Advances on Extrusion Technology and Simulation of Light Alloys

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Authors: P.T. Moe, Yawar Abbas Khan, Henry Sigvart Valberg, Sigurd Støren
Abstract: The article presents an outline of a scientific approach for testing constitutive relations for the aluminum extrusion process. By comparing ram force, container friction, die face pressure, outlet temperature measurement during rod extrusion with corresponding simulated data, inferences can in principle be drawn with respect to the validity models. The paper indicates that simulation results from the 2D ALMA2π program are in fair agreement with measurements during extrusion of AA6060, but more work needs to be done to control thermal conditions during extrusion.
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Authors: Mohamad El Mehtedi, Luigi Balloni, S. Spigarelli, E. Evangelista, G.I. Rosen
Abstract: One of the most challenging activities for magnesium industry is to increase productivity by introducing cost-effective processes. While die-cast magnesium alloys are in worldwide use, even in the demanding sector of automotive industry, where cost is the major asset, wrought magnesium alloys still not widely available. The aim of the present study was to evaluate the high temperature response by torsion testing of a ZM21 alloy, to calculate the constitutive equations to be used in FEM simulation of the extrusion process. The ZM21 alloy that was considered in the present study was Direct-Chill casted by Alubin Ltd., Israel. Torsion tests were carried out in air on a computer-controlled torsion machine, under strain rates ranging from 10-2 to 5 s-1 and temperatures from 200 to 400°C. The equivalent peak flow stress was related to temperature and strain rate by means of the conventional power-law and by the sinh equation. The microstructure of the alloy, even at 300°C, appeared largely unrecrystallized, with elongated grains; also at 400°C, the structure is more equiaxed, but elongated structures still appears.
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Authors: Carlo Bruni, Lorenzo Donati, Mohamad El Mehtedi, M. Simoncini
Abstract: The present investigation aims at studying and modelling the flow behaviour of the AZ31 magnesium alloy by means of torsion tests performed in extended ranges of temperature and strain rates. Two types of rheological models were considered. The former is based on the power law equation, whilst the latter is based on the Sellars and Tegart approach. The effectiveness of the two constitutive models in describing the flow behaviour of the AZ31 magnesium alloy under investigation was evaluated. It was observed that both the equations are able to predict the flow behaviour of the material at different temperatures and strain rates. In particular, the former is very effective in predicting the hardening stage of the flow curve, whilst the latter allows to fit the softening stage. The models were used for the finite element analysis of a complex extrusion process and the results, in terms of the load-stroke curves, compared to each other.
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Authors: H.J. McQueen, E. Evangelista
Abstract: The modeling of extrusion of various Al alloys and their particulate metal matrix composites was conducted by DEFORM™ finite element analysis to develop strain rate, stress and temperature distributions through the peak load and into steady state following development of the hot zone. The hot strength and ductility, constitutive constants and microstructural evolution had been determined by hot torsion. The relative load-stroke curves were determined for several billet temperatures, extrusion ratios and ram speeds. The grid distortion and distributions of important internal parameters define the evolution of microstructure. The extrudability was estimated on the basis of load, ductility and the potential for modeling the microstructure developed.
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Authors: Hong Yan, Ming Fu Fu, Xu Chun Tao, Hong We Hu
Abstract: The traditional extrusion and thixo-extrusion processes of wrought magnesium alloy were studied with both computer numerical simulation and experimental methods. The thixo-extrusion set-up was made. The constitutive model of semi-solid AZ61 alloy was established in our prior literature. The comparison of two forming processes had been done. Results indicated that smaller load and uniform strain & stress were acquired in thixo-extrusion process. Simulation results were in good agreement with experimental ones.
