Papers by Author: Trond Furu

Abstract: In this paper, a numerical simulation methodology has been applied to optimize the design of extruded aluminium products. The methodology, PRO^{3 TM} , incorporates product properties, production-and material costs as well as CO₂ footprint in an optimisation procedure. This allows for multi-objective optimisation and avoids sub-optimisation of for instance properties on the expense of production costs or CO₂ emissions. The outcome that follows from this multi-objective optimisation procedure, is that the resulting profile cross section will be different when the optimisation is based solely on property considerations, than when costs and CO₂ emissions are introduced in the optimisation procedure. The present methodology requires that the main processes and operations along the aluminium process chain are represented by physics based, predictive models of various types, including material-and mechanical models, in addition to cost-, and sustainability models. A standard multi-objective optimization algorithm is used to combine the models and for automatic running through-process simulations in iterations. In this article, the PRO^{3 TM} methodology has been applied for optimisation of the profile cross section in case-studies with various user requirements. It has been demonstrated that the resulting cross section geometry depends on the specified relative importance of conflicting requirements like the desire for high productivity on the one hand, and the desire for low material costs and low CO₂ emissions on the other.

Abstract: Hot tearing is a well-known limitation when trying to maximize the throughput rate in aluminium extrusion. In the present work an analytical modelling framework is presented which can be used to predict the maximum extrusion speed that can be applied in production without formation of this type of surface defect. The modelling framework allows almost instantaneous estimates on the resulting productivity in terms of maximum extrusion speed. This is obtained by developing an analytical model for the maximum temperature at the die exit which incorporate the effect of alloy composition and billet processing. The results are consolidated into extrusion limit diagrams, mapping the maximum allowable extrusion speed as a function of billet pre-heat temperature, alloy composition, and homogenisation heat treatment. The calculated temperatures and extrusion limit diagrams obtained from the analytical model are compared with measured temperatures and critical extrusion speeds from extrusion tests of various 6xxx series alloys for a simple rod-shaped geometry. The comparisons indicate that the presented modelling approach gives sufficiently accurate predictions for future application in optimisation of alloy composition and process parameters in extrusion of profiles.

Abstract: DARE2C (Durable Aluminium Reinforced Environmentally-friendly Concrete Construction) project is to develop a more environmental-friendly concrete and use aluminium (Al) as reinforcement material, instead of steel. The new concrete uses supplementary cementitious materials (SCM), which provides a low alkaline environment suitable for aluminium reinforcement. Unlike steel, aluminium has a better stability in medium pH environment, which can largely improve the durability of the new Al-reinforced concrete (RC). Cover thickness can be reduced since aluminium withstands environment and carbonation does not pose a threat. The usage of lighter aluminium as reinforcement would help greatly reduce the total weight of the Al-RC structure. The objective of this work is to investigate the compatibility of different aluminium alloys in the new DARE2C concrete by gas chromatography measurement during the cement hydration. Together with the pull-out test results, the best aluminium candidate will be determined.DARE2C (Durable Aluminium Reinforced Environmentally-friendly Concrete Construction) project is to develop a more environmental-friendly concrete and use aluminium (Al) as reinforcement material, instead of steel. The new concrete uses supplementary cementitious materials (SCM), which provides a low alkaline environment suitable for aluminium reinforcement. Unlike steel, aluminium has a better stability in medium pH environment, which can largely improve the durability of the new Al-reinforced concrete (RC). Cover thickness can be reduced since aluminium withstands environment and carbonation does not pose a threat. The usage of lighter aluminium as reinforcement would help greatly reduce the total weight of the Al-RC structure. The objective of this work is to investigate the compatibility of different aluminium alloys in the new DARE2C concrete by gas chromatography measurement during the cement hydration. Together with the pull-out test results, the best aluminium candidate will be determined.

Abstract: The present paper describes an innovative methodology that has been developed for optimization of product properties, production costs, and environmental impact in fabrication of aluminium alloys. The main idea is to represent each operation along the process chain by predictive models, which include material, mechanical, cost, and sustainability models. A multi-objective optimization platform is used to combine the models into a common software environment, which allows fully automatic simulations. The optimization tool runs the models in iterations until user-defined acceptance levels on properties, costs, and sustainability indices are obtained. In this paper, the methodology has been applied for fabrication of 6xxx-series aluminium extrusions. As a demonstration of practical relevance, the software tool was used to optimize mechanical properties and electrical conductivity by manipulation of alloy chemistry, processing parameters, and microstructure characteristics like grain structure, precipitates, dispersoids, and solid solution concentrations. At the same time material and production costs, as well as CO₂ emissions along the value chain were attempted to be kept at minimum levels.

