Vol 27, No 3 (2025)

Introduction. The resistance spot welding (RSW) process has proven to be widely applicable across various industrial sectors, especially for mass production. Typical fields of application include aerospace, automotive, furniture manufacturing, and other industries. However, the RSW process presents certain challenges when welding aluminum and its alloys. Generally, aluminum alloys produce poor welds due to their physical and metallurgical properties such as oxide formation, thermal expansion and contraction, lower weldability, and the formation of intermetallic compounds. This study aims to evaluate the feasibility and mechanical characteristics of RSW joints in Al-5 Mg aluminum alloys. The purpose is to assess the potential of resistance spot welding for aluminum alloys and to determine the influence of key RSW parameters on the microstructure and properties of the weld. Research methods. Al-5 Mg aluminum alloy sheets in as-received condition were used. Spot welding was performed using a stationary resistance spot welding machine MT-4240. Samples for analysis were cut, polished, and subsequently examined under an optical microscope. Hardness measurements were carried out using a microhardness tester along two directions: radially across the nugget and through the sheet thickness, employing a 100 g load. An Instron electromechanical testing machine was utilized for shear testing at a constant traverse speed of 1 mm/min until complete joint failure at room temperature. The nugget diameter was measured on the fracture surface after shear tensile testing. Results and Discussion. Optimal input parameters for welding 2.5 mm thick aluminum sheets were identified, and three output variables were analyzed: tensile strength, joint hardness, and nugget diameter. It was observed that joint strength improved significantly with increased process parameters (welding current and welding period). Nugget diameter showed a clear correlation with input parameters related to current and welding period. An increase in process parameters, i.e., weld cycle time, electrode force, and welding current, led to an increase in nugget size. The ratio of weld strength to base metal strength reached approximately 0.9. It is demonstrated that resistance spot welding of 2.5 mm thick Al-5 Mg aluminum sheets is feasible and can be employed in various industrial applications.

Introduction. Ti-Ni based shape memory alloys (SMAs) are functional materials that find widespread practical application in engineering and medicine. Functional properties of Ti-Ni based alloys are sensitive to the chemical composition. To develop alloys with specific properties, ternary SMAs are being actively developed. For example, TiNiHf ternary alloys are characterized by a high-temperature shape memory effect. Today, there is a demand for SMAs used in the production of functional elements with a response temperature of more than 120 °C. These alloys must also have sufficient ductility to obtain deformed semi-finished products for the subsequent manufacture of heat-sensitive functional elements. Also among the current issues of developing the practical application of TiNiHf alloys is the lack of technological schemes for obtaining semi-finished products from TiNiHf SMAs. The purpose of this work is study the feasibility of conducting deformation processing of the studied TiNiHf alloys with a high-temperature shape memory effect and to identify the relationships between phase composition and mechanical characteristics and the applied processing method. In this work, the possibility of producing sheets and rods from TiNiHf alloys with 5 and 10 at.% Hf and 50.0 at.% Ni by longitudinal rolling, caliber rolling, and rotary forging was investigated. The research methods were: X-ray analysis, differential scanning calorimetry, and measurement of Vickers hardness. Results and discussion. It was found that the TiNiHf alloy with 10 at.% Hf has insufficient ductility. From the alloy with 5 at.% Hf, blanks in the form of sheets and rods of various sizes were obtained by using longitudinal rolling and rotary forging processes. It was shown that hot deformation allows increasing the hardness of the studied TiNiHf alloy with 5 at.% Hf compared to the cast state, from 232 HV to 242–264 HV. Cold deformation leads to a significant increase in hardness values up to 362–394 HV. Characteristic temperatures of the forward and reverse martensitic transformation are quite stable. The obtained results indicate the potential of using longitudinal rolling and rotary forging to obtain semi-finished products of TiNiHf alloys with 5 at.% Hf and to improve the functional and mechanical properties of the alloy after smelting.