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Authors: Lorenzo Donati, J.S. Dzwonczyk, Jie Zhou, Luca Tomesani
Abstract: In this paper, a deformation test method to reproduce, on a laboratory scale, the microstructure evolution of aluminium alloys occurring during industrial forming processes with a limited number of tests is presented. A hot inverse extrusion setup was designed in order to generate, inside one single specimen, a wide range of strains at a given temperature and ram speed. Two commercial aluminium alloys (AA6060 and AA6082) were investigated at different processing conditions (temperatures and forming rates). Detailed optical microstructures were examined and grain sizes were determined at different spots of each specimen. Thermo-mechanical coupled simulations of the deformation tests were performed using the DEFORM 3D FEM code. On the basis of recrystallization equations, the distributions of strains, strain rates and temperatures were correlated to the grain sizes measured through linear regression. Finally, FEM simulations were run again with the established recrystallization model, and the results were compared with the experimental data.
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Authors: T. Kayser, Farhad Parvizian, C. Hortig, Bob Svendsen
Abstract: The purpose of this work is the modeling and simulation of the material behavior of aluminum alloys during extrusion processes. In particular, attention is focused here on aluminum alloys of the 6000 series (Al-Mg-Si) and 7000 series (Al-Zn-Mg). The material behavior of these alloys during extrusion is governed mainly by dynamic recovery and static recrystallization during cooling. The current material model is based on the role of energy stored in the material during deformation, as it acts as the driving force for microstructural development. The concept of internal variables is used to describe state quantities such as dislocation density, average grain size and average grain orientation. The focus of the current paper is on some of the numerical aspects of the extrusion process simulation such as contact problems and adaptive mesh refinement which should be considered in order to obtain more accurate and robust results.
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Authors: Lorenzo Donati, Luca Tomesani
Abstract: This work summarizes the outcome of recent research by the authors on modeling the formation of seam welds in aluminum extrusion and on evaluating the related mechanical properties on the final products. A profile with a seam weld in the middle section was produced with different die designs in order to investigate the relation between die design and local welding parameters, such as contact pressure, temperature, time of contact, strain and strain rate paths. The local welding conditions were evaluated by complete thermo-mechanical 3D FEM simulation of the processes. Specimens were extracted from the profiles and tensile tested, the resulting mechanical properties being discussed with respect to the local welding conditions. The possibility to adopt criteria for assessing the welding quality is discussed, together with the effect of high speed damage cracking.
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Authors: Luigino Filice, Francesco Gagliardi, Fabrizio Micari
Abstract: Nowadays, many researchers are involved in studies aimed to the explanation of some peculiar aspects regarding manufacturing processes. In this paper, an experimental campaign was carried out in order to reproduce tube extrusion starting from a cylindrical billet. In particular, the development of a proper equipment is presented: the aim was to measure both the total load, by using the testing machine load cell, and the local pressure value on the porthole. The latter task was carried out performing a proper system based on the use of a small load-cell. The tube was extruded with a good surface quality and the external area does not show any welding line evidence. Pure Lead was used for the experimental analysis; this material was chosen due to its high ductility which allows to carry out the process at room temperature. The material was characterized by compression tests at different strain rates and the obtained material law was used to perform a numerical analysis using SFTC Deform 3D numerical code. The Numerical analysis was carried out to show both the advantages and drawbacks of the modern FE codes when extrusion processes are investigated.
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Authors: Gang Liu, Jie Zhou, K. Huang, Jurek Duczczyk
Abstract: A detailed analysis of metal flow through a porthole die to produce a rectangular hollow aluminium profile was performed by means of three-dimensional FE simulation using DEFORM 3D. It was aimed at revealing the flow patterns of a medium-strength aluminium alloy 7020 through a porthole die and gaining an insight into the formation of longitudinal weld seams inside the welding chamber during extrusion. In the case of extruding a rectangular hollow profile through a porthole die with four ports, two neighbouring ports were different from each other. Using an FE model including these two ports, different flow patterns of two individual metal streams were revealed. The 3D FE simulation also showed how two unequal metal streams contacted each other and became bonded in the welding chamber under a certain hydrostatic pressure and at a certain temperature, before the metal flew through the die bearing. The difference in velocity between the metal streams led to uneven flow at the die bearing and thus a wavy extrusion nose.
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