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Frontmatter

Alumina and Bauxite

Frontmatter

Bayer Process/Quality

Evolution of the Technology for the Production of Alumina from Bauxites

This article covers the description and systematization of different technologies for the production of alumina from bauxites and the substantiation of the advantage in the application of “Bayer-hydrochemistry, hydro-garnet version” technology for the processing of low-quality bauxites and red muds.

V. V. Medvedev, S. N. Akhmedov

Approaches to the Processing of Jamaican Bauxite with High Goethite Content

Jamaican bauxite deposits can broadly be classified into two types, catchment and hillside, depending on their form and topographic setting. The major iron phase in catchment deposits is hematite, while in hillside deposits this is aluminous goethite. The difference in topographical setting between the catchment and hillside deposits has affected their degree of weathering, hence the degree by which the bauxite deposits have undergone secondary surficial alteration under the influence of ground water and humic acids. The dissolution and re-precipitation mechanism of surficial alteration has caused the original hematite and goethite in hillside bauxites to be transformed into aluminous goethite. Studies as well as plant experience have shown that aluminous goethite rich bauxites present several processing challenges especially under low temperature digestion conditions. This paper examines the major processing challenges and available approaches for their resolution. This is particularly important since the aluminous goethite rich bauxites become increasingly abundant in plant feeds as stocks of hematite rich deposits are getting depleted.

Desmond Lawson, Ab Rijkeboer, Dejan Dajkovich, Marvin Jackson, Horace Lawrence

Improvement of Processing Characteristics of High Carbonate and High Silica Diasporic Bauxite by Enriching Roasting

Behavior of rock forming minerals of Ural bauxite (diaspore, pyrite, carbonates, chamosite) was investigated in a wide range of temperatures depending on different conditions (size, temperature, holding time, atmosphere). Conditions were selected allowing to transfer diasporic material into an easier recoverable form and to reduce significantly the content of detrimental impurities (sulfur, carbonates, organic matter, moisture, ferrous iron).Investigation was made of process characteristics of roasted bauxite and feasibility is shown of its processing by a simplified Bayer cycle eliminating the necessity of soda, sulfates and other impurities removal from the process which brings about reduction in the cost as compared with processing of raw bauxite at Ural refineries.

Alexander G. Suss, Alexander N. Fedyaev, Andrey V. Panov, Irina V. Paromova, Dmitry V. Finin, Anna A. Damaskina

New High-Performance Crystal Growth Modifiers to Improve Alumina Trihydrate Quality and Yield

Nalco first introduced its Crystal Growth Modifiers (CGM) technology to the alumina processing industry more than 25 years ago. Since then the use of CGM to enhance agglomeration, improve productivity and increase particle toughness has now been well established, with many plants using CGM dosage as a critical tool for process control in precipitation. Nalco continues to better understand the mechanisms and activity of CGMs, resulting in the development of a range of new CGM products with improved performance and with specific properties, for example, enhanced or reduced oxalate impact, or improved antifoam capacity. When compared to ‘more conventional’ CGMs, these new formulations are expected to 1) allow further increases in liquor productivity by improving agglomeration and coarsening, and 2) provide comparable or improved activity while adding less organics into the process. Together with existing Nalco CGM technologies, these new CGMs provide a broader selection of products to meet the wide and ever-changing producer needs.

Ryan Chester, John Kildea, Everett Phillips

Process Control

Votorantim Metais — CBA Alumina Refinery Precipitation Modeling

Precipitation is one the final Bayer Process stages in an alumina refinery and its objective is to crystallize the tri-hydrated alumina. Precipitation is influenced by liquor temperature and composition, residence time in the precipitators, seed charge and others.Many plant indicators are directly affected by the performance of this stage, for example, productivity and production.In order to predict the behavior of the precipitation process, a mathematical model was developed using process simulation software. This solution became an important tool in decision making and process control, in addition to operational improvement and technological developments.The current work presents the modeling development, results, challenges and the possibility to replicate the methodology in other refinery areas.

Thiago Teixeira Franco, Roberto Seno Junior

Value of Systems Integration to Optimize Operation in Alumina Refineries

Construction of modern Refineries is a complex endeavor, technically and organizationally. Shareholders are expecting quick ROI and full optimization of the capital invested during the project. When fully commissioned, new and especially old plants are facing significant operating cost pressures. One key approach used to manage this pressure are automation, process control and production systems to optimize plant processes, manage quality, prevent equipment damages, stream line maintenance data flows and focus on problems anticipation. On the other hand, the challenge Refineries are facing is to ensure the right integration and business alignment of these systems, still be user-friendly and with low TCO (total cost of ownership). This paper will present why Automation & Process Control systems are critical and how proper systems integration can make the difference for new and existing facilities. It will present how OPEX (operating expenditures) can be reduced and major risks mitigated during commissioning and operation.

Hugues Tremblay

Study of Influences on the Bauxite Moisture and Solids in Filtrate in the Hyperbaric Filters through Design of Experiments (DOE) Statistic Tool

Part of bauxite which is used in Hydro Alunorte comes from MBP (Mineração Bauxita Paragominas) by pipeline to 240 Km away through seven cities. This mine provides bauxite to five production lines in the Hydro Alunorte. The objective of this work was to study the influence of the variables that influence the control cake moisture bauxite and solids in filtrate. We conducted an experimental plan based on statistical tool DOE. The parameters evaluated were: rotation speed, basin level and air pressure. The interaction between rotation speed, pressure and basin level was the condition of greater influence on the moisture. Alone the rotation was the most influential variable, followed by pressure. The experimental design in hyperbaric filtration process showed the factor of influence of each control parameter study and determined the strategy to achieve the goal of reducing the moisture content of bauxite.

Alex Pinheiro, Américo Borges, Enio Laubyer

Increased Operational Flexibility in CFB Alumina Calcination

Operational flexibility with regards to production rates and fuel usage in alumina calcination is becoming increasingly important in today’s market. Outotec has a range of technologies, which can be retrofitted in old plants, or offered as options in new developments, that are aimed at improving the plant flexibility and performance, while maintaining product quality.Process stability is critical for product quality and energy consumption and also to reduce material and refractory wear, increasing the operational life of the calciner. In the Outotec® SmartFeed product, the feed and fuel control is automated to reduce temperature fluctuations in the circulating fluidized bed (CFB) furnace. A feed forward function, build into the fuel controller, takes into account any changes in feed rate or hydrate bypass level and adjusts the fuel correspondingly and in advance.Additional operational flexibility and improved service life can be gained through Outotec’s Burner Management System concept. This system is designed to reduce the downtime of the calciner and to allow maintaining the temperature in the CFB furnace during shutdowns by keeping the pre-heat burner in operation continuously.

Linus Perander, Ioannis Chatzilamprou, Cornelis Klett

Increasing Extraction Efficiency Using a Closed Grinding Circuit

Votorantim Metais — CBA’s alumina refinery produces 0.9 Mtpa of SGA. Recently the particle size of the rod-ball mill product has suffered an increase of 35% in the +590 μm fraction. This results from higher grinding charge and variation of bauxite blend, with a rise in proportion of higher Work Index bauxite. Additionally, the top entry design digesters favor low residence time, compromising digestion efficiency even further. This increases residue generation with alumina and caustic loss.The solution studied was a Closed Grinding Circuit, which aims to control particle size by sieving the mill product at 590 μm, returning the oversize to grinding. This improves digestion efficiency, since smaller particles react faster and suffer less shortcircuits.This work describes the study and estimated gains, along with tests conducted to prove the residence time distribution and analyze the effects of residence time and particle size in digestion efficiency.

Julia Mourão Meira, Roberto Seno Junior

Cost Reduction/Alumina Recovery

A Review of Two Phase Flow Modeling and Its Applicability to the Bayer Process

The premature failure of interconnecting flash tank piping in the Bayer Process costs the industry millions each year in replacement of materials and downtime of process equipment. The underlying driving force of the recuperative heating unit of a digester is that slurry at saturation conditions is counter currently de-pressurized and cooled along the saturation curve by means of stage wise flash evaporation. The movement of a near boiling slurry between flash tanks requires careful consideration as vapour forms whilst the slurry slowly de-pressurizes due to in pipe frictional losses and net changes in momentum energy as the fluid pressure falls below the vapour pressure. The failure to interpret the specific points at which large rises in pipe velocity due to a change in phase can result in mis-interpretations in design which in turn result in accelerated pipe erosion and eventual rupture with implications to operations, health and safety.

Alessio Scarsella, Hans-Werner Schmidt

Pipeline Scaling Prevention and Removal Methods in Bayer Digestion Process

Indirect heating digestion process can greatly reduce the energy consumption and raise economic benefits in alumina production. In the digestion process of diaspore type bauxite, Since the silicon titanium compound precipitation, the device wall will form a hard, dense encrustation, causes the device to heat transfer coefficient decreased. In view of Chinese high silicon insoluble diaspore type bauxite mineral characteristics, the microstructure of the silicon titanium scaling and mineral composition have been analyzed. The scale prevention and removal methods have been studied. Using bauxite slurry fully predesilication and predetitanium can effectively reduce and prevent fouling formation, application of catalytic acid leaching can loose hard, dense silicon titanium scaling, and high pressure water washing, such scaling can be easily washed away.

Cao Wenzhong, Li Haining, Tian Weiwei, Zhong Hong

Using of Siliconate-Type Polymers as Inhibitor of Scaling at Aluminate Liquors Heating and Evaporation

At heating and evaporation of aluminate liquors the liquid organic silicon polymers of siliconate type were used. This type of material is characterized by antiadhesive properties and at sufficient surplus of polymer, can cover an inside wall of the heat exchange tubes with a thin layer on which the sodalite is less likely to stick. This reagent can greatly reduce or even completely eliminate sodalite scaling in heat exchangers, pipes, etc. what are confirmed in pilot plant, and plant tests. Obtained positive data at heating and vaporization of high silica liquors at presence of 50–100 mg/l (15–30 ppm to dry substance) scale inhibitor allow concluding about an opportunity of heating and vaporization these liquors in heat exchangers of recuperative type. The result of use of the inhibitor is expressed in decrease in the charge of vapor to the evaporation and increase in its throughput.

Vladimir G. Kazakov, Vadim A. Lipin

Crystal Structure and Alumina Leaching Property of Na2O Doped C12A7

Material of Na2O doped 12CaO·7Al2O3 (C12A7-Na2O) was prepared by the sol-gel method. And the precursor was sintered at 1623K for 3h. The phase composition and crystal structure of C12A7-Na2O was investigated by XRD analysis. The results indicated that Na2O would occupy the position of CaO or vacancy of C12A7 lattice and promote the formation of C12A7 when calcium/aluminum ratio (CaO/Al2O3, molar ratio) was 1.4. Na2O would promote the formation of C3A when calcium/aluminum ratio was 1.7. The lattice parameters also proved the solid solution between C12A7 and Na2O. Alumina leaching experiments were carried out in sodium carbonate solution and the relationship between leaching ratio and doping content, calcium/aluminum ratio were established.

Wang Bo, Zong Shufeng, Sun Huilan, Zhang Jianxin, Zhang Yubing, Liu Dongdong, Liu Jiajia

Decomposition Property of γ-2CaO·SiO2 during Leaching Process of Calcium Aluminate Slag

γ-2CaO·SiO2 is one of the main phases of calcium aluminate slag, which is obtained under 1500°C. Although γ-2CaO·SiO2 is more stable than β-2CaO·SiO2, it will still be decomposed by sodium carbonate solution during alumina leaching process, and this will cause the occurrence of secondary reaction. The effect of liquid-solid ratio, caustic alkali, and temperature on decomposition property of γ-2CaO·SiO2 are studied. The secondary reaction mechanism is discussed by XRD analysis. The results indicate that the amount of decomposed SiO2 increase with the increase of caustic alkali concentration, which varies from 30g·L-1; to 70g·L-1. Leaching temperature affects the decomposition of γ-2CaO·SiO2 and secondary reaction obviously. When temperature is above 75°C the influence degree of the latter is more serious than that of the former. XRD results indicate that the stable product of secondary reaction is hydrate garnet at lower temperature, but under higher temperature, hydrate garnet transforms into sodium hydrate alumina-silicate.

Sun Huilan, Wang Bo, Zhang Jianxin, Zong Shufeng

Effect of Calcium/Aluminium Ratio on Crystal Structure and Al2O3 Leaching Property of 12CaO·7Al2O3

12CaO·7Al2O3 (C12A7) with different calcium/aluminum ratio (C/A) were synthesized by sol-gel method and high-temperature sintering method in the paper. The phase composition of sinters was analyzed by XRD and the lattice constant was calculated by celref software. Finally, the alumina leaching experiments on sinters obtained from different synthesis methods were carried out. The results show the C/A of sinter with single phase C12A7 is 1.7 and the range of the best alumina leaching rate is between 1.6 and 1.8 when sol-gel method is used. On the other hand, the C/A is 1.6 and the range is between 1.4 and 1.6 when high-temperature sintering method is used. And the alumina leaching rate is direct proportion to the content of C12A7 and is inversely to the lattice constant under a certain conditions. Compared to sol-gel method, high-temperature sintering process can reduce the optimal C/A of C12A7.

Wang Bo, Zhang Jianxin, Zong Shufeng, Sun Huilan

Multi-Steps Carbonation Treatment of Calcified Slag of Red Mud

Aluminum industry is one of the most important industries in China’s nonferrous metallurgy industry. With the development of China’s alumina output, red mud emission get 50 million ton at 2011. Under this condition, “Calcification-Carbonation Method” was put forward to deal with red mud by Northeastern University, the main purpose of this method is to change the balance phase of red mud into 2CaO·SiO2 and CaCO3 with hydrometallurgical process. This paper mainly research on the effect of carbonation conditions and steps on alumina extraction and dealkalize efficiency. The results indicate that: through multi-steps carbonation treatment of calcified slag by the new method, A/S of the new structure red mud lowed below to 0.24 and the Na2O content lowed below to 0.26% at carbonation temperature 120°C, CO2 pressure of 1.2MPa with 5-steps carbonation treatment. The new structure red mud could be used in cement industry directly.

LV Guozhi, Zhu Xiaofeng, Zhang Ting’an, Guo Fangfang, Pan Lu, Liu Yan, Zhao Qiuyue, Li Yan, Jiang Xiaoli, He Jicheng

Non-Bayer Process

Tests on Comprehensive Recovery of Iron Minerals And Bauxite from High Iron Diasporic Bauxite by Medium Temperature Metal-Based Roasting

China, the largest aluminium producer, is seriously lacking of bauxite reserves. However, there are more than 200 million tons high iron diasporic bauxites cannot be properly utilized because there is no technical and economically viable technology. The medium temperature metal-based roasting technology will hopefully solve this problem. The grain growth mechanism of iron minerals, the influences of roasting temperature, roasting time, coke dosage, grinding fineness and magnetic field intensity were studied respectively. In comparison with high temperature smelting process, the energy consumption is lower. The iron minerals and bauxite in the ore are utilized effectively, and the results are desirable.

Sichun Hu, Henqin Zhao, Min Guo

The Influence of the Mineral Composition of Low-Grade Aluminum Ores on Aluminium Extraction by Acid Leaching

As part of the hydrochloric acid technology elaboration for processing of non-Bayer raw materials to alumina the conditions of acid leaching of Siberian non-bauxite aluminous ores were studied. Based on the minerals’ structure the mechanism of aluminum transition to acidic solutions was suggested. The conditions of the acid leaching process which required for different kinds of aluminum raw materials were determined.The phenomenon of silica and titanium partial dissolution with subsequent transformation to colloidal form as a result of aging is found. The methods of artificial ageing of such liquors and slurries are suggested to produce sufficiently filterable residues.

Alexander G. Suss, Alexander A. Damaskin, Alexander S. Senyuta, Andrey V. Panov, Andrey A. Smirnov

Dry Sintering of Nepheline — A New More Energy Efficient Technology

A new more energy efficient technology for dry sintering of nepheline and limestone has been developed in collaboration between Pikalevo Soda, FLSmidth and the Russian National Mineral Resources University. The new technology is a result of laboratory research activities and semi-industrial tests conducted by FLSmidth in Denmark and USA.The technology tested semi-industrially consists of a 3-stage preheater with calciner and rotary kiln. This type of equipment has already been in operation in the cement industry for more than 40 years.The tests proved a success due to the ability to control feed chemistry and particle size distribution as well as temperature profile and retention time in kiln system. Control of the above parameters is the basis for achieving high quality sintering and required alumina extraction.This paper presents the results of the semi-industrial tests and compares it to the existing wet technology applied at the Pikalevo site.

Sine Bøgh Skaarup, Yuriy A. Gordeev, Victor V. Volkov, Victor M. Sizyakov

A Study on Sintering Process Optimization of Alumina Attraction from Fly Ash

Fly ash is an industrial by-product generated during the combustion of coal in power plant. In Inner-Mongolia, the content of Al2O3 in fly ash can reach as high as 50wt%. In this paper, alumina was attracted through soda-sintering process, the work was based on six sigma approach in order to optimize the sintering variables, analysis of various critical process parameters and the interaction among them was carried out with response surface method- logy (RSM), the optimized parameters obtained using RSM were then tested to meet the predicted parameters.

Yongfeng Xiao, Qi Sun, Baodong Wang, Xiaotong Liu, Xiaohuan Wang, Lijun Zhao, Gengzhi Yu

Effect of Pressure on Alumina Extraction from Low-Grade Bauxite by Acid-Leaching Method

Hydrochloric acid leaching of Low-grade bauxite with high content of iron oxide was studied at atmospheric conditions and pressure conditions. The results indicate that the alumina extraction rate is lower at atmospheric conditions, and the extraction rate less than 51.5% at the condition with 99 – leaching temperature, 180 min leaching time and liquid to solid ratio at 3:1. Under pressure, the alumina extraction rate increased significantly with increasing the leaching temperature. When the leaching time is 60 min, liquid to solid ratio is 4:1, leaching temperature is 160 –, the alumina extraction rate reach 98.35%.

Yusheng Wu, Laishi Li, Mingchun Li

Extraction of Alumina from Coal-Derived Pyrite Flotation Tailing by Pre-Desilication–Bayer Process

A large amount of tailing from the flotation processing of pyrite ore are accumulated and landfilled, resulting in serious environmental pollution and a waste of valuable elements such as Al, Ti, Si, etc. Aiming to extract alumina from coal-derived pyrite flotation tailing, the process has been proposed based on activation roasting-alkali leaching for desilication, followed by alumina extraction via Bayer process. Proper parameters of the desilication system and Bayer process were investigated in this work. Under the optimized conditions of desilication in the pilot scale experiment, an alumina concentrate with 69.49% Al2O3 and alumina to silica mass ratio (A/S) of 5.93 was obtained from a pyrite flotation tailing bearing 46.22% Al2O3 and 28.33% SiO2, and the corresponding desilication ratio was 73.06%. Then, under the appropriate conditions of Bayer process, the digestion of alumina was 78.42%. The results provide a new way for utilization of pyrite tailings.

Jun Luo, Mingjun Rao, Mingxia Liu, Guanghui Li, Tao Jiang

Extracting Alumina from Low Grade Bauxite with Ammonium Bisulfate Leaching

Using ammonium bisulfate solution to extract alumina from low grade bauxite process was developed. Most alumina and ferric oxide of the bauxite was leached into the solution. All of silica was retained in solid phase. The separation of aluminum and silicon was realized by this method. The conditions were studied in the lab, which are leaching temperature, leaching time, concentration of the ammonium bisulfate solution and mass ratio of ammonium bisulfate and the gibbsite. Metallurgical grade sandy alumina, ferric hydroxide and residue with high silica were gotten. The alumina extracted rate can be about 82% to process low grade gibbsite from Indonesia.

Li Laishi, Wu Yusheng, Liu Yingying

Hydrochemical Method of Low-Quality Raw Materials Processing to Alumina

The technological substantiation of the process flowsheet for low-quality bauxite, nepheline, coal fly ash and other kinds of raw materials with high silica content processing by hydrochemical method is presented. According to this process, silica changes to calcium hydrosilicate in autoclave conditions at the low concentration of the caustic. This allows conducting the alumina production at low consumption of energy resources, high regeneration of the heat and at the low vapor consumption for the liquor evaporation. Besides the hydrochemical method may be used to different kinds of alumina content processing solid waste. Thus the ecological problems are solved. Besides the hydrochemical method processing may be used to various kinds of alumina content processing solid waste. Thus environmental problems may be solved.

Vladimir G. Kazakov, Vadim A. Lipin

Waste Recovery

The Enexal Bauxite Residue Treatment Process: Industrial Scale Pilot Plant Results

The main by-product of the Bayer process is the bauxite residues (BR), a red slurry consisting of the un-dissolved portion of the bauxite ore. On a dry basis BR are produced at an almost 1:1 mass ratio with alumina, amassing to a total of 100 to 120 million tones per year globally. Due the lack of an economically viable processing method all BR are disposed in artificial ponds or landfills. A novel process for treating BR has been developed; Through EAF carbothermic smelting the BR are fully converted into two marketable products: pig iron and mineral wool fibers. No solid or liquid by-products are produced. This novel process has been applied for more than a year in an industrial scale pilot plant housing a 1MVA EAF and a melt fiberizing line. The mass and energy balance of the process, along with a preliminary scale up calculations are presented in this paper.

Efhtymios Balomnenos, Dimitrios Kastritis, Dimitrios Panias, Ioannis Paspaliaris, Dimitrios Boufounos

Sustainability and Bauxite Deposits

Sustainability plays a growing role in the development of (future) projects in the mining and minerals industry, including the Bauxite and Alumina industry. The relationship between sustainability criteria and structures, and their applicability to our industry is not always clear. In addition it may appear sometimes that the implementation of sustainability criteria for new projects affects project economics negatively.This paper provides a background on sustainability in the mining and minerals industry, and explores the relationships between sustainability and quality criteria for bauxite deposits.

Peter-Hans ter Weer

Valorization of Alumina Red Mud for Production of Geopolymeric Bricks and Tiles

The production of red mud in almost 1 to 1 mass ratio in relation to metallurgical alumina renders its valorization a first-priority issue for any alumina plant. The huge amount of red mud produced annually all over the world renders necessary the development of several valorization alternatives so that each alumina plant to have the ability to choose among them the ones that are more proper taking into account geographical and economic parameters. The use of red mud as a filler in production of geopolymeric massive bricks and tiles seems to be a technically feasible valorization alternative. The red mud/metakaolin and the red mud/slag geopolymeric systems proved to be effective and the materials produced have promising mechanical, satisfactory physical and excellent thermophysical properties.

Dimitrios Panias, Ioanna Giannopoulou, Dimitrios Boufounos

Study of Alternative Technologies for Residue Disposal (Red Mud)

Environmental agencies are becoming increasingly stringent and restrictive in release areas for disposal of industrial residues and mining tailings. Because of this, studies are being conducted to enable the maximum use of areas already licensed and impacted with residue disposal. The alternatives considered are aimed at disposal of a greater volume of residue in a smaller area, increasing the lifetime of existing disposal systems. This paper presents a comparative study of residue disposal alternatives in a dam operated by the conventional method (residue in pulp). The alternatives studied use filtering the residue to reduce the amount of water in that for final disposal. Lifetime comparisons were made between the use of conventional method, dry stacking and dry disposal, in addition to tests for characterization of the dry residue to disposal.

Kellen Nery, Joaquim Ávila, Milton Scarmínio, Luciana Bittar, Rodrigo Moreno, Roberto Seno

Economic Analysis of Producing Alumina with Low-Grade Bauxite(Red Mud) by Calcification-Carbonization Method

Calcification-carbonization is a new method of producing alumina with low-grade bauxite (red mud). Low-grade bauxite (red mud) are all converted into garnet hydration during calcification process, then garnet hydration are treated with CO2 and the new structure red mud are gained by digestion. Main components of the new sturcture red mud are CaSiO3 and CaCO3, it can be used directly for cement industry and Bauxite resource recycling is carried out. A series of experiments were done by our team and confirmed that the new method was feasible, A/S of new structure red mud dropped to 0.21 and the content of sodium is under 0.2%. Process calculation software METSIM was used to design and simulate the new process of producing alumina with low-grade bauxite (red mud) by calcification-carbonization method, and its economic with series process and bayer process was analyzed.

Zhao Qiuyue, Zhang Zimu, Zhu Xiaofeng, Liu Yan, Lv Guozhi, Zhang Ting’an, Wang Shuchan

Recovery of Titanium Oxide from Undigested Sand of an Indian Alumina Refinery and Preparation of Value Added Titanium Carbide

During the process of alumina production through Bayer’s process, around 60% of unwanted gangue is rejected as ‘undigested sand’ and ‘Red Mud’. This industrial waste material poses environmental and disposal problems. Aluminum oxide constitutes only 38 to 60% of bauxite ore. The rest is made up of Fe2O3, SiO2, TiO2 and some other metallic oxides. After dissolution of alumina in caustic soda, these impurities remain in suspended form which is separated out as undigested sand and subsequently as red mud. Out of these metal oxides, around 8 to 25% of titanium oxide is lost in to this waste. Titanium oxide, present as rutile and ilmenite in the undigested sand, was processed through Wilfley table. A concentrate containing 38% TiO2 with 47.30% recovery was obtained. This concentrate was subjected to smelting with activated carbon in an extended arc plasma reactor. Titanium carbide was formed as a fused mass within 5 minutes.

B. K. Mohapatra, S. K. Singh, C. R. Mishra, B. K. Mishra

Aluminum Alloys: Development, Characterization and Applications

Frontmatter

Development and Application

AMAG 6XXX Series Alloys for Chassis Application in the Automotive Industry

One of the most important topics in the automotive industry is reduction of fuel consumption and the associated decrease of CO2-emissions. The use of aluminum alloys with the accompanying positive effect of weight reduction can realize these requirements of the OEMs.In the present work a newly developed 6xxx series alloy with balanced Mg/Si-ratio is presented which was optimized regarding intergranular corrosion resistance, formability in delivery temper T4 and high mechanical properties after artificial aging with the typical heat treatment cycle 205 °C / 60 min. At present, in chassis applications non-heat treatable 5xxx series alloys are used and by using the herein presented alloy the mechanical properties can be significantly increased resulting in lower weight of the component due to thickness reduction.

Josef Berneder, Ramona Prillhofer, Josef Enser, T. Grohmann

Heat Treating of High Pressure Die Cast Components: Challenges and Possibilities

Improving the mechanical properties of high pressure die-cast (HPDC) components through T6 heat treatment is still a challenge due to surface blistering. In the current study, theoretical formulation of porosity growth in cast aluminum, EN AC 43100, has been developed along with differential scanning calorimetry and wave dispersive spectrometry to determine temperature ranges of phase transformations and Al-matrix enrichment of solutes. Optimal combinations of time and temperature for maximum possible Mg dissolution in the Al-matrix without blistering as well as tensile testing on samples extracted from HPDC components and samples from the gradient solidification technique that offers samples with low porosity levels have been performed. The results demonstrate that even if the Mg level in the Al-matrix increases and no blisters on component surface are apparent, the strength outcome is limited and can be degraded. Consequently no guarantees are granted that with a seemingly well performed T6 treatment, strength improvement will be realized.

