Experimental and Numerical Investigations on Metal Flow during Direct Extrusion of EN AW-6082

Abstract

In extrusion processes metal flow has an important influence on the microstructure and the mechanical properties of the extrudates. Thus, a deep knowledge about the metal flow during the forming process is required as basis for further computations of the microstructure evolution. In this study experimental and numerical investigations on the influence of friction on the metal flow in extrusion processes were carried out using visioplastic methods and finite element method (FEA). The objective was to determine the influence of ram speed, ram displacement and billet temperature on the material flow during extrusion of the aluminum alloy AlMgSi1 (EN AW-6082). For this purpose the forming stroke was varied at constant temperature so that a butt length of 100 mm and 150 mm could be produced. Further the influence of different ram speeds at 4.22 mm/s, 6.33 mm/s and 8.44 mm/s was investigated. In order to identify the metal flow and in special the shear zone as well as the dead metal zone, the billets of 250 mm length and a diameter of 140 mm were prepared with round aluminum indicator pins with a diameter of 4 mm which were placed in the plane of symmetry of the billet. For the experimental investigations a compact direct extrusion press with a nominal force of 10 MN (SMS Eumuco) was used. The numerical simulations were carried out using the commercial FEA system simufact.forming 8.1. After extrusion the billets were cut in the plane containing the indicator pins and the surface was polished and etched. The visioplastically determined flow lines and calculated strains were compared with computed flow lines in order to verify the results and to parameterize the simulation. Tresca’s friction model was used in the simulations to describe the frictional conditions between the billet and the tool components. The results of the experimentally and numerically determined strains of the billet at the container wall show a good similarity. With respect to the rigid modeling of the tool components and the fact that Tresca’s friction model considers relative speeds only indirectly the computed ram force curves show also quite good agreement with measured curves. However, the simulation results demonstrates that in further numerical studies advanced plastic flow criteria and flow rules should be used that take into account the anisotropy and inhomogeneity due to the changing grain size and microstructure of the workpiece material.