Abstract: The present paper describes a novel methodology for optimization of product properties and production costs in fabrication of aluminium alloys. The main idea is to represent each operation along the process chain by predictive tools, which include material-, mechanical-, cost-and logistics models. An optimisation tool is used to collect the simulation models into a common software environment, which allows fully automatic simulations to be carried out. When this coupling is established, the models are run in sequence using different types of optimisation strategies. The methodology has been applied for optimisation of strength, grain structure and costs of 6xxx series aluminium extrusions. The results indicate that the present methodology is sufficiently relevant and comprehensive to be used as a tool in fabrication of various aluminium products, for instance in optimisation of end-user properties and production costs of extruded, rolled or foundry based alloys.

Abstract: Tensile properties and fracture behavior of an AA6060 alloy were investigated at room temperature (295K) and cryogenic temperature (77K). It was found that both ultimate tensile strength and elongation increased with decreasing temperature. In particular, the latter increased with increasing strain rate at 77K. The changes in mechanical properties were thought to be due to a higher working hardening rate at low temperature, while the effect of strain rate on strain hardening was obscure at both temperatures. The hardness after tensile testing at 77K increased due to an increased accumulated dislocation density. Fracture occurred in a semi-ductile transgranular manner at 295K, while a mixture of intergranular and transgranular mode with less slip localization occurred at 77K. Moreover, a decreased testing temperature led to a decreased size of dimples. The rotation of grain orientations can lead to increased Schmid factors and change of the latter was strongly dependent on the deformation temperature, which was clarified by compression tests.

Abstract: Tensile tests on smooth and notched axisymmetric specimens were carried out to determine the large strain work-hardening curves and the ductile fracture characteristics of an AA6060 aluminium alloy for three different processing routes. The alloy was processed in three subsequent steps: 1) casting and homogenization, 2) extrusion, and 3) cold rolling and heat treatment to obtain a recrystallized grain structure. After each processing step, the material was tested after natural ageing for more than one week. A laser-based extensometer was used to continuously measure the average true strains to failure in the minimum cross-section of the specimens and the true stress-strain curves were calculated. Since these curves are influenced by necking, they do not represent the correct work-hardening of the material. Accordingly, finite element (FE) simulations of the tensile tests on the smooth axisymmetric specimens were conducted to determine the work-hardening curves to failure, using an optimization tool that interfaced with the nonlinear FE code and the experimental stress-strain curves as objectives. The microstructure of the alloy was characterized after the three processing steps by optical and scanning electron microscopy, and fractography was used to investigate the failure mechanisms.

Abstract: The microstructure evolution in commercial AlMgSi alloys during and after extrusion of a simple U-shaped profile has been modelled. The strain, strain rate and temperature along a set of particle paths are taken from FE-HyperXtrude simulations and used as input to the work hardening model ALFLOW, to predict the evolution of the subgrain size and dislocation density during deformation. As soon as the profile leaves the die, the subsequent recovery and recrystallization behaviour is modelled with the softening model ALSOFT. This procedure enables the modelling of recrystallization profiles, i.e. the fraction recrystallized through the wall thickness of the extruded profile. The sensitivity to chemistry (alloy composition), profile deflection and the cooling rate at the die exit has been investigated by means of a set of generic modelling cases.

Abstract: A recent work hardening model developed by Nes and co-workers at NTNU, Trondheim provides a unified theory for warm and cold stress-strain behaviour which in principle accounts for alloy aspects such as effect of dispersoids (size and number density) and solute content, including dynamic strain aging for Mg containing aluminium alloys. In the present paper the applicability and predictive power of the model are tested for multicomponent alloys to account for the combined effect of different solute elements in solid solution and dispersoids, with a special focus on hot deformation of a range of Al-Mg-Mn alloys. It is demonstrated that the model, without any re-tuning, only accounting for the variations in alloy chemistry and deformation conditions is capable of predicting the stress-strain for a range of compositions, strain rates and temperatures.

Abstract: Since October 2006 the Hydro Casthouse Reference Centre has been operating. The centre is a full scale state of the art pilot casting centre for extrusion ingot, sheet ingot and foundry alloys, consisting of a 17Mtons furnace with a metal loop, a launder system including modular in-line melt treatment units such as ceramic foam filters (CFF) and inline melt refining units (Hycast SIR) and a casting pit with the possibility to cast full size geometries and a casting length of 5.5m. A two strand horizontal casting machine further adds the possibility of continuous casting of extrusion ingot and foundry alloy ingot. The centre has a state of the art superior control system (SCS) and a lay-out, including control room facilities, well suited for training and demonstration purposes. In addition the centre has access to state of the art software codes for simulating the casting process (Alsim) and the as cast microstructure (Alstruc). The present paper gives some examples on how the centre is operating and the support that is offered to casthouses in Hydro. This includes (i) simulation of the casting processes (hot tearing and as cast structures) applying the Alsim and Alstruc codes, (ii) pilot scale testing of casting and melt treatment equipment, (iii) testing of new parameters and procedures for melt treatment and casting (iv) production of trial orders of new alloys and (v) practical training of casthouse operators (basic for molten metal handling, emergency situations and response, casting principles and trouble shooting, etc.).