Salem Seifeddine, Darya Poletaeva, Mohammad Ghorbani, Anders Jarfors

Influence of the Chemical Composition on the Ductility of an AlSiCuZnFe Recycling foundry Alloy

The secondary foundry alloy of the type AlSiCuZnFe is one of the most common materials for several applications, mainly in the automotive industry. The main alloy within the AlSiCuZnFe family is the foundry alloy A226 (AlSi9Cu3(Fe)), which is a recycling alloy. The relatively low ductility of Af < 3 % is not sufficient for various applications leading to a limited applicability of the A226. This study focuses on the investigation of the systematic compositional variations within and outside of the alloy’s tolerance band and illustrates the achievable values for the elongation to fracture. It can be shown, that yield strength of permanent mold cast samples ranges from 80 MPa to 200 MPa, while elongation varies between 1 % and > 12 % in the as-cast state, just by varying the alloying elements. This microstructureproperty relationship is interpreted in the light of thermodynamic calculations and metallographic investigations.

P. Pucher, H. Böttcher, H. Kaufmann, H. Antrekowitsch, P. J. Uggowitzer

Assessment of Hot Cracking During Tig Welding of B206 Aluminum Alloy

In this study, the hot cracking susceptibility of B206 aluminum (Al) alloy during TIG welding was investigated using the moving torch Varestraint test method. B206 Al alloy billets were cast with and without the addition of titanium-based grain refiner. The billets were then machined to 3mm thick plates and tested. In all, two levels of titanium (i.e. 0.02 and 0.05 wt%) were used. The results suggest that addition of titanium significantly reduced the hot cracking susceptibility in B206. This was attributed to a finer and more equiaxed grain structure throughout the welding regions. In addition, residual stress measurements (carried out using neutron diffraction) showed that the cracked sample contained a lower magnitude of stress as a result of relief from cracking, while a crack-free sample was found to have relatively higher magnitude of residual stress, since the stress remained ‘locked-in’ to resist the formation of hot cracks.

F. D’Elia, A. Lombardi, C. Ravindran, D. Sediako, K. P. Rao

Influence of Microstructure on the Folding Behavior of Crash Relevant Aluminum Extrusion Parts

Aluminum, especially extrusions of the 6xxx series, has considerable potential to make cars lighter and thus more economical. Over time, requirements have been changed to higher strength for profiles with lower wall thickness including, in particular, better energy absorbing behavior. Crash relevant aluminum parts in aluminum spaceframe constructions should have high mechanical properties combined with highest energy absorption capability. Such parts absorb energy by controlled folding.Until now, the factors of influence on the folding behavior are not completely clarified. Possible factors are microstructure parameters such as grain size, grain structure and phase structure. Therefore the TRIMET Aluminium SE investigated the correlation between the folding behavior and various microstructure parameters. This paper describes material, the heat treatment experiments for varying the microstructure und the correlations between the folding behavior and the microstructure. Finally conclusions and recommendations for optimizing the folding behavior are described.

Marcel Rosefort, Ruven Baumgart, Christiane Matthies, Hubert Koch

Effect of TiC Powder Addition on the Grain Refinement Response of B319 Aluminium Alloy

In this research, efficiency of grain refinement of permanent mold cast B319 aluminum alloy using titanium carbide (TiC) grain refiner was investigated. The grain refiner was added at 0.031, 0.05 and 0.1 wt%. In-situ solidification analysis was carried out, along with microsctructure and mechanical testing characterization. The results of cooling curve analysis suggest that addition of TiC delayed the time to reach the solidus temperature, increased the liquidus temperature, and decreased the amount of undercooling. Scanning Electron Microscopy (SEM) and chemical analysis revealed that Ti was present in solution uniformly throughout the matrix.

Vishank Kumar, Lukas Bichler

Properties of AlZn10Si8Mg Alloys for High Performances Application

In this paper a self-hardening Al-based alloys (AlZn10Si8Mg) with potential application in automotive industry have been proposed.Samples produced with different solidification rate have been considered. Mechanical strength, hardness evolution, morphological behaviour and corrosion resistance of the prepared samples with different content of Mg (in the range of 0.5÷3 wt%) have been investigated. Fracture surface analysis has been carried out to identify the presence of defects on the fractured surface and finally to correlate them to the mechanical performances.As expected, higher solidification rate favours the development of the finest microstructure connected to good mechanical performances. A uniform distribution of a very fine Zn-based intermetallic phase, responsible of the self-hardening feature of the alloy was detected.Addition of Mg up to 1% contribute to enhance the alloy mechanical performances and its resistance to the corrosive media.

Mario Rosso, Ildiko Peter, Christian Castella, Roberto Molina

Processing, Texture and Formability

An Experimental and Modeling Investigation on High-Rate Formability of Aluminum

This work describes the integrated experimental and modeling effort at PNNL to enhance the room-temperature formability of aluminum alloys by taking advantage of formability improvements generally associated with high-strain-rate forming. Al alloy AA5182-O sheets were deformed in near plane-strain conditions at strain-rates exceeding 1000 /s using the electrohydraulic forming (EHF) technique, and at quasi-static strain-rates via a bulge test. A novel capability, combining highspeed imaging with digital image correlation technique, was developed to quantify the deformation history during high-rate forming. Sheet deformation under high rates was modeled in Abaqus and validated with experimentally determined deformation data. The experimental results show a ~2.5x increase in formability at high rates, relative to quasi-static rates, under a proportional loading path that was verified by the experimental data. The model shows good correlation with the experimentally determined strain path. It is anticipated that such integrated experimental and modeling work will enable room-temperature forming of Al and industrial implementation of high-rate forming processes.

Aashish Rohatgi, Richard W. Davies, Elizabeth V. Stephens, Ayoub Soulami, Mark T. Smith

Influence of Chemical Composition and Process Parameters on Mechanical Properties and Formability of AlMgSi-Sheets for Automotive Application

The heat treatable AlMgSi-alloys of the 6xxx-series are widely used for automotive sheet applications due to their good combination of strength and formability. Magnesium and silicon are the main alloying elements in this group forming the agehardening phase Mg2Si. Moreover intentional addition of copper, manganese and also impurities (for example iron) can have a significant influence on the mechanical properties and on the forming behavior of automotive body sheets. Beside the chemical composition also thermo-mechanical process parameters can lead to changes in material properties. The purpose of this work is to investigate the influence of alloying elements and process parameters on (I) strength and (II) ductility in temper T4 and after the typical paint bake cycle at 185°C/20min. Furthermore (III) the formability of different AlMgSi-alloys is studied with bending tests, cross-die tests, hole expansion tests and FLC-analysis.

R. Prillhofer, J. Berneder, G. Rank, H. Antrekowitsch, S. Pogatscher, P. J. Uggowitzer

High Strength Aluminum Brazing Sheets for Condenser Fins of Automotive Heat Exchangers

Aluminum brazing sheets for automotive heat exchangers are extensively used and their mechanical properties are mainly related to the microstructure of core alloys. In this study, strip-cast 3000-series aluminum alloys having high strengths are used as core alloys for aluminum clad sheets. The high strength 4343/3003M/4343 clad sheets are fabricated by the roll bonding process and further cold-rolled down to the thickness of 0.08 mm. Intermediate annealing (IA) is conducted during cold rolling at 270~350°C with 20~40% of final reduction in thickness. Tensile test is performed with the clad sheets before and after brazing heat treatment and sag resistance is evaluated measuring the deflection of sheet under the brazing condition. Ultimate tensile strength (UTS) of the as-rolled clad sheets increases in proportion to the final reduction in thickness up to 228MPa (IA 270°C, 40% reduction) and decreases with increasing intermediate annealing temperature. Post brazing UTS remains in the range from 167 to 185MPa although decreases by brazing heat treatment.

Kwangjun Euh, Hyoung-Wook Kim, Su-Hyeon Kim

High-Temperature Processes Occurring During Homogenization of AA6082 Aluminum Alloy

Homogenization conditions of the 6082-type aluminum alloy were tested by means of electrical resistivity measurements and in-situ heating SEM experiments. It was shown that close to 540 °C a partial local melting of dendrite cell boundaries occurs accompanied by a significant Mn, Mg and Si solid solution enrichment. The process is significantly accelerated and the surface damage due to the local melting is more pronounced when the temperature is risen to 560 °C. At higher temperatures a full surface melting and alloy degradation occurs.

Miroslav Cieslar, Jan Bajer, Michal Hájek, Vladivoj Očenášek

Solutioning and Aging Behavior

A Study of The Artificial Ageing on The Low Temperature Creep of AlMgSi (AA6201) Wires

The study topic focuses on testing low-temperature rheological processes in wires made of AlMgSi conductor alloys. The need for research on the creep process in AlMgSi alloy wires results form the fact that they are used in the construction of selfsupporting overhead power lines. One of the main operational hazards for overhead conductors are rheological processes that result in permanent length increases in conductors hanging in spans (creep process) Due to the fact that these processes take place in a temperature range below 100°C, they do not result in immediate destruction of the material, as is the case in high temperature processes; however, they are a cause of emergency line disconnections. The study, which has an experimental character, identifies opportunities to control AlMgSi wires creep.

Beata Smyrak, Tadeusz Knych, Andrzej Mamala, Kinga Korzeń

Precipitates in Long Term Aging Al 5083 Alloy

Al 5083 alloy aged at 343 K (70 °C) for 3–30 months was evaluated by high resolution transmission electron microscopy (HRTEM) results show that both thickness and continuity of β phase formed at grain boundaries increase with time. GP zones are observed in Al 5083 aged at 343 K for 3 months for the first time. TEM results reveal that GP zones can form homogeneously with the help of vacancies as well as heterogeneously at dislocations near grain boundaries, and the mechanism are explained in detail. Mg2Si precipitate was found to form at the grain boundary and energy-dispersive X-ray spectroscopy (EDS) results reveal that a Mg, Si (atomic ratio 1:1) rich phase nucleates at the interface of Mg2Si-matrix. β’ phase(Al3Mg2, hexagonal) is observed to form at grain boundaries of Al 5083 alloy aged at 343 K for 30 months. β phase was found at the grain boundary of Al 5083 aged at 343 K for 12 months using EDS.

Gaosong Yi, Yakun Zhu, David A. Cullen, Alexander T Derrick, Michael L. Free

Effect of Modified Aging Treatments on the Tensile Properties, Quality Indices and Fatigue Life of Cast Components of Aluminum Alloy 354

With the drive to build higher performance automobile engines, there has been a steady demand to further improve the mechanical behavior of the cast aluminum alloy 354 through improvements in processing. The present study explores the possibility of improving the tensile properties, quality indices Q & QC and fatigue life of the alloy over those obtained by standard T61 treatment by adopting different modified aging treatments. These include i) lowering the artificial aging temperature ii) interrupted aging cycles similar to T6I4 referred to in the published literature and iii) artificial aging in two steps instead of in single step. Based on the results, a few modified aging treatments could be identified which lead to a comparable combination of tensile properties, but with improved fatigue life and a shade higher quality level.

G Dinesh Babu, M Nageswara Rao

Effect of Vanadium Additions on the Structure of Aluminium (AL99.5) And 6XXX Aluminium Alloys

Vanadium additions of up to 0.4% introduced to the 6xxx series aluminium alloys affect their plastic properties. The mechanism of vanadium effect on the aluminium alloy structure is not fully understood.The influence of vanadium additions on the precipitation of Mg2Si and Al2Cu phases in various stages of the technological process was investigated.To explain the phenomenon of microstructural changes, TEM examinations were performed on a high-purity aluminium (Al99.5) with 0.2% V after casting and heat treatment.After ageing, higher vanadium content in the 6xxx series aluminium alloys reduced the degree of strengthening with Mg2Si and Al2Cu phases and increased the content of AlFeSi and AlMgV particles in the range of sizes from 50 to 500nm. The high-resolution observations indicated that after 4 hours of aging, in the 6xxx series alloys, coherent strengthening phases were formed.It was found that in aluminium alloys during plastic working, AlV particles may act as inhibitors for the newly created AlFeSi and AlMgV phases.

S. Boczkal, M. Lech-Grega, J. Morgiel, K. Piela

Aluminum Tailor-Welded Blanks for High Volume Automotive Applications

Design of Experiment based approach is used to systematically investigate relationships between 8 different welding factors and resulting weld properties including strength, elongation and formability in 1.2mm-2mm thick friction stir welding of AA5182-O for TWB application. The factors that result in most significant effects are elucidated. The interactions between several key factors like plunge depth, tool tilt, pin feature and pin length on the overall weld quality is discussed. Appropriate levels of factors that lead to excellent weld properties are also identified.

Yuri Hovanski, Piyush Upadhyay, Siva Pilli, Blair Carlson, John Carsley, Susan Hartfield-Wunsch, Mark Eisenmenger

Corrosion and Fatigue

A New Approach for Evaluation of Fatigue Life of Al Wire Bonds in Power Electronics

Ultrasonically bonded Al wire bonds on Al metallization pads are widely used in power semiconductors. The required long time reliability of the devices is highly dependent on the interfacial quality of Al wire and the bond pad. Reliability of wire bonds is commonly assessed by thermal and power cycling tests. Accelerated mechanical fatigue testing can be used as an alternative to these time consuming procedures. In the present study, lifetime of thick Al wedge bonds on Si substrates was investigated using a novel mechanical fatigue testing technique operating at high frequencies and elevated temperatures. The influence of microstructure, testing temperature and frequency on lifetime of Al wire bonds was investigated. Finite element analysis was applied to calculate the stress distribution at the interfacial region and to establish life time prediction curves. The results of mechanical isothermal fatigue curves were compared and correlated with thermal cycling data of Al wire bonds.

Golta Khatibi, Martin Lederer, Bernhard Czerny, Agnieszka Betzwar Kotas, Brigitte Weiss

Long and Small Fatigue Crack Growth in Aluminum Alloys

Fatigue crack growth (FCG) studies at various stress ratios (R=0.1, 0.5, 0.7) were performed on solution-strengthened (cast A535) and precipitation-strengthened (cast A356, 319, A390 and wrought 6061) aluminum alloys. Microstructures were altered through processing, chemistry, and heat treatment (T4, T6, T7) to shed light on the effects of various intrinsic material characteristic features on FCG (e.g. Si amount/type/morphology, grain size, secondary dendrite arm spacing, precipitate type/size). In this context, mechanisms of long and small fatigue crack growth at the microstructural scale of the studied alloys were identified, and loading-microstructure-damage mechanisms design maps were created. The differences in FCG responses between long, physically-small, and microstructurally-small cracks were systematically evaluated, and an original fracture mechanics — materials science combined model that accounts for these differences was developed, having both material and crack size dependency. Examples of the use of this integrated methodology for design and fatigue life predictions will also be given.

Anthony Spangenberger, Anastasios Gavras, Diana Lados

Alumina Silica Brick Corrosion by Different Aluminium Alloys

In the last few years two major trends can be observed in the secondary aluminium industry.On the one hand the producing companies were obliged to reduce their production costs of standard Al-alloys by increased use of external low quality aluminium scraps.On the other hand the production-boost of high-alloyed Al-alloys typically used in the automotive industry and the aircraft industry but also in military and space applications provides new operation situations.The aim of this work is to investigate the infiltration and corrosion mechanism of refractories exposed to melts during the melting process of aluminium alloys by means of chemical and mineralogical characterization of provided used brick samples as well as of samples from laboratory corrosion tests.

G. Monsberger, C. Majcenovic, G. Praseta

Effect of Salt Solution Corrosion on Tensile Properties of Vacuum High Pressure Die Cast A356 Alloy Subjected to Heat Treatment

Nowadays, vacuum high pressure die casting (V-HPDC) aluminum alloys are increasingly used because of the smooth surfaces and excellent dimensional accuracy of the products. In this study, the effect of corrosion on mechanical properties of VHPDC Al alloys A356 was investigated. Prior to corrosion testing, the T4 and T6 thermal treatments were applied to the rectangular plates of A356 cast by V-HPDC. The treated V-HPDC plates were subjected to immersion corrosion in 3.5% NaCl solution. The corroded plates were tensile tested. The results of tensile testing indicated that for the T4 treated A356, corrosion had more effect on elongation than strength. However, compare to T4, corrosion has limited effect on tensile properties of T6 conditions. The microstructure analyses suggested that microstructure variation in T4 and T6 treatment should be responsible for the extent of corrosion effect on V-HPDC A356 tensile properties.

Yanda Zou, Henry Hu, Patrick Cheng, Yeou-Li Chu

Effect of the Thermo-Mechanical Treatment on IGC Susceptibility of AA 5083 Alloy

This work reports on the effect of thermo-mechanical treatment on IGC susceptibility of the AA 5083 alloy. Specimens underwent varied amount of cold work and final annealing was conducted at 240°C. Extent of the cold work affected the IGC susceptibility of the alloy significantly. Microstructure characterization showed that depending on the amount of the cold work different deformation substructure was created, which, in turn, influenced morphology of precipitated β-phase (Al3Mg2). Formation of continuous film of the β-phase at the grain boundaries was observed in the specimens that were subjected to lower degree of the cold work and which were IGC susceptible. Better corrosion resistance characterized the specimens that underwent higher degree of the cold work (over 30–40%) due to β-phase precipitation in the form of discrete particles at the grain boundaries and in grain interiors.

Tamara Radetić, Akram Halap, Miljana Popović, Endre Romhanji

Material Characterization and Modeling

Role of Ni and Zr in Preserving the Strength of 354 Aluminum Alloy at High Temperature

The aim of numerous research projects has always been to achieve a high output, in conjunction with outstanding efficiency of the designated alloys, making them applicable at higher temperature. The present work investigates the effects of minor additions of Nickel and Zirconium to hypoeutectic 354 alloy containing 9%Si, 1.85%Cu, 0.5%Mg, 0.2%Ti, and 0.015%Sr. Ni and Zr were added to these alloys in amounts of 0.2% and 0.4% each, individually or in combination, to investigate their effect on the high temperature mechanical properties of the alloys studied. The alloys were cast in the form of tensile test bars (using an ASTM: B108 mold). The bars were solution heat treated for 8 hrs at 505°C, quenched in warm water, followed by aging at 190°C for 2 hrs. The aged bars were tested at 155°C and 300°C after preheating at these temperatures for times up to 100 hrs.

G. H. Garza-Elizondo, S. A. Alkahtani, A. M. Samuel, F. H. Samuel

Stress-Strain Curves of Pure Aluminum and Al-4.5mass%Cu Alloy in Semi-Solid State

The information of the mechanical properties, such as elastic modulus, is necessary to be calculated the hot tearing by CAE. The stress-strain curves in semi-solid state of pure aluminum and Al-4.5mass%Cu alloy, whose deformation behaviors had been classified into four stages in the previous study, were investigated in this study. Shapes of stress-strain curves in semisolid state changed with temperature as same as deformation behaviors. Elastic modulus calculated from stress-strain curves were smaller than that calculated by general commercial software. This difference of elastic modulus was about three to five orders of magnitude in Pa. This difference would be caused by the melting of grain boundary and the disappearance of connection between solid phases in general commercial software. Elastic modulus obtained by the stress-strain curve should be more appropriate for calculation of the hot tearing by CAE than that calculated by commercial software.

Nobuhito Sakaguchi

Modeling Texture Evolution of Pure FCC Alloy During Annealing

During the annealing process of deformed materials, static recrystallization is an important phenomenon which can lead to significant texture changes in pure FCC alloy. In this paper, an integrated model was developed to describe the deformation and annealing process. The deformation process was firstly simulated in ABAQUS/Explicit, where crystal plasticity model was implemented into the FE package by developing the user subroutine. Then, a phase field model was proposed to simulate grain growth and texture evolution during annealing process. The outputs parameters of the deformation simulation, such as the orientation and deformation energy of each individual grain, were used as the inputs for phase field models. The nucleation of new grains was assumed to take place at grains which have the lowest deformation energy. This integrated model was applied to calculate the texture distribution of pure FCC sheet after annealing. The predicted texture distribution qualitatively matches the experimental results.

Shiyao Huang, Ruijie Zhang, Mei Li

Microstructure and Mechanical Properties of 3003 Aluminum Alloy with Mg and Ni Addition

A study of effects of adding elements and processing on the microstructure and mechanical properties of 3003 aluminum alloy has been carried out with a special focus on the effects of Mg alone and in combination with Mg and Ni in order to ensure it is able to withstand high temperatures. The additions of Mg or Mg+Ni can decrease grain size of the alloys under different processing conditions, and have AlMnFeSi and AlMnFeNiSi compound appearance. The tensile strength of 3003+0.3Mg and 3003+0.3Mg+0.2Ni alloys is increased to about 25% and 55% at room temperature, and 58%, 80% at 200– and 53%, 100% at 250– respectively. Especially, the creep resistance of 3003+0.3Mg+0.2Ni alloys has been significantly improved with a steady state creep rate decrease in two orders of magnitude. The relationships among microstructure, composition and properties are also discussed, which explains the reason of property improvement, especially high temperature performance.

Zhijiao Tang, Ye Pan, Tao Lu, Yabiao Lin

Lightweight Construction for Electric Mobility Using Aluminium

The worldwide growing demand for individual mobility with an increasing scarcity of fossil fuels and a rising need for sustainable environmental protection are the motivating factors for technology changes in automotive engineering. In this context lightweight construction is the big challenge in transportation currently and will remain so. Especially for electric mobility lightweight construction is essential due to range extension and the high weight of the battery. Besides constructional changes the intelligent use of material will be the solution to this task.In this paper, in order to illustrate electro mobility lightweight construction by using aluminium, two innovative automotive components -wheel hub motor and oil pan for a range extender are mentioned. In the wheel hub motor part, the concept to reduce weight and the important tasks of this concept are introduced first. After that, the requirements of Al alloys to be the suitable material, especially the method to increase the heat conductivity are shown. Also the mechanical properties and the corrosion behaviour of the new optimised AlSi8.5Mg-Alloy are presented. Moreover, the production concept and approach for weight reduction of the stator are provided. In the oil pan part, the heat balance and the reduction of the noise emission lead to the motivation to develop a new oil pan. According to this, the implementation of heat insulation and damping capacity by closed foam structure during oil pan construction are described. Following this, the methods to form foam structure are discussed. In addition, some results of the characterization of the foam structure material are shown.

Andreas Kleine, Marcel Rosefort, Hubert Koch

Emerging Technologies

Deformation of Open-Cell Microcellular Pure Aluminum Investigated by the Acoustic Emission Technique

Acoustic Emission (AE) is used to characterize the plastic deformation of open-cell pure aluminum foams produced by salt replication. Measurements were performed on samples with cells 25, 75 or 400 μm in average diameter, all with a relative density near 24%. AE signals were measured during compression tests conducted with a constant cross-head speed. Deformation is uniform along the porous metal samples. Recorded AE accompanying plastic deformation of the cellular structure exhibits intermittent behaviour, with the probabilities of AE event energies distributed according to a power-law similar to those previously found in many different materials. The present study thus confirms the universal scale-free character of global plastic deformation dynamics and extends the observation to pure aluminum.

Michal Knapek, Patrik Dobroň, František Chmelík, Mariia Zimina, Josef Pešička, Etienne Combaz, Andreas Mortensen

The Research on Process of Impact Factors of Hard Anodic Oxidation for 6061 Aluminum Alloy

In order to improve the performance of hard anodic oxidation film of the 6061 aluminum alloy the significantly influential factors were screened by orthogonal test at room temperature. The results showed that the significant factors which contribute to increase the anode oxidation film hardness were as follows: malic acid, lactic acid, current density, sulfosalicylic acid, triethanolamine, sulfuric acid and oxidation time. And with the decreasing of malic acid, lactic acid, current density, sulfosalicylic acid, sulfuric acid and oxidation time, with the increasing of triethanolamine, the hardness of oxide film increased. We can rank these significant factors which are in favor of increasing anode oxidation film corrosion resistance by its effects as follows: current density, oxidation time, sulfosalicylic acid, sulfuric acid, aluminum sulphate and concentration of triethanolamine. Also as the current density, oxidation time and triethanolamine concentration increased, as the sulfosalicylic acid, sulfuric acid, aluminum sulfate concentration decreased, the corrosion resistance of oxide film was improved.

Wang Jiexiang, Zhang Zhengfu, Sun Junsai, Huang Shiguo, Han Yamei, Du Jiang

Using Scrap in Recycling Alloys for Structural Applications in The Automotive Industry

After studying CO2 emissions caused by vehicles itself, automotive manufacturers now also consider CO2 emission during the production of vehicles and attempt to reduce them according to a holistic approach. This is where AUDI AG as first OEM together with AMAG Casting applies this approach at the production of structural components, which have been produced by primary alloys up to now. This component segment, which is significantly growing by now, requests mainly high ductility values, in order to absorb as much energy as possible in the case of a crash. In addition to the Fe-content, recycling alloys also have further tramp elements, which occur inevitably at scrap treatment. Besides Cu and Zn there are also elements like Bi, Cr, Ni, Sb, Sn etc. which have to be considered, since they influence the requested alloy properties in a negative way. The results of the existing work show that skilled scrap input at the alloy production can reduce this negative effect close to zero.

Werner Fragner, Kurt Baumgartner, Helmut Suppan, Marc Hummel, Dominik Bösch, Heinz-Werner Höppel, Peter J. Uggowitzer

Residual Stress Analysis in Semi-Permanent Mold Engine Head Castings

In heat treatable cast aluminum alloys used for engine head manufacturing, typical heat treatment includes solutionizing followed by rapid cooling (quenching) of the material. Depending on the quenching technique the cooling rates can be quite different; these also vary greatly at different locations throughout the cylinder head. This results in residual stresses of different magnitude and complicated stress profiles. Engineering and optimization of the manufacturing process, therefore, has to incorporate consideration of the resulted stress profiles because of the fact that areas of the castings that are in tension, require less loading before possible failure.Neutron diffraction was employed in this study to characterize residual stresses along the valve webs to the depth of 10~14 millimetres. The focus of this paper is to demonstrate the ability to measure and analyze residual stresses at various locations of heat treated cylinder heads, therefore enabling improvements in part design and heat treatment methods.

M. J. Walker, D. R. Hess, D. G. Sediako

Tensile and Shear Mechanical Properties in a Thermo-Mechanical-Electrical Processed Spot Weld

This study offers a novel approach to characterize the microstructure-property relationship of RSW Al6061-T6 aluminum alloy lap joints. Here, the mechanical properties are determined from quasi-static tensile tests along with shear punch tests through the weld regions. Using measured shear and tensile data, a linear correlation is obtained to quantify the yield and ultimate strengths across the weld region. Furthermore, shear punch tests were also performed in the rolling, transverse, and normal directions of the weld and rolled plate to quantify material anisotropy due to underlying solidification induced microstructure. Future work will explore how the observed mechanical responses are correlated with changes in the microstructures using neutron diffraction and stereological techniques.

S. A. Turnage, K. N. Solanki, W. R. Whittington, R. S. Florea, M. A. Tschopp, K. A. Darling

Development of High-Strength and Highly Ductile Hypo-Eutectic Al-Si Alloys by Nano-Refining the Constituent Phases

Among the structural light weight materials, Al-Si alloys can be the most widely used Al-alloys for aerospace and automotive applications. Our recent experiments using Ba additions of 1-3wt% into the melt of hypo- and hyper-eutectic Al-Si alloys have shown considerable promise in terms of both Si refinement of nano-scale (verified with both by SEM and TEM studies) and limited mechanical testing. The preliminary experiments indicate that the solidification conditions together with the new hypothesis of Si refinement can besuccessfully used with permanent mold casting. Recent permanent mold casting of such Al-8%Si-1.8%Ba hypo-eutectic Al-Si alloys have resulted cast alloys that without any further processing revealed a microstructure in which eutectic silicon assumes nano-fibrous morphology and where the primary aluminium phase shows dendrites of very fine size. The alloys in as cast conditions exhibit UTS values of around 172 Mpa and ductility values of about 15%.

