Russian Journal of Non-Ferrous Metals最新文献

Among all the conventional routes for the production of metal foams, combustion synthesis can yet be conducted as a novel method to produce self-propagating aluminum-alumina (Al–Al₂O₃) composite foams which are referred to as self-propagating high temperature synthesis (SHS). In this study, an aluminum matrix reinforced by submicron alumina particles was successfully fabricated via combustion synthesis through the reaction of aluminum (Al) powder and sodium nitrate (NaNO₃) powder as the blowing agent and the effect of their molar ratio on mechanical properties and the phase generated in the foam were investigated. Optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), Image J software, X-ray diffraction (XRD), and compression mechanical test were utilized to study Al₂O₃ dispersion, matrix microstructure, elemental composition, pore size, final phases, and mechanical behaviour of the foams, respectively. According to the results, it was concluded that by increasing the molar ratio of aluminum in the precursors, the Al₂O₃ amount was decreased which was also confirmed by XRD results. Likewise, the combustion synthesis reaction was moderated followed by a decrease in the average pore size from about 40 to 21 µm. Study of pore morphology along with mechanical behaviour showed that the optimum molar ratio of the powders that produced open pores with an average size of 32 µm and an average plateau stress of 72 MPa through a sustainable combustion synthesis reaction was about NaNO₃ : Al = 2 : 13.3.

The corrosion resistance and biocompatibility of ultrafine-grained (UFG) Zn–1% Li–2% Mg and Zn–1% Mg–1% Fe zinc alloys, which exhibit unique mechanical properties as a result of severe plastic deformation (SPD) processing, were investigated. The corrosion rate in the UFG Zn–1% Li–2% Mg alloy was found to be 0.0891 mm/year, and this rate in the UFG Zn–1% Mg–1% Fe alloy was found to be 0.061 mm/year. The conducted comparative tests with their coarse-grained (CG) analogs have shown that corrosion processes most intensely occur at the periphery of UFG samples, which are characterized by a greater degree of accumulated deformation, strong refinement of structural elements, intense phase transitions, and completeness of dynamic aging. The increase in the corrosion rate in UFG Zn–1% Li–2% Mg alloy in comparison with its CG analog is explained by the presence of the Mg₂Zn₁₁ phase of high content, increased weight fraction of the Zn phase alloyed with Li and Mg atoms, precipitation of Mg₂Zn₁₁ particles in it, and decrease in the ~LiZn₃ fraction. The growth of the corrosion rate in the UFG Zn–1% Mg–1% Fe alloy is also explained by the increase in the Zn doped phase and precipitation of precipitates in the Zn and Mg₂Zn₁₁ phases. In addition, the phase transition of FeZn₁₃ into its FeZn_10.98 modification (FeZn₁₃ → FeZn_10.98), which is uncharacteristic for the CG state, was found in the near-surface layers of the UFG sample when aged in Ringer’s solution. The results of Alamar Blue metabolic test demonstrated biocompatibility of MG-63 cells for 1 day (more than 50%) and proliferative capacity for 7 days (more than 30%) when incubated with 12.5% extracts of UFG Zn–1% Mg–1% Fe and Zn–1% Li–2% Mg alloy samples. The causes of MG-63 cell death when the content of extracts of zinc alloy samples was increased were analyzed.

The effects of temperature difference between two precursor melts and angle between two gates for pouring the two melts on the microstructure of controlled-diffusion-solidified Al–8Si alloy were investigated by simulation and experiment. The simulation results showed that only the temperature difference was higher than 50 K, the nucleation rate during mixing could reach a critical value (corresponding to ~30% of solidified mesh number in simulations), and thus, a microstructure with small and spheroidal primary grains was obtained. Increasing the gate angle was beneficial for achieving a mixed melt with smaller and more alloy 1 pockets, and thereby was helpful for increasing nucleation rate and obtaining an ideal nondendritic microstructure. The subsequent experiment results confirmed these simulation results. When the temperature difference and gate angle were at 80 K and 140° respectively, an Al–8Si casting with grain size of 52.0 μm and a shape factor of 1.40 was achieved.

The results of the study on determining the true fracture stresses of cylindrical samples with an ultrafine-grained structure of alloy 6001 obtained by the ECAP-C method are presented. These results are compared with similar data for a coarse-grained structure of the same alloy produced through standard heat treatment. This work was conducted to accurately describe the mechanical behavior of the material in both the coarse-grained (CG) and ultrafine-grained (UFG) states. The analysis revealed that the true strain to failure in the artificial aging (AA) state and the UFG state of alloy 6101, taking measurement errors into account, is the same. However, the true fracture stress of samples with a UFG structure is significantly higher than that of samples with an AA structure. The increase in strength and yield point resulting from ECAP-C processing is determined by the reduction in grain size according to the Hall–Petch relationship. An explanation for the increase in true fracture stress of samples during grain refinement is proposed on the basis of a compilation of the Hall–Petch relationship and the Zener–Stroh model, which involves a criterion for pore formation in particles when the stresses at the matrix/particle interface reach critical values.

