Модифицирование литейных алюминиевых сплавов системы Al–Mg–Si обработкой жидкой фазы наносекундными электромагнитными импульсами

The AA 511 alloy of the Al–Mg–Si system was used as an example to demonstrate that aluminum melt irradiation with nanosecond electromagnetic pulses (NEPs) leads to a significant change in the nature of structure formation during crystallization. It was found that an increase in the frequency of melt irradiation with NEPs is accompanied by the refinement of the alloy structural components, while the greatest grain size reduction of the α-solid solution and intergranular inclusions of the eutectic Mg2Si phase is observed at a NEPs frequency f = 1000 Hz. An increase in the NEPs frequency leads to a significant increase in the concentration of magnesium in the α-solid solution and the fragmentation of Mg2Si phase intergranular inclusions, which is released in the form of compact isolated inclusions when the melt is irradiated at a frequency of 1000 Hz. It was shown that melt processing with NEPs leads to an increase in the Brinell hardness of as-cast specimens, as well as to a significant increase in the microhardness of α-solid solution grains (from 38.21 HV in the initial state to 61.85 HV after irradiation with a frequency of 1000 Hz). It was assumed that the effect of a pulsed electromagnetic field leads to a decrease in the critical values of the Gibbs free energy required to initiate nucleation processes, and to a decrease in the surface tension at the «growing crystal – molten metal» interface, which causes a modifying effect on the alloy structure due to a decrease in the critical size of crystal nuclei.На примере сплава АА 511 системы Al–Mg–Si показано, что облучение алюминиевых расплавов наносекундными электромагнитными импульсами (НЭМИ) приводит к существенному изменению характера структурообразования при кристаллизации. Установлено, что повышение частоты облучения расплавов НЭМИ сопровождается измельчением структурных составляющих сплава и перераспределением в них легирующих элементов. При этом наибольшая степень уменьшения размеров зерен α-твердого раствора и межзеренных включений эвтектической фазы Mg2Si наблюдается при частоте НЭМИ f = 1000 Гц. Повышение частоты НЭМИ приводит к значительному увеличению концентрации магния в α-твердом растворе и фрагментации межзеренных включений фазы Mg2Si, которая при облучении расплава с f = 1000 Гц выделяется в форме компактных изолированных включений. Показано, что обработка расплавов НЭМИ приводит к повышению твердости (по Бринеллю) образцов в литом состоянии, а также к увеличению микротвердости зерен α-твердого раствора (с 38,21 HV в исходном состоянии до 61,85 HV после облучения с частотой 1000 Гц). Было сделано предположение, что воздействие импульсного электромагнитного поля приводит к понижению критических значений свободной энергии Гиббса, необходимых для инициации процессов зародышеобразования, и снижению поверхностного натяжения на границах раздела «растущий кристалл – металлический расплав», что обусловливает модифицирующее воздействие на структуру сплава за счет уменьшения критического размера зародышей кристаллизации

A programmed cell death pathway in the malaria parasite Plasmodium falciparum has general features of mammalian apoptosis but is mediated by clan CA cysteine proteases

Several recent discoveries of the hallmark features of programmed cell death (PCD) in Plasmodium falciparum have presented the possibility of revealing novel targets for antimalarial therapy. Using a combination of cell-based assays, flow cytometry and fluorescence microscopy, we detected features including mitochondrial dysregulation, activation of cysteine proteases and in situ DNA fragmentation in parasites induced with chloroquine (CQ) and staurosporine (ST). The use of the pan-caspase inhibitor, z-Val-Ala-Asp-fmk (zVAD), and the mitochondria outer membrane permeabilization (MOMP) inhibitor, 4-hydroxy-tamoxifen, enabled the characterization of a novel CQ-induced pathway linking cysteine protease activation to downstream mitochondrial dysregulation, amplified protease activity and DNA fragmentation. The PCD features were observed only at high (μM) concentrations of CQ. The use of a new synthetic coumarin-labeled chloroquine (CM-CQ) showed that these features may be associated with concentration-dependent differences in drug localization. By further using cysteine protease inhibitors z-Asp-Glu-Val-Asp-fmk (zDEVD), z-Phe-Ala-fmk (zFA), z-Phe-Phe-fmk (zFF), z-Leu-Leu-Leu-fmk (zLLL), E64d and CA-074, we were able to implicate clan CA cysteine proteases in CQ-mediated PCD. Finally, CQ induction of two CQ-resistant parasite strains, 7G8 and K1, reveals the existence of PCD features in these parasites, the extent of which was less than 3D7. The use of the chemoreversal agent verapamil implicates the parasite digestive vacuole in mediating CQ-induced PCD

Effect of Microalloying with Nickel Aluminides and Rare-Earth Metals on the Structure of Al-5% Cu Aluminum Alloy