Mohammad Shamsuzzoha, Laurentiu Nastac, Anwarul Haque

Anodization and Optical Appearance of Sputter Deposited Al-Zr Coatings

Anodized Al alloy components are extensively used in various applications like architectural, decorative and automobiles for corrosion protection and/or decorative optical appearance. However, tailoring the anodized layer for specific optical appearance is limited due to variation in composition and microstructure of the commercial alloys, and even more difficult with recycled alloys. Sputter coating methods promise to control the chemical composition of the Al alloy surfaces and eventually modify the microstructure of the surfaces with heat treatments thus enabling the freedom on the substrate quality. This paper evaluates the use of magnetron sputtered Al-Zr coatings on Al combined with heat treatment and anodizing for obtaining required optical properties. Metallurgical and optical characterization was carried out to investigate the effect of coating microstructure and anodizing parameters on appearance of the anodized layer. The microstructure of the coating is found to influence the appearance of anodized layer owing to the presence of completely or partially dissolved second phases during anodizing process. Oxidation status of the second phase particles in the coatings affected the light absorption and scattering phenomenon there by imparting different appearances to the anodized alloy surfaces.

Visweswara Chakravarthy Gudla, Stela Canulescu, Rajashekhara Shabadi, Kristian Rechendorff, Jørgen Schou, Rajan Ambat

Poster Session

Friction Coefficients on Compression Testing Of AA6060 and 42CrMo4 with Different Lubrication Conditions

Friction at the interface of compression die/work piece plays an important role in the overall behaviour of metal forming processes. This work is dealing with the determination of the friction coefficient on compression loading of the aluminum alloy AA6060 and the steel 42CrMo4 as under different lubrication conditions.The coefficient of friction was determined using cylindrical specimens with different diameter do/ height ho ratio (do/ho = 0.5, 0.67, 1.43 and 2.0). The initial specimens diameter was 4mm. Different lubrication conditions were applied: (a) dry, (b) lubrication with Molykote, (c) one Teflon layer and (d) two Teflon layers with oil film between them. The test materials were the aluminum alloy AA6060 and the steel 42CrMo4. Friction coefficients as a function of the strain were determined by the description of the curves of the deformation resistance against the do/ho values at different deformation degrees and different lubrication conditions. A comparative flow curves were determined after the elimination of the friction effect of the different do/ho values.

Sabbah Ataya, Tobias Emde

Effect of TIN on the Corrosion and Electrochemical Behavior of Al-Zn-Mg Alloy in Sea Water

The effect of tin on the corrosion and electrochemical behavior of Al-Zn-Mg alloy in 3.5 wt.% NaCl solution was investigated by open-circuit potential measurements (OCP), polarization techniques and electrochemical impedance spectroscopy (EIS). The Morphology of the alloy after corrosion was studied by scanning electron microscopy (SEM). The results showed that the anodic dissolution of Al-Zn-Mg alloy increased with increasing tin content. EIS measurements showed that the polarization resistance decreases with increasing tin content. Moreover, surface analysis indicated that Sn reduced intergranular corrosion of the aluminum alloy and promoted the formation of the corrosion products.

M. M. Sadawy, K. M. Zohdy

Interface Evolution in the Process of Fabricating Aluminum Foam Sandwiches

Aluminum foam sandwiches (AFS) which have the properties of high impact strength, efficient capacity of energy dissipation, high damping and thermal insulation, were obtained by combining steel face sheets with a lightweight closed-cell aluminum foam core. The steel sheet was hot-dipped in pure aluminum and the precursor was prepared by powder metallurgy method. The precombination of the precursor and the hot-dipped steel sheet was carried out by using hot-pressing technology. The three-layer composite was baked rapidly in a furnace to fabricate AFS. It was found that the steel sheet coated by pure aluminum combined very well with the precursor by hot-press. Then the further diffusion was promoted in the foaming process. The boundary of the AFS which was between the foam core and the face sheet had a high strength by diffusion bonding. Simplified theoretical diffusion model was introduced to explain the evolution of the boundary in the hot-pressing process.

Hao Lin, Hongjie Luo, Wei Sun, Guangchun Yao

Alloy AlZn9 Casted in the Process of Rapid Solidification and Consolidated in the Process of Plastic Forming

AlZn alloys with high Zn content have good strength properties. The basic problem in the production of the classical methods of casting alloys AlZn containing Zn above 7% is cracking of the ingots during casting. One of the methods of obtaining alloys with unusually high content of components is casting method of rapid solidification and subsequent consolidation in the process of plastic forming.This paper presents the results of the structure and properties of cast alloy AlZn9 casted in rapid solidification process on the wheel and consolidated in the process of extrusion and continuous rotary extrusion. The study was conducted using light microscopy, scanning electron microscopy and transmission electron microscopy. Property specified in the Brinell hardness test, static compression and tensile tests.

Wojciech Szymanski, Marcin Szymanek, Maciej Gawlik, Mariusz Bigaj, Sonia Boczkal, Bartłomiej Płonka

Aluminum Processing

Frontmatter

Rolling & Twin Roll Casting

Evolution of Microstructure and Texture During Severe Cold Rolling and Annealing of Al-2.5%Mg and Al-2.5%Mg-0.2%Sc Alloys

Evolution of microstructure and texture in Al-2.5%Mg and Al-2.5%Mg-0.2%Sc alloys during severe cold rolling and subsequent annealing was studied using electron back scatter diffraction (EBSD). These alloys were first thermo-mechanically processed to sheets of average thickness (~1mm) with well recrystallized microstructures. These sheets were subsequently severely coldrolled up to an equivalent strain of 4.32 using a combination of Accumulative Roll Bonding and conventional cold-rolling. The deformed alloys were subjected to isochronal annealing treatment for one hour in a wide temperature range. Development of Ultrafine lamellar microstructure subdivided by high angle grain boundaries (HAGB) and pure metal or copper type texture was observed in both the alloys during deformation. Al-Mg-Sc consistently showed higher hardness as compared to the Al-Mg. Al-Mg recrystallized around ~ 2500C but in Al-Mg-Sc the recrystallization was greatly delayed up to 500°C and the deformation texture components were retained during annealing. The differences in the recrystallization behavior of two materials were discussed with regard to the deformation microstructure and presence of fine precipitates.

J. R. Gatti, P. P. Bhattacharjee

Dynamic Simulation of Internal Logistics in Aluminum Downstream Manufacturing

Rolled or extruded aluminum products show an enormous variation of mechanical properties and surface qualities. Therefore, the manufacturing processes comprise a multitude of fabrication steps including forming, heat treatment and finishing that appear in arbitrary order. Accordingly this material flow includes a frequent stocking and buffering of material with process related waiting times and a corresponding number of transport and handling operations, named the internal logistics of a manufacturing plant.Dynamic simulations based on discrete event simulation models are effective tools to support planning processes in downstream manufacturing plants. Logistics simulation models ideally accompany improvement and modernization projects and the design of new production facilities to quantify the resulting overall equipment effectiveness. This paper outlines the principles of mapping the material flow of rolling mills and extrusion plants by configuration of generic simulation models and by modeling of specific handling equipment and production facilities under consideration of process models.

Anton Winkelmann, Sverre Brandal, Stefan Neumann, Juliens Desjardins

Influence of the Twin-Roll Casting Parameters on the Microsegregation in Thin Strips of the Aluminium Alloy EN AW-6082

Twin-roll casting is a modern process for the production of thin strips directly from the melt with a minimum of energy and material consumption. Nowadays, lightweight thin strips of agehardenable aluminium alloys with medium and high strength are widely used in the machine building and construction. However, the wide application of twin-roll casting technology for the strip production from high-alloyed 6XXX- and 7XXX-series aluminum alloys is limited due to the presence of characteristic near-surface microsegregation in the strips caused by non-uniform deformation over their thickness in twin-roll caster. Microsegregation leads to inhomogeneous microstructure of the strips and consequently deteriorates their mechanical characteristics, corrosion resistance and surface quality. This paper focuses on the influence of twinroll casting speed on the microsegregation in strips of the aluminum alloy EN AW-6082. Analysis of 3 mm thickness strips obtained by twin-roll casting at different speeds is carried out using metallographic and electron microscopy methods.

Olexandr Grydin, Mykhailo Stolbchenko, Florian Nürnberger, Mirko Schaper

Determination of Aluminum Rolling Oil And Machinery Oil Residues on Finished Aluminum Sheet and Foil Using Elemental Analysis and Fourier Transform Infrared Spectroscopy Coupled with Multivariate Calibration

The surface characteristics of rolled aluminum products such as sheets and foils are strongly affected by the particular rolling process and the type of aluminum rolling oil compositions. After the rolling process, coiled aluminum sheets and foils undergoes annealing to form desired crystal structure and remove the rolling oil residues. Depending on the time and the temperature that rolled aluminum exposed for annealing, rolling oil residues are mostly removed from the coiled aluminum products but if there is any contamination in rolling oil due to hydraulic and gearing parts of the rolling systems these heavier oils are not easily evaporates from the aluminum surfaces especially inner parts of the coiled aluminum sheets and foils. These rolling oil contaminants create serious problems for the some specific applications of these aluminum products in certain industries such as automotive and coating as remaining thin oil layer prevents proper painting and coating. Therefore, it is very crucial for the rolling industry to be able to monitor the heavy oil contamination on the rolled products and determine the source of these contaminants .In this study, it was aimed to develop a nondestructive infrared spectroscopic method combined with chemometric multivariate calibration techniques for the quantitative determination of rolling oil residues and contaminants on the rolled aluminum products. To be able to generate multivariate calibration methods, an industrial elemental analysis system was adopted for the quantitative determination of heavy oil contaminants on the rolled aluminum products and these were used as reference values for infrared analysis of the same samples. In addition, apart from conventional use of elemental analysis systems for the total organic analysis, the raw data (raw chromatogram) obtained from elemental analysis was used to directly generate multivariate calibration models for each contaminant by using synthetically contaminated surfaces as the calibration samples. The results promised that elemental analysis can be used not just for the total organic content but also specifically to determine amount of each contaminant on the aluminum surfaces. İt is also, expected that infrared spectroscopy with grazing angle spectra collection accessories can be used for nondestructive analysis of these contaminants.

Özlem İnanç Uçar, Hatice Mollaoğlu Altuner, Mert Günyüz, Mustafa Murat Dündar, Durmuş Özdemir

Extrusion & Miscellaneous Processes

A Numerical and Experimental Study of Homogenization of Al-Si-Mg Alloys

Homogenization is important for alloys to obtain a good surface finish, low flow stress and minimized recrystallization during extrusion. A numerical and experimental study of the homogenization process for Al-Si-Mg alloy was done. A finite volume diffusion model, coupled with a cellular automaton to predict phase change, was developed to study the dissolution kinetics for the as-cast microstructure for ternary systems. The required thermodynamic and kinetic data was provided to the model from Thermocalc and DICTRA. Homogenization at 4 different temperatures was simulated. The volume fraction of the precipitates decreases exponentially with time. The length scales of the precipitates predicted matched the experimental length scales. The effect of cooling rate after homogenization on the precipitation behavior of the Mg2Si phase was also studied using a finite difference model. The volume fraction and mean radius of the Mg2Si particles is found to decrease with increasing cooling rate while the average Mg concentration of the matrix increases with increasing cooling rate, in accordance with the hardness results reported in [15].

Pikee Priya, Matthew J. M. Krane, David R. Johnson

Effect of Mg2Si Phase on Extrusion of AA6005 Aluminum Alloy

The extrusion behavior and mechanical properties of aluminum alloys are very sensitive to the microstructure of the billets after homogenization. In order to optimize the homogenization practice for the extrusion process, the influence of different cooling rates from soaking temperature during homogenization was investigated for an AA6005 alloy. The specimens were soaked at 580°C for 8 hours, and then cooled by 3 different cooling rates: water quenching, air cooling and furnace cooling. The homogenized microstructures from specimens exhibit an increase in both amount and size of Mg2Si particles with a decreasing cooling rate. The hardness at room temperature and the flow stress at preheating temperature (450°C) and real extrusion temperatures (500–550°C) also generally decrease with a slower cooling rate. However, re-precipitation of Mg2Si is observed upon reheating to 450°C and dissolution is observed at 500°C and 550°C. A fast cooled billet is identified to have fully solutionized microstructure but requires higher extrusion pressure and is sensitive to preheating rate, while a slow cooled billet is easier to extrude but is not sufficiently solutionized after extrusion.

Yiwei Sun, David R. Johnson, Kevin P. Trumble, Pikee Priya, Matthew John M. Krane

Analysis of the Evolution and Deformation of Pore Morphology During Compression

In this paper, the X-ray tomography is used to observe the evolution of pore morphology during the compression of aluminum foam. The pore morphological tomography images for every cross-section were obtained, and the evolution regularity was analyzed in different compression stages. The results of the research work show that the pore morphology evolution is closely related with the cell wall structure. There are non-uniform pore structure and cell wall defects generated in the preparation process of aluminum foams. Foam Al-Si alloy presents brittle fracture in the process of compression as for the reason of brittleness in its base metal. This crack first appears in the area of the cell wall with defects. As the pressure increases, the crack continues to expand and deepen with fractures appearing in some cell walls, and eventually forming a fracture zone; finally, the entire sample is compacted and crushed. Foam magnesium alloy presents good ductility in the process of compression. Bending deformation of the cell wall occurs, and expands to the central area until the entire sample is compacted.

Li Wei, Tingan Zhang, Yuan Fang, Yunan Tian

Aluminum Reduction Technology

Frontmatter

Potline Operations — Cell Operations

Cell Electrical Preheating Practices at Dubal

DUBAL has extensive experience of electrically preheating cells since its initial operation in 1979. The electrical preheating at DUBAL has evolved, including the type of material used, the setup of the cell and the equipment needed to carry out preheat. Traditionally, a thick coke bed fully covering the surface below the anodes was used. In order to reduce the amount of material and energy for preheat, the grain size and shunt design were optimized. Further progress, which allowed elimination of the shunts, was achieved by using low resistivity material partially spread over the surface below the anodes. To minimize heat loss and air burn during preheating and to prepare the cell for bath-up, crushed bath is used at the anode sides and mineral wool and crushed bath are used on the top. Finally, the preheat equipment design was improved. The application of the most recent preheating technique for DX and DX+ technologies is described.

Alexander Arkhipov, Abdalla Zarouni, Dr. Maryam Al Jallaf, Ibrahim Baggash, Sergey Akhmetov, Michel Reverdy, Vinko Potocnik

Dubal Cell Voltage Drop Initiatives Towards Low Energy High Amperage Cells

In recent years, DUBAL has focused its energy and resources towards reducing energy consumption of aluminum electrolysis cells. The main ambition, though, was to take the available worldclass DX+ Technology, the highest cell amperage technology currently operating in DUBAL, and build upon it further. For that, several voltage drop initiatives were initiated and trials have been conducted on numerous DUBAL cell technologies to demonstrate and prove the newly developed low energy concepts, and more importantly to facilitate the transition from DX+ cell technology to DX+ Ultra cell technology which incorporates all the voltage drop solutions. The initiatives tackled lower energy concepts around four fundamental categories; anode voltage drop, bath voltage drop, cathode voltage drop, and external voltage drop. Indepth mathematical models were used, through commercial software packages to design and predict these concepts. In addition, measurement programs were setup and organized with trials conducted to validate the model predictions. In this paper, the voltage initiatives and trials shall be evaluated in detail, with particular emphasis on the analysis of copper insert cells.

Marwan Bastaki, Abdulla Zarouni, Bernard Jonqua, Nadia Ahli, Lalit Mishra, Amal Al Jasmi, Ali Al Zarouni, Michel Reverdy, Vinko Potocnik

Startup of Shut-Down Pots — Problems and Solutions to Improve Results

Due to the operational crisis at Votorantim Metais CBA in 2011 (VSS Soderberg technology – 128kA), some anodes were lost, consequently the cathode lifetime and conditions were compromised. With the high amount of shut-down pots, and with the need to resume production (pots in operation), a so-called“recovered cathode pot” was decided to be made, in which the pot side walls (the refractory and ramming paste layers) were cleaned, the refractory and ramp replacement for cold ramming paste was realized and, subsequently, the baking of anodes was carried out. The recovered cathode pots have different lifetimes ranging from 600 to 2700 days. Compared to the normal line pots, these pots, showed high amount of leakages, premature failures and lower current efficiency. After several meetings with the technical pot room team, in May 2012 the previous process parameters were altered in order to increase the lifetime, reduce the number of the leakages and improve the current efficiency.This paper will show the implemented changes and the better results of lifetime, leakages and current efficiency to these pots.

Diego Cota Marinho, Lauro Fabri, Nilzandro Gama

Thermal Events of the Early Life of an Aluminum Electrolysis Cell

The efficient and long operation of an aluminum reduction cell strongly depends on the early period of the pot-life. In order to have a record of the events of the cell structure’s thermal state, the temperature in the sidewall was monitored. The unsteady thermal events were compared with the cell voltage as well as correlated with various events during the early pot-life.We found that with the proper positioning of the thermocouples, major events can be detected. Apart from the detection of the effect of different events along the sidewalls, the temperature signals can provide further information. We propose various signal properties such as frequency content, amplitude and phase information, which can be exploited in the thermal diagnostics of an electrolysis cell.With in-situ measurement examples we demonstrate that the temperature signal of the sidewall provides useful information in both operation and the diagnostics of the aluminum electrolysis cells.

Ádam Ugron, László I. Kiss, Jean-François Bilodeau, Sébastien Guérard

Regulation System to Improve Quality of the Metal Sucked During Tapping Operation

One of the objectives you can target from the whole process of primary aluminium production is to deliver a metal free from impurities. The tapping operation consisting in sucking liquid aluminium from the pot in a crucible through a tapping tube remains an operation requiring precautionary measures. On one hand, the operator has to correctly insert the tapping tube into the electrolytic cell at the lower part of the metal pad. And on the other hand, the volumetric flow during tapping is difficult to regulate. If the flow is excessive, it can result in bath being sucked with the metal. Bath adjunctions have many negative effects both on electrolytic cell operation and equipment soiling but above all on metal casting.To avoid such concern, ECL works in close collaboration with Rio Tinto Alcan in order to develop and adapt a system described in patent and based on components of the shelves. This system allows the control and the regulation of the flow rate of aluminium sucked from the pot by means of loops control and signal processing in PLC which controls a valve on the compressed air supply. 200 tapping operations have been performed in Alma’s plant resulting in ensuring the efficiency and reliability of the solution and significant benefits such as less equipment cleaning cycle and better metal casting.

Steve Bouchard, Pierre-Marie Canis, Serge Despinasse, Anne-Gaëlle Hequet, Patrick Marchand, Frédéric Potvin

Key Success Factors Deploying a Manufacturing Excellence Solution (Mesal™) in Rio Tinto Alcan

High capability information systems are now a mandatory enabler to achieve Operational Excellence in a modern smelter. Realizing full potential of new and existing assets, by reducing operating costs and increasing production capacity at low capital cost, is supported by the best practice use of a capable Manufacturing Execution System.In order to realise this goal, Aluminium Pechiney, a company of Rio Tinto Alcan has developed MESAL™, a Manufacturing Excellence Solution for Aluminium to enhance management of all aspects of smelter operations.This platform developed with a world leading IT company provides framework and dashboards for operation management, process quality follow-up, measurement and analysis of production performance and optimized inventory management.This paper describes how Rio Tinto Alcan has launched the global deployment of MESAL™ based on a strategy that aims at standardizing and centralizing expertise in competencies centres.

Manuel Chareyre, Steve Boivin

Cell Design and Performance — Cathodes and Anodes Joint Session with Electrode Technology

Influence of the Cathode Surface Geometry on the Metal Pad Current Density

In the recent years, the Chinese aluminum industry has started to extensively use irregular top surface cathode blocks in its new cell designs. The increase popularity of these new types of cell designs in China is explained by the fact that they can be operated at a much lower cell voltage.The cell voltage can be reduced because irregular top cathode surface designs seem to increase the MHD cell stability which allows the cell to be operated at a reduced ACD. No satisfactory explanation as to why the usage of irregular top cathode surface promotes MHD cell stability has been presented up to now.The present work concentrates on the influence of the cathode surface geometry on the metal pad current density as potential cause of the change in the MHD cell stability behavior.

Marc Dupuis, Valdis Bojarevics

On the Influence of Mhd Driven Convection on Cathode Wear

Non-uniform cathode wear observed in industrial aluminium reduction cells limits the cell life and thus presents a great challenge for the industry. The mechanism for cathode wear is not fully understood, although current densities, bath and metal convection and dissolution of aluminium carbide appear to play an important role. This work describes the two phase magnetohydrodynamic (MHD) flow in a simplified representation of an electrolysis cell, with emphasis upon the flow conditions at the cathode surface, which in turn drive mass transfer which is used to determine the cathode wear. Different cases are considered, focusing on current density distribution and electrode topology, simulating different operational conditions. The overall shape and magnitude of the wear rate obtained in the current simulations correspond well with measured wear rates, indicating that the MHD flow close to the cathode can shed new light upon cathode wear.

Kristian Etienne Einarsrud, Egil Skybakmoen, Asbjørn Solheim

Effect of Innovative Cathode on Bath/Metal Interface Fluctuation in Aluminum Electrolytic Cell

A three-dimensional transient magnetohydrodynamic model has been developed to investigate the effect of innovative cathode on interface fluctuation of bath/metal in aluminum electrolytic cell. A homogeneous multiphase flow model of three phases including molten aluminum (metal) and molten cryolite (bath) using the volume of fluid (VOF) approach is used to describe phases interaction. Moreover, the electrical potential method is adopted for the electric current and magnetic field. The Electromagnetic force is recalculated at each time step and then is implemented in the momentum equation of bath and metal as a source term. Then the mathematical model is employed to investigate the effect of the innovative cathode on the electric current, magnetic field, flow field, and bath/metal interface fluctuation. The results show that the interface fluctuation would be suppressed with the help of innovative cathode. In addition, the gas bubbles also float up more quickly which is good to energy saving.

Qiang Wang, Jianping Peng, Baokuan Li, Naixiang Feng

Simulation and Optimization of Cathode Current Distribution to Reduce the Horizontal Current in the Aluminum Liquid

In an aluminum electrolysis cell, the movement of molten aluminum is driven by electromagnetic forces resulting from the current fields in the cell. A rapid movement of the aluminum liquid results in a noisy operation of the cell with an increase in both the voltage and the energy consumption. For a long time designers have endeavored to reduce the magnetic field intensity and decrease the Lorenz force to lower the flow speed of the aluminum liquid by optimizing the layout of the bus bars. In the present work, the effect of the design and the material of the cathode on the horizontal current in aluminum liquid were studied by .

Wangxing Li, Yanfang Zhang, Dengpeng Chai, Jianhong Yang, Shilin Qiu, Yueyong Wang

Numerical Simulation of Full Life Cycle Cathode Assembly Performances for Design Optimization

The importance of the cathode assembly thermal-electrical and thermal-mechanical performance cannot be overstated when designing an aluminum reduction cell. However, it is extremely difficult to measure in-service cathode assembly performance or to infer in-service behaviour from any measurements of cathode assemblies at room temperature. A complete thermo-electrical and thermo-mechanical modelling approach has been developed to conduct sequentially coupled simulation of the cathode assembly lifecycle performance. The modelling starts with the cathode rodding process which allows the air gap between the cast iron and carbon to be predicted. The results are built into the subsequent thermo-electrical and thermo-mechanical models of the in cell operation. The cathode voltage drop is then estimated by coupling the predicted contact pressure and temperature with the electrical contact resistance. The model predicted air gaps as well as cathode voltage drop savings due to design changes have been validated by carefully designed experimental measurements for various cathode assembly designs.

Guorong Cao, Xinquan Zhang, Hao Zhang

Bar to Block Contact Resistance in Aluminum Reduction Cell Cathode Assemblies

Contact resistance between the collector bar and cathode block has been previously estimated at 10 Ωmm2contributing roughly 100 mV to cell voltage. This paper proposes four mechanisms as contributors to high contact resistance through low contact pressure and large scale intermittent contact. These mechanisms are: temporary bowing of the bar during solidification of cast iron joints, shrinkage of the bar during the phase change from ferrite to austenite, mismatch of iron and carbon surface texture due to axial thermal expansion, and reduced contact pressure due to creep in the steel bar.

Richard Beeler

Anode Rod to Beam Contact

The anode rod to beam contact for modern aluminum smelting technology is more sensitive to contact condition than it is to applied force [1]. The contact can consume in excess of 12 kW per cell if not prepared and maintained carefully. There can be significant variation in contact resistance across the contacts onany one cell. Validating improvements of only a few mV for the anode rod to beam contact for operating cells can be very challenging.The purpose of this paper is to (i) discuss the variation due to measurement technique, and (ii) establish both theoretical and practical benchmarks for common sized connections. The benchmarks presented here are validated against actual plant datameasured at several smelters.

D. Molenaar, T. Kilpatrick

Towards Decreasing Energy Consumption of Aluminum Reduction by Using Anodes with Holes and Channels

In aluminum electrolysis the energy power consumption can be decreased by lowering the cell voltage and by increasing the current efficiency. By using anodes with holes and channels, the discharge distance for the anode gas from the molten bath can be reduced. For the anode gas, the period of staying in the bath is decreased and the penetrated depth in the bath will decrease. By such measures the current efficiency of the cell can be increased and the cell voltage can be decreased. In the Qingtongxia smelter, 350 kA aluminum reduction cells are operating with anodes having holes and channels.

Feng Naixiang, Peng Jianping, Niu Qingren, Zhan Lei, Kang Ning, Liao Xian’an, Gong Xiaofeng

Environment I

Comparing Different Measurement Approaches to Characterize All PFC Emissions

Different measurement approaches have been used to characterize PFC emissions coming from aluminum smelting. In the past, those techniques were developed mainly to measure PFC emissions during the so called Anode Effect (AE). More recently, the variable but notable presence of PFC emissions outside AE was confirmed by many authors. In this paper, we analysed the results obtained by using two different PFC measurement approaches: one using an FTIR with in-situ and real time analysis, and one using an extractive procedure with sampling bags and GC-MS analysis integrating all emissions over an extended period of time. Results for the same sampling location are given for both methodologies and their pros and cons are discussed in light of a proper accounting of non-AE PFC’s. These will need to be carefully considered in future measurement campaigns to provide the most accurate information depending on user needs.

Simon Gaboury, Anne Gosselin, Patrice Tremblay, Jerry Marks

Anode Effect Phenomena During Conventional AEs, Low Voltage Propagating AEs & Non-Propagating AEs

Anode effect (AE) phenomena in aluminium cells can be separated into several categories. Firstly, ‘conventional’ AEs (>8V) are typically initiated on one or two localized anodes and then, due to an abrupt increase in current density, rapidly propagate to the other anodes in the cell thereby providing the typical emission spectrum of PFCs. Secondly, ‘low voltage propagating’ AEs (<8V) result from localized AEs rapidly propagating to a limited section of anodes with the cells remaining below conventional AE voltage; these AEs often undergo electrical shorting, especially at narrow ACDs, resulting in rapid self-termination. In contrast, the continuous background emission of PFCs should be categorized as a third type of AE or ‘nonpropagating’ AEs. The fundamental mechanisms that initiate continuous PFCs very likely still apply, but the localised AEs do not propagate sufficiently to other anodes for a cell to exhibit a voltage signature characteristic of a low voltage AE.

