Papers by Keyword: Thixoextrusion

Abstract: The thixoextrusion process could become an important technique to extend the complexity of extruded profiles. However, the complex thixotropic flow behavior of semi-solid, during thixoextrusion is still partly characterized. The study described in this paper investigates thixoextrusion for 7075 aluminium alloy at different temperature conditions. A complete die filling and a good surface state of parts was obtained at high solid fraction (f_S = 0.70), in heated dies, for an extrusion ram speed of 416 mm/s. The thixoextrusion process is simulated using the finite element code Forge2009©. The constitutive equation used for these simulations is based on a micro-macro model for the semi-solid evolution. The tendency of the experimental curves evolution, preserving the same parameters of the micro-macro constitutive model, for each values of solid fraction, was reproduced, except the last step of the ram displacement.

Abstract: 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.

Abstract: The A357 Al-Si-Mg cast alloy is commonly used for cast production of automotive components in conventional HPDC and in semi-solid processes. The aim of this work is to study the application of A357 cast alloy in thixoextrusion processes. This technology offers new possibilities of application for cast alloys and several advantages in from of conventional processes of hot-extrusion: lower pressure, minor friction forces, higher material fluidity and longer tool life. The thixoextrusion was experimented in a pilot plant, at different speeds and temperatures, with an induction furnace and a 400 Tn press. With ingots of A357 as cast, a tool with a ratio of 8.5 and with temperatures of extrusion around 560 °C, it is possible to obtain extrusion speeds more than 3 m•s-1. In all cases, when the speed of extrusion increases, the press of extrusion decreases. The effect of heat treatments and extrusion speed in the microstructure of the extruded product is evaluated.

Abstract: 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.

Abstract: This study was carried out to characterize thixoextruded AZ31 Mg alloy in terms of its symmetric behavior through the optical microscope, electron back scattering diffraction and mechanical test. The elongated grains to the extrusion direction were generally observed during hot extrusion, while the thixoextruded microstructures were isotropic. Texture of hot extruded bar showed the strong fiber component, while that of thixoextruded bar was random distribution. The aspect ratio of hot extruded bar was irregular at each position. On the contrary, the aspect ratio of thixoextruded bar was almost uniform below 2 at each position.

Abstract: 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.

Abstract: The aim of this study was to improve extrudability limit, eliminate welding line and obtain optimum thixoextrusion conditions for manufacturing tubes of 7075 Al wrought alloy. By thixoextrusion, it was possible to improve deformability, control isotropy with extrusion direction, eliminate welding line (seamless) and save cost due to low energy consumption compared with conventional extrusion processes. The welded part was not observed at the welding line area. The grains of thixoextruded tube were homogeneously distributed and equiaxed grains were observed. Therefore, thixoextrusion is the most effective variable for the control of the magnitude of the welding line.

Abstract: Isothermal semi-solid extrusion experiments using steel grade X210CrW12 as work material were performed on an industrial forging machine. An improved and up-scaled tool design was applied, based on the concept of self-heating ceramic dies tested in previous laboratory-scale studies and allowing for die preheating temperatures of up to 1400°C. Steel rods of complex cross sectional geometry were formed at low extrusion forces. Shape accuracy of as-formed rods is accurate and metallurgical examination yields no evidence of liquid phase separation. With a view on the intended industrial implementation construction of ceramic tools has to be improved in order to avoid rupture of ceramic parts due to thermo-mechanically induced stresses and to benefit from the advantages inherent to ceramics in metal forming.

Abstract: Extrusion is a well established technology for the production of complex sections of aluminium alloys. Thixo-extrusion in comparison to traditional hot-extrusion offers several advantages such as lower extrusion and friction forces, higher material fluidity, longer tool life etc. Aluminium alloy 5182 is an important commercial alloy characterized by high strength and ductility, high corrosion resistance and good formability; it is commonly used for the production of wrought automotive components and it is also suitable for semi-solid applications thanks to its wide solidification range. The aim of this paper is to attempt the shaping of 5182 Al-Mg alloy through the thixo-extrusion process using a ceramic tool and evaluating the effect of different routes of making the feedstock on the semisolid microstructure. Particularly, two different methods were investigated: Near-solidus casting and Roll-casting using a cooling slope. All the samples produced were characterized by metallographic analysis in order to measure globule size and shape factor, as the main criteria used for assessing thixo-formability.

Abstract: A direct semi-solid bar extrusion process is characterised by inserting a feed stock in a container and extruding through a forming die with a punch. Compared to conventional bar extrusion the use of semi-solid material complicates the process due to the requirement of solidification of the material. To achieve the solidification of the semi-solid bar, different basic tool concepts are presented. With a combination of these concepts experiments were carried out using the steel alloy X210CrW12 to detect the influence of the most influencing parameters press velocity, extrusion channel diameter, length and geometry. Numerical simulations enable a better understanding of the process mechanics like temperature development in the billet and forming die as well as the material flow in the deformation zone.