The effect of the complex ligature with nickel and REM (Ce, La) aluminides on the structure formation, the nature of the distribution of the elements, and the microhardness of the structural constituents of Al-5 wt.% Cu aluminum alloy were investigated. On the example of microalloying of the Al-5 wt.% Cu alloy with a master alloy containing Ni and REM (Ce, La) aluminides it was shown that a redistribution of Al and Cu occurs in α-solid solution and eutectic. This is reflected in the refinement of α-solid solution and eutectic at 0.15 wt.% of the master alloy addition and, accordingly, increases the microhardness of α-solid solution by 100 MPa and eutectic by 125 MPa

Crystallization Behavior and Properties of Hypereutectic Al-Si Alloys with Different Iron Content

Understanding the influence of iron impurity on the formation of the structure and the properties of hypereutectic aluminum-silicon alloys are important for achieving the required quality of castings, especially those obtained from secondary materials. In the present work, the influence of different iron contents (0.3, 1.1, and 2.0 wt.%) on the crystallization process, microstructure and mechanical properties of the Al-15% Si alloy was studied. It is shown that the presence of iron impurity in the Al-15% Si alloy leads to increasing the eutectic crystallization time from 6.2 to 7.6 s at increasing the iron content from 0.3 wt.% to 1.1 wt.%, changing the structure of the alloy eutectic in the solid state. The primary silicon and β-Al5SiFe phase coexist in the structure of the Al-15% Si alloys at a temperature below 575°C in the range of iron concentrations from 0 to 2 wt.% in equilibrium conditions. In the experimental alloys structure, the primary crystals of the β-phase were metallographically detected only in the alloys containing 1.1 and 2 wt.% of iron impurity. Increase of the iron content up to 2 wt.% significantly reduces the mechanical properties of the Al-15% Si alloy due to the formation of large platelet-like inclusions of β-Al5SiFe phase

Application of Liquid Glass Mixtures with Improved Knocking-Out Ability in Castings Production for Railway Transport

Analysis of the use of the Russian materials (liquid glass and softening additives) has been made in accordance with the modern requirements for use in the technological processes of casting as binding materials in the production of large-sized steel railway casting. The reasons for poor knockout of liquid glass mixtures have been investigated. A complex action softening additive has been recommended for a better knocking-out ability. This solution provides a softening effect at the points of maximum formation of the liquid glass matrix strength in the processes of polymorphic transformation of the material under the influence of elevated temperatures as the result of filling the mold cavity by the melt. It has been shown that the use of additives of complex action leads to the decrease in the specific work of the knockout by four – seven times depending on the composition of the mixture and the design features of the casting. Experimental-industrial tests of the proposed method for softening the liquid glass mixtures have been made and the "Front Buffer Stop" casting has been made (for the rolling stock of locomotives and railway wagons). The tests confirmed the effectiveness and expediency of implementation of new liquid glass mixtures with softening additives in conditions of foundry enterprises

Characterization of Tobacco Mosaic Virus Virions and Repolymerized Coat Protein Aggregates in Solution by Small-Angle X-Ray Scattering

The structure of tobacco mosaic virus (TMV) virions and stacked disk aggregates of TMV coat protein (CP) in solution was analyzed by synchrotron-based small-angle X-ray scattering (SAXS) and negative contrast transmission electron microscopy (TEM). TMV CP aggregates had a unique stability but did not have helical symmetry. According to the TEM data, they were stacked disks associated into transversely striated rod-shaped structures 300 to 800 Å long. According to modeling based on the crystallographic model of the 4-layer TMV CP aggregate (PDB: 1EI7), the stacked disks represented hollow cylinders. The calculated SAXS pattern for the disks was compared to the experimental one over the entire measured range. The best correlation with the SAXS data was found for the model with the repeating central pair of discs; the SAXS curves for the stacked disks were virtually identical irrespectively of the protein isolation method. The positions of maxima on the scatter curves could be used as characteristic features of the studied samples; some of the peaks were assigned to the existing elements of the quaternary structure (periodicity of aggregate structure, virion helix pitch). Low-resolution structural data for the repolymerized TMV CP aggregates in solution under conditions similar to natural were produced for the first time. Analysis of such nano-size objects is essential for their application in biomedicine and biotechnology

INFLUENCE OF FLUX COMPOSITION ON HYDROGEN CONTENT IN ALUMINUM MELTS

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.The paper is aimed at evaluating the quality and performance characteristics of industrial fluxes, which are intended for refining processing of aluminum melts and used in production conditions of RUSAL JSC (Russian Federation). The results of the work were obtained using X-ray diffraction and thermogravimetric analyzes, as well as standardized procedures for determining the hydrogen content in metallic melts. It is shown that fluxes containing crystalline hydrates and hygroscopic water can be a source of saturation of aluminum melt with dissolved hydrogen. The mechanism of dehydration of crystalline hydrates in the composition of fluxes is given. According to the results of the research, technical solutions aimed at reducing hydrogen saturation of aluminum melt during flux processing are proposed