David S. Wong, Alton Tabereaux, Pascal Lavoie

Monitoring of Continuous PFC Formation in Small to Moderate Size Aluminium Electrolysis Cells

The existence of continuous or non-anode effect formed perfluorocarbons (PFC) has been documented for larger size aluminium electrolysis cells. It has been proposed that less uniformity in dissolved alumina for larger cells may elevate individual anode overvoltage sufficiently to produce PFC. Continuous PFC was monitored after the dry scrubber on a train of 28 cells at a Norwegian smelter. For this work a fourier-transform infrared spectrometer was used. Equipped with a mercury cadmium telluride detector and retrofitted with a 35 m / 11 L measurement cell it was possible to get the detection limit down in the low ppb range needed for this study.It was discovered that also small cells could emit PFC that was not directly related to the full anode effect. Continuous formation of PFC was found to be in the form of CF2, for the most part; however, the results indicate that C2F6 may also form outside the full anode effect. No numerical data for the contribution of non-anode effect emissions to the overall PFC was calculated, nonetheless, judging by the difference in intensity it will be small for this particular smelter.

Henrik Åsheim, Thor A. Aarhaug, Alain Ferber, Ole S. Kjos, Geir M. Haarberg

At-Line Analysis of Polycyclic Aromatic Hydrocarbons in Aluminium Primary Production

Emissions of Polycyclic Aromatic Hydrocarbons (PAH) from prebake anode production are closely monitored. The PAH concentrations downstream the gas treatment facility are normally in the ultra-trace range[1]. Rigorous sampling and analytical procedures are required in order to estimate the PAH release. The time from sampling to analytical result is therefore long. It is often of interest to study the dynamic gas composition. In this work, the applicability of Thermal Desorption (TD) combined with a transportable Gas Chromatography/Mass Spectrometry (GC/MS) instrument was investigated. The analytical setup was found to be capable of PAH quantification in the parts per trillion range. With short sampling times required, the total analytical time required was about 30 minutes. The limiting factor was the GC elution time. The analytical methodology was used to evaluate the efficiency of a prebake anode factory dry scrubber. At-line analysis made possible the direct evaluation of PAH emission as function of the operational set points.

Ole S. Kjos, Thor A. Aarhaug, Bernd Wittgens, Anders Brunsvik

Raw Gas Particles and Depositions in Fume Treatment Facilities in Aluminium Smelting

The trace element distributions in depositions found in the gas treatment centres (GTCs) exhibit striking similarities with the coarse pot gas particulates captured in a standard cyclone. To gain a better understanding of possible scale formation mechanisms and components involved, several analysis techniques were applied and compared. Pot exhaust coarse and fine particles, as well as scale samples collected form the gas treatment centre of the same Al-smelter were evaluated. LECO and Sintasyzer results, XRD, IR spectra and XPS pattern of grey scale samples and raw gas particle fractions are presented. Recrystallization of sodium fluoroaluminates due to HF adsorption reactions in combination with moisture is suggested as one formation mechanism.

Heiko Gaertner, Arne Petter Ratvik, Thor Anders Aarhaug

The Nature of Particles and Fines in Potroom Dust

Potroom dust or particulates are major contributors to a smelter’s total environmental burden. A wider study on the environmental contribution of these particulates was conducted across multiple prebake smelters, part of which was to determine the composition and particle size distribution of this dust and its material sources. This has provided an understanding of the fate of particles within the potroom, after the point of emission. In general, anode cover material and feed alumina were found to be contributors of coarser dust that tends to settle on various surfaces in the potroom (floor, pot superstructures, rafters), thereby becoming a source of recirculating dust. In contrast, bath fume was found to be the dominant contributor to fines/ultrafines, from operations involving open cells and hot, fuming materials in the potroom. Such fines are fluoride-based, highly mobile and readily emitted from the potroom. Particles also tend to decrease in size at higher potroom elevations.

David S. Wong, Nursiani I. Tjahyono, Margaret M. Hyland

Predictive Tools in Evaluating Re-Entrainment of Exhausted Particulate in Different Ventilator Configurations for Different Heat Process Applications

Selection of proper roof ventilators to match application and environment standards is key to both smelter function and interior working conditions. Computational fluid dynamic simulations can predicatively demonstrate to end users and assist engineers, coupled with traditional calculations and physical modeling, in the optimization of smelter ventilation reducing total installed costs while assuring that the proper solution is in place for the complete lifecycle of the process equipment and manpower that will spend many man-hours working. Our research and practice has developed number ventilation methods, which can be predicatively verified utilizing CFD simulation techniques.Results have been fully implemented on a number of smelter applications and we continue to study, optimize and innovate as new tools become available to provide the best possible engineered solutions for particular applications

Siegmar U. Baltuch, Edmund G. Baltuch

Economic and Environmental Alternative for Destination of Spent Pot Lining from Primary Aluminum Production

The residue from the demolition of electrolytic cells for the production of primary aluminum is the Spent Potlining (SPL). This material is classified as Class I (non-inert — traces of cyanide) waste. Among the possibilities of neutralizing the SPL there are the process at elevated temperatures with the formation of silicates and calcium compounds. The processes of secondary metallurgy of steel are characterized by high temperature and the slag is from the CaO-Al2O3-SiO2 system saturated with CaO. Additionally, other fluidizing components used are found on the composition of SPL. In this work was investigated and evaluated the possible development and application of SPL as alternative in steelmaking.

Bruna Meirelles, Henrique Santos

Fundamentals — Chemistry

Improving XRD Analysis for Complex Bath Chemistries — Investigations and Challenges Faced

An accurate bath composition analysis is essential for regulating an electrolysis cell’s mass and thermal balance. XRD is widely utilised in smelters to analyse % excess AlF3 (xsAlF3) and Cryolite Ratio (CR) of bath samples. However, the conventional method of analysis can provide misleading results for the more complex bath chemistries usually found in, but not limited to, Chinese smelters. This complexity is due to the presence of Li, K and Mg constituents coming into the bath from alumina impurities. They react with AlF3 and cryolite, producing additional AlF3-containing phases other than chiolite and Cacryolite, which are not accounted for in the conventional xsAlF3 or CR analysis.Improvement of the xsAlF3 analysis for complex bath chemistries was investigated and presented in this paper. The aim was to provide an XRD methodology to measure the LiF, KF and MgF2 levels in the bath through an intensity calibration method, so that they can be integrated into the xsAlF3 and CR analyses. The challenges faced will also be discussed in this paper.

Nursiani Indah Tjahyono, Tania Groutso, David S. Wong, Pascal Lavoie, Mark P. Taylor

Al2O3-Na3AlF6 Man-Made Ledge Composites for Aluminum Electrolysis Cells

Man-made Al2O3-Na3AlF6 composite ledge for aluminum reduction cell was developed because of the disadvantages of traditional self-forming ledge and the composite material was prepared by pressureless liquid-phase sintering under air atmosphere. The effect of Na3AlF6 mass fraction on the relative density, compressive strength, high-temperature stability and microstructure of Al2O3-Na3AlF6 composites was investigated. The results show that with the increasing of Na3AlF6 mass fraction from 0 to 15 wt%, the relative density increases from 62.05 % to 67.19 %, the compressive strength increases from 9.74 MPa to 17.81 MPa, and the high-temperature stability of composites under 1100 °C gradually becomes worse. However, compared to traditional self-forming ledge, Al2O3-Na3AlF6 composites have more excellent high-temperature stability. Such results indicate that Al2O3-Na3AlF6 composite is a promising man-made ledge for aluminum reduction cell.

Lv Xiaojun, Zhang Chao, Lai Yanqing, Tian Zhongliang, Jia Ming, Li Jie

Structural Characterisation and Thermophysical Properties of the side Ledge in Hall-Héroult Cells

In the modern Hall-Héroult cells, a frozen bath layer — the side ledge — protects the sidewalls from the very corrosive liquid bath. This frozen bath layer has a significant impact on the heat balance of the cells as well as on the bath chemistry. For this reason, the geometry, the structure, the distribution of the chemical composition and certain physical properties of the side ledge must be studied. Those characteristics are important to the development of a mathematical model for the Hall-Héroult cells. Despite of all the research efforts invested, only a few results are available in the published literature. This paper presents a few results and observations, obtained by the analysis of side ledge samples, extracted from post-mortem cells. The results show a very inhomogeneous structure and a strong dependence of the thermophysical properties on material structure and temperature.

Sándor Poncsák, László Kiss, Rémi St-Pierre, Sébastien Guérard, Jean François Bilodeau

The Melting Behaviour of Aluminium Smelter Crust

Crust is the bottom consolidated part of the anode cover, which plays an important role in the performance of aluminium reduction cells. The melting of the crust contributes to the deterioration of the anode cover. Several crust samples were taken from an aluminium smelter. A DTA system was established, and calibrated by measuring the melting temperature of cryolite. The DTA test results show that the melting temperature of the crust samples is depressed due to low cryolite ratio (CR) and high fluoride additives content. In chiolite enriched crust, incongruently melting of chiolite component at 725 °C was detected. Because of the melting of cryolite in the liquid, the chiolite enriched crust had a broader melting temperature range than that with high CR. To our knowledge, few studies have discussed the melting temperature range of the crust and its impact on crust thermal stability at cell operating temperatures.

Qinsong Zhang, Mark P. Taylor, John J. J. Chen

Key Physical Properties of Smelter Grade Alumina

The properties of Smelter Grade Alumina, SGA, vary from refinery to refinery, and they also vary over time. Some physical properties, such as high fines content, have the potential to impact key smelting performance indicators more than others. These may affect production efficiency as well as environmental performance. Often the barriers to optimal performance have as much to do with the equipment that is used to handle alumina, its layout, and how alumina inventories are managed, as with the physical properties of SGA. In this paper the author offers insights into which parameters are key focal points; for the properties of SGA, and upon handling equipment & methods.

Stephen J. Lindsay

Modeling the Behavior of Alumina Agglomerate in the Hall-Héroult Process

During the feeding of the Hall-Héroult cell, cold alumina comes into contact with the electrolyte bath and tends to agglomerate due to the formation of a frozen bath layer that holds physically the alumina together. This agglomeration, producing alumina agglomerates, called also lumps or sludge, affects both the rate of alumina dissolution and the stability of the cell. In this paper, all the physical phenomena (heat and mass transfer) between the formation and the complete dissolution of agglomerate will be described and are defined by a set of equations. This mathematical model allows observing the strong coupling between the mechanisms of heat and mass transfer e.g. the solidification with diffusion of chemical species, the infiltration of the bath in the porous agglomerate and the dissolution of sintered alumina. A parametric study using this model might identify the most important factors related to the lifespan and behavior of alumina agglomerates.

Véronique Dassylva-Raymond, Laszlo I. Kiss, Sandor Poncsak, Patrice Chartrand, Jean-François Bilodeau, Sébastien Guérard

Wetting Characteristics of Cryolite-Based Melts on Spinels Substrate

Spinels have recently been proposed as ledge free sidewall material for aluminium smelter, mainly due to its low solubility in cryolite. A ledge-free sidewall will have a direct contact with electrolyte and therefore its wetting properties become important as it determine the penetration of the electrolyte into the sidewall which in turn may affect its corrosion level. In the present study, the wetting properties of cryolite based melts on various spinels substrates have been studied by sessile drop approach. The apparent contact angle of the melts on NiFe2O4 and MgAl2O4 substrates under argon atmosphere at 1030 °C was measured. It was found that spinels were wetted by the melts with apparent contact angles ranging from 9° to 19°. It was also observed that the capillary effect play a significant role in the infiltration of the melts into the substrates. The average infiltration rate was found to be 8.5 mm3/s.

Reiza Z. Mukhlis, Muhammad Akbar Rhamdhani, Geoffrey Brooks, Kathie McGregor

Environment II

Abart CDS — A New Compact Multi-Pollutant Pot Gas and Alumina Handling System

A new modular Abart CDS has been developed that integrates silos, alumina handling, heat exchangers, fans, SO2 scrubber and stack into a compact and efficient multi-pollutant pot gas treatment and recovery technology with incomparable footprint. The system is based on standardized modules that allows for short delivery time and early start-up. Each module includes an individual fan and optional SO2 scrubber located directly on top of the module. This compact design reduces overall pressure drop and energy requirements for operation of the fans. This paper updates the previously reported experiences from the first full scale installation in Norway with new results on the integrated SO2 scrubbers that were retrofitted in 2012/13.

Sivert Ose, Anders Kenneth Sørhuus, Geir Wedde

Development on Electrolytic Cell Gas Cooling

The construction of smelters in hot climates and the increase in pot amperage are forcing the industry to consider methods of cooling the gases upstream of the GTCs. In 2012, Fives Solios presented a paper describing four methods to cool down gases: dilution air, hairpin coolers, water spray cooling, and heat exchangers. At that time, some solutions were not fully validated with operational data. This paper will present the performance achieved with those technologies on existing sites: hairpins at Ma’aden smelter, water spray cooling at Sohar smelter and pilot heat exchanger at Hydro Ardal smelter. Cooling capacity, pressure drop across the cooling device and power consumption of auxiliaries will be compared. Maintenance issues will be discussed and ideas for improvement will be presented. The CAPEX and OPEX of each solution will be updated to provide an overview of the available solutions.

Antoine de Gromard, Chin Lim, El Hani Bouhabila, Bernard Cloutier, Mathieu Frainais

15 Years of GTC Operation at Aldel: Long-Term Assessment of GTC Performance

In 1998, a new Gas Treatment Center (GTC) was taken into operation at the ALDEL Aluminum Smelter located in Delfzijl, the Netherlands. This GTC was designed and built by Danieli Corus (former Hoogovens Technical Services) according to the Pleno IV design. This year, the GTC at ALDEL is operating successfully and reliably for 15 years, which is the reason for looking back at the past performance. In this article, the design and operation as well as the performance and availability of this GTC over the past 15 years will be discussed.

Anita Folkers, Jan de Weerdt, Peter Klut, Erik Dupon, Edo Engel

Pot Gas Cooling Technologies

The development of cooling techniques to reduce the temperature of the pot gas has been increased enormously by the suppliers of pot gas treatment plants, since the proven cooling concept by dilution air doubles the size of the GTC’s in GCC countries. Alternative options are evaporative cooling by water injection and the use of heat exchangers, however both have the risk of fouling and scaling. Danieli Corus studied several possibilities with their pros and cons to determine the optimal way of cooling the pot gas and developed a new concept of cooling. To maintain the highest availability for GTC’s is one of the major topics for designs with cooled pot gas.

Peter Verbraak, Travis Turco, Peter Klut, Erik Dupon, Edo Engel

Modelling HF Generation: The Role of Ambient Humidity

HF generation in aluminium reduction cells is known to occur by the reaction between fluorides (in a variety of forms) and a source of water or hydrogen. Studies on the generation of HF indicate that the major sources of moisture for hydrogen fluoride generation appear to be alumina, in the form of structural hydroxides (LOI 300–1000) and adsorbed moisture (LOI 25–300), and the ambient humidity. Several models have been developed to estimate the amount of hydrogen fluoride generated but these do not consider the individual sources of fluoride generation and cannot be easily used to assess the impact of changes in relative humidity. This paper presents a new model, still under development, which simulates the hydrolysis of pot gas from an open feeder hole. Initial results suggest that, in an open feeder hole, the high background concentration of hydrogen fluoride (3000–5000 ppm) presents, inhibiting the hydrolysis of pot gas, and thus the ambient humidity has relatively limited influence on the total fluoride emission. While the influence of ambient humidity has been the focus of this study, the model developed is intended to provide a framework that can be used to assess the sensitivity of fluoride emissions to other factors.

Youjian Yang, Margaret Hyland, Chris Seal, Zhaowen Wang

Online Monitoring of Aluminium Primary Production Gas Composition by Use of Fourier-Transform Infrared Spectrometry

Online monitoring of aluminium primary production raw gas is challenging due to the high concentration of HF in the presence of water. Tunable Diode Laser (TDL) analyzers retrofitted with sapphire optical windows allow for online monitoring of raw gas composistion. These systems are however limited to one or two gas constituents. In order to make use of multi-component analyzers like Fourier-Transform InfraRed Spectrometers (FTIR), HF must be selectively removed by filtration. This work presents some results from complete mapping of raw gas composition by comparing results from HF filtrated as well as non-filtrated measurements. The multivariate calibration models established for mapping of the raw gas is discussed. Open-path FTIR spectroscopy was applied in order to quantify fugitive emissions of HF and SO2. Quantitation showed good correlation with reported emissions. Monitoring of fugitive PFC emissions was also evaluated.

Thor A. Aarhaug, Alain Ferber, Ole Kjos, Heiko Gaertner

Fundamentals — Modeling

On the Prediction of the Crust Evolution Inside Aluminum Electrolysis Cells

A model for predicting the evolution of the crust inside aluminum electrolysis cells is presented. The model takes into account the effects of heat transfer, solid/liquid phase-change, and chemical transformation of anode covering material (ACM). The model predicts: 1) the temperature field inside the cell, 2) the evolution of the ACM conversion into crust, 3) the melting/solidification processes inside the cell and, 4) the time-varying heat losses at the top of the cell. The model is validated with experimental data taken on an industrial electrolysis cell. Results show that the model captures the essential behavioral features of the industrial cell. However, further experiments must be performed in order to provide reliable data on the crust formation. These experimental data are needed for a thorough validation of the mathematical model.

Marc LeBreux, Martin Désilets, Alexandre Blais, Marcel Lacroix

An Improved Finite Element Model for Thermal Balance Analysis of Aluminum Electrolysis Cells

Thermal balance analysis, through which the insulation construction and daily operations of aluminum cells can be determined to keep electrolysis temperature stable, is of capital importance for the cell design. This paper propose an improved thermal-electric coupling model based on finite element software ANSYS for thermal balance analysis. Besides ohmic heating effect and heat dissipation outside the cell, the model also takes into consideration the thermal effect caused by tapping, spent anode removal, fume/air extraction and raw materials heating. The numerical model is applied to a 305kA cell and is verified by comparing results with industrial measurements.

Cui Xifeng, Zhou Yiwen, Yang Jianhong

A Modelling of Heat Losses in Aluminium Reduction Cell With Slotted Anodes

The heat losses of aluminium reduction cells depend strongly on the heat transfer coefficients between the bath and side ledge or anodes. Using of anodes with slots can greatly change heat transfer. In order to investigate the heat loss dynamics in reduction cells with slotted anodes, a modeling of heat transfer coefficients in cells was firstly undertook. This enables understanding of how slotted anode changes heat dissipation from the bath. Then, a thermal field was been calculated by using heat transfer coefficients obtained in the first step. All these studies were carried out with 500kA cells.

Yang Shuai, Li Jie, Xu Yujie, Zhang Hongliang, Lv Xiaojun, Jia Ming

AP60 Cell Start-Up: Thermal Electrical Mechanical Quarter Cell Model

In the present article, a thermal electrical mechanical quarter cell model is presented. Compared to slice models, this one has the advantage of including the cell corner and of capturing longitudinal deflection. This leads to more realistic predictions, particularly for structural entities such as shell displacement and deformation. The presented model is tuned according to thermalelectrical-mechanical measurements carried out during the startup period of an AP60 cell.This model is useful to study different problematical issues such as lining material behaviour, current distribution heterogeneities, shell deformation during start-up and several start-up scenarios. Such a model will also be able to answer some questions regarding early infiltration risks and their potential impact on the cell lifespan.

Lyès Hacini, Jean-François Bilodeau, Yves Caratini

A Numerical Approach for the Design of Anode Beam Mechanical Systems

Anode beam mechanical systems play an active role in the operation of modern aluminum reduction cells by enabling the anode bridge vertical displacement, and consequently, control of the anode-cathode distance. At the most basic level, however, they transfer motion from actuators to the anode beam while transmitting anode panel loads to the superstructure’s fixed beam.Said loads depend not only on the mass of both suspended anodes and crust but also on operational procedures: while the total suspended weight varies from startup to steady-state operation, weight distribution varies throughout the anode cycle. Different anode setting patterns yield different load distributions and significant dynamic loads arise from beam movements.An approach for the analysis and design of anode beam mechanical systems was developed using ANSYS™-based numerical simulation and in situ measurements. A test case is presented and the impact of increased anode weight, selected operational procedures and design details is discussed.

Andre Felipe Schneider, Olivier Charette, Daniel Richard

MHD Stability for Irregular and Disturbed Aluminium Reduction Cells

The MHD stability of regular cells in pot line is well represented in the literature, and validated numerical tools are available to optimize their performance. The presence of irregular cells is more of a rule than an accident in the commercial practice requiring additional flexibility when modeling such cells interspersed between normal ones. The new options in the code for MHD analysis permit to include such technological variations as change of anodes at arbitrary position, parallel change of several anodes, variation of the contact resistances in anode clamps, cathode flex joints, collectors, electrolyte and overvoltage. The extended model capabilities include the presence of anode channels, cell bottom non-uniformities and variable bottom ledge. Options to build a user specified magnetically compensating bus network, to account for a stopped neighbor pot (shunted) and end of line pots with significantly disturbed magnetic field are numerically tested for the 500 kA cell pot line.

Valdis Bojarevics, Sharnjit Sira

Revised Benchmark Problem for Modeling of Metal Flow and Metal Heaving in Reduction Cells

Stationary metal flow and metal heaving impact both heat balance and cell stability and affects pot tending as well. For improving cell performance and productivity, a good knowledge of these quantities is indispensable. However, limited access restricts the precise determination of the metal flow and heaving by measurements, and sought information must thus be derived from mathematical modeling of the magnetohydrodynamic (MHD) flow. The literature is scarce when it comes to benchmark problems for MHD flow in a cell and those cases which are available often suffer from insufficient level of detail, lack of input data and some inconsistencies. In this paper, a benchmark problem is given, resolving the deficiencies identified in the literature. A newly developed MHD model based on ANSYS FLUENT and User Defined Functions is applied to simulate the resulting flow pattern and interface heaving of the two immiscible bath/metal fluids in reduction cells.

Jinsong Hua, Christian Droste, Kristian E. Einarsrud, Magne Rudshaug, Robert Jorgensen, Nils-Haavard Giskeodegard

Dynamic Simulation of Cell Voltage Resonance Effect in Aluminum Electrolysis Cell

An equivalent circuit of aluminum electrolysis cell has been implemented to model the current distribution and cell voltage fluctuation using the Matlab/Simulink simulation software. Given disparity of liquid aluminum fluctuation frequency under each anode carbon block, the datum of these frequencies constitute a set of series. The current distribution and cell voltage fluctuation were investigated when the series is an ordered sequence and a random sequence. Then the dispersion of current distribution was calculated, of which the trend line was applied to determine the resonance effect. The simulation results show that cell voltage resonance effect is caused, with great cell voltage enlargement and anode current redistribution. Furthermore, the span and cycle of the resonance are closely associated with the vibration frequency.

Yongliang Wang, Jun Tie, Ganfeng Tu, Shuchen Sun, Rentao Zhao, Zhifang Zhang

Analysis of the MHD Instabilities in Reduction Cells with Lyapunov Method

In this paper, MHD instability in reduction cells is analyzed with Lyapunov method. This paper shows that there are 3 types of status for fluids flow motion in reduction cells: asymptotic stability, stability, and instability. The vertical magnetic field was divided into the same dimensionless component with Taylor series, and the effect on the MHD instability of each component was being studied. New criteria equations are proposed for instabilities in aluminum reduction cells.

Yang Yi, Yao Shihuan, Yi Xiaobing

Potline Operations — Equipment

A Novel Design Criterion for Alumina Feeders in Aluminium Electrolysis Cells

The theoretical possibility of agglomeration-free alumina feeding in aluminium reduction cells is addressed. The treatment is based on calculated times for dissolution of alumina particles and their terminal velocity in the bath. It was found that the dissolution rate from a few hundred grams of alumina kept in dispersion is sufficient to supply the entire cell. To derive a criterion for dispersion as single particles and avoiding agglomeration, two types of consideration were made; 1) The volume fraction of solid alumina sinking through the bath at a rate corresponding to the consumption must be considerably below unity, or 2) Particles landing on the bath surface must have time to sink away before they are hit by succeeding particles. The two considerations end up with very similar mathematical expressions. Based on the derived criteria, normal point feeding produces agglomerates, while continuous feeding to the same surface area may produce single particles.

Asbjørn Solheim

Non-Linear Behavior of a Metallic Foam for the Reduction of Energy Losses at Electrical Contacts in the Aluminum Industry

Electrical contacts are found at many positions in an aluminum plant. Transformers, rectifiers, breakers, shunts, busbars connections, risers on the electrolysis cell and collector bars to the busbars are all electrical interfaces that show electrical contact resistances. The use of a specific metallic foam suppresses more than 80% of the electrical resistance. Measurements on Cu/Al and Al/Al contacts are presented. Non-linear effects such as the decrease of the electrical resistance with the increase of the current density and temperature are discussed. The impact of the pressure between the plates is also discussed.

René von Kaenel, Jacques Antille, Michel Pillet, Matthieu Lindeboom

Influence of Heat Source Cooling Limitation on ORC System Layout and Working Fluid Selection: the Case Og Aluminium Industry

Energy recovery from the raw gas in aluminium production plant is investigated in this paper. This hot gas contains acid compounds and it should not be cooled below its dew point in order to avoid corrosion problems. This limitation is generally not considered in the published literature Common working fluids were screened, with two heat recovery configurations:Direct and indirect (thermal oil loop) systems. The power production loss for an indirect heat recovery system compared to a direct system was relatively small, about 5%. The acid dew point temperature restriction had less influence on the indirect system, which could utilize fully the low heat sink temperature available on the site. This factor almost fully compensates for the temperature loss induced by a second heat exchanger.Indirect systems can use standard ORC modules which could reduce the cost of the plant

Yves Ladam, Monica Børgund, Erling Næss

Concept and Design of Dubal Pot Start-Up Fuses

Before start-up, aluminium reduction pots are connected together by short circuiting the cathode busbars of two adjacent pots. Most of DUBAL pot technologies use aluminium wedges for this purpose. At pot start-up these wedges are removed with wedge pullers. To minimize electrical arcing during removal of the wedges, DUBAL uses specially designed start-up fuses which are made of aluminium plates and connected in parallel with the wedges. The cross section of fuses is chosen so as to stay connected while the wedges are inserted and to break shortly after disconnecting the wedges. DX and DX+ pot technologies use welded fuses for potline start-up and clamped fuses for pot restarts due to practical considerations. In this paper, the concept and design of these fuses is presented along with industrial trials and design validation. Comprehensive 3D modeling of these fuses was carried out during the design process, using ANSYS software package and excel based analytical calculations.

