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ALUMINIUM SMELTING INDUSTRY Casting and solidification For fabricating aluminium alloys, it is useful to understanding solidification during casting and to predict the phases that are likely to precipitate during cooling. A Scheil solidification calculation of the alloy AA7075 was performed by using the real alloy composition (Al, 0.11 Si, 0.28 Fe, 1.36 Cu, 2.49 Mg, 0.19 Fig. 2: Calculated isothermal section of the Al-Cu-Mg-Zn quaternary system at 600 °C and 6 wt.% Zn compared with experimental work of Strawbridge [10] Cr, 5.72 Zn, wt.%). The calculation predicts that Al 45 Cr 7 solidifies primarily before the formation of (Al) although it had not been experimentally observed. Considering that it is probably the only Cr-bearing phase in this alloy, its formation would be almost certain. Due to its small amount, however, its formation can hardly be observed in the DTA trace or in the solidified microstructures. The formation of (Al) was followed by the Al 13 Fe 4 , Mg 2 Si, T and V (MgZn 2 ) phases, which agrees well with the experimental results. Imposed on the diagram shown in Fig. 1 (see previous page) are the accumulated solid phase fractions at different temperatures, which have been evaluated from the experimental DTA trace obtained by Bäckerud et al [8]. It should be noted that DTA can only allow a qualitative evaluation. Nevertheless, it is suggested by the comparison that the real solidification significantly deviates from the equilibrium solidifi-cation, but can be reasonably approximated by a Scheil solidification simulation. Heat treatment The controlled heat treatment of aluminium alloys allows the metallurgist to optimise, control and generate a reproducible and predictable change in the microstructure of the alloy. This serves to influence properties such as strength, ductility, fracture toughness, thermal stability, residual stress, dimensional stability and resistance to corrosion and stress corrosion cracking [9]. The main heat treatment procedures for aluminium alloys are homogenisation and annealing, as well as precipitation hardening, which involves the three steps of solution heat treatment, quenching and aging. Computational modelling tools, such as those described here, can give insight into each of these stages. For example, the purpose of solution heat treatment of aluminium alloys is to put the maximum practical amount of the hardening solutes, such as Cu, Mg, Si, Zn or other elements, into a state of solid solution in the Al matrix. Multicomponent phase diagrams calculated using Thermo-Calc can aid this type of analysis without the need to perform timeconsuming experiments. The 7000-series alloys are heat-treatable wrought aluminium alloys, and it is useful to perform equilibrium calculations at solution treating temperatures and at aging temperatures in order to predict the phase formations in these alloys. As an example, Fig. 2 shows a calculated isothermal section of the Al-Cu-Mg-Zn quaternary system at the typical solution treating temperature of 460 °C, and at a Zn content of 6 wt.%; the calculation was in very good agreement with the experimental data from Strawbridge et al [10]. This diagram can be used to generally account for the phase constitution at the solution temperature for a number of 7000 series alloys, e. g. AA7010, AA7050, AA7075, AA7175, AA7475 and AA7178, etc. Andreatta [11] reported that Al7Cu 2 Fe and Al 23 CuFe 4 are the most abundant of the intermetallics in AA7075 and AA7475, together with traces of Mg 2 Si, Al 6 Fe, S, T and Al 12 (Fe,Mn) 3 Si, after being solution treated. In such cases, it is necessary to perform equilibrium calculations using real alloy compositions by including other minor elements. Because of the high Fe content, the calculation using TCAL1 shows that Al 7 Cu 2 Fe forms in alloy AA7075 with an amount up to 1%, and Al 13 Fe 4 coexists in a small amount. However, for alloy AA7475, Al 7 Cu 2 Fe is calculated to be the only main intermetallic. Summary The materials community is increasingly using computational modelling tools, and is applying them more widely to material design and process optimisation. For more than two decades, CALPHAD- based software and databases have been employed within the aluminium industry and they have served to improve the understanding of existing alloys, to accelerate the development of new alloys and also to model and understand better materials processing routes. The quality of the predictions depends on the quality of the thermodynamic and kinetic databases that they use. Some examples have been given here to illustrate how these tools are being used within the aluminium industry in the areas of