HfC and ZrC carbides by the single-stage electrothermal explosion (ETE) method under pressure. Adiabatic flame temperature and phase composition of the equilibrium final product were calculated on the basis of thermodynamic data. It was shown that, when the ZrC content in the final product is less than 20 wt %, the adiabatic flame temperature reaches 3800–3900 K, and the combustion product contains hafnium and zirconium carbides. The effect of mechanical activation modes in an AGO-2 planetary centrifugal mill used for a reaction mixture containing Hf, Zr, and C powders on its properties, phase composition formation, and the microstructure of carbide solid solutions was studied. It was shown that high-energy mixing in hexane leads to the destruction of the crystal structure of Hf and Zr particles and the formation of amorphous composite particles. The synthesized samples of ultrahigh temperature ceramics were studied by X-ray diffraction and microstructure analyses. It was shown that exothermic synthesis leads to the formation of single-phase solid solutions of HfC and ZrC carbides with the average particle size of 1.5–0.2 µm. The residual porosity of the binary carbides obtained is 10–12%. It was found that, despite the high temperature of sample heating during ETE under pressure, the particle size of the resulting solid solutions is significantly (by an order of magnitude) smaller than the particle size of similar complex carbides (20–50 µm) obtained by other methods (SPS and hot pressing). This is associated with the rapidity of the exothermic interaction of the reagents (10–50 ms) during ETE.

Phase transformations taking place during synthesis of WC by electrothermal explosion (ETE) were investigated within the following range of process parameters: T = 293–3700 K, 49.8–50.2 at % C, P = 96 MPa, V = 10 V, I = 20 МА/m², sample diameter of 20 mm. The thermogram of the ETE process was subdivided into four stages (I–IV). Stage I, warmup, temperature range of 293–563 K, endothermic reaction (isothermic plateau), input electric energy Q = 2.96 kJ, specific input energy Е = 111.6 kJ/mol. Low-temperature stage II, 563–1190 K, ignition, Q = 5.46 kJ, Е_а = 109.2 kJ/mol. High-temperature stage III, 1190–2695 K, eutectoid decay, order–disorder transformation, Q = 14.25 kJ, Е_а = 424 kJ/mol. Stage IV, melting, 2695–3695 K, Q = 14.31 kJ, Е_а = 143.2 kJ/mol. The rate of ETE reaction is highly sensitive to applied pressure, concentration of reagents, sample shape, oxide film, etc. Variation in E affords facile control of the ETE process.