Introduction. In developing a mathematical model for the sound pressure generated by the grinding process, it became necessary to determine the actual values of the integral elastic parameters of grinding wheels to use as inputs in the model. This will expand the applicability of the model and maximize its practical utility. This paper describes an approach to determining Poisson's ratios and Young's moduli for grinding wheels with different characteristics. The elastic properties of the tool are the subject of this study. The purpose is to establish the relationship between actual values of integral elastic parameters and grinding wheel characteristics via modal analysis. The research method combines experimental investigation of natural frequency spectra and modal analysis, implemented via the finite element method in specialized software. Additionally, regression analysis is employed to derive empirical dependencies of the integral elastic parameters of grinding wheels on abrasive grain size and hardness. Results and discussion. The main result of this work is the determination of the actual values of Poisson's ratios and Young's moduli for grinding wheels with the studied characteristics. The selection of grinding wheel characteristics allowed for the investigation of the influence of abrasive grain size and hardness on its integral elastic properties. The development of a mathematical model for sound pressure generated by the grinding process, along with a methodology for predicting the service life of grinding wheels based on this model, will improve grinding operation efficiency by reducing the machine-setting time, increasing processing time, reducing consumption of manufacturing resources, and optimizing tool lifespan utilization.

Introduction. JSC Volzhsky Abrasive Plant is the sole producer of silicon carbide in Russia and the largest producer in Europe. The company employs various methods, equipment, and technologies for grinding abrasive materials, which influence the geometric parameters of the grains. The most prominent and widely used methods for grinding silicon carbide in current production are roller-press grinding and rotary grinding. The purpose of this work is to study the effect of the roller-press and rotary methods of grinding black silicon carbide, which are used at the JSC Volzhsky Abrasive Plant, on the shape factor, length, and width of the grains in the sample fractions. Research methods. The initial material obtained in accordance with the current technological process was selected after crushing in a rod mill. One sample was crushed using the roller-press method, and the other was crushed using the rotary method. The crushed silicon carbide was sieved into fractions using a Ro-Tap sieve analyzer. The geometric parameters and grain shape were determined in five fractions, and 800 grains were measured in each fraction. The horizontal projection of the grain profile was obtained using an Altami SM0870-T optical stereoscopic microscope. Special software was used to process the projections and determine the geometric parameters. Results and discussion. It has been established that the shape factor and grain length follow the maximum value law, while the width follows the normal distribution law. The strength of the correlation between geometric parameters ranges from weak to strong, and the direction of the relationships varies from positive to negative. Graphical dependencies are presented, demonstrating the correlation and regression relationships between the geometric parameters of the grains in the fractions. Rotary grinding results in an average increase of 5% in the number of isometric grains compared to roller-press grinding, while the number of needle-like grains decreases by a factor of 3. The research findings are intended for optimizing the formulation and manufacturing technology of abrasive and refractory products.

Introduction. Currently, one of the most studied high-entropy alloys (HEAs) is the CoCrFeNi system with the addition of a fifth component. An example of such an alloy is AlCoCrFeNi alloyed with additional elements. Nb alloying promotes the formation of a solid solution and a secondary Laves phase in the alloy, and leads to the formation of eutectics between these phases. The optimal combination of mechanical properties achieved in the hypoeutectic alloy AlCoCrFeNiNb0.25 was the basis for the choice of this alloy for further studies under heat treatment conditions. Purpose of the work. To investigate the effect of heat treatment, including heating to temperatures of 900°C, 1,000°C and 1,100°C with subsequent cooling in air, on the structure and properties of AlCoCrFeNiNb0.25. The methods of investigation were optical metallography, X-ray diffraction analysis, microhardness measurement, and compression tests. Results and Discussion. AlCoCrFeNiNb0.25 alloy retains the solid solution structure based on the BCC phase not only in the cast state, but also after heat treatment. Irrespective of heat treatment parameters, the alloy retains the hypoeutectic structure consisting of solid solution dendrites and eutectic with the Laves phase in the interdendritic space. Heat treatment leads to changes in the phase composition of the alloy and refinement of structural components. When heated to 900°C, along with the existing solid solution and Laves phase, σ-phase is released in the structure, which increases the microhardness of the alloy, but does not provide improvement of strength properties due to its low plasticity. The strength properties of the alloy are significantly improved by heat treatment with heating up to 1,000°C and 1,100°C. Heating up to 1,100°C is accompanied by an increase in residual strain. The main reasons for this effect may be transformations occurring both in the solid solution of the BCC phase (dissolution of the B2 phase, rearrangement of the substructure, increase in the lattice parameter) and in the eutectic (increase in the proportion of the Laves phase, refinement of eutectic cells).

