Key Engineering Materials Vol. 585

Abstract: AZ 31 Magnesium alloy was extruded under industrial conditions into both a solid shape and a hollow profile. A microstructure analysis of the solid shape revealed a bimodal grain distribution. The FEM process simulation was performed for double hat hollow profile, extruded through an eight-port-hole die using the modified flow stress model from literature. This allowed us to make a prediction of the extrusion process state variables. Additionally, a numerical simulation revealed some shortcomings in terms of a lack of predictive capabilities for extrusion welding. The integrity of the welds was analyzed using metallography techniques. The search for better mechanical properties has propelled alloy development research. Workability evaluations of new Magnesium alloys ZE20, ZE50 and ZE80 containing Zinc and Cerium were performed using compression tests under various temperature and strain rate conditions.

Abstract: A bridge die was designed for the simultaneous extrusion of two rectangular profiles and used in a strictly monitored aluminum extrusion process. Experimental investigations aimed at the measurement of the mandrel deflection, the local die temperature, and the pressure inside the welding chamber by means of special measurement equipment. AA6082 alloy was used as extrusion material. The influence of the extrusion speed on the aforementioned objectives is reported. The experiments were repeated at least three times under the same conditions in order to achieve a statistical validation of the acquired data. These data are provided as reference for the 2013 edition of the Extrusion Benchmark.

Abstract: Complex frictional effects occur during the extrusion process between the extrusion die and the extruded material. The recently developed Tribo-Torsion-Test is used to measure friction under thermo-mechanical conditions similar to the extrusion process. Investigations have not been carried out only with nitrided but also with two different chemical vapour deposited CVD coated samples. In the context of this study the Tribo-Torsion-Test is introduced and laboratory results are presented.

Abstract: A new axial friction set up for high speed friction was successfully developed and tested at the Extrusion Research and Development Center of TU Berlin. The friction behavior between the Aluminium alloy EN-AW 6060 and the hot-working steel 1.2344 at 300 °C and 400 °C was studied. The experiments were carried out with a relative friction speed from 0.1 to 50 mm/s, and a normalized contact/normal pressure of σ_n/k_f ~ 0 and 1.5. The friction stress curves were depicted and compared with the Tresca friction model. A similar tendency between them was found, however all the theoretical results were around 15 and 30 % higher than the experimental results. In general, higher friction forces were found at 300 °C. Moreover, the effect of normal stress on the friction stress could be studied. By increasing the normalized normal stress from 0 to 1.5 k_f the friction stress increases around 30 % at 300 °C and 10 % at 400 °C. A strong adhesion effect was observed especially at 400 °C, which represents around the 90 % of the total friction stress. The friction results can be reproduced using a friction factor of m= 0.85 at 300 °C and m= 0.7 at 400 °C.

Abstract: During the extrusion processes, very complex adhesion and friction effects between the die surface and the extruded material occur. They have a strong influence on the velocity distribution in the profile, as well as on the life-term behavior of the tools. In the framework of the virtual process modeling usually the Coulomb or the Shear Friction models are applied. The practical experience shows, that those simplified descriptions of the frictional behavior result in poor FEM results. The present work relates to experimentally evaluated tribological behavior of the Torsion-Tribo-test and shows how those data can be transferred to different new friction models.

Abstract: Extrusion processes can be utilized for production of parts characterized by complex shapes; furthermore, nowadays, the market needs are always more driving towards the manufacture of components with thinner thickness for weight and volume reduction. As a consequence, the process complexities are growing up but, nevertheless, quality and productivity have to be guaranteed by companies if they want to survive in an increasingly competitive society.In this work, a ductile criterion was utilized to highlight which variations due to thickness reduction can bring to superficial defects in extruded components. The study was carried out by using a suitable die geometry where thickness changes can be performed keeping constant the other geometrical variables. The die optimization was carried out by numerical simulations which were utilized for homogenizing the extruded velocity at the exit of the bearing zone. Different working conditions were numerically analyzed and geometrical die changes were performed to highlight their influences on the superficial integrity of the extruded parts.

Abstract: A new constitutive relationship based on the combination of the Garofalo and Hensel-Spittel equations has been developed and successfully used to model the plastic flow of a AA6082 aluminum alloy. Two regimes of temperature and strain rate were identified: the constitutive analysis suggested that in the low strain rate/high temperature regime, deformation was controlled by viscous glide of dislocations in atmospheres of Mg solute atoms, while in the high strain rate/ low temperature regime, deformation was controlled by climb.

Abstract: Die shape plays a key role in extrusion process through widely affects on the extrusion pressure and product quality. Therefore, prediction of the optimal die shape is the main objective for an effective extrusion process. In this study, the notion of Equi-Potential Lines (EPLs) was applied to 3D-die designing in extrusion process for the first time. To implement the analogy in the extrusion, the initial and final shapes were considered and two different potentials were assigned to them, and then EPLs were drawn between two shapes that show the minimum work path between the entry and exit cross sections. The drawn EPLs were connected to build up a 3D-die. The effectiveness of the proposed method was examined experimentally, by comparing the results between the designed die and the linear die (with the linear curve for the deformation zone). It was found that there was acceptable reduction in extrusion pressure for the designed die.

Abstract: The relative balance between the metal flow in two portholes in extrusion has been investigated by experiments and FE-analysis. The investigation deals with asymmetric extrusion, i.e., the billet is extruded through a die with portholes of unequal size. Metal flow has been characterized by an experimental grid pattern technique. An optimized FEM-model of the experiment has been built and the experimental metal flow is found to be mimicked accurately by this model. The velocity conditions in the two differently sized ports feeding material into the weld chamber, and further from here into the extrudate, have been investigated to see if the balance between the flow through the two channels changes as extrusion proceeds. Increasing asymmetri between the two portholes has been realized in the analysis by displacement of the die bridge laterally in relation to the direction of extrusion.