Amal Al Jasmi, Abdalla Zarouni, Lalit Mishra, Marwan Bastaki, Vinko Potocnik

A Novel Heat Recovery Technology from an Aluminum Reduction Cell Side Walls: Experimental and Theoretical Investigations

In this study, a comprehensive experimental and theoretical investigation is carried out aiming to develop an efficient and effective heat recovery technology from an Aluminum smelter side lines. The influences of the heat recovery system on the cell operation and side line ledge profile are also investigated in this paper. The experimental setup consists of an electrical furnace which provides the simulated hot side walls, the control and measurement instruments, the heat recovery unit, the cooling system, etc. The heat recovery unit is an externally insulated twophase loop thermosyphon designed and manufactured specifically for this purpose which is capable of extracting heat from the hot plate actively with very high performance. In addition, a simple smart mathematical model is developed for the heat recovery unit (Heat Pipe) and aluminum smelter side lines accounting for the dynamic ledge profile variations and phase change. Using the developed model, the heat recovery strategy and also the possible and applicable alternatives for the side walls heat collection and utilization system are investigated considering system flexibility and self-adjustment ability.

Yaser Mollaei Barzi, Mohsen Assadi, Håvard Møllerhagen Arvesen

On-Line Monitoring of Anode Currents: Experience at Trimet

Since early 2012, individual anode currents of one Hall-Héroult pot at TRIMET, Hamburg, have been monitored using a system that measures the currents by sensing the magnetic fields produced by the anode currents. The system reports all anode currents every second, as well as the pot voltage. Data are transmitted wirelessly from the pot to a receiving computer near the pot for processing and onward transmission to the TRIMET network as well as to WIT in California. Interactive real-time plots of individual anode currents are available to engineers and others at both locations. The paper summarizes the difficulties overcome in the initial stages of the installation and displays representative plots of currents before and during anode effects, after anode changes, current interruptions etc. Some thoughts are provided on the value of making individual anode current measurements.

Andreas Lützerath, James W. Evans, Ron Victor

Startup and Tuning of Material Distribution System at Aluminium Smelter in Qatar

The start of Qatar Aluminium (Qatalum) in 2009 saw the largest aerated distribution system (ADS) at that time.The Aerated Distribution System was designed to supply secondary alumina from silos to 704 electrolysis pots with a total design output of 585,000 tpa based on fluidized airslide conveyors In this article the technology of the aerated distribution system is briefly described to show its uniqueness and advantages.The main focus in the article is set on the experiences during the first operation of the ADS, highlighting challenges and breakthroughs; and how it was possible to optimize the system to be more functional than projected, especially under the Middle Eastern conditions.The measures that have been taken to achieve this target and the lessons learned are described in the article.This paper concludes technical features presented on earlier TMS Annual Meetings [1, 2, 3, 5, 6] and compares them with results from practice.

Jan Paepcke, Arne Hilck, Julian Sowah, Vivek Shroff, Santosh Kumar, Rahul Jain

Fundamentals — Electrochemistry and New Processes

Mass Transfer Reactions Near the Cathode During Aluminium Electrolysis

A laboratory cell was used to determine the current efficiency for aluminium during constant current electrolysis at 0.85 A/cm2. Current efficiencies ranging from ~ 89 – 93 % were obtained. Effects of additions of KF and LiF were investigated. The presence of dissolved impurity species in the electrolyte may influence key parameters such as current efficiency and metal quality during electrowinning of aluminium. Other electrolyte constituents such as CaF2, LiF or KF may also have some impact on the electrolysis. The mass transfer of impurity elements to the cathode was studied in industrial cells. Metals that are more noble than Al will deposit at the cathode at their limiting current densities. Mass transfer coefficients for dissolved manganese species were found to be of the order of 10-5 – 10-6 m/s.

Geir M. Haarberg, Peng Cui

Current Efficiency in Aluminium Reduction Cells: Theories, Models, Concepts, and Speculations

Some theories and concepts regarding current efficiency (CE) in aluminium reduction cells are reviewed. The Sterten-Solli model, which represents the current understanding, explains the CE loss as a result of the formation of dissolved metal at the cathode, notably sodium. Sodium is transported into the electrolyte across the boundary layer at the cathode, “stealing” electrons that would otherwise be used in the main cathode reaction. While dissolved species may be transported by ordinary mass transfer; it is also known that cryolitic melts containing dissolved metal exhibit electronic conductivity. The main content in the present paper is an attempt to separate between CE loss by ordinary mass transfer and CE loss by electronic conduction, and to explain the relationship between the two. This constitutes the basis for a new “integrated” CE model, which apparently implies a weaker relationship between CE and convection than what can be calculated by ordinary mass transfer.

Asbjørn Solheim

Effect of Current Density and Phosphorus Species on Current Efficiency in Aluminum Electrolysis at High Current Densities

Effect of phosphorus on current efficiency for aluminum deposition was measured in a laboratory cell with current densities of 0.8 and 1.5 A/cm2. Controlled amounts of AlPO4 were added to the bath at the beginning of the experiment, and the effect on the current efficiency was studied at current densities of 0.8 A/cm2 and 1.5 A/cm2. Phosphorus levels were monitored through sampling the bath using High Resolution Inductively Coupled Plasma Mass Spectrometry at regular intervals during the whole electrolysis. The deleterious effect of phosphorus on the current efficiency was found to be pronounced at low concentrations up to 220 ppm. The current efficiency was found to increase with increasing cathodic current density and have a maximum current efficiency of 95.5% at 1.5 A/cm2 for this particular cell design. A further increase of current density up to 2 A/cm2 resulted in a decrease of current efficiency.

Rauan Meirbekova, Jomar Thonstad, Geir Martin Haarberg, Gudrun Saevarsdottir

A Concept for Electrowinning of Aluminium Using Depolarized Gas Anodes

Aluminium is today commercially produced by the Hall-Héroult process using consumable carbon anodes. Consumable anodes have some concerns such as CO2 emission, continuous anodecathode distance adjustments and replacements of anodes. Replacing the consumable anodes with inert anodes has been a topic for many decades without commercial success so far. Using porous inert anodes where natural gas or hydrogen take place in the anode reaction has been shown in laboratory tests to reduce the anode potential and reduce the CO2 emission. However, formation of water results in evolution hydrogen fluorides which must be solved. Laboratory experiments using porous depolarized SnO2-based anodes with CH4 and H2-gases have been performed with off-gas analysis and with special attention to hydrogen fluoride evolution. Some ideas of how to deal with the additional HF evolution are presented.

Tommy Mokkelbost, Ole Kjos, Ove Paulsen, Bjarte Øye, Henrik Gudbrandsen, Arne Petter Ratvik, Geir Martin Haarberg

Investigations into Innovative and Sustainable Processes for the Carbothermic Production of Gaseous Aluminum

Considerable efforts have been applied to produce aluminum by alternative ways. Two novel processes for the carbothermic reduction of alumina towards gaseous aluminum production in Electric Arc Furnace (EAF) and solar furnace have been investigated both theoretically and experimentally. The EAF process was tested at ambient pressures and temperatures above 2500°C in a customized 25 KW hollow electrode EAF, while the vacuum process was preliminary tested at 0.03–2.6 mbar absolute CO partial pressure and temperatures of 1400–1850°C in an induction furnace. Results of both processes confirmed that the full reaction and volatilization of alumina to produce metallic aluminum in the vapor condensers can be achieved only at proper matching of temperatures and pressures at reaction and condensation zones. The solar reactor concept was further explored in a concentrated solar radiation furnace on a 10 kW scale.

Efhtymios Balomenos, Panagiotis Diamantopoulos, Dimitrios Gerogiorgis, Dimitrios Panias, Ioannis Paspaliaris, Christoph Kemper, Lars Peters, Bernd Friedrich, Irina Vishnevetsky, Michael Epstein, Martin Halmann, Andreas Haselbacher, Zoran Jovanovic, Aldo Steinfeld

A CFD-PBM Coupled Model Predicting Anodic Bubble Size Distribution in Aluminum Reduction Cells

In order to understand more details of anodic bubble formation, coalescence and movement mechanism under the horizontal anode bottom, a population balance model (PBM) was used to calculate the anodic bubble size distribution (BSD) in aluminum reduction cells. The proposed PBM was numerically solved with a class method (CM) which has been provided in ANSYS FLUENT. A CFD-PBM coupled model that combines the PBM and CFD model was used to simulate more complex flow behavior with proper coalescence and breakage mechanism of anodic bubble. A modified k-ε turbulence model was used to describe liquid phase turbulence in the simulation. The effects of current density, anode width and the presence of slots on the BSD have been investigated. In addition, the relative influence of the bath flow induced by the cell magneto-hydrodynamic (MHD) on the BSD is also discussed. The predicted BSD is in accordance with a series of literature experimental results.

Shuiqing Zhan, Mao Li, Jiemin Zhou, Jianhong Yang, Yiwen Zhou, Chenn Q Zhou

Simulation of Anode Bubble: Volume of Fluid Method

In an aluminum reduction cell, bubbles are generated on the anode surfaces. Before they get out of the bath, they linger over between gap of the anode and the cathode, which leads to additional voltage drop. The alumina concentration adjacent to the anode is also affected. How are the bubbles formed and what kinds of shape they have are the important issues. Numerical simulation can provide detailed information about bubbles. The volume of fluid model (VOF) was applied in the bubble simulation. The flow difference between different locations was presented.

Yiwen Zhou, Jiemin Zhou, Jianhong Yang, Wangxing Li, Shouhui Chen

EAF Carbothermic Co-Reduction of Alumina and Silica for the Direct Production of Al-Si Master Alloy

A key alternative for primary aluminum production could be the carbothermic reduction of alumina. Developed concepts face problems with the high solubility of carbon in liquid aluminum, the presence of the oxycarbide slag and the high volatilization of aluminum at elevated processing temperatures. In order to overcome some of these obstacles, in the framework of the ENEXAL FP7 project, research into the co-reduction of alumina and silica was made, aiming at the direct production of Al-Si master alloys. The latter are key commercial products for all casting applications, accounting for approximately 30% of all aluminum demand. As predicted by the thermodynamic study and verified by lab scale EAF experiments, the presence of silicon in the system suppresses volatilization phenomena, limits the oxycarbide slag formation and reduces carbon solubility in the metal phase.

Christoph Kemper, Efhtymios Balomenos, Dimitrios Panias, Ioannis Paspaliaris, Bernd Friedrich

Cell Design and Performance

Preparation and start-up of Arvida Smelter, AP60 Technological Center

A new milestone for the reduction technology has been reached with the startup of the Arvida Smelter, AP60 Technological Center in Jonquière (Canada). The Arvida Smelter, AP60 Technological Center establishes a new industry benchmark – the most cost-effective, energy-efficient and environmentally friendly smelting technology commercially available. The first phase has delivered 38 first generation AP60 cells with an annual production capacity of 60,000 tons of aluminum. Starting from the development of the first prototype AP60 cells, this article presents the construction, commissioning and startup of the new smelter in 2013. (Note: At the time this paper was written, potline start-up was still in progress and 19 out of 38 AP60 cells had been started)

René Gariépy, André Couturier, Olivier Martin, Bertrand Allano, André Machado, François Charmier

Industrial Running of the 530kA Potline in North-Western China

The 530kA potline has been put into industrial running in Xinjiang province, China. The potine includes 320 aluminum reduction cells and eighty cells are in production. It is the highest current potline in the world at present. A lot of new technologies were applied in the potline. Magnetic field was optimized, thus negative effect of vertical magnetic field was weakened and current distribution in cathodes was improved. Busbar allocation and installation was optimized, especially short-circuit busbar and upright-column busbar. High conductivity steel was used as cathode rods and three steel rods were installed in each cathode. Insulated layer was coated on each cathode steel rod near the cell sidewall. The potline has got low cell voltage and low anode effect frequency. Its cell voltage is about 3.90V and anode effect frequency is lower than 0.05 times per cell day. Further optimization and improvement need to be performed to get better performances.

Liang Xuemin, Chen Xiping, Guo Long, Li Jie, Ding Fengqi, Liu Shiwen, Ren Liangwen, Liu Youyuan

The end of an era for Søderberg Technology in North and South America

In the 1970s twenty three Søderberg smelters located in North and South America had a primary aluminum capacity over 3 million tpy. The largest operating Søderberg smelter, Companhia Brasileira de Aluminio with a plant capacity of 475,000 tpy built the last Søderberg potline in 2007. Today there are only five Søderberg smelters operating with a capacity of less than 1 million tpy. Compared with prebake technology, Søderberg cells have higher production costs, they are more difficult to automate and they have the greatest environmental and health challenges. Health studies from the middle of the 1970s show a clear link between Søderberg tar fume exposure and the incidence of various types of cancer lead companies to propose a program of replacement. Starting in the late 1970s a number of programs and actions were taken to reduce PAH emissions and worker exposure to fumes, but in Canada they were always seen as stop-gap actions until replacement was completed.

Mike Barber, Alton T. Tabereaux

Successful Start-Up of World Largest Greenfield Smelter

Emirates Aluminium Company (EMAL) is the largest single site Greenfield smelter. It was started up on December 2nd, 2009 and reached full capacity of 750ktpa by early 2010. While the construction of the smelter commenced in 2007, at the same time, in parallel operation team established the Operations Readiness Plan (ORP). Core to ORP was development of “Systems”, and establishing mechanisms to roll out these “Systems” and make contingency plans for workarounds with a clearly defined Future Desired condition (FDC).The paper covers in detail the methodology adopted for initiating number of initiatives under ORP framework by Operations team and propelling EMAL from Concept to Completion.As a result of the methodologies employed, EMAL achieved fastest, safest and uninterrupted startup of the biggest smelter in the world. The experience, knowledge & lessons learnt in Phase-1 was incorporated in the development, ORP commissioning & ramp-up of Phase-2 to achieve even better results.

Salman Dawood Abdulla, Raja Javed Akhtar, Mohammed Al Qassemi

Potline Operations — Control

Understanding and Managing Alumina Quality Fluctuations to Minimise Impact on Cell Performance and Metal Quality

The continuous technical improvements in Bayer process should improve alumina quality overall, which is not evident in thealumina shipments received at Dubal. Dubal receives alumina from various refineries in order to secure operations and optimize costs. However multi-sourcing can result in significant variation in process efficiencies and metal quality unless it is well controlled.This study attempted to apply fundamental and practical knowledge about the impact of alumina quality by deployment of Silo Management Strategy to minimize the negative impact of the alumina and maximize value-added product. Moreover improvements in signal processing such as “near AE logic” and enhancements in alumina feed logic and operational procedures have been implemented to ensure that product metal quality is unaffected although such efforts incur significant costs and time.An attempt has been made to financially quantify the impact of changes in alumina quality to balance the efforts of managing quality versus cost.

Maryam Mohammad Al-Jallaf, Andries Louw, Gregory Meintjes, Arvind Kumar, Daniel Whitfield, Mohamed Tawfik Boraie, Ghedyer Hamad, K. G. Venkatasubramaniam, Akhmetov Sergey

Developing a New Process Indicator Based On The Relationship Between an Electrolysis Cell Impurity Balance and its Incidents

Aluminerie Alouette recently studied the relationship between electrolysis cell operation and their impurities’ balance. It was observed in some cases that the concentration of impurities in the metal is lower than expected from raw material mass balance, mainly for iron, gallium, titanium and vanadium. These cells were inspected to find the cause of the imbalance; methodology and results of the inspection are presented in this paper. Analyses regarding cell performance were conducted with regard to cell impurities distribution (metal/crust/gas duct). The factors correlating these phenomena are discussed, with focus on operational results. It was found that anodic incidents are strongly related to very low impurity concentrations in the aluminium and it was possible to develop an indicator at Aluminerie Alouette to quickly detect anodic incidents using vanadium content in the aluminium. This process tool is presented and discussed in the article.

Lukas Dion, Laszlo I. Kiss, Dany Lavoie, Jean-Paul Arvisais

New Generation Control for Daily Aluminium Smelter Improvement Generation 3 Process Control for Potlines

Aluminium smelting is facing serious challenges in reducing energy consumption, increasing current efficiency and meeting constantly changing environmental expectations. Traditional control systems aim to achieve and maintain pre-determined smelter targets through adjusting process parameters in order to compensate for changes in inputs, operations and special causes of variation. These control systems are not designed to remove the causes of variation and cannot address the pace and complexity of the challenges in the industry.A new generation of process control, which not only brings the process back to the optimal operating range, but also improves it every day by early detection and diagnosis of the root causes of abnormalities is now required. Following earlier work by the authors in a number of smelters over the last 10 years, the present paper describes the development of a new generation process control, including a set of diagnostic tools and an embedded decision guidance process for people in management, supervision and operator roles within an aluminium smelter. The new generation process control has been tested successfully in a smelter. Its control architecture, implementation procedures and results are described.

Albert Mulder, Yashuang Gao, Dongfang Zhou, David S. Wong, Liu Ming, Pascal Lavoie, Mark P. Taylor, Xiaodong Yang

Current Status of Research and Development on Automatization and Intellectuality for Plants of Aluminum in China

Process automatization and intellectuality is becoming an important strategy when traditional electrolytic aluminum of China does its best to catch up with the world advanced level. With mechanization and automatization widely applied in pot controller, multi-function Crane, anode production and assembly and so on, the improvement of process on comprehensive properties and intellectuality also becomes a new development trend for large aluminum electrolysis enterprises in China. In this paper, researches and developments in recent years, which are concerned on automatization and intellect diagnosis of electrolytic aluminum production in China, are discussed from three aspects. One is control optimization in PTM, the other two are on-line monitoring on multi-physical field and diagnosis on cell status, respectively. The great significance of them in the new industrial revolution of aluminum electrolysis field in China is also given.

Jian-hong Li, Jing Liu, Ding-xiong Lu, Ji-hong Mao, Qing-chen Yang, Gan-feng Tu

Statistical Evaluation and Modeling of the Link between Anode Effects and Bath Height, and Implications for the ALPSYS Pot Control System

While anode effect benchmarks show that the near zero anode effect target is achievable using up-to-date process control logic, increasing constraints ranging from far lower ACD, power modulation to operational disturbances have led to a recent surge of PFC emissions in modern smelters pushing their technology towards the limits.After achieving a significant reduction in anode effect rate and increased current efficiency by introducing the new auto-adaptive alumina control logic presented in 2010, the ALPSYS R&D team has identified bath management as a priority to further improving control robustness.This paper recalls the main factors affecting bath height and the direct link between bath height and anode effects. It then shows the results of improved bath height management and the implications for process control procedures such as alumina control, instability treatment and power modulation.

Sylvain Fardeau, Arthur Martel, Pierre Marcellin, Patrick Richard

Cast Shop for Aluminum Production

Frontmatter

Macrosegregation and DC Casting

Mechanisms and Control of Macrosegregation in Dc Casting

Macrosegregation is a severe, unrecoverable defect often occurring in large-scale castings. This paper offers a critical review of mechanisms involved in the formation of macrosegregation during DC casting of aluminum alloys. These mechanisms include thermo-solutal and forced convection, shrinkage-driven flow and transport of solid crystals. It is demonstrated that the impact of melt flow on macrosegregation depends on the flow direction and pattern, and on the extent of the slurry zone in the sump. The shrinkage-induced flow contributes to the negative centerline segregation but this contribution depends on the shape of the macroscopic solidification front and on the permeability of the mushy zone. Accumulation of floating crystals will result in negative segregation but the occurrence of these grains and their composition depends on grain refinement and melt flow pattern. It is shown that macrosegregation can be controlled by practical means such as process parameters, structure modification and melt flow management.

Dmitry G. Eskin

Modelling of Micro- and Macrosegregation in Multicomponent Aluminium Alloys Accounting for Secondary Phase Formation

Realistic predictions of macrosegregation formation during solidification of aluminium alloys require an accurate modeling of solute microsegregation accounting for multicomponent phase diagrams and secondary phase formation. In the present work, the stand alone ALSTRUC model, a microsegregation model for industrial multicomponent aluminium alloys, is coupled with the continuum model ALSIM which calculates the macroscopic transport of mass, enthalpy, momentum, and solutes during solidification of aluminium. Alstruc deals with multicomponent alloys accounting for temperature dependent partition coefficients, liquidus slopes and the precipitation of secondary phases. The challenge associated with computation of microsegregation for multicomponent alloys is solved in ALSTRUC by approximating the phase diagram data by simple, analytical expressions which allows for a CPU-time efficient coupling with the macroscopic transport model. In the present work, a coupling strategy is proposed where macroscopic transport quantities such as the enthalpy and the solute compositions are used as input to the microsegregation model which then returns the temperature, solid fraction and the compositions in the solid and the liquid phases. The coupled solidification model is then applied in a case study to illustrate the effect of secondary phase precipitation on macrosegregation formation due to shrinkage induced flow.

K. Ellingsen, Mohammed M’Hamdi, Knut Tveito, Dag Mortensen

Macrosegregation Modelling of DC-Casting Including Grain Motion and Surface Exudation

The as cast chemical composition of a DC-cast billet or slab involves mechanisms as movement of solid grains, that are lean on alloying elements, as well as movement of interdendritic liquid, that are enriched on alloying elements. These phenomena can result in the composition being out of the specification at the surface area for billets or in the centre for large slabs. In this study macrosegregation including thermal and solutal convection, solidification shrinkage, grain motion and surface exudation is simulated on a billet cast at the Alcoa Lista plant. The model includes the air-gap formation against the mould during DCcasting and the flow of liquid through the semi-solid surface that is created under such conditions. Modelling results are compared with measurements of chemical composition through the billet from centre to surface and on the exuded layer itself as well as a characterization of the thickness of the exuded layer.

Dag Mortensen, Mohammed M’Hamdi, Kjerstin Ellingsen, Knut Tveito, Liss Pedersen, Geir Grasmo

A New DC Casting Technology for Extrusion Billets with Improved Surface Quality

A new casting technology, Low Pressure Casting (LPC), for aluminium extrusion billet casting has been developed by Hydro Aluminium and Hycast. The new technology produce billets with improved surface appearance and sub-surface microstructure. The technology is validated trough production in two casthouses in regular production. The technology is verified for the dimension range Ø152–405mm (6–16”).The new technology uses siphon feeding of liquid metal to the casting moulds, and has thus eliminated the metallostatic pressure in the liquid metal inside the moulds. The sub-surface microstructure is improved compared to billets cast with conventional technologies since exudation of enriched residual melt on the billet surface is eliminated. The surface segregation is significantly lower in depth and in alloying element enrichment compared to billets produced with conventional gas-assisted graphite wall moulds. The surface appearance is improved due to the elimination of the pulsing nature of the meniscus in conventional casting technologies and the elimination of exudation.The improved surface quality has the potential of giving increased yield and productivity in the extrusion process. For hard alloys the machining of the billet surface may be reduced or even eliminated.

Arild Håkonsen, John Erik Hafsås, Rune Ledal

An Innovative Automated Surface Inspection of DC Cast Billets

The visual surface inspection of a billet is mainly qualitative due to human interpretation. To reach higher quality standards and to reduce the overall operating cost, an automated surface inspection system developed by NYX Dimensions Inc. was selected. In 2013, a pilot of this innovative technology was integrated into the existing billet conveyor system at the Rio Tinto Alcan Arvida Works.The surface of each billet is scanned by four lasers while they are conveyed at normal speed prior to ultrasonic inspection. Two additional lasers measure the position of the defects as well as the billet length. Up to 26 million measurements are logged per billet. Dimensional analysis is used to categorize surface defects based on the topography of the surface and on the average billet diameter.The use of this innovative automated inspection system ensures to eliminate human decision errors and maintain customer satisfaction. In addition, the acquired data provides valuable information to improve process control.

Philippe Martin, Roch Larouche, Jean-Alain Laurin

Impact of Cooling Water Composition on Heat Transfer in Ingot Casting

It has long been known that variation in the composition of ingot cooling water can have an effect on the casting process. These effects can include discoloration, cracking, excessive curl and bleedouts. While several studies have been conducted to understand heat flux in ingot casting, there information in the literature is limited relating specific chemical species or interactions to heat transfer or relating specific solution properties to boiling heat transfer. In an effort to gain insight into the relationships between water chemistry and heat transfer, a broad literature review was conducted. Upon examining the literature beyond aluminum ingot casting, many examples were found in which components of cooling water had very different effects dependent on the heat transfer regime. This paper serves to summarize many of the findings in the literature and to propose mechanisms for the effects of cooling water composition seen in aluminum DC casting. A good deal of information was discovered in reviewing literature published related to the powergeneration industry.

David Gildemeister

Neutron Diffraction Measurement of As-Cast Residual Stresses in Aa7050 Rolling Plate Ingots: Influence of A Wiper

During casting, thermally induced deformations give birth to ingot distortions and residual stresses. For some high strength alloys, ingot cracking can happen during casting per se or during cooling down. Ingot distortions such as rolling face pull-in, but curl and but swell are rather easy to quantify as opposed to internal stresses. As aluminium is rather transparent to neutrons, residual stress measurements using neutron diffraction appeared to be a good way to validate the thermomechanical models aimed at simulating the stress build-up during casting. This technique has been applied to DC cast AA7050 rolling plate ingots with special attention to the stress generation in the transient start-up phase, i.e. in the foot of the ingot. Additional results using the hole drilling method complement the measurements. The measured stress distributions are compared with the results of a numerical model of DC casting for ingots cast with and without a wiper.

J.-M. Drezet, P. Celle, O. Ribaud, Th. Pirling

Recycling/Cast Shop

Life Cycle Assessment of Secondary Aluminium Refining

This paper presents a life cycle assessment (LCA) of various technologies for refining of post-consumer aluminum scrap. The goal is to identify the environmental performance of relevant refining technologies compared to the production of primary aluminum. The assessment is based on a given scrap composition and given purity limits to meet the technical requirements of a certain aluminum product which is currently produced from primary aluminum. From an environmental perspective lowtemperature electrolysis and fractional crystallization are the preferred refining methods. This is due to the low energy use in these methods, and that the environmental impact is mainly caused by the energy used during refining. Since the assessment is based on a specific scrap composition and specific purity requirements, it is suggested that other possibilities to reduce environmental impacts are investigated, for example better sorting processes or production of wrought alloys more suitable for recycling. Such methods are likely to be more relevant when the use of aluminum has increased even further and more stable sources of scrap are established.

Gro Gilstad, Johanne Hammervold

A Material Flow Model for Impurity Accumulation in Beverage Can Recycling Systems

Recycling of aluminum is beneficial due to reduced energy inputs, greenhouse gas emissions and raw material costs. Beverage cans are currently the second largest source of old scrap, and could become even larger with improved collection. However, impurities such as iron, titanium or lead may impede end-of-life recycling at higher levels, especially in closed-loop systems where they can accumulate over time. A generic material flow model for impurity accumulation in a simple recycling system is presented here. Sensitivity analysis was used to investigate the effect of key parameters on dynamics of accumulation and concentration at steady state. It was found that it takes longer to reach steady state at high collection rates, and that the steady state concentration is disproportionally higher. Increasing the U.S. beverage can collection rate from today’s 54% to the goal of 75% may cause more than a doubling of impurity concentrations unless better scrap treatment and remelting are developed in parallel or the scrap is used in other applications.

Amund N. Løvik, Daniel B. Müller

The viability of a “Voluntary Refund-Deposit System” for Aluminum can Recycling in the U.S.

The concept of a voluntary deposit system is developed and modeled in this paper in comparison to the current state of a voluntary non-deposit (R1) and mandatory refund-deposit (R2) hybrid system in the U.S. The R3 model is found to be optimal in comparison through an increase in the recycling rate, a reduction in operating costs, and the creation of a larger surplus to be used to pay for an IT-based tracking system and research grants to enable future innovations in the collection and processing of recyclables. In the R3 model, consumers are only burdened if they choose to not recycle, or they wish to have the convenience of curbside pick-up.