The dissolution process of zinc sulfide in sulfuric acid, particularly in the presence of oxygen, is critical for various industrial applications. This study investigates the dissolution kinetics of zinc sulfide in aqueous sulfuric acid under oxygenated conditions, simulating industrial leaching processes using an autoclave. The experimental results explore the influence of parameters such as initial mass of zinc sulfide, oxygen partial pressure, temperature, and sulfuric acid concentration on the dissolution kinetics. The study reveals complex interplays between dissolution kinetics, chemical reactions, and environmental factors, offering insights into optimizing industrial processes for efficiency and sustainability. Key findings include the direct proportionality between zinc sulfide dissolution rate and oxygen partial pressure, as well as the dependence of dissolution kinetics on temperature, acidity, and the presence of hydrogen sulfide in the solution. Additionally, a kinetic model is developed to describe the dissolution process, incorporating factors such as temperature, initial concentration of sulfuric acid, and oxygen partial pressure, enhancing our understanding of the underlying mechanisms governing the dissolution process and its industrial applications.

The aim of this study is to investigate the mechanical and tribological behaviours of aluminum hybrid composites (AHMCs) reinforced with particles of fly ash and titanium carbide (TiC) adopting the stir casting route. The aluminum matrix (LM25) was reinforced with a constant 5% fly ash and varying proportions of TiC (4, 8, and 12%) to evaluate the dispersion effect of added reinforcements on the fabricated AHMCs. Mechanical properties of tensile strength, hardness, and tribological properties were determined to evaluate the TiC-dispersed AHMCs. The outcomes of experimentation show that inclusion of the reinforcement particle of TiC particle enhances both the mechanical strength and hardness at 42.1 and 50.9% and reduction of wear and COF at 27.2 and 43.7%, respectively, for the fabricated AHMCs, which makes them a suitable material for lightweight applications in aerospace, automotive, and marine sectors. The tribo analysis shows that a significant amount of dispersed TiC makes a strong tribo layer on the contact surface, reducing the abrasive effect of the counter surface.

The microstructural, phase, acoustic, and elastic properties of nine cast magnesium alloys with an LPSO structure (X phase) were studied within a concentration range of Y, Gd, Zn, and Zr that are promising for practical applications, considering their subsequent thermal dispersion strengthening (Y ≤ 7.6, Zn ≤ 2.78, Gd ≤ 4.9, and Zr ≤ 0.68 wt %). A comparison of the experimental data revealed that the propagation rate of longitudinal and transverse waves in the alloys decreases, while the attenuation coefficient increases proportionally to the total weight percentage of alloying elements forming the X phase. Furthermore, the elastic and acoustic properties correlate more significantly with the total weight percentage of alloying elements in the Mg alloy rather than with the atomic parameters of the phase-forming alloying elements (Y/Zn) commonly used in metallurgy. It was shown that the variation in wave propagation rate in Mg alloys with the X phase predominantly correlates with an increase in their density. At a low content of the secondary phase, wave attenuation is determined by grain size, while in the presence of a secondary phase in the form of conglomerates at grain boundaries, it is influenced by the ratio of grain size, secondary phase size, and wavelength. It was found that the parameter of the ratio of secondary phase size to wavelength, introduced by analogy with the conventional acoustic parameter of the ratio of grain size to wavelength, weakly correlates with the acoustic properties of alloys with the X phase. Additionally, there is a discrepancy between the dependences of the attenuation coefficient on grain size and wave frequency. This discrepancy may be due to the unaccounted for influence of the X phase in the form of banded insertions into α-Mg grains, as well as the method of calculating the secondary phase size, which requires further investigation.

In this paper, we investigated the 7075 aluminum alloy obtained by casting in the as-delivered condition and after nitriding the alloy in an arc discharge using a plasma source with a hot cathode at a temperature of 350°C for 2 h in a gas mixture of 50% argon and 50% nitrogen, 0.5 Pa, 500 V. The surface of the sample after nitriding was represented by a grain structure with a nonuniform distribution of manganese, iron, and oxygen atoms. Nitriding contributed to an increase in the nanohardness of the material to 1.4 GPa and the Young’s modulus to 132 GPa, owing to the formation of a modified layer after nitriding the alloy surface. The depth of the nitrided layer of the studied aluminum samples was nonuniform and varied from 5 to 10 µm; in the cross section of the studied layer, areas with increased oxygen and manganese content were detected using the elemental mapping method. The average value of the crystal lattice parameter after nitriding of the material changed from 4.035 to 4.047 Å. This increase in the crystal lattice parameter may be associated with the formation of tensile macrostresses, which affect the mechanical properties of the material.

The paper presents the results of studies on the causes of defects on gold coins of Kazakhstani production—“zones of discoloration” which grow during storage. On the basis of the analysis of foreign research papers, it is shown that this phenomenon is also observed in products of mints in other countries. As shown by the results of studies, using the method of X-ray spectral microanalysis, the genesis of these defects is determined by ingress of silver microparticles, sulfur compounds, and atmospheric air moisture on the surface of gold coins. As a result of chemical reaction, hemioxide Ag₂O and hemisulfide Ag₂S are formed. Sulfuric acid electrolyte, formed on the surface of coins, contributes to the migration of silver ions and growth of defects. Depending on the time, the size, thickness, and composition of the pitting corrosion center do change, which causes formation of “discoloration zones.”