No 4 (2023)

The paper studies the Al–Mg–Si alloy that does not contain scandium and zirconium, as well as the silicon-rich Al–Mg–Si–Sc–Zr alloy. Multistage thermal treatment was carried out for the Al0.3Mg1Si0.3Sc0.15Zr alloy, which included annealing at a temperature of 440 °C for 8 h, high-temperature annealing at 500 °C for 0.5 h, and artificial aging at a temperature of 180 °C with soaking for 5 h. The Al0.3Mg1Si alloy was annealed at 550 °C for 8 h, and then artificial aging was carried out similarly to the alloy with Sc and Zr additives. To study the fine structure, transmission electron microscopy was used. In the as-cast condition and after each stage of thermal treatment, the mechanical properties of the alloys were determined. It has been found that in an alloy doped with Sc and Zr, the formation of Al₃Sc particles occurs already at the stage of formation of the cast structure. During subsequent artificial aging, the supersaturated solid solution decomposes with the formation of β" (Mg₅Si₆) particles improving mechanical properties. It has been found that in the scandium-containing alloy, fewer β" (Mg₅Si₆) particles are formed, as a result of which its strength properties are slightly worse than those of the base alloy are. Moreover, these particles are larger than in an alloy that does not contain scandium. This is explained by the fact that complete quenching is impossible for an alloy with scandium additives.

Magnesium alloys are an ideal material for creating lightweight and durable modern transport systems, but their widespread use is limited due to some physical and chemical properties. This paper considers the effect of nonlinear elastic unloading of the MA14 (ZK60, Mg–5.4Zn–0.5Zr) magnesium alloy in a coarse-grained state after recrystallisation annealing. The study found that the nonlinearity of the unloading characteristic, is formed when reaching a certain threshold stress level. It is expected that the effect under the study is associated with the deformation behavior of the alloy, during which the twin structure formation according to the tensile twinning mechanism is observed. The sample material microstructure was determined, by scanning electron microscopy using electron backscattered diffraction analysis. Determination of the threshold stress, for the formation of unloading nonlinearity was carried out by two methods: 1) by the value of the loop area formed by the nonlinearity of the unloading mechanical characteristics and the repeated loading (mechanical hysteresis) characteristics, and 2) by analysing the acoustic emission recorded during failure strain. A comparison of the results obtained, allows suggesting that the unloading nonlinearity is caused by twinning in grains, in which an unfavorable configuration (low Schmidt factor), for dislocation slip is observed. Rotating the twinned crystal at an angle close to 90° does not contribute to an increase in the Schmidt factor and activation of dislocation slip systems to secure the deformed structure through the dislocation strengthening mechanism. With a subsequent decrease in the external stress, detwinning and partial restoration of the crystal lattice configuration occur.

The data of a comparative analysis of the structure and hardness of pure metals with a face-centered cubic lattice – aluminum, nickel and copper, subjected to complex thermomechanical treatment (TMT), including isothermal cryogenic rolling at liquid nitrogen temperature and subsequent high-density electropulse treatment (EPT) were presented. The main stages, features and advantages of TMT, which first ensure strong work hardening of the processed material due to deformation at low temperatures and then its ultra-fast contact electropulse heating up to a specified temperature, were considered. A multi-level analysis of the metals structure evolution due to TMT was carried out using modern methods of scanning electron microscopy and X-ray diffractometry, recording a wide range of its linear and angular parameters. The kinetics and nature of the processes of the metals structure evolution under cryogenic rolling and EPT, their driving forces and controlling factors, as well as general patterns and temperature intervals of activation of the deformation structure recovery and recrystallization influenced by an electric pulse are identified and discussed. Based on the results of the analysis of the structural and mechanical behaviour of metals, it was concluded that the combination of severe plastic cryogenic deformation and a single-step treatment with ultrashort alternating current pulses is an effective way to obtain semi-finished products with controlled parameters of their structure and properties, including high-strength ultrafine-grain rolled products. At that the phenomenology and nature of the strengthening/softening of metals during cryogenic rolling and subsequent electropulsing are similar to those observed under cold rolling and furnace annealing.

