Ingot Casting Research Articles

Effects of recovery and recrystallization on microstructure and texture during annealing of a cold deformed superconducting Nb-50(wt.)%Ti alloy

A Nb-50(wt.)%Ti alloy was melted and remelted in an electron beam furnace and the cast ingot was subsequently deformed into a bar by cold swaging, undergoing a maximum reduction in the area of 90%. Samples of the cold deformed bar were subjected to isochronous annealing cycles for 1 h in the temperature range between 250 and 1000 °C. The microstructural changes of the samples were monitored by optical microscopy, scanning electron microscopy with backscattered electron diffraction (EBSD), X-ray diffraction for pattern and texture determinations, and Vickers microhardness measurements. Recovery is the main softening mechanism in the samples annealed at temperatures up to 600 °C, but recrystallization is significant at temperatures equal to or above 750 °C and might also contribute to softening. Grain growth is also noted after annealing at the temperatures of 900 °C and 1000 °C. The microstructures of the cold deformed sample and of the samples annealed at temperatures up to 600 °C display a curly structure caused by deformation bands and their dislocation substructures. At the annealing temperatures of 900 °C and 1000 °C, complete recrystallization occurs and eliminates the deformation bands, but the curly pattern still exists and is probably due to a residue of the microsegregation of elements that occurs during solidification of the ingot. An intense fiber texture that is typical of cold swaging is observed in the cold deformed sample and in those annealed at temperatures up to 750 °C, but annealing at temperatures of 900 °C and 1000 °C weakens this texture owing to complete recrystallization. The results of the present work show the importance of the strong interactions among the phenomena of recovery, recrystallization, and microsegregation in determining the microstructure and texture of cold deformed and annealed Nb-Ti alloys.

Numerical study on stress control of silicon ingot for photovoltaic applications

When continuous silicon ingot casting is performed using directional solidification—a metallurgical refining method for producing high-purity silicon ingots—the thermal stress and microstructure inside the ingots must be monitored for ensuring the desired yield and purity. This study determined the temperature gradient and thermal stress during silicon ingot casting by applying various controlled parameters to the process simulation. Our results indicate that the temperature gradient influences the thermal stress generated during casting; reducing the temperature gradient can help reduce the thermal stress. The ingot exhibited the lowest thermal stress at an electron beam (E-beam) power of 6 kW, an ingot growth rate of 0.02 mm/min, and a molten silicon level of −10 mm. Quasi-single crystalline silicon ingot was produced via crystal growth simulation under thermal stress-minimizing conditions with single-crystalline seed. The quasi-single crystalline silicon ingot maintained the [001] grain orientation and the purity increased from 2N to 7N6.

Study on heat transfer characteristics of hollow composite thermal barrier structure at high temperature

Air interlayers are often used as a part of thermal insulation structure and form a system with solid materials to reduce heat transfer. However, the heat transfer process in the composite structure is affected by many factors at high temperatures. In this paper, a series of heat preservation systems with air gap and solid structure were proposed. Based on the research background of heat preservation in the riser of ingot casting, the heat transfer process in the composite structure was systematically studied by means of numerical simulation and experiment. The heat transfer laws under different geometric structures, thermophysical properties of materials, and surface emissivity were obtained, which could provide theoretical basis for the design of heat preservation structures at high temperatures.

Numerical Study on the Influence of the Filling Angle on the Fluid Flow during the Ingot Side Teeming Process

High turbulence at the liquid steel−mold flux interface results in mold flux entrapments, which can generate nonmetallic inclusions during the ingot‐casting process. Those nonmetallic inclusions are detrimental to the final steel quality. The teeming process during ingot casting is typically conducted using the uphill teeming method. The authors propose a novel alternative method using a side teeming process, which decreases turbulence at the free surface. To define the optimum operational conditions, a 3D mathematical model is developed to investigate the effect of the filling angle on the motion of the free surface and the resulting shear stresses during the teeming process. The investigated filling angles are 0°, 30°, 45°, 60°, and 90°. The present findings suggest that using the filling angle of 90° between the mold and the runner is an effective way of reducing the number of inclusions due to mold flux entrapments and refractory wear.

