Characterization of extruded Aluminium

A new method of continuous extrusion of aluminium, utilizing a screw to compact scrap material into an extrusion prole, is being developed. Such direct recycling shows great advantages compared to traditional extrusion, especially in terms of the energy efficiency of the process. As a part of an industrial project aiming to developing this extrusion method within a set of specic goals, the present work contributes to characterization and understanding with regard to extrudate quality. A test scheme producing cylindrical extrudates at controlled parameters was carried out, where the extrusion was performed with variations in die temperature, material feed and the rotation speed of the screw. The eect of these parameter variations to the nal extruded material was studied. This included studies of the microstructure, mechanical properties and the materials response to heat treatment. The systematical variations in die temperature from 550 *C to 590 *C indicated that a low die temperature yields a material with a favorable microstructure and mechanical properties, where low die temperature gave material with less recystallized grains. The ultimate tensile strength, yield stress and elongation at fracture was highest for the extrudate produced at the lowest die temperature. By an increase in die temperature to 560 and 575 *C, more recrystallized grains was observed, and consequently a decrease in ultimate tensile strength, yield stress and elongation at fracture. With a die temperature of 590 *C, a more porous material was observed, and larger variations in the properties along the extrudate was observed. The feed rate was varied from 100 to 500 g/min and gave more visual eects on the material. At a feed rate of approximate 100 g/min, most of the deformation structure was retained in the material. Also, much less porosity was observed for this material. Only small band on the periphery of this extrudate was recrystallized after extrusion. This was re ected by the mechanical properties, i.e. this material showed the overall highest ultimate tensile strength. At feed rates of 300, 400 and 500 g/min, the amount of recrystallized grains was observed to increase, as well as the porosity. A decrease in ultimate tensile strength, yield stress and elongation at fracture was consequently observed at increased feed rates. By varying the rotation speed of the screw, a decrease in the amount of recrystallized grains was observed as the rotation speed was increased. The amount of retained deformation structure was gradually increasing, and as a consequence, the ultimate tensile strength and yield stress was increasing correspondingly. Compared to material extruded conventionally by direct extrsion from a billet, the general observation is that the microstructure in the screw extruded material favors the retardation of the deformation structure. The material produced from the billet had equiaxed recrystallized grains throughout the whole mass. Investigation of the material after heat treatment showed that the screw extruded material overall had a fairly good response to heat treatment. The heat treatment procedure used did not yield material with mechanical properties that was expected from the alloy content. Further investigation of a specic heat treatment procedure for the screw extruded material is needed. Particle analysis in SEM and TEM showed that the material contained iron rich particles. Wear was observed in the metal parts of the setup, but due to their composition and presence in the structure, the particles can be assumed to be fragmented primary particles containing AL-Mg-Si-Fe. Oxide particles from the surface layer of the particles was not found in the current investigation.