The microstructure and flow behaviour during thixo backward extrusion of 7075 aluminium alloy were investigated. Reheating the steel die and the aluminium billet placed into the die at the same time using an induction furnace provides rapidly a very homogeneous microstructure suitable for thixoforming. During thixoextrusion, despite the high solid fraction, the solid globules are weakly connected and slide over each other without any plastic deformation. The flow remains quasi homogeneous resulting in homogeneous induced microstructure of the component.
The deformation behavior of semi-solid aluminum alloy is strongly dependent on the microstructure. This paper illustrates several experimental research works concerning thixoextrusion of 7075 aluminum alloy which was carried out at “Arts et Métiers ParisTech” of Metz. Inductive re-heating of the aluminum billet is the method used in order to obtain the target liquid fraction for thixoextrusion. To minimize the heat losses, a sample obtained from a direct extruded bar is inserted in a die for reheating in semisolid state and thixoextrusion. During the experimental re-heating process, the temperature was directly controlled by using thermocouples for temperature measurements in the sample and also in the die. The influence of different working ram speeds and reheating temperature on the microstructure evolution was studied by optical microscopy. The experimental results on extrusion load and microstructure evolution of the component are reported.
In this paper, the cold simultaneous toothing of spur gears has been investigated. This method can be described as a press-rolling process. The influence of gear geometry such as teeth number and the deformation mechanism was investigated by 3D finite-element analysis using forge® software in terms of teeth forming and forming loads evolution. Based on these simulations, the experimental investigations were carried out to obtain a spur gear form with the good quality, using several billet dimensions. The experimental trials and simulations conducted for the spur gear (z = 23 teeth and m = 1.5 mm) showed premises to continuous flow lines formation at the base of the teeth. The maximum pressing force results from the numerical simulation agree with the experimental maximum force recorded.
Different types of semi-solid processing are used to produce a variety of components. In this context, the use of FE simulations to obtain the filling of the dies and to optimize the semi-solid processing is clearly of a great interest. To carry it out properly in an isothermal case, the semi-solid flow into the die and friction phenomena have to be correctly described. In addition, comparisons between experiments and simulations are needed to assess the reliability of the modeling and to improve the understanding of the processing. In situ visualization of the semi-solid flow during processing is complex since the dies are closed and opaque. One of the main recent work with transparent glass sided dies to film die filling is that by Atkinson and Ward (2006). The purpose of this work is to compare numerical simulations to these experiments. Numerical simulations were performed with the solid mechanics-based software FORGE©. A micromechanical model accounting for the liquid and solid behaviour and their spatial distribution within the material (Favier et al, 2009) was used. The model parameters were identified using rapid compression tests on the A357 aluminium alloy (Favier and Atkinson, 2011). The slurry temperature corresponds to 0.5 solid fraction. Comparisons were focused on the flow behaviour. The impact of the presence of an obstacle and of the shape of the obstacle was investigated. The numerical simulations reproduced quite well the flow behaviour for the case with and without central obstacle. However, the change in flow due to an increase of the ram speed from 250 mm/s to 1000 mm/s is not captured.
a b s t r a c tSemi-solid processing is a promising forming process for shaping metallic alloys in one shot. Numerical simulations are of great interest for optimizing the process. Generally, numerical simulation results are compared with interrupted flow experiments but these do not fully reflect the progress of material into the die because of the inertia of the flowing material which continues to move after the interruption to the shot. Results are available for in situ visualization of flow using transparent sided dies. Here die filling with a 90 • change of flow path was simulated using the FORGE © finite element code and a constitutive equation based on a micro-macro modelling approach. The predicted flow behaviour was compared to the in situ visualization images obtained with a transparent glass sided die and reported in the literature. The impact of the presence of an obstacle, ram speed and friction coefficients on the material flow front is discussed. The initial solid skeleton is broken as soon as the material is deformed. The effect of the ram speed on the flow front is successfully represented by keeping the same parameters for the constitutive laws but requires a change in the friction coefficients. Friction modelling using the Coulomb law limited by Tresca cannot represent the ram speed effect on experimental friction conditions for the in situ visualisation tests used for the comparison here. However, the effect of an obstacle within the die on the material flow front is predicted well.
Thixo-extrusion processing could become an important technique to extend the range and complexity of extruded profiles. This work presents the results of thixo-extrusion process applied on aluminium alloy and they were carried out with both computer numerical simulation and experimental methods. The thixo-extrusion set-up was made. Backward extrusion tests were particularly studied and simulated using Forge 2005 software. The constitutive equation used for these simulations is based on a micro-macro model for the semi-solid evolution. The constitutive equation parameters were identified due to comparisons of the simulated load-displacement responses with experimental ones for backward extrusion tests on 7075 semi-solid aluminium alloy, for different temperatures.
The deformation behavior of semi-solid aluminium alloy is strongly dependent on the microstructure. This paper illustrates several experimental research works concerning thixoextrusion of 7075 aluminium alloy which was carried out at “Arts et Métiers ParisTech” of Metz. The microstructure obtained by two reheating systems and flow behavior during thixoextrusion tests were investigated. To minimize the heat losses, a sample obtained from a direct extruded bar is inserted in a die for reheating in semisolid state and for thixoextrusion. Reheating the steel die and the aluminium billet placed into the die at the same time using an induction furnace provides rapidly a very homogeneous microstructure suitable for thixoforming. During the experimental re-heating process, the temperature was directly controlled using thermocouples for temperature measurements in the sample and also in the die. The experimental results on extrusion load and microstructure evolution of the component are reported.
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