Influence of Mg Content on Texture Development during Hot Plain-Strain Deformation of Aluminum Alloys

The study addresses the effect of magnesium and other alloying elements on rolling “β-fiber” texture formation during hot deformation of aluminum alloys. For the study, flat cast ingots from three aluminum alloys with variable magnesium content were deformed in a Gleeble testing unit with different parameters of thermomechanical treatment. Immediately after completion of deformation, the samples were quenched using an automatic cooling system and the microstructure and crystalline texture was analyzed by optical microscopy and X-ray analysis. The analysis demonstrated that an increase in alloying components, magnesium in particular, leads to an increase in brass-type texture and a decrease in S and copper-type texture. The reason was that the simulation of the deformation texture development revealed a great contribution of impurity atoms rather than the decrease in stacking fault energy.

Modelling melting and grain destruction phenomena during globular equiaxed solidification

Melting or re-melting accompanies solidification in many technical castings. For example, during ingot casting, some crystal fragments or equiaxed grains can enter the superheated region and re-melt, while solidification continues in other regions. Solidification and remelting occurring simultaneously at different locations present an important species/energy transport mechanism, which impacts the structural/compositional homogeneity of the castings. The re-melting is typically understood as a reduction in the equiaxed grain size, but it can also lead to the destruction (disappearance) of equiaxed grains. Existing process-based models cannot treat the solidification/melting by considering both grain nucleation and destruction properly. Therefore, a new model is proposed based on a two-phase volume-average approach. In this model, nucleation of equiaxed grains occurs when inoculants (free growth sites) are activated by undercooling, while destruction of equiaxed grains occurs only when the equiaxed grains are completely re-melted by superheating. The mass, momentum, species, and enthalpy conservation equations are solved for the solidification/melting. The transport equations for the number densities of equiaxed grains and inoculants are calculated separately. A test casting (Al–7 wt.% Si) is calculated to illustrate the modelling features. This study improves understanding of grain melting and grain destruction as well as their impact on the as-solidified structure.

Life cycle greenhouse gas emissions of aluminum based on regional industrial transfer in China

AbstractAluminum production is a major energy consumer and source of greenhouse gas (GHG) emissions. The regional transfer of the primary aluminum (PA) industry, which mainly consists of the processes of electrolysis and aluminum ingot casting, is currently an important international trend in aluminum industrial development. However, the changes in GHG emissions from aluminum production for such transfers are unclear. This study has established a life cycle assessment model of aluminum industry based on regional transfers in the context of China, determined the GHG emissions of PA and secondary aluminum (SA) production, examined the GHG emission changes of PA production based on regional industry transfer between the years 2007 and 2017, and explored seven driving factors that affect GHG emissions in the aluminum industry. GHG emissions per unit PA and SA production in China decreased by 18.6% and 6.3%, respectively, but the total GHG emissions from aluminum industry still increased by 2.2 times between the years 2007 and 2017. The driving factor analysis showed that the major positive effects of GHG emissions from China's aluminum industry from 2007 to 2017 included the production scale effect of SA and the energy structure effect. Existing regional transfers (between the years 2007 and 2017) did not deliver significant annual GHG emissions reductions. Currently, Xinjiang, Henan, Shandong, and Inner Mongolia are the main PA production provinces in China, although regional transfers have been implemented. This study provides a basis for the improvement and sustainable development of the aluminum industry, suggests policies for regional aluminum development, and proposes a beneficial layout of the aluminum industry.

Synthesis of AA7075 Based 10 wt.% Graphite Reinforced Composites for High Damping Capacity

The damping capacity improvement in under seawater for torpedo cone is the main of the research work. In the proposed work, an induction furnace was used to fabricate aluminum alloy AA7075 by melting individual elements such as pure Al, Zn, Mg, and Cu, followed by 10 wt.% graphite with varying sizes of reinforcement C1 (3 to 10μm), C2 (53 to 66μm), and C3 (106 to 150μm). Ingot casting was made in steel mold of 45 45 120mm3 and then hot forged at 490ᵒC, followed by solutionizing and artificial aging. Composites characterized for optical, SEM, hardness, and DMA analysis for loss factor. The improved performance in damping capacity by 50% observed for the threshold modulus of particulate (volume to the surface) for C2 composite. The processing cycle of fabrication of composites has been established.