Microarc oxidation is a promising technology for producing wear-resistant anticorrosive coatings for goods made of valve metals and alloys and is used in many industries. One of the main problems of this technology is low controllability caused by the complexity and interconnectedness of physical and chemical phenomena occurring during the coating process. To solve such problems, digital twins are currently actively used. The paper covers the development of mathematical models that are advisable to use as structural elements of the digital twin of the microarc oxidation process. An equivalent electrical circuit of a galvanic cell of microarc oxidation is given, which takes into account the electrolyte resistance, the part coating resistance in the form of a parallel connection of nonlinear active resistance and capacitive reactance. The authors propose a mathematical model describing the behavior of the equivalent electrical circuit of a galvanic cell of microarc oxidation. A technique for determining the parameters of this model was developed, including the construction of a waveform of changes in the resistance of the cell and its approximation, estimation of the values of resistances and capacitance of the galvanic cell equivalent circuit. The authors proposed a calculation method and developed a Simulink model of the microarc oxidation process, which allows simulating the current and voltage waveforms of a galvanic cell. The analysis of the model showed that the model is stable, controllable and observable, but poorly conditioned, which leads to modelling errors, the maximum value of which is 7 % for voltage and 10 % for current. By the parametric identification method using experimental current and voltage waveforms, the dependences of the parameters of the galvanic cell equivalent circuit on the oxidation time are obtained. It is found that the change in the period average of the galvanic cell active resistance correlates with the coating thickness.

Self-propagating high-temperature synthesis (SHS) is one of the promising methods for producing strong and wear-resistant composites. The use of copper as a matrix due to the unique combination of electrical and thermal conductivity is of particular interest. Monolithic SHS composites of the Cu–Ti–C–B and Cu–Ti–C systems are currently little studied. The information on the phase composition of such composites is contradictory, and data on micromechanical properties is practically absent. The paper presents the results of a comparative analysis of the structure and micromechanical properties of composites of the Cu–Ti–C and Cu–Ti–C–B systems. It is found that the matrix of both composites is a copper-based solid solution supersaturated with titanium, in which nanosized Cu₄Ti intermetallic compound particles precipitate upon cooling. TiC particles (Cu–Ti–C composite) and TiC and TiB₂ particles (Cu–Ti–C–B composite) are the strengthening phases resulting from SHS. In the Cu–Ti–C–B composite, the original particles of unreacted B₄C boron carbide were preserved, the microhardness of which was 3680 HV 0.1. The most ductile structural constituent in the Cu–Ti–B system composite is the Cu+Cu₄Ti mechanical mixture, due to which further plastic deformation is possible to obtain parts of a given shape. During the study of micromechanical properties, the maximum strength indicators of H_IT, HV, W_e, R_e, H_IT/E* were recorded in the Cu–Ti–C–B system composite, which allows expecting high wear resistance of products made of it.

The Fe–Ga alloy is a promising magnetostrictive material thanks to of the optimal combination of functional properties and relatively low price due to the absence of rare-earth elements in the composition. To obtain the maximum magnetostriction in Fe–Ga polycrystals, it is necessary to create a crystallographic texture with a predominance of the <100> direction, since the tetragonal magnetostriction constant is the largest. Traditional methods of thermomechanical treatment do not lead to the formation of such a texture in a bcc alloy. In this paper, for the first time, the authors propose to use inclined rolling to increase the proportion of favorable texture components. Warm rolling with a deformation degree of 70 % was carried out at angles of 0, 30 and 90° to the direction of hot rolling. The deformation texture was examined using X-ray texture analysis and the texture and structure of the material after recrystallization was analyzed by electron backscatter diffraction (EBSD) on a scanning electron microscope. Quantitative texture analysis was carried out using the orientation distribution function (ODF) method using the ATEX software. The volume fraction of some texture components was calculated. The study shows that a significant change in the deformation textures and primary recrystallization occurs during rolling at an angle of 90°. The sample after such rolling contains the largest amount of the planar component {100}. The study identified a relationship between the texture of deformation and recrystallization in Fe–Ga: to increase the proportion of components with the <001> crystallographic direction during recrystallization, the presence of planar components {111} in the deformation texture is necessary, which is associated with the predominant growth of favorable components in the deformation matrix with such a texture.