Introduction. Electron beam additive manufacturing (EBAM) is a promising method for producing new alloys with unique properties. At the same time, existing problems with obtaining a high-quality structure require a search for a technical solution that ensures grain refinement and the formation of a more homogeneous microstructure. For strain-hardened copper alloys, severe plastic deformation (SPD) methods are effective ways to control their structural state and mechanical properties. Currently, the effect of severe plastic deformation on the structure, mechanical, and tribological properties of Cu-Al-Si-Mn bronze, which is promising for industrial application, has not been studied. The aim of this work is to study the relationship between the structural state formed as a result of severe plastic deformation and the mechanical and tribological properties of Cu-Al-Si-Mn bronze samples. The paper studies samples of Cu-Al-Si-Mn bronze, made from bronze (3% Si-1% Mn) wires and commercially pure aluminum using multiwire electron beam additive manufacturing. For targeted changes in structure and properties, the resulting additively manufactured blanks were subjected to severe plastic deformation. Multi-axial forging and rolling were used as SPD methods, aimed at significant grain refinement and increased strength characteristics. The work uses such research methods as transmission electron microscopy (TEM) for a detailed analysis of the submicron structure after SPD, X-ray diffraction (XRD) to identify the phase composition of the alloy, tensile tests to determine key mechanical properties such as tensile strength, yield strength, and percentage of elongation, microhardness measurements to assess the hardening of samples using Vickers loads, confocal laser scanning microscopy (CLSM) for three-dimensional analysis of the surface topography and studying the morphology of worn surfaces, and dry sliding friction tests to assess the wear resistance of the material and the friction coefficient in the absence of lubrication under specified loads and sliding speeds. Results and discussion. Based on the data of transmission electron microscopy, it was found that the use of multi-axial forging and rolling led to significant changes in the structure of the material, as well as its phase composition. Based on the X-ray diffraction analysis, it was revealed that severe plastic deformation contributed to the deformation-induced dissolution of the γ- and β-phases. The results of tensile tests showed that the highest strength is achieved after intense plastic deformation by rolling, after multi-axial forging. SPD by multi-axial forging and subsequent rolling led to an increase in the microhardness of bronze. The results of tribological tests showed that SPD contributes to a decrease in the friction coefficient (FC) compared to the material in the printed state. Heat treatment of samples after SPD led to an increase in FC and an increase in fluctuations in its value. SPD by multi-axial forging and subsequent rolling contributes to a significant increase in the wear resistance of samples under dry sliding friction conditions. Low-temperature annealing after SPD leads to a decrease in the wear resistance of deformed samples. Thus, the use of SPD makes it possible to increase the strength and wear resistance of bronze samples of the Cu-Al-Si-Mn system.

Introduction. Traditionally, the most common technology for producing parts from nickel alloys involves casting followed by heat treatment to achieve the required phase composition. Significant disadvantages of this method include the segregation of chemical elements, the presence of large undesirable inclusions such as Laves phase and eutectic structures, and the non-uniform distribution of strengthening phases throughout the workpiece cross-section. At the same time, many complex-shaped parts are assembled into a single combined structure using welding. An analysis of the hardening characteristics of nickel alloys and the products derived from them suggests that additive manufacturing techniques are a promising approach for fabricating such workpieces. The structure and phase composition of the material volumes formed via layer-by-layer deposition will differ significantly from those obtained by conventional methods. In the case of producing combined structures using additive methods, identifying the patterns of structure and phase composition formation becomes an even more complex challenge. Therefore, the purpose of this work is to identify the structural features of “steel - nickel alloy – steel” gradient layers fabricated by direct metal deposition. The study examines dissimilar joints produced using the “Welding and Surfacing Complex based on a Multi-Coordinate Arm and a Fiber Laser” at the S.A. Khristianovich Institute of Theoretical and Applied Mechanics of the Siberian Branch of the Russian Academy of Sciences, employing direct metal deposition technology. Research methods. A Carl Zeiss Axio Imager A1m light microscope and a Carl Zeiss EVO 50 XVP scanning electron microscope, equipped with an INCA X-Act energy-dispersive X-ray spectroscopy (EDS) attachment, were utilized for microstructural investigations of the fabricated layers. Phase composition analysis of the samples was performed using an ARL X'TRA X-ray diffractometer. Microhardness testing was conducted using a Wolpert Group 402 MVD Vickers hardness tester. Results and discussion. It was observed that the maximum layer height (up to 7 mm) was achieved when implementing the following parameters: 1,000 W laser power with a scanning speed of 35 mm/s, and 1,500 W laser power with a scanning speed of 15 mm/s. In the first case, minimal material mixing at the fusion boundary was noted. In all fabricated compositions, defects in the form of unmelted powder particles were observed, as well as cracks in the first steel layers. During the deposition of Inconel 625 onto 316L stainless steel, the transition zone exhibited solidification modes consistent with the formation of iron-based alloys, specifically FA (ferrite-austenite), AF (austenite-ferrite), and A (austenite) sequentially. When depositing 316L stainless steel onto Inconel 625, the transition zone exhibited a solidification mode characterized by the formation of only the austenite phase. The microhardness values were found to be 230 ±15 HV for 316L stainless steel and 298 ± 20 HV for Inconel 625.