Segregations in Steels during Heat Treatment – A Consideration along the Process Chain

Abstract Segregation is an unavoidable phenomenon in continuous or ingot casting of steel for thermodynamic reasons. If costly processes that explicitly reduce segregation are not carried out, the segregations remain until the final product. Therefore, an understanding of the development and effects of segregation along the entire process chain is necessary. The focus in this publication is on the treatment of segregations in low alloy steels. First, the characterisation of segregation is presented. An overview of the formation and development of segregations during primary shaping and forming processes is given. The focus is on segregation-related effects during heat treatment with regard to inhomogeneous microstructure and negative heat treatment results such as distortion or hardening cracks. In a short outlook, the influence of segregation on the component behaviour is described. ◼

Production of Primary Silumins Ingots Modified with Strontium

The article examines a number of regularities in the production of primary cast ingots of AlSi7Mg, AlSi7MgSr, AlSi11Mg, and AlSi11MgSr. Peculiarities of melting and cast of these alloys, as well as the effect silicon and strontium have on the formation of the shrinkage cavities, have been explored. It has been demonstrated that strontium, when used as a modifier, changes not only the morphology of silicon, but also the nature of solidification and shrinkage of the alloy. Defects formed in the ingots manufactured from near – eutectic AlSi11MgSr alloy have been studied in greater detail.

Grain Refinement of the CrMnFeCoNi High Entropy Alloy Cast Ingots by Adding Lanthanum

The effect of lanthanum addition on the grain refinement of CrMnFeCoNi high-entropy alloys (HEAs) was investigated experimentally. When 9.3 pct lanthanum was added, the equiaxed zone faction enlarged sharply from 41.17 to 76.58 pct. The number of grains < 200 µm increased obviously, and the mean grain size in the equiaxed zone decreased from 331 to 144 μm. Compositional undercooling induced by lanthanum addition caused grain refinement of the HEAs.

Experimental and Numerical Study of the Free Surface During the Side Teeming Ingot Casting Process

The flow pattern affects the interaction between the mold flux and liquid steel, especially during the initial entry of liquid steel into the mold. Strong turbulence can cause mold flux entrapments during the ingot casting process. If this happens, nonmetallic inclusions are generated, which decreases the quality of the final product. Herein, the side teeming process is introduced as an alternative to the traditional uphill teeming process to decrease mold flux entrapments. Both physical experiments and mathematical modeling are conducted to study the free surface. Specifically, the Weber number is also evaluated to predict the possibility of mold flux entrapments at the free surface. The results show that a calmer free surface is formed in the side teeming process compared with the uphill teeming process. Also, the results show that the Reynolds stress model is more suitable to predict the free surface compared with the realizable k–ε model. The present findings strongly suggest that an implementation of a side teeming process would be an effective way of reducing the risk for mold flux entrapments.

Study of recrystallization kinetics of aluminium alloy 1565ch with low degree of cast structure conditioning

The present study addresses recrystallization process in Al – Mg 1565ch system alloy samples (Russian classification). The samples are taken from cast ingot, produced by continuous casting in DC mold and homogenized based on standard commercial mode. Then the samples were heated to 350–500 oC and rolled in lab mill with different process schedules to cover the entire range of temperature and strain rates, applied in rolling. After rolling the samples were annealed at 350, 400 and 450 oC, their resultant microstructure was examined by optic microscope. The rate of new grains nucleation, their growth speed, analytical notations, describing recrystallization kinetics, were obtained within the frames of the study to be applied during this alloy recrystallization modelling; the main alloy-specific recrystallization features were identified and compared with alloy АА5182 (classification of American Aluminum Association). It is demonstrated, that 1565ch recrystallization has a number of specific features in case of as-cast structure deformation with low strain levels (ε = 0.14÷0.56): first, high rate of new grains nucleation; second, low grain growth speed to the extent of complete process blocking. Optimal recrystallization temperature is identified as 400 oC, at this temperature the process is over 75% complete, the temperature drop (350 oC) causes incubation period extension, while recrystallization subsides at recrystallized structure volume of about 30%, in case of temperature rise (450 oC) the structure is saturated with fine new grains nuclei, probably, emerging during heating, but due to high intensity of recovery and polygonization, recrystallization driving force drops to zero, the process stops with mixed structure and max recrystallized grains volume of 20%. This research was funded through a grant by the Russian Science Foundation, Project 18-79-10099.