Jack Buffington

Oxide Skin Strength Measurements on Molten Aluminum — Manganese Alloys with and Without Salt on Surface

The strength of the oxide skin on molten aluminum is important in many metal processing steps. Among others, it affects the surface finish of DC-cast ingots through the dynamics of the meniscus, feeding in low pressure die casting, and the yield of metal recovery when dross is processed.This paper presents recent measurements of oxide skin strength on molten aluminum. The measurements were done on Al + 1%Mn and Al + 5%Mn, and are compared to earlier measurements on pure aluminum. Also the effect of a commercial salt mixture on the oxide skin strength on AlMn alloys is presented.

Martin Syvertsen

Oxidation of Manganese-Containing Aluminum Alloys

During remelting of aluminum alloys, industrial experience has shown a tendency toward increased oxidation losses with manganese-containing alloys. A goal of this work is to increase current knowledge of oxidation of Mn-containing aluminum alloys and relate this knowledge to reducing oxidation losses.An oxidation study was performed on 99.99% Al, Al-1%Mn and Al-5%Mn materials in a thermogravimetric furnace with different atmospheres, and in a muffe furnace with air. The mass gain behaviour for these materials was studied and compared for different temperatures and surface preparations.The results show that there was no Mn in the oxide on either the extruded or heated Al-1%Mn samples. The mass gain at 800 and 1000OC. for O2, CO2 and N2 atmospheres (with and without H2O) and for different surface treatments was less than 0.35%, and does not appear to explain increased oxidation losses experienced in industry when remelting Mn-containing alloys.

S. C. Wilson, A. Kvithyld, G. Tranell, T. A. Engh

Development of a Sampling Device for Furnace Dross

A series of tools for sampling dross generated by aluminium melting furnaces were developed and tested in furnaces at Sapa Heat Transfer, Sweden and Hydro Sunndalsøra, Norway. The goal was to create a device that is easy to use and gives samples representative of the dross inside the furnace. Metallic aluminium content was measured by re-melting the samples of the furnace dross with salt flux, separating the oxide and metal, and weighing the mass of the recovered metal. The key to a successful result was choosing a sampling device with the correct design to allow metal to drain as the sample was taken.

Anne Kvithyld, Sarina Bao, Arne Nordmark, Martin Syvertsen, Mark Schlesinger, Anders Johansson

Grain Refinement/Solidification

Grain Refinement of Aluminium Alloys: Recent Developments in Predicting the As-Cast Grain Size of Alloys Refined by Al-Ti-B Master Alloys

This paper presents the results of recent research on the grain refinement of aluminium alloys. There has been considerable development in our understanding of the mechanisms controlling grain refinement over the last decade and these will be briefly described. In particular, the Interdependence Model has clearly explained the interdependence between the growth of grains and the nucleation potency of refining particles in causing a wave of nucleation events throughout a casting. This interaction determines the final as-cast grain size. A key factor identified by this research is the formation of a nucleation-free zone in front of a growing grain that prevents nucleation up to the point where a critical amount of constitutional supercooling is established allowing the next nucleation event to occur. Thus, the grain size is determined by the size of the nucleation-free zone and the distance to the next most potent particle. The Interdependence Model can, therefore, be used to predict grain size changes with composition and nucleant particle density. In this paper the Interdependence Model is used to develop equations for predicting the grain size of aluminium alloys when refined by Al-Ti-B master alloys. The performance of Al-5Ti-1B and Al-3Ti-1B master alloys are compared in the light of the Model.

Mark A. Easton, David H. StJohn, Arvind Prasad

A Comparison of the Effects of Al-Ti-B Type Grain Refiners from Different Makers on Pure Aluminum

Al-Ti-B grain refiners are used by aluminum alloy casting manufacturers to reduce the grain size of castings. Both Al-5Ti-1B and Al-3Ti-1B are common Al-Ti-B grain refiners that are produced by several grain refiner manufacturers. The grain refining effectiveness with respect to time of four Al-5Ti-1B refiner samples from four grain refiner manufacturers and two Al-3Ti-1B refiner samples from two manufacturers was tested on commercial purity aluminum. Among the same type of grain refiners, the result of comparing grain refining efficiency from different grain refiner makers has been discussed in this paper. The composite particles of the grain refiner samples were observed by SEM and analyzed in an attempt to approach and understand the result of grain refinement under stirring.

Wei Dai, Xiaoming Wang, Weitao Zhao, Qingyou Han

Improved Grain Refinement of AA6060 Extrusion Billets

Improving grain refinement practice in production is time consuming although the benefits of reduced costs, improved quality and better control of finished product grain size are highly desirable. A project has been undertaken at Trimet Aluminium SE to improve grain refinement of extrusion alloys involving three stages. The first stage comprised making small scale tests using the Opticast method on 4 kg melts at the Opticast laboratory in Stockholm. In stage two testing was carried out on the R&D casting pit at Trimet in Essen where single billets were cast from a 5t furnace. Finally production casts of AA6060 billets will be made using Optifine grain refiner. The small scale tests predicted that grain refiner addition rate could be reduced by 88% and the results of the subsequent R&D casting pit production tests to confirm this are reported.

John Courtenay, Isabell Klauke, Rein Vainik, Giuseppe Esposito, Marcel Rosefort

On the Performance of A Novel Grain Refiner in Hyper-Eutectic Al-Si Cast Alloys

The stringent requirements for pollution reduction are pushing the automotive industry towards the employment of lightweight structures and, therefore, aluminium and its alloys play a remarkable role. Al-Si casting alloy with eutectic or hypereutectic compositions are, normally, employed for the production of high performance automotive products such as pistons and engine blocks which have to withstand critical loading conditions (i.e. high temperature, high pressure and corrosive exhaust gases). In metals, adequate mechanical properties can be easily obtained providing that a sufficiently fine grain size is achieved but this is not the case for Al-Si cast alloys where commercial grain refiner developed on the base of the Al-Ti-B ternary system are highly ineffective due to the poisoning effect of silicon on titanium. The performance of a novel grain refiner in the form of powder addition developed at Brunel University, which can efficiently and reliably refine Al-Si alloys, are assessed in this work. Particularly, the effect of the addition of this novel grain refiner on the microstructural features of both binary hyper-eutectic and commercial Al-Si alloys is studied.

L. Bolzoni, M. Nowak, N. Hari Babu

Analysis of Boron Treatment for V Removal Using AlB 2 and AlB 12 Based Master Alloys

Boron treatment is a widely used practice in industry for removing transition metals such as Ti, V, and Zr. Mostly, Al-B master alloys containing AlB2 and AlB12 are used for the treatment. This paper describes the analysis and comparison of the boron treatment using these two types of Al-B master alloys. Kinetic experiments of V removal using the two alloys were carried out for alloy Al-1wt %V at 750°C in a resistance furnace. Samples were taken at regular interval and characterized using scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The change of V concentration, analyzed using ICP (inductively coupled plasma) analysis, was also tracked with reaction time. It has been shown that the kinetics of boron treatment using AlB2 based alloy was faster compared to those using AlB12, which was related to the particle size and available interfacial area for reaction. Boride particles settling was also analyzed in the present study using multi-locations sampling technique that revealed faster settling for AlB12 based master alloys compared to AlB2.

A. Khaliq, M. A. Rhamdhani, G. A. Brooks, J. Grandfield

The Effect of Trace Levels of Ni And V on the Microstructure and Properties of Four Common Aluminum Alloys

The effect of nickel and vanadium with concentrations from <100ppm to ~550ppm on microstructure, mechanical properties and corrosion behavior has been investigated for aluminium alloys 356, 6060/6063, 3004 and 5182. While the Ni and V additions appeared to have no adverse effect on strength, ductility was reduced by the presence of Ni but it was improved by the presence of V for all alloys. Low Ni combined with high V levels gave the best corrosion performance in all four alloy systems. However, there was no difference in corrosion between alloys with low (50ppm) Ni and low (150ppm) V and other combinations. It appears that Ni and V levels may be allowed to increase together within current alloy specifications without detrimental effects on properties. However, high Ni and low V concentrations may reduce ductility and corrosion performance. Some caution should be exercised in allowing Ni to increase alone.

John Grandfield, Lisa Sweet, Aiden Beer, Suming Zhu, Xiaobo Chen, Mark Easton

Evaluation of Functional Properties of the Rapidly Solidified Cast AlSi30 Alloy As A Material for Transport Applications

The AlSi30 alloy obtained by melt spinning in the Rapid Solidification process, after fragmentation and consolidation, was subjected to plastic forming. As a result, extrusions in the form of 18 mm rods were obtained, and after forging and heat treatment (T6) were tested for selected functional properties. Mechanical properties, corrosion resistance and tribological properties were determined. Finally, a material with unconventional chemical composition was obtained, which confirmed its applicability for, among others, components operating in the transport industry, mainly pistons.

Bogusław Augustyn, Marcin Szymanek, Dawid Kapinos, Marek Nowak, Wojciech Pakieła

The Near-Rapid Solidification Behavior of AA1070 Aluminum Alloy

Continuous strip casting process creates a near-rapid cooling condition. In this paper, the solidification behaviors of AA1070 alloy under near-rapid cooling condition have been investigated using the metallographic-EDX method. Although the AA1070 is a commercial pure aluminum alloy with limited amount of iron and silicon, its solidification behavior is quite complicated under the condition of near rapid solidification. When the alloy solidified under the condition of equilibrium or near-equilibrium solidification, the elements of iron and silicon segregated to the final solidification zone and formed coarse phases at the grain boundaries. With the increase in cooling rate to near-rapid cooling, some fine eutectic structures appeared at grain boundaries and inter-dentrites. Both binary eutectic of α-Al+AltFe and ternary eutectic of α-Al+AltFe(Si)+AlmFe(Si) were observed.

Y. L. Liu, L. Zhang, Y. H. Zhao, J. J. Wang, C. Z. Liu

Furnaces and Energy

Computational Analysis of Thermal Process of A Regenerative Aluminum Melting Furnace

To understand melting behavior of a regenerative aluminum melting furnace, a computational fluid dynamics based on process model was developed and integrated with user-developed melting model, oxide loss model, burner reversing and burning capacity model. Simulations of melting process were made to model the flow and thermal phenomena in such a furnace. The rules of thermal process on melting behavior are obtained: Aluminum temperature increases slowly with melting time in solid-liquid zone, but rises faster when leaving solid-liquid phase lines. Furnace temperature first increases with melting time, then stepwise decreases, lastly periodically increases. Oxide weight parabolically increases with melting time. Aluminum temperature parabolically increases with oxide thickness. In early meltingstage, flue gas temperature reduces with liquid fraction, yet in later melting stage increases. Oxygen concentration in flue gas increases with liquid fraction in early melting stage yet remains constant in later melting stage.

Ji-min Wang, Yuan-yuan Zhou, Hong-jie Yan, Jie-min Zhou

Electromagnetic Stirring in Melting Furnaces — a Critical Evaluation

Although electromagnetic stirring has been in industrial use in the aluminium industry since the sixties of the 20th century, it has faced a revival in recent years under the pressure of increasing energy prices, challenges to raise production in existing installations and the appearance of innovative and competing stirrer systems in the market. The usually claimed benefits vary between 5 and 20 percent reduction in energy consumption, cycle time and dross generation. The authors will present an overview of their efforts to develop a modeling toolset to analyze the advantages of the different technologies and will describe the difficulties to develop an objective picture to monitor the improvements in real installations. The future challenges in modeling will be discussed and recommendations will be given for a better comparison of the performance of the different systems.

Andreas Buchholz, Georg Rombach, Gerd-Ulrich Gruen

Sampling Tool for In-Depth Study of Furnace Processes

The need for ever more efficient and reproducible processes in furnace operations is increasing. Conversely the development trend is towards more complexity in furnace technology and flexibility in input material capability. These demands have produced a startlingly large number of furnace designs and operational strategies. To better understand the various metallurgical processes occurring in the furnace and the potential operational and economic impact of changes to the furnace technology, operation or input material, a simple, but robust technology to selectively take samples throughout the three dimensional geometry of the melt has been developed. This allows the construction of a time dependent 3-D performance map of the furnace which can be used to optimize operational performance, economics or in combination with simulation techniques compare different furnace technologies and operational strategies. This paper introduces the sampling technology and presents results of a small demonstration study

Stephen Instone, Mark Badowski, Daniel Krings

Transient Properties of Refractory Castable with Hydraulic Binders

Refractory castables based on hydraulic binders have a widespread use in aluminium casthouses (furnaces, launders, etc.). Their selection is based on properties such as corrosion resistance to molten metal, mechanical behavior and insulation. Few studies concern the hydric exchanges between the refractory materials and the surrounding atmosphere, while this can affect their microstructure, durability or the quality of the produced metal, and may even have safety impacts. In this work, these exchanges have been studied in the case of refractory launders. A model has been built to describe the transient thermal behavior in the thickness of the launder material. The results have been compared to measurements obtained on an instrumented launder part. At the same time, an experimental approach has been developed to assess the transient hygrothermal behavior of refractory samples, through testing of moisture pick up in a climatic chamber at both ambient and at high temperature by thermogravimetric analysis. Observations have been correlated to hydration reactions at different temperatures.

Mohamed-Ali Maaroufi, Cécile Diliberto, André Lecomte, Olivier Francy, Pierre Le Brun

A Novel Method of Online Measurement to Develop Specific Heating-Up Procedures for Industrial Furnaces

The proper drying and initial heating-up of monolithic furnace linings is a task that has to be accomplished by the refractory producer, the aluminium producer and not the least by the heating-up service team. A too quick dry-out procedure of the refractory lining can cause critical vapour pressures within the refractories that exceed their tensile strength. As a result typical explosions, spalling or cracks can occur. On the other hand a very slow and cautious procedure causes a loss of aluminium production and consequently a loss of money. To consider both arguments most of the plants are working with a compromised heating-up program. In the given paper a new online steam pressure measuring method is presented, that allows a safe, fast and economical heating-up of industrial furnaces. Based on laboratory setups and by the help of an industrial test this novel method will be explained and discussed.

Thomas Schemmel, Günter Thieser, Norbert Pfitzner, Uwe Kremer

Metal Treatment

20 Years of LiMCA Utilization in the Aluminum Industry: A Review of the Technology Development and Applications

Since its introduction to the aluminum industry at the TMS Conference in 1994, the LiMCA technology has been successfully used by most aluminum producers worldwide for the measurement of inclusions in molten aluminum. The versatility of the LiMCA II instrument has been demonstrated by its ability to be used at various positions in the casting process. It has been very successful from a process understanding, optimization and control point of view. In 2004, a fixed implementation, the LiMCA CM, best suited for process control applications was introduced to the industry.This paper reviews the development of the LiMCA technology and its successful application for process understanding and optimization through examples of applications presented by numerous contributors at the TMS conference over the past 20 years. The criteria for future generations of LiMCA instruments will be discussed.

Thomas L. Buijs, Daniel Gagnon, Claude Dupuis

Clean Aluminum Processing: New Avenues for Measurement and Analysis

Aluminum alloy castings are becoming commonplace in important and critical applications in the automotive and aerospace industries where materials failure is not an option. In order to meet such property demands, tight control over the cleanliness of the melt, namely, mitigation of inclusions and dissolved hydrogen must be achieved. Having a cleaner melt will yield sound castings with more reliable performance. In order to control cleanliness, it must first be well defined and measured. Very few techniques exist in industry that can quantitatively measure inclusion levels in-situ. In addition, there are no practical methods in which all quality detractors can be measured simultaneously. The use of laser-induced breakdown spectroscopy (LIBS) has shown promise as a technique to quantify all facets of quality in aluminum melts. Current progress of this work is presented and discussed.

S. W. Hudson, D. Apelian

Metallurgical Performance of Salt and Chlorine Fluxing Technologies in Casting Furnaces

Gas fluxing with the addition of chlorine or salt is widely used in the Aluminium industry to remove soluble impurities and nonmetallic inclusions and to produce a dry dross with lower Aluminium content. In particular the removal of alkaline metals Na, Ca and Li is important to achieve the appropriate product quality. The metallurgical performance of this furnace treatment process determines the treatment time required. This can have a significant effect on the furnace cycle time and subsequently overall cast house productivity.This paper presents the results of an extensive production scale study conducted by Hydro Aluminium Rolled Products into the performance of furnace salt and chlorine fluxing technologies. Emphasis is placed on the following metallurgical aspects, alkaline removal kinetics, reduction rate of non-metallic inclusions and dross formation. Safety aspects and the effect of the treatment process on the furnace cycle time is also reviewed.

Mark Badowski, Stephen Instone, Markus Hagen

Metal Cleanliness Evaluation of Reusable Ceramic Foam Filters

Filtration practices have been developed by the casthouse at Aluminerie de Bécancour that allow ceramic foam filters to be reused for multiple casts. The filter box, which contains two filters in parallel, keeps the filters submerged in molten metal between casts. Rules have been developed dictating the maximum allowable tonnage through the filters based on the alloy and product. Automation and casting practices minimize the possibility of filter releases. A campaign of metal cleanliness measurements using LiMCA and PoDFA was conducted to validate the performance of this process over the allowable filter life for both 3xxx slab and 6xxx billet. The results demonstrate that this practice can reduce filtration costs without adversely impacting metal cleanliness.

D. Corleen Chesonis, Edward M. Williams, Louis Gendreau, Louis-Pierre Clément

Parallel Laboratoryand Industrial Scale Aluminium Filtration Tests With Al2O3 And Sic Based CFF Filters

Filtration experiments with Al2O3 and SiC based CFF filter types were conducted both in laboratory scale and in industrial scale.The laboratory scale set-up was designed so that melt with the same inclusion content flowed through the two filter types with the same pressure drop.The metal flow through each filter was continuously recorded during the experiments. Image analysis was used on the filter cross sections after the filtration test in order to determine difference in filtration efficiency between the two filter types.The same filter types were also tested in industrial scale experiments. LiMCA II was used to measure the inclusion content in the melt before and after the filters. A recently published method was used to calculate the removal efficiencies in the filters.

Martin Syvertsen, Anne Kvithyld, Sarina Bao, Arne Nordmark, Anders Johansson

New Developments of the I-60 SIR Melt Refining Unit

The Hycast® inline melt refining unit, I-60 SIR, has during the last few years been modified to be able to meet several demands in the market.The latest development of the I-60 SIR technology is to be able to control the alkaline metal level in the unit and being able to perform inline metal treatment of alloys containing high amounts of Zink (7xxx alloys). In this paper the challenges related to these new features, and how they were solved, will be described and discussed.

Terje Haugen, Arild Håkonsen, John Olav Fagerli, Mats O. Jönsson

A New Vacuum Degassing Process For Molten Aluminum

Molten aluminum reacts with the water vapor to form hydrogen which can dissolve in the aluminum melt and be released during the solidification of casting as a harmful gas, resulting in porosity in the casting. There have been quite a few methods of degassing molten aluminum in industry. However, the hydrogen content will increase with the increasing of the time even if the effective degassing has been carried out carefully. In order to keep a low hydrogen content all the time during the continual pouring (such as the case in low pressure die casting, high pressure casting and permanent gravity casting), a patented degassing method is investigated. A porous refractory absorber that is connected with a vacuum system is immersed in the molten aluminum. The vacuum is started inside the porous absorber and the dissolved hydrogen atom will diffuse towards the absorber. In this way, the hydrogen in the melt is removed through the vacuum system. The absorber is made of mullite and of porous structure. It is permeable with gas but can’t be penetrated by the molten aluminum. RPT experiment (Reduced Pressure Test) and density test were conducted to evaluate effectiveness of the new method. The experiments indicate that use of the absorber can improve the metallurgical quality of the melt

Jianmin Zeng, Bolin Wu, Zhiiu Hu, Linjiang Wang, Deguang Cao

General Cast Shop

Development and Demonstration of a Molten Metal Cooling Trough to Improve Casthouse Performance

The management of casting temperature is an important aspect in today’s casthouses. For example, in ingot remelt casthouses, nonalloyed and non-treated aluminum will translate into higher temperatures in the furnaces and hence, possibly into longer cycle times, lower casting speeds and limited mold life.This paper presents a new patent pending technology [1] that allows cooling molten metal directly into the trough while casting is underway, thus reducing or eliminating the previously mentioned drawbacks. Heat extraction in the cooling trough can be controlled according to the molten metal temperature in the furnace and the molten metal flow rate.This innovative approach gives the opportunity for a more efficient use of equipment and a potential reduction of the equipment needed (i.e. number of furnaces) to meet casthouse productivity. Furthermore, this innovative technology offers alternatives for smaller footprint casthouses where molten metal could be cast directly from the transport crucibles. This paper also presents the work that was done using smelter simulation software to assess the concept of smaller compact ingot remelt casthouses.

André Larouche, Frédéric Borel, Jean Crépeau

Commissioning and Start-Up of Ingot Casting Machines in the Biggest Integrated Aluminum Complex in the World

This paper describes the current Maaden/Alcoa joint venture in the Kingdom of Saudi Arabia (KSA) with particular focus on the commissioning and start-up of the standard ingot casting machines. These are installed in the first standard ingot cast house in KSA built during 2012. This is part of the largest fully integrated aluminum complex in the world which starts at the mine and follows an aluminum processing chain that runs through to final products being shipped from the Cast House and Rolling Mill operations. The paper will describe Ma’aden experience in ingot casting machines: commissioning and start-up, the challenges faced particularly with de-molding machines, robots and strapping machines and the latest equipment’s and technology being implemented. The Ma’aden cast house include a TAC facility which gives the advantages of less dross and more pure metal leading to a high quality product. Ma’aden also implemented ingot height laser control which makes ingots and bundles weight control well managed, also implemented latest version of MES (Manufacturing Execution System) which is doing multiple functions including: management life-cycle, resource scheduling, order execution and dispatch, production analysis for (OEE), and materials track and trace.

Abdullah Al-Garni, David Humphreys, Khalid Al-Azmi, Nasser Al-Shammari, Kalyana D. Sundaram

Preventing Explosions in Maintenance Pits under Furnaces

The maintenance pit under a furnace is a molten metal explosion hazard that has been overlooked in our industry for far too long. P. D. Hess and K. J. Brondyke’s landmark study, “Causes of Molten Aluminum Water Explosions and Their Prevention” failed to address this issue. This paper addresses the issue of molten metal explosions originating in these areas with special attention on new industry best safety practices for mitigating this hazard. Specifically I will be looking at the use of a specific organic coating that has been proven to prevent molten metal explosions. I argue that numerous catastrophes in our industry where molten metal explosions occurred could have been prevented if a certain organic coating was applied to the pit walls and floor. Future injuries and fatalities can be prevented if the maintenance pit under a furnace is identified as a hazard where molten metal explosions can occur.

Alex W. Lowery

The Effect of Magnesium Supply on the Quality of Aluminum Melts

Domestic aluminum producers are increasingly turning to alternate suppliers of alloying materials in order to lower costs and meet demand. Occasionally, problems arise due to this practice. One Alcoa facility had just such an issue with magnesium supply. The effects of magnesium concentration, temperature, and time on oxidation rate are quite well documented. This paper will present a comparison between the effects of commercially pure magnesium sources on a continuous casting process. Metal cleanliness data using LiMCA and PoDFA will be presented as well as TGA results, SEM, and visual documentation. Significant differences in oxidation behavior were observed among the three magnesium sources that were evaluated.

Heather Drieling, D. Corleen Chesonis

Effects of Microstructure And Defects on Tensile and Fracture Behaviour of a Hpdc Component: Potential Properties and Actual Outcome of En AC-44300 Alloy

The aim of present work is to study the influence of microstructure and defects on the mechanical properties of a structural high pressure die cast (HPDC) component of a commercial Al-Si based foundry alloy, EN AC-44300. The alloy which contains mainly 12% Si and 0.7% Fe, is a successful application of a die-casting alloy for the automotive market. Tensile test specimens were extracted from both high pressure die cast components and from ones with comparable microstructures produced through gradient solidification technique, which offers specimens with low levels of defects. The microstructure and defects available in the component were well mapped via X-ray inspection system, optical and scanning electron microscopy. The results clearly confirmed the components’ performance dependency to configuration of defects and Si morphology as well as revealed the potential of the alloy in terms of ultimate tensile strength and ductility.

Mohammadreza Zamani, Salem Seifeddine, Anders E. W. Jarfors

Thermal Parameters Analysis During Directional Solidification of Al-Cu Eutectic Alloys

Al-Cu eutectic alloy samples (Al-33.2wt.%Cu) were solidified directionally upward under conditions which produce the columnar-to-equiaxed transition (CET) phenomenon.The position of the CET was located in each sample and the distance from the bottom of the ingot was measured. During solidification the distribution of temperatures were measured by means of thermocouples located strategically. From the measured temperatures the following parameters were obtained; local temperature gradient, cooling rate of the liquid and solid and growth rate. Three different velocities of heat extraction were employed and the temperature gradient reaches values of 2.1 ºC/cm, 0.1 °C/cm and 4.3ºC/cm, , respectively. The results are presented and discussed comparing with the results obtained in the case of CET in dendritic Al-Cu alloys

Alex Ivan Kociubczyk, Federico Cabello, Carlos Enrique Schvezov, Ricardo Walter Gregorutti, Alicia Esther Ares

Electrode Technology for Aluminum Production

Frontmatter

Anode Raw Materials

Impurity Level Distribution in GPC And CPC and Impact on Anode Properties

Aluminum smelter specifications for trace metal impurities in calcined petroleum coke (CPC) are based on a bulk analysis of the coke. Recent experience shows that it is important to understand the distribution of impurities when considering new sources of green petroleum coke (GPC). Most GPC sources have a uniform distribution of impurities like vanadium, iron, silicon and calcium throughout the particle size range but some sources show a concentration of iron, silicon and calcium in the fines fraction. The paper presents a review of the origin and distribution of impurities in GPC and the results of an investigation into the root cause of elevated calcium levels in a GPC source used in an anode-grade CPC blend. High levels of calcium in the fines fraction of the CPC had a significant negative effect on anode CO2 reactivities. The paper highlights the need to be cautious when using new GPC sources.

Les Edwards

Determination of Contact Angle from Raw Material Properties Using Linear Multivariable Analysis

Carbon anodes are made by baking a compacted mixture of calcined petroleum coke, recycled anodes and butts, and coal-tar pitch. Pitch is utilized as a binder for the dry aggregate. Good interaction between coke and pitch is essential for the generation of a satisfactory bond between them, and the contact angle is a measure of this interaction. A program was developed using the linear multivariable analysis to predict the contact angle for a given coke/pitch pair at different times. Normalized coke and pitch properties and their corresponding contact angles were used to train the program. The precision of the model depends on the amount of data available for training. The value and the sign of the weighting factors indicate the effect of the input parameters on the contact angle. The model gives information on the effect of raw material properties such as composition and impurities on the contact angle.

Arunima Sarkar, Duygu Kocaefe, Yasar Kocaefe, Dipankar Bhattacharyay, Brigitte Morais, Charles-Luc Lagacé

Use of Coal Tar Pitch Coke for Producing Prebaked Electrodes

The utilization of coal tar pitch coke as a substitute for petroleum coke in anodes was tested in the lab. The study was conducted in order to (1) find an alternative material to petroleum coke due to its high cost and deteriorating properties, and (2) determine the feasibility of using a current Chinese source of coal tar pitch coke for producing aluminum industry anodes.

