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

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

Influence of Flux Composition on Hy-drogen Content in Aluminum Melts

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

INFLUENCE OF ATOMIC AND MOLECULAR HYDROGEN IN SILUMINS MELTS ON THEIR MECHANICAL PROPERTIES

We study the influence of gas porosity caused by the presence of dissolved hydrogen on the mechanical properties of Al–Si alloys. The results are obtained by testing cast samples with identical contents of hydrogen and a given (atomic or molecular) form of hydrogen inclusions. The dependence of the me-chanical properties of alloys on the density index is statistically established. It is shown that if the densi-ty index increases and hydrogen is released in the atomic form, the mechanical properties remain practi-cally unchanged, whereas the presence of hydrogen in the molecular form in silumin deteriorates the mechanical properties of the meta

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

ФИЗИЧЕСКИЕ МЕТОДЫ ОБРАБОТКИ РАСПЛАВОВ МЕТАЛЛОМАТРИЧНЫХ КОМПОЗИТОВ: СОВРЕМЕННОЕ СОСТОЯНИЕ И ПЕРСПЕКТИВЫ

This review focuses on the known theoretical and experimental results in the field of obtaining metal matrix composite materials by processing the melts using physical methods in the conditions of casting and metallurgical processes. The possibilities, advantages and disadvantages of various physical impact methods are considered from the standpoint of their effect on the structural and morphological characteristics, physicomechanical and operational properties of cast composite materials based on aluminum and its alloys. The paper provides a classification and a detailed description of physical methods used for melt processing when obtaining metal matrix composites depending on the melt state during processing (melting, pouring and crystallization) and according to the physical principle of the effects applied (thermal, electromagnetic, cavitation, mechanical, etc). The paper describes a contemporary view of the laws and mechanisms of the effect exerted by melt processing using physical methods on the structure and phase formation processes of as-cast metal matrix composites. The currently known effects of the impact on their structure are described from a qualitative and quantitative point of view, in particular, effects associated with a change in the wettability of particles, their distribution, dispersion and morphology, as well as with a change in the structural state of the matrix material. The paper systematizes the data on the properties of metal matrix composites obtained using physical impacts on the melt during melting and crystallization. The research shows the prospects for the development and practical application of physical impact methods for melts in the production of metal matrix composites based on various matrix materials and reinforcement systems including endogenously, exogenously and integrally reinforced composite materials. Priority areas of theoretical research and experimental development are discussed highlighting discussion areas and issues in the field of obtaining metal matrix composites using physical impacts on melts during melting and crystallization. Areas for future research in this field are proposed based on the systematic analysis of key problems limiting the widespread industrial use of physical methods for melt processing.Настоящий обзор посвящен известным теоретическим и экспериментальным результатам в области использования физических методов обработки расплавов при получении металломатричных композиционных материалов в условиях литейно-металлургических технологических процессов. Рассмотрены возможности, преимущества и недостатки различных способов физических воздействий с позиции их влияния на структурно-морфологические характеристики, физико-механические и эксплуатационные свойства литых композиционных материалов на основе алюминия и его сплавов. Представлена классификация и дано развернутое описание физических методов обработки расплавов при получении металломатричных композитов в зависимости от состояния расплава в ходе обработки (при плавке, заливке, кристаллизации) и по физическому принципу накладываемых воздействий (тепловые, электромагнитные, кавитационные, механические и др.). Изложены современные представления о закономерностях и механизмах влияния обработки расплава физическими методами на процессы структуро- и фазообразования металломатричных композитов в литом состоянии. С качественных и количественных позиций описаны известные к настоящему времени эффекты воздействия на их структуру, в частности связанные с изменением смачиваемости частиц, их распределения, дисперсности и морфологии, а также структурного состояния матричного материала. Систематизированы данные о свойствах металломатричных композитов, полученных с применением физических воздействий на расплав при плавке и кристаллизации. Показаны перспективы развития и практического применения физических воздействий на расплавы при получении металломатричных композитов на основе различных матричных материалов и систем армирования, включая эндогенно-, экзогенно- и комплексно-армированные композиционные материалы. Обсуждаются приоритетные направления теоретических исследований и экспериментальных разработок, раскрываются дискуссионные области и вопросы в области получения металломатричных композитов с применением физических воздействий на расплавы при плавке и кристаллизации. На основе системного анализа ключевых проблем, ограничивающих широкое промышленное использование физических методов обработки расплавов, предложены области будущих исследований в данном направлении