Effects of content and distribution of Zn and Gd on formation ability of I phase and W phase in Mg‒Zn‒Gd‒Zr alloy

The solid solution and compounds in Mg‒Zn‒Gd‒Zr magnesium alloy semicontinuous casting ingots were effectively separated by phase separation technique，the solid solution quantity of Zn and Gd as well as the mass ratio of Mg3GdZn6 (I phase) and Mg3Gd2Zn (W phase) compounds were determined, and the mass fraction of I phase and W phase were calculated. The results show that increasing the initial Zn/Gd ratio in as-cast alloys increases the ratio of I and W phases, increasing the content of Zn and Gd under a certain Zn/Gd ratio increases the amount of I and W phases simultaneously. I phase and W phase form in the residual melt of primary α-Mg crystallization, the changes of the distribution of Zn and Gd in the alloy will affect the composition of the residual melt, thus affecting the forming ability of I phase and W phase. After homogenization, I phase disappears, W phase increases and total amount of ternary phase decreases. The Gd element in the newly formed W phase comes from the decomposed I phase and the supersaturate solid solution, while the Zn decomposed from I phase and more than that required for the newly formed W phase diffused to the solid solution.

Investigation of cold rolling modes of 1580 alloy by the method of computer simulation

A computer model was developed and a study of the cold rolling modes of 1580 alloy sheets was carried out. The model provided for the achievement of the maximum total degree of reduction in cold rolling of 60% in the minimum number of passes, the rolling force should not exceed 90% of the maximum allowable for the rolling mill, and the Cockcroft-Latham criterion was not reach value 1, so that cracks do not occur along the edges of the rolled products. The simulation results were tested on a billet cut from a large-sized ingot cast at an industrial enterprise by the method of semi-continuous casting. Hot rolling was carried out on a two-roll mill with a roll diameter of 330 mm and a barrel length of 520 mm. For cold rolling a two-roll mill with a roll diameter of 200 mm and a barrel length of 400 mm was used. Based on the simulation results, cold rolling was carried out, as a result of which a 2-mm-thick strip without cracks along the edges was obtained from a hot-rolled billet 5-mm-thick in 8 passes. At the same time in all passes, the rolling force values did not exceed 90% of the allowable for the rolling mill, and the Cockcroft-Latham criterion was less than 1. Thus, it is shown that computer modeling allows to optimize the rolling route of thin sheets of alloy 1580 and to carry out cold rolling with a total reduction rate of 60% for a minimum number of passes to obtain high-quality sheet semi-finished products.

Dynamic recrystallization behavior and texture evolution of as-cast Fe-4.53%Si non-oriented electrical steel during hot compression

The dynamic recrystallization behavior and texture evolution of surface, quarter and center layers of as-cast Fe-4.53%Si non-oriented electrical steel during hot compression were studied by optical microscope and electron backscatter diffraction. The surface layer of cast ingot exhibited elongated columnar grains with pronounced {001}&lt;130&gt; and {001}&lt;120&gt; textures, while the quarter and center layers of ingot were mainly large equiaxed grains corresponding to strong {100}&lt;0vw&gt; texture. During hot compression, the shear bands were easy to form in the deformed grains with higher stored energy such as {110}&lt;001&gt;, {014}&lt;114&gt; and {312}&lt;332&gt; grains which is conducive to promoting recrystallization. Due to that the shear band was not easy to form in the {100}&lt;0vw&gt; grain with lower stored energy, the large grains corresponding to strong {100}&lt;0vw&gt; texture in the quarter and center layers of ingot undergone obvious deformation and slight orientation transformation during hot compression process which proved the good heritability of as-cast {100} texture.