Shoulei Gao, Chongai Bao, Baiyuan Xia, Rifu Lin, Joe Woo, Guanghui Lang, Euel Cutshall

Characterization of Dry Aggregates in Carbon Anodes by Image Analysis

Carbon anode is one of the key components in the electrolytic production of primary aluminum. Anodes are mainly composed of dry aggregates such as calcined petroleum coke and recycled materials with pitch as the binder. Granulometry of the dry aggregates is important to obtain good physical, chemical, electrical, and mechanical anode properties. Sieving can indicate the size range of particles, but it does not reveal much information about the shape or nature of the individual particles. This article presents an image analysis technique to study not only the granulometry, but also the physical characteristics (e.g. aspect ratio, roundness, form factor, etc.) of each and every particle. The custom-made software for the image analysis can also separately identify the butt and coke particles based on different shape parameters. This technique could help track changes in granulometry at different stages of the anode production and consequently improve the quality.

Dipankar Bhattacharyay, Duygu Kocaefe, Yasar Kocaefe, Arunima Sarkar, Brigitte Morais, Jerome Chabot

Paste Plant Operations

Characterization of Packing Ability of Coke Particles

This work aimed to investigate the reliability of the vibrated bulk density (VBD) test for estimating the void fraction and packing ability of coke particles. VBD is conventionally used in the anode industry to characterize the calcined coke and to determine the required amount of pitch and fine coke. High VBD may be achieved by dense particles while they do not necessarily result in a highly packed bed of particles since packing properties depend on particle shape factors. The apparent density of coke fractions was measured using image analysis. Then the inter-particle void fraction was calculated from the VBD. This void fraction indicates the packing ability of particles. VBD results did not follow the void fraction trend. It is shown that different cokes with equal VBD values might present different inter-particle void fractions. Nor is the VBD necessarily in agreement with intraparticle porosity. It is thus suggested to consider complementary parameters such as shape factors and particle porosity along with the VBD.

Kamran Azari, Asem Hussein, Houshang Alamdari, Donald Ziegler, Mario Fafard

Texture Analysis Of Anode Paste Images

An important issue for the anode manufacturers is the increased variability of the raw materials and its negative impact on baked anode quality. This variability could be reduced by timely corrective actions applied on selected manipulated variables at the green mill (i.e. process control). However, the lack of rapid sensors for measuring anode quality is an important limitation to implementing feedback/feedforward control. Weekly averages of lab measurement are available too late to be used for feedback control. This work investigates the use of machine vision for sensing paste properties. The effects of changes in pitch demand of the aggregate and its particle size distribution, and mixing temperature on the visual appearance of laboratory paste image were studied. The 2D discrete wavelet transform (2D-DWT) was used to extract textural features for each image, followed by their analysis using Partial Least-Squares regression (PLS). Preliminary results show that the imaging sensor is sensitive to variations in pitch demand and aggregate size.

Julien Lauzon-Gauthier, Carl Duchesne, Jayson Tessier

High Temperature Compression Test to Determine the Anode Paste Mechanical Properties

In order to develop a constitutive law for Hall process anode finite element modelling, a compression test method was developed to identify the hot paste properties which evolve with the density. A thin stainless steel cylindrical mould was placed in a furnace mounted on a press. The mould was instrumented with strain gages in the axial and tangential directions to capture the strain as a function of the axial load applied on the paste. The compression test meets the need for characterizing the paste mechanical properties. Loadings were designed to excite the specific mechanical properties, as a function of density, useful for the numerical model. The deformation of the mould shell allowed evaluation of the paste Young’s modulus. A compaction test was performed and a tomography scan was realized on the resulting sample to confirm that the green compact density is almost uniform.

Stéphane Thibodeau, Hicham Chaouki, Houshang Alamdari, Donald Ziegler, Mario Fafard

Viscoplastic Modeling of the Green Anode Forming Process

To model the forming process of green anodes, a nonlinear viscoplastic constitutive law using the concept of natural configuration has been developed. For this purpose, a Helmholtz free energy was proposed in order to take into account the nonlinear compressible behaviour of the anode paste and a dissipation potential was introduced to characterize the irreversible deformation process. An experimental study based on compaction tests of the anode paste at 150 °C was carried out. To characterize the Poisson’s effect, which leads to a non-negligible radial pressure, a thin steel instrumented mould was used. An inverse identification procedure using finite elements analysis showed that the model is able to reproduce experimental results in a good agreement.

Hicham Chaouki, Stéphane Thibodeau, Houshang Alamdari, Donald Ziegler, Mario Fafard

Characterization of Homogeneity of Green Anodes Through X-Ray Tomography and Image Analysis

Homogeneity of green anode has a direct effect on final properties of baked carbon anodes. This work aimed to study the influence of mixing parameters on the homogeneity of laboratory-scale anodes. Anode pastes were made using different mixing times and temperatures and then underwent a compaction procedure. Homogeneity was characterized by the distribution of coke, pitch and porosity throughout the anodes as well as the variations in binder matrix thickness (fine coke + pitch). X-ray tomography was used as a non-destructive tool to evaluate the material distribution within the samples. The microscopic images of the green samples were analyzed to measure the mean thickness of binder matrix. The lowest variations in material distribution and the minimum thickness of binder matrix were obtained for the sample mixed at 178 °C for 10 minutes. The most homogeneous sample with the lowest binder matrix thickness had the maximum green and baked apparent density.

Kamran Azari, Behzad Majidi, Houshang Alamdari, Donald Ziegler, Mario Fafard

Field Experience with the Buss Kneader Type KX: Highest Quality and Throughput Targets Attained

The oscillating screw kneader continues to set dependability and efficiency benchmarks in mixing anode paste. The first of the new-generation Buss Kneaders now in service upholds this reputation. Current and future process technology requirements were analysed together with users and EPCs in order to set realistic industrial targets as follows:- Fully optimized product flow geometries to ensure dependable, absolutely trouble-free feed of dry materials und binders- Uniform wetting of coke particles without affecting their structure and size- Adequate retention time and narrow residence time distribution to ensure homogeneous product characteristics- Optimal mixing of the various fractions for uniformly high anode densities- Fast and easy maintenance during long production runsThe new Buss Kneader type KX — with a capacity of more than 60 tons/h — was thoroughly tested for target verification under industrial production conditions. All the requirements listed above have been met in full.

Hans-Ulrich Siegenthaler, Christian Hauser

Maximizing Green Anode Slots Height through a Rigorous Methodology and Finite Elements Modeling

Anode slots benefits are maximized when they are high enough to last the entire anode service life: around 450 mm height for the AP30 technology. The most cost effective method for making slots is to form them at the green stage, directly in the vibrocompactor or press. However, plants struggle to form slots higher than 300 mm due to cracks and segregation in the anode. The alternative is to saw the slot in the baked anode but it is CAPEX and OPEX intensive. The challenge has been taken by RTA and Alouette Smelter to form 400mm high slots. Each step of the anode manufacturing and handling process was reviewed through an in-depth risk analysis, teaming up finite elements modeling specialists with process, production and equipment manufacturing experts. Technical solutions were found to increase the height of the slots and to ensure a low scrap rate through new slot design and adaptations to the existing transport and handling equipment.

Jean-Louis Abeille, Patrick Sornin, Yann El Ghaoui, Philippe Contard, Alexandre Gagnon, François Moralès, Marc Gagnon, Franck Fruleux

High Performance of “Eolios” Pitch Fume Treatment System

Since the introduction of paste cooling in the fabrication process of anodes, the generation of pitch fume volatile compounds has drastically increased. In parallel, standards of emissions and operational exposure became more stringent. Consequently, technologies to treat such emissions have evolved to comply with those new requirements.Fives has developed Eolios, a system that optimizes the combination of a dry scrubber based on the adsorption of PAH on coke fines, and a RTO using oxidation technology, which minimizes the energy consumption and the carbon footprint while maximizing the pitch fume treatment efficiency.The first system was installed at an anode plant in Norway in 2007 to treat the higher concentration streams with very high destruction efficiency on PAH.Early 2013, outstanding emission levels were also achieved thanks to Eolios, at a paste plant in Qatar, which sets this new technology as a standard in the industry.

Salima Sendid, Alix Courau

Bake Furnace Design and Operation

Improving Fuel Gas Injection in Anode Baking Furnace

Anode baking process requires large amounts of fuel gas. Heating the refractory walls to bake the anodes is performed by direct gas injection from the top of the furnace. The resulting flame, called diffusion flame, has an impact on the anode baking performance and on pollutants formation. While combustion emissions, particularly the oxides of nitrogen (NOx), has become a major issue in most industries consuming fossil fuels, no major studies have been published in the field of anode baking. In 2010, Fives Solios launched a program dedicated to characterizing the combustion in anode baking furnace to develop a clean and efficient injection technology. Experimental approach was preferred rather than numerical simulation. A testing unit including an actual scale refractory flue wall with experimental instrumentation was designed and commissioned in 2012. Promising results in terms of NOx abatement and thermal distribution, and implementation on an existing anode baking furnace, will be discussed.

Pierre Mahieu, Patrice Sedmak

Anode Baking Furnace Firing System Lean Engineering

Smelters are more and more implementing Lean manufacturing principles in the way they manage operations. Rio Tinto Alcan, deeply involved in this approach, has been applying Lean principles also to the engineering process for the development of its new ‘in house’ anode baking furnace firing system in 2011. First, the new firing system has been designed to fit the voice of customer. A large survey was conducted across RTA smelters to collect client feedback on existing equipment/systems and their recommendations for system improvement and user flexibility. Secondly, an efficient internal partnership was established within RTA (Technology and R&D and Alesa) to define and develop the system with the support of a very experienced smelter team for the industrialization process (St Jean de Maurienne). Finally, the time to market was exceptionally fast with the first full-scale firing system being commissioned flawlessly in April 2013 at the Aluminium Dunkerque smelter.

Philippe Contard, Christophe Bayard, Yann El Ghaoui, Yvan Foster, François Ordronneau, Peter Sulzberger, Edgard Altmann, Raphael Grange, Jérémie Lhuissier, Patrick Noraz

Effect of Heating Rate on the Crack Formation During Baking in Carbon Anodes Used in Aluminum Industry

The quality of carbon anodes used in aluminum industry depends on the raw material properties and the manufacturing process parameters. It is one of the key factors directly related to the aluminum production cost. The degradation in anode quality such as crack formation increases the energy consumption, the environmental emissions, and the smelter’s overall operating cost.The objective of this work is to investigate the formation of cracks in several industrial green anode samples during baking at different heating rates and to determine the influence of this baking parameter on the crack formation. The samples were characterized before and after baking by measuring a number of physical properties (electrical resistivity, density, etc.) which define the final quality of the anode samples. Also, techniques based on ultra-sound and scanning electron microscopy were used to determine the extent of cracking after baking.

Salah Amrani, Duygu Kocaefe, Yasar Kocaefe, Brigitte Morais, Gerry Blaney

Structured Approach to Modernization of Fume Treatment Centers

Although a Fume Treatment Center (FTC) is designed for the end of life performance of the anode baking furnace, aspects such as changing anode dimensions, increasing production or drifting quality of green anode materials are likely to drive the FTC towards the boundaries of its capacity and henceforth impose limits upon the anode baking furnace. A structured approach to debottlenecking the FTC has been developed, accommodating the owner’s and operator’s objectives in terms of cost, capacity and energy and emission limitations. The result of this approach is an optimum solution with respect to both CAPEX and OPEX, found by setting targets for overall pressure drop to meet capacity and energy consumption requirements, while maintaining environmental performance. Solutions are evaluated based on investment per unit of additional flow capacity. This article discusses the debottlenecking concept, illustrated by a practical case study as well as major technology step changes that were developed during this process.

Erik Dupon, Edo Engel, Rick Oliana, Bas Admiraal, Peter Klut

Upgrade of an Existing Fume Treatment Plant at Aluar to Cope Higher Production in the New Open Type Anode Baking Furnaces

Aluar Aluminio Argentino has been operating with two closed type furnaces for the production of baked anodes for more than 35 years. Due to the continuous expansion by amperage increase in the potlines, these furnaces were replaced by two new open type baking furnaces, Due to present anode requirements only one was started. As a result, the existing Fume Treatment Plant had to be upgraded to cope with higher volume and temperature requirements.This paper explains the most economical solution for an FTC concept upgrade, which integrates major existing components but in parallel enhances the plant with new equipment and process technologies to attain the targets. Finally it outlines the actual results achieved by presenting key performance figures, including emission levels.

E. Cobo, L. Beltramino, J. Artola, F. Heinke, D. Maiwald, D. Di Lisa

Anode Quality and Performance

An Approach to Help Control Air Permeability of Pre-Baked Anodes

Air permeability is one of the most important properties that impact the performance of pre-baked anodes in aluminum smelters. In this paper, the main factors that affect air permeability are identified, as well as the key process control points that could improve air permeability. A practical and effective approach to decrease air permeability and improve anode quality was developed.

Shoujun Zhang, Wenxiang Li, Jinlong Jiang

Optimising Anode Performance in Dubal Reduction Cells

DUBAL has improved its anode performance in terms of Gross Carbon Consumption (GCC) and anode problems, while sustaining Net Carbon Consumption (NCC) in the potlines despite continuous amperage increase, raw material quality variations and multiple cell technologies. A 5% reduction in GCC was achieved over the past four years through optimisation of anode quality, modification of anode design and adjustment of pot operating parameters and practices. Optimisation was done based on the statistical analysis of key parameters, e.g., anode weight, butt parameters, bath height and line amperage. Anode parameters were monitored using a proprietary Rod and Anode Tracking System (RTS), which reconciles information pertaining to the anode with respect to butt location in the pot and its characteristics, raw materials, green and baked anode quality and the pot operating parameters. Statistical Reports were developed to facilitate faster and better decisions.

Edouard G. M. Mofor, Sergey Akhmetov, T. K. Sahu, Jose Blasques, Daniel Whitfield, Gregory Meintjes, K. S. Rajwinder, Ali Jassim, Saleh A. Rabba, H. Devadiga, Kamel Al Aswad

Paste Production and its Performance in Søderberg Smelters

The evolution of the capacity of Søderberg smelters and of the pot technology over the past two decades is addressed. Today’s figures of specific energy consumption and current efficiency are reviewed along with the paste performance in view of anode voltage drop, skimmed carbon and paste consumption. Bench mark performance figures are commented as a function of the technology using dry, semi-dry or wet carbon pastes.Laboratory testing of paste and baked artefacts is overviewed and the typical worldwide ranges of the key properties are given. The impact of the pitch and fines content on the intrinsic paste properties is quantified and the effects of raw materials are illustrated. The importance of the baked paste properties for the carbon consumption is explained. The peculiarities of dry aggregate preparation and paste production in the carbon plants are discussed with their impact on the paste quality and consistency.Modern Søderberg smelters with point feeders and hooded high amperage cells comply with severe emission limits and continue to be profitable. Modernization of the existing carbon plants is thus mandatory to keep up with the pot requirements.

Markus W. Meier, Raymond C. Perruchoud

Study of Manufacturing Technology for High Quality Anodes

Based on R&D for the GPC from the different areas in China and anode manufacturing process a series of high quality anode manufacturing technologies are developed and shown in this paper, such as blending of GPC with different properties and element distributions, aggregate and high density paste recipe, pressure vibration forming and advanced baking system etc. By application of the mentioned above technologies the bulk density, conductivity and CO2 reactivity are greatly improved for high quality anode manufacturing. And the production technology of the complex configuration and structure anodes are developed and put into operation.

Zhao Qingcai, Zhao Jingli, Zhao Qingbo

Understanding Anode Overpotential

In aluminium electrolysis cells the anodic process is associated with a substantial overpotential. Industrial carbon anodes are produced from coke materials, but the effect of coke type on anodic overpotential has not been well studied. In this work, labscale anodes were fabricated from single source cokes and electrochemical methods were used to determine the overpotential of the anode materials. Attempts were then made to explain these trends in terms of both the physical and chemical characteristics of the baked anodes themselves and their raw materials. Routine coke and anode characterisation methods were used to measure properties such as impurity concentrations and reactivity (to air and CO2), while non-routine characterisation methods were applied to study surface and structural properties. It was found that the overpotential trend of the anodes correlated well with many of the properties studied, and explanations for these observed correlations are suggested. These findings offer exciting possibilities for reducing the energy demand of the anodic process.

Rebecca Jayne Thorne, Camilla Sommerseth, Ann Mari Svensson, Espen Sandnes, Lorentz Petter Lossius, Hogne Linga, Arne Petter Ratvik

Cathode Materials and Wear

Room Temperature Creep Behaviour of Ramming Paste Baked at Different Temperatures

To simulate the thermo-mechanical behaviour of ramming paste in aluminium electrolysis cells, experimental data are required to feed 3D constitutive models. Both axial and radial strain measurements are necessary to design constitutive laws and to identify the parameters. However, radial strains are difficult to obtain at high temperature due to limitations of measuring devices. Moreover, samples need to be sufficiently large to acquire significant radial strain amplitude. Hence, the creep behaviour of ramming paste was studied at room temperature so the radial behaviour could then be extrapolated for the high temperature case using the axial strain evolution as a function of the temperature. Mechanical properties of ramming paste, baked at temperatures ranging from 250 °C to 1000 °C, were measured at room temperature. Uniaxial creep tests were performed at three different stress levels for each baking temperature.

Pierre-Olivier St-Arnaud, Donald Picard, Houshang Alamdari, Donald Ziegler, Mario Fafard

Characterisation of the Material Behaviour of Cathode Steel Collector Bar at High Temperatures and Low Stress Levels

The study of the deformation behaviour of the collector bar at conditions experienced within the aluminium reduction cell is of great importance to optimizing the efficiency and increasing the life span of the cell. This paper communicates the results of an experimental program carried out on the steel collector bar material (AISI 1006) to investigate its behaviour in relation to its thermal, mechanical and the creep properties. Tests were carried out in compression at low stresses, 0.5 to 2 MPa and high temperature, 900 °C. Different behaviour was observed at low stresses below 2 MPa, which can be characterised by time and applied stress level. For the test at 2 MPa, a conventional creep curve with dominating secondary creep region was obtained. Oxidation and corrosion were factors considered due to the aggressive environment of the test condition. Metallographic inspection showed effect of oxides on tested sample.

Femi Fakoya, Donald Picard, Guillaume Gauvin, Houshang Alamdari, Richard Beeler, Mario Fafard

Cartography and Chemical Composition of the Different Deposits in the Hall-Heroult Process

The formation of solid deposits on the cathode surface is problematic for the performance of the electrolysis cell (cathode voltage drop, cell stability, cell life). Furthermore, its mechanism is still not well understood. Although alumina feeding is tightly controlled in industrial cells, the formation of solid deposits is still observed at the interface between the cathode block and aluminum. In order to understand the formation mechanisms and reduce the occurrence of solid deposits, many samples taken from different positions of the interface were analyzed for both the industrial and laboratory electrolysis cells. The effect of the alumina feeding rate and the impact of a thermal gradient on the composition of the deposits were also evaluated. The analysis of industrial and experimental samples demonstrated a concentration gradient of Al2O3 and AlF3 within the deposits implying a variation in the liquidus temperature of the deposit. This study provides insight into the mechanisms responsible for the formation of solid deposits at the cathode surface.

François Allard, Marc-André Coulombe, Gervais Soucy, Loig Rivoaland

Interaction of Sodium Vapor and Graphite Studied by Thermogravimetric Analysis

Intercalation of sodium in carbon materials is of paramount importance for the Hall-Héroult process. The interaction of sodium and graphite has been investigated for decades, but despite considerable efforts, the transport and nature of sodium in carbon materials are still poorly understood. Here we report on a study of the interaction between graphite and sodium vapor by thermogravimetric analysis. A graphitized carbon material was exposed to sodium vapor, and the equilibration of sodium uptake in the carbon material was monitored. The kinetics of the sodium uptake is discussed with respect to surface adsorption, bulk diffusion and the solid solubility of sodium in graphite. The kinetics of the reaction was analyzed with support from finite element method simulations. Finally, recent density functional theory simulations of sodium intercalation compounds are presented, demonstrating the low thermodynamic stability of such sodium intercalation compounds reflecting the low reactivity of sodium with carbon.

Z. Wang, A. P. Ratvik, E. Skybakmoen, T. Grande

N-SiC Side Lining — Variations of Materials Structure

The key process in fabrication of Nitride bonded silicon carbide side lining of reduction pots is the reaction between Nitrogen and Silicon. Silicon may react with Nitrogen in solid, liquid and gaseous phase. The reaction is strongly exothermal.Almost all N-SiC refractory materials of more or less big shapes have the gradients of porosity from middle to the edges. The reason for these gradients may be the overheating of the middle part of shapes, compared to near surface layers, due to the exothermal effect and consequent increased concentration of volatile Silicon. Volatile Silicon tends to move to areas of lower temperature and the gradients of porosity are 1–2 %, but sometimes it may reach 5–7%.The problems with side lining of reduction pots may be because of the design of the pots, due to the overheating of the bath, yet the structure of N-SiC materials might be also critical.

Andrey Yurkov, Oxana Danilova, Alexey Dovgal

Rodding Operation and Anode Electrical Connections

Improving Energy Efficiency at Albras: A Case Study in the Rodding Shop

Aluminum industry is very competitive on international level, which is forcing aluminum smelters to reduce their costs. Electrical power accounts for the biggest part of the aluminum production cost; consequently, there is a drive for increasing energy efficiency of the smelters. In 2012, Albras launched an Improvement Program to reduce its production costs. So, more than 1000 suggestions were received from the employees to reduce the cost with fast return to help Albras overcome the crisis. The focus of the rodding shop was on the reduction of the energy consumption of the inductions furnaces and the fans of the baghouses. These together represent 72.8% of energy consumption in the plant. Effort was also concentrated on educating the plant personnel on saving energy. This paper shows how the rodding shop reduced the total energy consumption from 879 MWh/month to 720 MWh/month and the specific energy consumption (per anode) from 75.82 kWh/ton to 67.7 kWh/ton (2010 to 2013).

Paulo Douglas S. de Vasconcelos, Marcelino Pascal Rodrigues Vasconcellos, José Fernando Nunes

Arts-Anode & Rod Tracking System — A New Tool for Optimization of Anode Performance

ARTS is a combination of an Anode and Anode Rod identification and Tracking System, including a customized database and analytical software.ARTS effectively tracks both, anodes and rods, helping to control the quality of anodes and improve the overall smelter performance and rodshop operations and efficiency.The system has recently been installed and is now successfully in operation at ALUMINIJ d.d. in Mostar, Bosnia & Herzegowina (hereinafter shown as AM).The system provides permanent identification of rods and identification of anode blocks, thus enabling the control of anode performance in the smelter and rodding shop operations. Through the analysis of anode data recorded by the system and action taken based on this, improved anode quality and efficiency of operations can be achieved.In this paper, the functionality and the key elements of ARTS are described, and an overview of the installation of the system at AM is provided, along with operational results.

Aluminij d.d, Ivan Grle, Alfred Harwardt, Manfred Beilstein

Anode Rodding Basics

The joint between the rod and carbon anode in aluminium smelters has three primary functional requirements; it must (i) provide an adequate mechanical, thermal, and electrical connection, (ii) be able to be re-processed cost effectively, and (iii) withstand the extreme process conditions. There are also two further important performance requirements; (iv) the joint materials must not adversely affect Occupational Health, Safety and Environment (OHS&E) conditions or metal purity, and finally (v) the manufacture, maintenance and operation of the joint should be managed holistically to minimize smelter costs. To achieve these requirements, the basic production steps in anode rodding must be done to an acceptable standard, all of the time. Not meeting these standards has a detrimental impact on smelter performance and costs.This paper first outlines acceptable standards for the basic steps of rodding anodes, and then reviews the state of the art, challenges, opportunities and future directions for the rod-anode connection.

D. Molenaar, B. A. Sadler

Anode Electrical Resistance Measurements: Learning And Industrial On-Line Measurement Equipment Development

The electrical resistance of anodes is recognized as a significant parameter for pot performance as the carbon material itself contributes to half of the anode assembly voltage drop. An R&D apparatus for measuring the anode electrical resistance (MIREA) was recently developed by Rio Tinto Alcan. In the last two years, six measurement campaigns were held at different anode plants around the world during which more than 600 anodes were characterized. The MIREA apparatus used during these campaigns helped to highlight resistance heterogeneity problems such as highly resistive tops and helped to detect non-optimized vibroformers. A better understanding of the resistance variability was acquired during these campaigns and justified the development of the apparatus at an industrial scale. The 2nd Generation MIREA was developed to allow smelter process teams to monitor electrical resistance of all anodes produced. This equipment was designed to reliably achieve more than one anode measurement per minute and to deliver comprehensive data interpretation.

Guillaume Léonard, Sébastien Guérard, Denis Laroche, Jean-Claude Arnaud, Stéphane Gourmaud, Marc Gagnon, Marie-Josée Chollier, Yvon Perron

Automated Crack Detection Method Applied to CT Images of Baked Carbon Anode

Computed tomography (CT) is a powerful non-destructive technique providing a large amount of useful data to characterize carbon anodes. Previous works employed this technique to characterize baked anode samples and some relationships have been proposed for apparent density and total porosity as a function of X-ray attenuation coefficients. In this paper, an existing method of crack detection in 2D was applied on CT images of full-scale baked anode to estimate the amount of cracks. The crack detection method has however been modified to improve the termination procedure of the algorithm which was essentially based on the calculation of circularity of the percolated region. The improvement consists of calculating other percolated region properties in order to end adequately the percolation process. The proposed method has been applied to anode slices with and without stub holes.

Donald Picard, Julien Lauzon-Gauthier, Carl Duchesne, Houshang Alamdari, Mario Fafard, Donald Ziegler

Development of A New Methodology to Measure Contact Pressure Along A Thermo-Electo-Mechanical Interface

Contact pressure and temperature fields are two of the significant factors which affect the anodic and cathodic voltage drops of Hall-Héroult cell. Although, the temperature field has been measured using some capturing devices, the contact pressure distribution along the thermo-electro-mechanical (TEM) interfaces, such as cast iron/carbon, has never been measured. In this study, a new methodology is proposed to measure the contact pressure distribution along TEM interfaces. Furthermore, a new sensor device is developed. The functionality of the proposed methodology as well as the developed sensor is examined via an experimental test in laboratory, representing the real industrial thermo-electro-mechanical behavior of the contact between the collector bar and the cathode block.

Mohammadreza Emami, Daniel Marceau, Martin Désilets

Rodding in Hall-Héroult Cells: An Fea Model that Predicts Room Temperature Mechanical Properties and Cracking Tendency of Thimbles

The quality and extent of the contact between the thimble and the anode comprising the anode assembly of a Hall-Héroult cell are influenced by the mechanical properties of the thimble. The contact is established when the thimble differentially expands with increasing temperature during the cell start-up phase and touches the anode surface. The size and shape of the contact area and the magnitude of the interfacial pressure are subsequently modified as the thimble deforms with further increases in temperature. Crucially, this deformation mechanism is complicated by the fact that the thimble properties vary from location to location based on processing history unique to each location. It is therefore necessary to account for such variations if realistic predictions are to be made for electrical and thermal flux profiles across the critical thimble-anode interface. In the present work, a fully coupled transient thermal-mechanical model is developed for thimble solidification using the finite element code Abaqus. This continuum scale model predicts the local mechanical properties of the slightly hypereutectic gray iron casting at room temperature by recreating the phase fractions based on local non-equilibrium cooling rates. These properties may be modified for elevated temperatures using experimentally obtained relationships available in the literature. The model also predicts the cracking tendency of the solidifying thimble based on calculated equivalent plastic strain profiles. The computation time for this model is relatively short.

