Russian Journal of Non-Ferrous Metals最新文献

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.”

The article considers the influence of the parameters of friction stir welding modes on the formation of the outer surface and microstructure of the welded joint of sheets made of aluminum (AD1) and pure copper (M1). Changing the rotation speed of the welding tool from 600 to 1000 rpm and the range of welding speed from 20 to 100 mm/min allows one to control the amount of input energy, which allows one to transfer the welded materials to a plastic state. The paper considers the thermal cycles measured under the shoulder of the welding tool from the side of aluminum and copper sheets. The maximum temperature was 900 K on pure copper. The parameters of the welding modes also affect the formation of intermetallic layers. If the thickness of the intermetallic layer does not exceed 4–5 μm, then increased values of the mechanical strength of the welded dissimilar joint are observed.

The study explores the mechanical assessment of thin film coatings through nanoindentation and nanoscratch testing methodologies, crucial for understanding and enhancing their mechanical properties. It examines the composition, microstructure, and behavior of various thin films, such as ZrAlN, TiCrN, and rGOF/EP, under different test settings. Nanoindentation measures hardness, elastic modulus, and plasticity index, providing insights into the impact of filler content and matrix interactions. The study highlights the importance of correct filler quantities and stoichiometric ratios for desired mechanical properties, as evidenced by nanoscratch testing, which measures adhesive strength, elastic restitution, and scratch resistance. Comprehensive testing in diverse settings and precise management of film composition and microstructure are emphasized to achieve optimal mechanical properties. Future research may explore novel materials, refine testing procedures, and develop predictive models, making nanoindentation and nanoscratch testing essential for advancing high-performance thin film coatings.

Low corrosion resistance of magnesium alloys is a challenging problem that hinders their wide implementation in industry and medicine. In this regard, the study of the mechanisms and patterns of corrosion processes in magnesium and its alloys, including the analysis of the kinetics of these processes, is an urgent task. However, the set of methods available for studying the kinetics of corrosion with sufficient time resolution is very limited. Several studies have been published that demonstrated the high sensitivity of the acoustic emission (AE) method to corrosion processes occurring on the surface of magnesium alloys. Although these studies suggested that AE is associated with the release of hydrogen bubbles accompanying corrosion, no direct relationship has yet been established between the amount of hydrogen released and the AE characteristics. The present study aims at filling this gap. To conduct the study, a special setup with a corrosion cell was developed that allows monitoring changes in the volume of hydrogen released from the corroding surface of the sample, concurrently with recording AE signals and changes in the open-circuit potential (OCP) accompanying the corrosion process. Using this technique, the corrosion of ZK60 alloy in a 0.9% NaCl solution was examined. It was found that intense AE accompanied the corrosion process of this alloy from the beginning to the end of the test. A correlation was found between the AE characteristics, the volume of released hydrogen, and the OCP values at various intervals of the test. In particular, a linear relationship was discovered between the number of AE signals and the volume of hydrogen released during the corrosion process. The sensitivity of the method based on AE registration to the released hydrogen volume is shown to be several orders of magnitude higher than that of the conventional method of collecting hydrogen using a burette.