casting and solidification as well as heat treatment. References [1] N. Saunders, A.P. Miodownik, Calphad (Calculations of Phase Diagrams): A Comprehensive guide, Pergamon Materials Series, vol. 1, ed. R.W. Cahn (Oxford, OX: Elsevier Science Ltd, 1998). [2] National Research Council, Integrated Computational Materials Engineering: A Transformational Discipline for Improved Competitiveness and National Security. Washington, DC: The National Academies Press, 2008. [3] http://www.whitehouse.gov/sites/default/files/ microsites/ostp/materials_genome_initiative-final. pdf [4] A.K. Gupta et al., 2006, Materials Science Forum, 519-521, 177 [5] H. Onda et al., 2007, Materials Science Forum, 561-565, 1967 [6] J. Senaneuch et al., 2002, Materials Science Forum, 396-402, 1697 [7] S.N. Samaras, G.N. Haidemenopoulos, 2007, Journal of Materials Processing Technology, 63-73, 194 [8] L. Bäckerud, G.C. Chai, J. Tamminen, Solidification Characteristics of Aluminium Alloys, Vol. 1 and 2. Sweden (1990) [9] H. Moller, 2011, Heat Treatment of Al-7Si-Mg casting alloys, Aluminium International Today, 16- 18, Vol 23, No 6 [10] D.J. Strawbridge, W. Hume-Rothery, A.T. Little, The constitution of aluminium-copper-magnesium-zinc alloys at 460 °C. J. Inst. Metals (London) 74 (1947) 191-225 [11] F. Andreatta, Local electrochemical behaviour of 7xxx aluminium alloys, PhD thesis, 2004 Authors Paul Mason is president of Thermo-Calc Software Inc., based in McMurray, PA, USA. Hai-Lin Chen is with Thermo-Calc Software AB, based in Stockholm, Sweden. 66 ALUMINIUM · 1-2/2013
SPECIAL ALUMINIUM SMELTING INDUSTRY ECL – A privileged equipment supplier to the primary aluminium industry A.-G. Hequet, ECL Created in 1947 and based in Ronchin, a suburb of Lille, ECL entered the aluminium business in 1955. In 1962 it commissioned the world’s first pot tending machine. By the 1970s the company concentrated mainly on the aluminium industry and has become a key partner of most smelters around the world. It is now part of the Rio Tinto Alcan group and its products are used in the reduction, carbon and casthouse areas of the smelter. The product range includes pot tending machines, cranes and transfer equipment for the potlines, as well as a wide range of products and services for the carbon sector. These include green and baked anode handling equipment and specialised cranes, complete anode rodding shop, and metal and bath handling systems. The involvement of ECL does not end with the conception, production, erection and commissioning of its products. The company offers a wide range of supporting services including training, technical assistance, spare parts, on-site maintenance management, equipment audits, refurbishment and upgrades. The machines are adaptable to all the potline technologies used in today’s smelters. To better serve its customers around the world on a 24/7 basis, ECL has a network of seven subsidiaries around the world. Solutions for all sectors of the aluminium smelter © ECL ECL Pot Tending Machine Reduction: Pot equipment is a significant part of what ECL offers to the reduction sector, with more than 15,000 pots equipped by the company worldwide. However, ECL’s flagship product is doubtless the Pot Tending Machine (PTM). Adaptable to all the reduction technologies, each crane is designed to each smelter’s specification. The ECL PTM is still evolving: safer, more efficient, more reliable and more compact, while also being cheaper to commission and to operate. The potline offer also includes anode beam raising mechanisms, anode jacking frames, crust breaking and feeding devices, J hooks and fixings, anode clamps and sealing jaws. Carbon: ECL offers equipment for the whole carbon sector, from single machines to turnkey rodding shops for all types of anodes, including the building. The company also delivers furnace ALUMINIUM · 1-2/2013 67
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Special: aluminium smelting industr
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CONTENTS Volker Karow Chefredakteur
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CONTENTS Power upgrade of Isal Potl
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NEWS IN BRIEF Aluminium China’s b
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NEWS IN BRIEF 14 to 18 May 2013, Mi
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WIRTSCHAFT Produktionsdaten der deu
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ECONOMICS Five hundred participants
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Page 96 and 97: RESEARCH 4 Al (l) + 3 C (s) → Al
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THE ULTIMATE SERVICE... FOR CARBON
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