Introduction. Aluminum-based metal matrix composites (MMCs) have garnered considerable attention recently due to their enhanced mechanical properties, making them suitable for a wide range of industrial applications. While other methods exist for incorporating reinforcements into the base metal, stir casting is a particularly efficient process as it promotes a more uniform distribution of reinforcement particles throughout the matrix. The purpose of this work. It has been demonstrated that adding silicon carbide (SiC) reinforcements to alloys from the 7XXX series enhances their fatigue strength. The impact of SiC reinforcements on the mechanical properties of A356 composites, such as elongation, compressive strength, tensile strength, and hardness, has also been investigated. However, there is a need for more research on how hybrid reinforcement particles affect the mechanical properties of Al7075-T6 alloy. Methods. Considering the broad application spectrum of aluminum matrix composites (AMCs) in the automotive and aerospace sectors, this study examines the influence of varying ratios of nano-sized SiC and graphene reinforcements on the hardness and tensile strength of stir-cast Al7075-T6 aluminum alloy. The scanning electron microscopy — energy-dispersive X-ray spectroscopy (SEM-EDS) analysis of the composites' microstructural and fractographic surfaces is also included. The objectives of this work are to develop lightweight, high-performance hybrid metal matrix nanocomposite materials and to explore the feasibility of integrating graphene and SiC nanoparticles into Al7075 alloy. Particular emphasis is placed on the discussion of the mechanical characteristics of these hybrid materials. Results and discussion. This study found that mechanical stirring improved the bonding, wetting, and cohesion between the reinforcements and matrix while reducing porosity. Compared to composites produced without stirring, stirred composites exhibited improved strength and toughness due to microstructural changes. The study suggests that appropriate mixing strategies can significantly impact the mechanical properties and surface morphology of Al7075 nanocomposites. The results indicated that the hybrid reinforcement nanoparticles significantly improved both the hardness and tensile strength of the Al7075-T6 alloy. Moreover, a distinct correlation between the ratio of silicon carbide to graphene nanoparticles and the mechanical properties of the specimens was observed. Specifically, an Al7075 specimen reinforced with 0.5 wt.% graphene and 3 wt.% silicon carbide nanoparticles demonstrated superior hardness and tensile strength compared to unreinforced Al7075 and other combinations of silicon carbide and graphene nanoparticles considered in this study. With a 0.5 wt.% graphene content and 1–3 wt.% SiC content, the Al7075-based nanocomposites consistently exhibited a well-defined grain structure with distinct, continuous grain boundaries. The resulting finely dispersed nanoparticles, ranging in size from 62.57 to 91.54 nm, facilitated effective load transfer, grain refinement, and impeded dislocation motion, leading to enhanced mechanical properties. An Al7075-based nanocomposite exhibited superior mechanical performance characterized by a dense, dimpled surface featuring uniform microvoids and minimal particle pull-out. This behavior was attributed to ductile fracture resulting from strong matrix-reinforcement bonding and efficient load transfer. Consistent with these observations, the study indicates that the mechanical behavior of hybrid Al7075-based nanocomposites is significantly influenced by the reinforcement ratio, particle size, and dispersion quality. This information is valuable for advanced industrial applications. The study further demonstrates that a balanced combination of graphene and silicon carbide nanoparticle reinforcements can enhance the mechanical properties of Al7075, emphasizing the need for further investigation into these synergistic effects.