D. R. Gunasegaram, D. Molenaar

Temperature Fitting Method for Predicting Equidistant Voltage Drop of Anode Rod in Aluminum Reduction Cell

In this paper, the temperature equation for an anode rod of aluminum reduction cell is derived based on principles of energy conservation and heat sources superposition. Electrical heat is used as the first inner heat source, while heat coming from surrounding media is used as the second inner heat source. All relevant parameters for representing inner current of anode rod are deduced completely. They are relative to rod’s length, rod temperature, temperature and velocity of surrounding gas. A new test method and a series of curve fit equations for representing the state of equidistant voltage drop are presented. Large amount of on-line monitoring data on different anode rods show that the agreement between the curve which is obtained from curve fit equations and experimental curve of equidistant voltage drop is good, and the correlation coefficient is larger than 0.90.

Jian-hong Li, Gan-feng Tu, Xi-quan Qi, Jing Liu, Hui Dong, Ying Zhang

Inert Anodes, Cathode Design and Alternative Processes

Effect of La on the Electrolysis Performance of 46Cu-25Ni-19Fe-10Al Metal Anode

With addition of La element for modification of 46Cu-25Ni-19Fe-10Al metal anode material, the 200A/815°C electrolytic test showed that the precipitation of La element at the grain boundary hindered the outward migration of metal atoms and the inward diffusion of oxygen atoms. Meanwhile, a compact composite oxide scale (including Cu2O, NiO, CuFe2O4 and NiFe2O4.) is formed on the surface of the anode during the test. Due to the pinning effect of La elements, the oxide scale was closely combined with the metal matrix and impeded the electrolyte penetration, thereby reducing anodic corrosion rate and dissolution of the oxide scale. This alloy has a potential to be an inert anode in industrial aluminum electrolysis.

Peng Weiping, Liu Ying, Guo Jie, Zhao Ruilong, Yang Jianhong, Li Wangxing

Evaluation of a Pre-Oxidation Treatment for Limiting Electrolyte Penetration in Cu-Ni-Fe Anode during Al Electrolysis

A comparative study on untreated and pre-oxidized Cu65Ni20Fe15 inert anodes for aluminium electrolysis in low temperature (700°C) KF-AlF3 electrolyte was conducted. The pre-oxidation treatment was performed at 700°C under Ar-20%O2 for 3 h, leading to the formation of a CuO-NiFe2O4 layer on the anode. This preformed oxide layer has a positive impact on the anode corrosion resistance by favoring the formation of a denser oxide scale with limited electrolyte infiltration during Al electrolysis.

G. Goupil, E. Gavrilova, B. Davis, D. Guay, L. Roué

Inert Anodes: An Update

This overview covers the development of inert anodes for the primary aluminium industry in the period 2010 – 2013. It continues the review of cermets, including their mechanical and physical properties, their behaviour and their manufacture, especially Cu (NiO-NiFe2O4) cermets in cryolite melts. However, the overview focuses particularly on the manufacture and behaviour metal anodes, including steels and Ni-Fe alloys. Low-temperature electrolytes are essential to avoid aggravated corrosion; KF-based electrolytes have proved suitable for low-temperature electrolysis. Inert anodes were tested on laboratory and bench scales, and Rusal announces industrial scale tests in the near future.

Rudolf P. Pawlek

Investigating the Corrosion Behaviors of Fe-Ni-Cr Anode Material for Aluminum Electrolysis

Corrosion resistance in cryolitic melts is the most important property for inert anode used in aluminum electrolysis. Ni-Fe-Cr alloy anodes were prepared with a protective layer on their surface through a pre-oxidation procedure, and corrosion tests were carried out in a laboratory aluminum electrolysis cell at 950 °C. The microstructures of the anodes before and after the electrolysis were inspected using XRD and SEM techniques. It is found that a starting protective layer formed after 10 – 20 hour pre-oxidation could be sufficient to make the anode maintaining function during the corrosion tests. A corrosion layer with varying thickness on the metal anodes at a current density of 0.75 A/cm2 was formed in aluminum electrolysis in the cryolitic melts, where various metal fluorides were involved in the surface reactions. Detailed analysis revealed that the chemical compositions of the corrosion-oxide protective layers on the metal anodes varied due to selective corrosion and migration of Fe, Ni, Cr, and O crossing the interface. The results may provide useful technical data for materials design and process development for metal inert anode that can maintain the function through a dynamic oxide protective layer during aluminum electrolysis.

Zengjie Wang, Jilai Xue, Luxing Feng, Fangyin Dai

The Metal Phase Selection of 10NiO-NiFe2O4-Based Cermet Anodes for Aluminum Electrolysis

xNi/(10NiO-NiFe2O4) cermet, xCu/(10NiO-NiFe2O4) cermet and x(20Ni-Cu)/(10NiO-NiFe2O4) cermet (x=5,10,17) were prepared for aluminum electro-winning and their corrosion resistance into a classical electrolyte was studied in laboratory electrolysis. The results show that preferential corrosion of Ni metal was observed and electrolytes are penetrated into the anode during electrolysis. Nevertheless, this corrosion mechanism was not necessary observed in the cases of xCu/(10NiO-NiFe2O4) cermet and x(20Ni-Cu)/(10NiO-NiFe2O4) cermet. Moreover, the thickness of the depleted metal zone of cermet inert anode with 20Ni-Cu is thinner than that of Ni and Cu (x=5,10,17).According to Gibbs free energy change and wear rate calculations, the corrosion resistance of x(20Ni-Cu)/(10NiO-NiFe2O4) cermet is better than that of xCu/(10NiO-NiFe2O4) cermet and xNi/(10NiO-NiFe2O4) cermet. Because of the higher electrical conductivity and the better wettability with ceramic matrix, we observed that nickel addition improves relative density of x(20Ni-Cu)/(10NiO-NiFe2O4) cermet and copper enhances the electrical conductivity of x(20Ni-Cu)/(10NiO-NiFe2O4) cermet. Thus, the corrosion resistance of x(20Ni-Cu)/(10NiO-NiFe2O4) cermet was found better than both xCu/(10NiO-NiFe2O4) cermet and xNi/(10NiONiFe2O4) cermet

Hanbing He

Study on the Anode and Cathode Configuration of Aluminum Reduction Cell

The authors of this paper using the thermo-electric field simulation software secondary development based on ANSYS studied the horizontal current distribution in liquid aluminum pad of two cases, namely the cathode and anode configuration adopting “correspondence” and “non-correspondence”. The results showed that the effect of reducing horizontal current is not obvious when anode and cathode using “correspondence” configuration, especially during the actual production cannot eliminate the uneven distribution of anode current, and also can not eliminate the horizontal current caused by anode change. The structure of modern reduction cell determined the horizontal current in the liquid aluminum pad mainly derived from cell width direction, namely the direction of current in and out. Therefore, the reducing of horizontal current should also be more considerate on the cell width direction. The number of cathode should not be previously determined during the bus configuration around the cell.

Ban Yungang, Mao Yu, Mao Jihong, Liu Jing, Yang Xiaoling

Study on Cathode Structure Optimization of Aluminum Reduction Cell

The authors of this paper using the thermo-electric field simulation software secondary development based on ANSYS studied the difference of horizontal current, cathode voltage drop, steel bar maximum current density when adopting different techniques, such as slotted steel bar, partial insulation steel bar, and low resistivity steel bar technologies. The results showed that the partial insulation steel bar technology to reduce the horizontal current of liquid aluminum pad is most obvious, and current distribution uniformity is also the best. The effect of reducing horizontal current is limited when adopting slotted steel bar technology. The using of low resistivity bar is more conducive to reducing the cathode voltage drop.

Ban Yungang, Mao Yu, Mao Jihong, Liu Jing, Yang Xiaoling

Light-Metal Matrix (Nano)-Composites

Frontmatter

Microstructure-Property Relationships I

Effect of Process Control Agent on the Microstructure and Mechanical Behavior of an Aluminum and B4C Metal Matrix Composite

AA5083 and B4C powders were cryomilled in liquid nitrogen utilizing oleic, caprylic and stearic acids individually in order to determine the effect of each process control agent on the resultant microstructure and mechanical properties. The microstructure of the powders was examined and consolidated samples were mechanically tested in compression. Chemical analysis was performed to determine impurity concentrations of nitrogen, hydrogen and oxygen. Microstructural analysis of the powders revealed three types of agglomerates: composite powders of AA5083 with uniformly distributed B4C particulate, un-milled spherical AA5083 powder and deformed AA5083 powder. These three types of agglomerates were found in similar size and proportion regardless of the process control agent used. Nitrogen concentration correlates directly to the oxygen concentration in the sample. There was a slight increase in compressive strength with the increase in oxygen and nitrogen concentrations.

C. Hofmeister, A. Giri, S. Brennan, Y. H. Sohn, T. Delahanty, K. Cho

Microstructure and Damping Properties of Ultra Fine Grained Al Wires Reinforced by Al2O3 Nanoparticles

Commercial purity Al and Al based composite wires reinforced with alumina nanoparticles were produced via powder metallurgy route. Powder of Al and Al with 2 wt.% of nano-Al2O3 particles were processed by high-energy ball milling. The powders were consolidated by hot extrusion into billets and then rolled to wires down to a square section of 1 mm2. Commercially pure Al and Al-2wt.% Al2O3 powders were successfully consolidated by hot extrusion at 400°C and cold rolled down to wires of 1 mm2 in section without failures. The ball milling process led to the fragmentation of the native oxide layer that covers the Al powders into nano-sized particles and favored the embedding of these phases in the Al matrix. Then, also commercially pure Al wires took advantage of the strengthening effect of the hard particles. The nanocomposite exhibited higher hardness (about 10%) and higher internal friction than the Al sample.

R. Casati, M. Vedani, A. Tuissi, E. Villa, D. Dellasega, X. Wei, K. Xia

Elevated Temperature Deformation Behavior of High Strength Al-Cu-Mg-Ag Based Alloy Reinforced By TiB2 Particles

TiB2 has been known as an outstanding reinforcement particle in aluminum matrix composite due to its excellent properties compared to other particulate reinforcements. There has been intensive effort undertaken recently in development of Al-TiB2 composites, however no literature appears to be available on the application of TiB2 reinforcement in very high strength wrought Al-Cu-Mg-Ag alloys. In this study, the elevated temperature deformation behavior of TiB2 reinforced Al-Cu-Mg-Ag alloy is investigated. Microstructural observation prior to deformation process shown fine equiaxed grain with TiB2 particle distributed homogeneously along the grain boundaries and occasionally in the interior of the grains. Uniaxial compression testing was conducted to understand the thermo-mechanical behavior of this material at elevated temperature. The flow behavior during hot deformation processing of Al-Cu-Mg-Ag-TiB2 composites was analyzed. Emphasis is given on the description of dynamic recrystallization by means of electron back scattered diffraction.

Martha Indriyati, Vit Janik, Richard J. Dashwood

Microstructure-Property Relationships II: Modeling and Advanced Characterization

Understanding the Role of Nanodispersions on the Properties of A390 Hypereutectic Al-Si Cast Alloy

In this work a series of castings of hypereutectic aluminiumsilicon samples (A390) were cast from different pouring temperatures (liquid, liquid-solid, and solid-liquid temperatures) with and without adding Al2O3 nanoparticles in liquid and semisolid states, with mechanical stirring. The microstructure features and the tensile strength properties were evaluated and analyzed. The results obtained in this work show that the introduction of Al2O3 nanodispersions together with the stirring effect induces a refining role on the Si particles associated with an increase in the tensile strength and ductility of the alloy. This work also illustrates the significance of optimizing type and amount of nanoparticles, addition temperature and pouring temperature to maximize the effect obtained by these parameters.

I. El Mahallawi, Othman A. Othman, M. H. Abdelaziz, H. Raed, T. Abd El-Fatah, S. Ali

Phase Formation and Mechanical Properties of Al-Mg-Mn-Ti-B-Zr-Sc Composite Material

In this work composite alloys Al-2Mn-1.5Ti-2B-0.25Zr-0.1Sc, Al-4Mg-1Mn-1.5Ti-2B-0.3Sc and Al-4Mg-1Mn-2B-0.3Sc were obtained using casting technology. Thermodynamic calculations showed that the most probable chemical reaction during composite alloys casting is the formation of titanium aluminide. Formation of titanium and zirconium borides is also possible, but undesirable. Analysis of the structure and mechanical properties of composite alloys confirmed the interaction between boron, zirconium and scandium. Metallographic researches showed that the particles AlB2 transfer into composite alloys and look like compact agglomerations of inclusions. Also takes place the formation of acicular phases of scandium and zirconium borides, and possibly more complex phases.

Nikolai Belov, Elena Kurbatkina, Alexander Alabin

Physico-Mechanical and Electrical Properties of Aluminum-Based Composite Materials with Carbon Nanoparticles

Nanocomposite materials with the matrix of an A356 alloy reinforced with 0.2 and 1 wt% of high-elastic nanodiamonds were produced by ultrasonic dispersion of nanoparticles in the melt followed by casting in a metallic mold. The structure as well as the physical and mechanical properties of the cast samples were examined using optical and scanning electron microscopy, hardness and tensile testing. It is shown that the hardness, Young’s modulus and electrical resistivity increase with introduction of nanodiamond particles.

S. Vorozhtsov, D. Eskin, A. Vorozhtsov, S. Kulkov

Contactless Acoustic Wave Generation in a Melt By Electromagnetic Induction

Ultrasound treatment of molten metals is used for degassing, to refine microstructure, or disperse immersed particles. The process is most effective when vibrations lead to cavitation. A contactless method of generating sound waves is investigated using electromagnetic (EM) induction. Advantages over an immersed sonotrode would be lack of contamination in reactive melts, strong induced stirring due to Lorentz forces and application to high temperature materials. The induction coil surrounding the crucible — also used to melt the alloy — may be adopted for this purpose with suitable tuning. Numerical simulations of the sound generation have been performed for various cases, with and without resonance in the melt volume, with and without an auxiliary DC field. A computational acoustics approach is coupled with Maxwell’s equations, and likely cavitation zones are identified using the Rayleigh-Plesset equation. Near-resonance conditions are most likely to produce cavitation without mechanically endangering the crucible.

Georgi Djambazov, Valdis Bojarevics, Bruno Lebon, Koulis Pericleous

Brownian Motion Effects on the Particle Settling and its Application to Solidification Front in Metal Matrix Composites

Studying the interactions between the reinforcement particles and solidification front of metal-matrix composites (MMCs) and/or metal-matrix nanocomposites (MMNCs) synthesized using solidification processing is essential to understand the particle strengthening mechanism of these materials. Previous models describing such reinforcement particle and solidification front interactions predict that large particles will be engulfed by the solidification front while smaller particles and nanoparticles will be pushed. However, these models cannot explain the evidence in MMNCs produced by solidification processing that nanoparticles can indeed be engulfed and distributed throughout the material and are not necessarily concentrated in grain boundary or interdendritic regions. In this work, an analytical model of particle size effects on the particle settling due to gravity and the pushing/engulfment during solidification is described that accounts for both Stokes’ law and Brownian motion. The model shows a clear transition from Stokesian- to Brownian-dominant behaviors of ultra-fine nano-sized reinforcement particles, which indicates that these fine particles may be engulfed rather than pushed by the solidification front.

J. B. Ferguson, B. F. Schultz, P. K. Rohatgi, C.-S. Kim

X-Ray Tomography and Small-Angle Neutron Scattering Characterization of Nano-Composites: Static and In Situ Experiments

To meet the future EU challenges of lightweighting and pollution reduction, especially relevant in transportation, it is necessary to develop innovative materials and processing techniques. The addition of reinforcing nanoparticles coupled with melt treatment by external fields (electromagnetic or ultrasonic) was identified as a promising route to improve light alloys properties. The purpose of this study is to present combined results obtained from smallangle neutron scattering and X-ray tomography on Aluminium (6082) and Magnesium (AZ91) nano-composites in static conditions with different reinforcements. We will discuss the morphology, size, and spatial distribution of particles as well as their influence on the solidification microstructure. We will also present some and pollution reduction, especially relevant in transportation, it is necessary to develop innovative materials and processing techniques. The addition of reinforcing nanoparticles coupled with melt treatment by external fields (electromagnetic or ultrasonic) was identified as a promising route to improve light alloys properties. The purpose of this study is to present combined results obtained from smallangle neutron scattering and X-ray tomography on Aluminium (6082) and Magnesium (AZ91) nano-composites in static conditions with different reinforcements. We will discuss the morphology, size, and spatial distribution of particles as well as their influence on the solidification microstructure. We will also present some in situ experiments using X-ray tomography and Small Angle Neutron Scattering (SANS) carried out to investigate the influence of ultrasonic vibration on the agglomeration and deagglomeration of particles.

Sofiane Terzi, Rémi Daudin, Julie Villanova, Prakash Srirangam, Pierre Lhuissier, Luc Salvo, Elodie Boller, Ralf Schweins, Peter Lindner, Jean-Jacques Blandin, Peter Lee, Hartmut Lemmel

Emerging Processes

The Physical-Mechanical Properties of Aluminum Nanocomposites Produced by High Energy Explosion Impact

The present paper uses explosion compacting of Al nanoparticles to create light nanocomposite with increased physico-mechanical properties. Russian civil explosive Uglenit was chosen as high energy material for compacting. The formation of the structure and properties of aluminum based materials after shock-wave impact was studied. It was found that shock-wave treatment of different samples a) aluminum powder and b) powder mixtures Al +10 wt.% C (in the form of detonation diamonds) and c) Al +10 wt.% Al2O3 produces nanostructed materials with almost the theoretical density. X-ray diffraction analysis showed that in the samples with the addition of carbon and aluminum oxide was formed two-phase state of aluminum with a significantly different structure parameters. In this case, the lattice parameter of nanophase increased by 0.5%, which testifies to its nonequilibrium state. This increase of the parameter may be due to compressive stress, evaluation of which gives the value of 350 MPa. It was shown that the materials have high values of mechanical properties — hardness, compressive yield strength.

S. Vorozhtsov, A. Vorozhtsov, S. Kulkov, V. Komarov

Processing of Metal Matrix Composites under External Fields and Their Application as Grain Refiner

In an attempt to develop an efficient grain refiner by application of external fields, aluminium-based metal matrix composite Al-Mg-Ti/TiB2, has been processed by mechanical stirring and treated by external field such as ultrasonication. In this study we present the microstructural features of the composite and the grain structure of Al- Mg-Ti alloy when this composite is added as a master alloy. Preliminary tests with the addition of Al-3% Mg-0.01% Ti/TiB2 master alloys to Al-3% Mg-0.01% Ti showed indication of grain refinement and improvement in Brinell hardness.

E. Djan, S. Vadakke Madam, N. Hari Babu, J. Tamayo-Ariztondo, D. G. Eskin, Z. Fan

Grain Refinement and Nanoparticle Dispersion Using Traveling Magnetic Field

Improvement in the mechanical properties of different alloys can be achieved by the reduction of the crystallite (grain) size and promoting an equiaxed microstructure. This can be achieved by the use of micro- and nano-particles as grain refiners, effectively dispersed within the material. Simap lab has developed a Bridgman furnace equipped with a traveling magnetic field (TMF) with the objective to produce grain refinement in alloys. TMF is utilized to stir molten material and disperse the particles within the matrix material. In addition, TMF-induced stirring will increment the nucleation points due to the breaking of the dendritic arms at the solidification front, and homogenize the temperature of the liquid metal, which also helps to produce equiaxed dendrites. Experiments carried out, supported with numerical simulations performed by University of Greenwich and ESI Group, will demonstrate the benefits obtained from the use of TMF combined with an accurate temperature control.

Mariano Garrido, Yves Fautrelle, Laurent Davoust, Valdis Bojarevics, Koulis Pericleous, Mustafa Megahed, Ole Koeser

Nanoparticles Distribution and Mechanical Properties of Aluminum-Matrix Nano-Composites Treated with External Fields

Aluminum-matrix nano-composites have been produced after incorporating various hard ceramic nanoparticles (Al2O3, AlN and SiC) and Al2O3 microparticles into liquid metal by mechanical stirring. The mechanical stirring process is optimized to obtain distribution of nanoparticles in entire volume of the liquid. However, locally, nanoparticle clusters have been found. Application of the ultrasound to the slurry containing nanoparticles resulted in significantly improved particle dispersion and reduced nanoparticle clusters density. Nano-composites have been characterized by optical and scanning electron microscopy to see dispersion enhancement. Hardness was measured to study the local mechanical properties of these composites.

J. Tamayo-Ariztondo, S. Vadakke Madam, E. Djan, D. G. Eskin, N. Hari Babu, Z. Fan

Manufacturing of Nano-Surface AA7075 Composites by Friction Stir Processing

Friction stir processing (FSP) is a novel processing technique that has been used for surface composite development and microstructural modification. The fabrication of Al2O3 nanoparticles (~40 nm) reinforced aluminum matrix composite (AMC) using FSP is studied in this paper with the aim of manufacturing high specific strength, hardness, wear and corrosion resistance surface nanocomposites for lightweight transportation applications. The Al2O3 nanoparticles were packed into the groove of 1 mm width and 7.5 mm depth that were machined in 15 mm thick plate of Aluminum alloy AA7075-O. Single pass FSP was performed using tool of cylindrical probe tool of 6 mm diameter and 20 mm diameter shoulder, constant rotation rate and traverse speed of 840 rpm and 40 mm/min respectively. A multipass FSP was performed to improve both dispersion and uniformity of the Al2O3 nanoparticles. The effect of post processing heat treatment after incorporating Al2O3 nanoparticles into different temper conditions of AA7075–T6 and AA7075-O was investigated. The fabricated AMC nanocomposites were analyzed and characterized using optical microscope, scanning electron microscope (SEM) and hardness testing. The hardness of the AMC increased with 89% higher versus that of the matrix alloy.

M. M. Z. Ahmed, M. Refat, I. El-Mahallawi

In-Situ Synthesis and Novel Additions

Novel Ultrafine-Grained Aluminium Metal Matrix Composites Prepared from Fine Atomized Al Powders

The paper reviews the developments to date of novel ultrafine-grained (UFG) Al metal matrix composites (MMCs) reinforced and stabilized with nanometric Al2O3 phase produced in situ by compaction of fine gas-atomized Al powders. This is followed by a discussion of the recent developments of the novel UFG Al-AlN MMCs produced by partial nitridation of fine gasatomised Al powders. The paper summarizes previously published data with an addition of the new unpublished results.

M. Balog, F. Simancik, P. Krizik, M. Nosko, W. Rajner, M. Walcher, M. Qian

The Structure, Phase Composition and Mechanical Properties of Hot Pressed Metal Matrix Nanocomposites Al-Al4C3

It was shown that hot pressing of powder mixtures Al-C (ndiamond) leads to the formation of aluminum carbide Al4C3 in the metal matrix; the intensity of the phase Al4C3 formation is greater the higher the carbon content in the initial mixture. According to the X-ray analysis the compound Al4C3 was finely structure with an average crystal size for the metal matrix was 40 nm and for aluminum carbide — 30 nm. Was found that increasing the volume fraction of the phase Al4C3 in the aluminum matrix leads to increased mechanical characteristics of the composite. For samples with 5% C in initial mixture, the ultimate strength was 400 MPa, whereas for 10% C and a half times higher - 600 MPa. Furthermore, increases as the total inelastic deformation to failure from 3 to 5% and the effective elastic modulus (Eef).

S. Vorozhtsov, A. Vorozhtsov, S. Kulkov

Mechanical Properties of Aluminium-Based Nanocomposite Reinforced with Fullerenes

Aluminum has been spot-lighted due to its earth-abundant and light-weight nature. However, usages of aluminum as an engineering material have been limited by its low strength compared to other engineering metals such as steel and titanium. One possible way to strengthen aluminum is reinforcing it with carbon-based nano-materials, which exhibits superior elastic modulus and yield strength. Here, we develop aluminum-based composite, in which each of fullerenes are intended to be uniformly dispersed via three-step ball-milling processes: first, using a planetary-milling process the fullerene particles were shattered into smaller particles by shear force with two different control agents of stearic acid and ethyl alcohol, respectively; second, planetary milling process was repeated to mix the primarily ball-milled fullerenes and pure aluminum powder; third, attrition milling process was carried out for grain refinement of aluminum as well as further dispersion of fullerenes. Finally, the composite powder was consolidated using hot-pressing or hotrolling. The composite, containing 2vol% fullerenes milled with stearic acid, shows ~220 Hv in Vicker’ hardness.

Kwangmin Choi, Se-eun Shin, Donghyun Bae, Hyunjoo Choi

The Effect of Mechanically Exfoliated Graphene Dispersion on the Mechanical Properties of Aluminum/Graphene Composites

Effect of few-layer graphene on mechanical properties is investigated for aluminum (Al) based composites with different volume fraction of graphene. Al/few-layer graphene composites are produced by hot-rolled of ball-milled powders. Few-layer graphene prepared by the mechanical exfoliation of graphite flakes are attached to Al powder using a low energy ball milling, and then graphene are embedded and dispersed in the Al matrix using a high energy ball milling. Few-layer graphene with 100 nm in long axis and 5 layers thick play a great role as reinforcing agent in the Al matrix by obstruction of dislocation movements and grain growth in the composites. Therefore, the yield strength increases with increasing content of the graphene which demonstrates efficient load transfer between the Al matrix and graphene. The result can be suggested being the wider applications of graphene with improvement in mechanical properties of the composites.

Seeun Shin, Donghyun Bae

Development of Al/C60 Composites with Nano-Network Structures

It has been challenging for metals to synthesize optimal nano-structures with a desirable performance. Herein, we propose a new idea for the development of nano-network structures in Al/C60 composites by the self-assembly of Al-C phases. Carbon atoms, dissembled from the individually dispersed C60-fullerenes, are intercalated into the interstitials of aluminum, producing Al-C phases with artificially moderated lattice structures. The isolated Al-C phases grow with a strong anisotropy derived from lattice mismatch, meet neighbor Al-C phases, and then self-assemble into network structures. The novel nano-structures, extremely stable at high temperatures, offer significant potential for the development of thermally-stable high-strength structural aluminum. The controlled lattice provides a new paradigm for atomic level design of crystalline materials.

Hyunjoo Choi, Donghyun Bae

Addendum

Frontmatter

Light Metals 2013

AlTi5B1 Grain Refiners on the Casting of DIN 226 Aluminum Alloys

In recent years, several mechanisms have been suggested to explain the formation of fine grains during grain refinement process. All conducted studies indicate that TiB2 and Al3Ti particles create nucleus zones in molten metal. Offering an exact explanation for the grain refinement mechanism was purposed by using Electron Probe Micro Analysis (EPMA) technique for a comprehensive investigation of grain boundaries in terms of elemental distribution. In this study, DIN 226 high pressure die casting (HPDC) aluminum alloy was employed as the matrix system. 0.2%, 0.4% and 0.6% AlTi5B1 (by wt.) which is a common grain refiner master alloy was added to the smelting charge and samples were taken with different durations. Hardness and grain size tests were preformed on these samples.

Onuralp Yucel, Ceyhun Yapıcı, Ahmet Turan

Backmatter

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