Processing and characterization of vertical twin roll cast aluminium alloy sheets of A356, A6061 and A6005

Aluminum alloys A356, A606 and A6005 were twin roll cast in sheets 3 mm thickness using a vertical twin roll caster. Microstructure, hardness and wear characteristics of the cast sheets were investigated. VTRC processed sheets showed finer grain size depending upon the solidification range of alloy. It was observed that hardness values of VTRC alloys were significantly higher than those of corresponding ingot cast alloy products. Approximate Hall-Petch calculations show possibilities of additional strengthening mechanisms other than grain boundary for VTRC processed alloys. Extensive wear studies were performed using a pin on disc wear testing machine. The parameters like wear constant, specific wear rate and average friction coefficient were determined to understand the wear behaviour. The wear results show that all the alloy sheets exhibit wear in the mild wear regime.

Modified aluminum alloys of Al – Zr system for power transmission lines of Uzbekistan

The energy sector of Uzbekistan has undergone significant changes in recent years. To diversify the electricity generation sources of the country, it is planned to bring atomic energy sector to the country and further expand more traditional energy production sources, such as wind, solar and other mixed sources. The effectiveness of electricity generation sources is determined by the consumers as well as by the quality and the number of ways to transfer the generated electricity from the source to the consumer. The power lines are considered as an effective tool for transmitting the electricity all around the globe. The main conductive part of the power lines is composed of steel wires that possess a combination of high electrical conductivity and sufficiently high strength. However, the development of new materials with increased conductivity and preferable strength-to-weight ratio compared to steels is an urgent task. The aluminium, owing to its higher electrical conductivity than that of steel, can be alternative material, even though the strength of aluminium and its alloys is noticeably inferior to those of steel. In addition, the Al alloys are widely used in the electrical industry, particularly, cable industry, due to their low density, low melting point, high corrosion resistance and good mechanical properties. The aim of this work is to develop Al-based alloy with high electrical conductivity and enough level of strength for use as a material to produce power lines. The work established the possibility of producing the ingots from Al alloy containing Zr in industrial scale, and then, through subsequent processing of the ingots, obtaining a wire having a combination of preferable strength and electrical conductivity that meet the requirements of the energy sector of Uzbekistan. Mass production of wire for power lines requires significant adjustment and control of the modes of melting and casting of ingots compared to conventional alloys.

Tismice jako produkční a nadregionální centrum Čech 8. a 9. století Tismice as a Production and Supra-Regional Centre of Bohemia in the 8th and 9th Centuries

The central Bohemian hillfort-type site in Tismice is one of the largest (20–22 ha) in Bohemia from the Early to Middle Hillfort period (8th–9th century) and has been studied for years using non-destructive methods. The study, which presents the results of the complete geophysical survey of the site as well as the results of small-scale trenching from 2013, is focussed on an analysis of non-ferrous metal ornaments (c. 170 pcs., mostly belt and horse harness decorations) and analyses of evidence of craft production – jewellerymaking, metalsmithing and metal casting (ingots, blanks). It presents the earliest evidence of work with gold in early medieval Bohemia (2018 excavation) as well as natural science radiocarbon and magnetic absolute dates, which supplement dating on the basis of Carolingian coin and imports. The internally divided hillfort was an elite residence (gilded ornaments, spurs, coin) and for a short time served as a supra-regional centre that not only received and redistributed but also produced items of statutory importance (belt and horse harness ornaments, pendants, spurs). Radiocarbon dating places the multiphase early medieval settlement and fortifications in the period from the final third of the 8th century until the end of the 9th century. A detailed evaluation of the stratigraphy will be another step towards a comprehensive interpretation of this site. Key Words: Early Middle Ages, hillfort, Avar period metal ornaments, spurs, long-distance contacts, goldsmithing, metalsmithing tools, Carolingian coin, central Bohemia

Structure formation of cast Al-Mg-Si alloys during the melts irradiation with nanosecond electromagnetic pulses

An assessment of the grain refining effect of nanosecond electromagnetic pulses on the structure of cast aluminum alloys of the Al-Mg-Si system is carried out. The relationship between the amplitude of nanosecond electromagnetic pulses (5, 10, 15 kV) and the structural and morphological parameters of the irradiated aluminum alloys is shown. It was found that the processing of the melts at an amplitude of 15 kV is accompanied by the greatest refinement of the structural components of the alloy, and also by a change in their morphology and a decrease in microporosity in the structure of cast ingot. Theoretical analysis of the influence of nanosecond electromagnetic pulses on the structure and properties of aluminum alloys from the standpoint of the theory of the microheterogeneous structure of metal melts is given.