Russian Journal of Non-Ferrous Metals最新文献

The article discusses the features of radial shear rolling (RSR) of the aluminum alloy Al–Mg–Sc. The modeling of the RSR process by the finite element method in the QForm 3D program with variation of the elongation ratio per pass and the rolling speed has been implemented. On the basis of the results obtained, a study of the temperature field of the rod in the deformation zone has been carried out taking into account the cyclic deformation and the configuration of the flow trajectories. It is found that changes in the temperature field of the rod in the deformation zone are determined by the difference in the trajectory flow of the metal in the surface layers and in the axial zone. When the elongation ratio is varied from 1.6 to 2.4, heating occurs inconsistently from the center to the surface. The largest increase occurs for an area that is approximately 0.3R from the surface. For the axial zone, the temperature change in the deformation zone occurs smoothly and with an insignificant temperature difference of 5–10°C. The temperature on the surface of the rod has the greatest temperature fluctuations, which are explained by deformation heating and simultaneous contact with a cold roll during each deformation cycle. With a decrease in the rolling speed, a picture of the distribution of the temperature field of the rod in the deformation zone is observed, when the temperature of the central layers exceeds the surface temperature. Because of the long contact time of the rod with the roll, the surface temperature fluctuates up to 40–50°C with each deformation cycle. With an increase in the rolling speed, the amplitude of temperature fluctuations on the surface decreases, and the deformation heating increases. The obtained data on the relationship of controlled technological parameters with a change in the temperature field of the rod can be useful in the design of technological modes of rolling.

Zirconium is one of the widely demanded materials, while the existing methods of its production are multistage and energy-intensive. The paper proposes a method for extracting zirconium from its oxide by electrolysis of low-temperature oxide-fluoride melt KF–AlF₃–Al₂O₃–ZrO₂ with a temperature of 750°C. For this purpose, the potentials for the electroreduction of zirconium and aluminum ions on a glassy carbon electrode have been determined by means of voltammetric methods. It was shown that the electroreduction of aluminum ions in the KF–AlF₃–Al₂O₃ melt occurs at a potential more negative than –0.05 V relative to the aluminum electrode with the formation of a cathode peak in the potential range from –0.18 to –0.2 V. With the addition of 1 wt % of ZrO₂, cathode current on the voltammogram begins at a potential more negative than 0 V, and the cathode peak is formed at a potential of about –0.1 V. Similar results were observed in the study of the cathode process in the KF–AlF₃–Al₂O₃ melt with and without the addition of ZrO₂ by means of square-wave voltammetry. It has been suggested that, because of the lower bond energy, zirconium-containing electroactive ions are discharged at a potential that is 0.05–0.08 V more positive than the discharge potential of aluminum-containing ions. At a graphite cathode potential of –0.1 and –0.3 V relative to the aluminum electrode, the electrolysis of the KF–AlF₃–Al₂O₃–ZrO₂ melt was carried out, and the elemental and phase composition of the obtained deposits was determined by X-ray phase analysis, scanning electron microscopy, and energy dispersive microanalysis. It was shown that, at a potential of –0.1 V, a deposit with 98.5–99.5 wt % zirconium can be obtained. This indicates a reliable possibility of selective extraction of zirconium by the proposed method.

In magnesium alloys castings, the casting defects such as shrinkage porosity often occur. Such defects can be suppressed by repair welding or surfacing using a special filler rod. Unfortunately, in Russia, a low amount of filler rod is consumed. Therefore, domestic enterprises do not manufacture it, limiting themselves to imports or homemade low-quality substitutes. Nevertheless, there is a need for filler rod, and recently it has become unprofitable to replace them with imported materials owing to a significantly increased price. Therefore, there is a need to study the technology of its production to replace imported filler rod with domestic material. Magnesium alloys based on the Mg–Zn–Zr (La, Nd) system SV1, SV122, and ZK51 (ML12) that used as a filler rod for repair welding of ZK51 alloy castings were studied in this work. The samples were obtained by permanent mold casting into aluminum molds followed by hot extrusion into a filler rod with a diameter of 4 mm. It was shown that all the investigated alloys could be obtained in the form of a rod with a diameter of 4 mm. Therefore, the investigated rod samples from the SV122 alloy were used as filler material for repair welding of ZK51 magnesium alloy castings. The weld seam in the T1 condition has an ultimate tensile strength (UTS) about 80% of the UTS of the casting material.

Mn/Al/B mixed powders were used as raw material for the thermal explosion reaction in a tubular furnace to rapidly prepare Mn₂AlB₂ ceramics with high content at low temperature. The effects of raw material ratio, raw material particle size, and NaCl additives on the synthesis of Mn₂AlB₂ were studied systematically. The formation mechanism of Mn₂AlB₂ was proposed. The thermal explosion reaction was induced when the preheating temperature was approximately 686.9°C. The materials with MnB, Al, and Mn₂AlB₂ were synthesized as main phases. Mn₂B and AlMn_x were obtained in small amounts. Increasing the content of Al or refining the Mn and B size in the raw material reduced the content of MnB and other impurities in the product significantly, thereby promoting the synthesis of Mn₂AlB₂. The thermal explosion products were porous, and the sintering degree was weak. Many lathed Mn₂AlB₂ grains with an approximate size of 4 μm were obtained. A mechanism for the thermal explosion synthesis of Mn₂AlB₂ was proposed.