Characterization of extruded Aluminium
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- Institutt for kjemi 
A new method of continuous extrusion of aluminium, utilizing a screw tocompact scrap material into an extrusion prole, is being developed. Suchdirect recycling shows great advantages compared to traditional extrusion,especially in terms of the energy efficiency of the process. As a part of anindustrial project aiming to developing this extrusion method within a setof specic goals, the present work contributes to characterization andunderstanding with regard to extrudate quality. A test scheme producingcylindrical extrudates at controlled parameters was carried out, where theextrusion was performed with variations in die temperature, material feedand the rotation speed of the screw. The eect of these parametervariations to the nal extruded material was studied. This included studiesof the microstructure, mechanical properties and the materials response toheat treatment.The systematical variations in die temperature from 550 *C to 590 *Cindicated that a low die temperature yields a material with a favorablemicrostructure and mechanical properties, where low die temperature gavematerial with less recystallized grains. The ultimate tensile strength, yieldstress and elongation at fracture was highest for the extrudate produced atthe lowest die temperature. By an increase in die temperature to 560 and575 *C, more recrystallized grains was observed, and consequently adecrease 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 visualeects on the material. At a feed rate of approximate 100 g/min, most ofthe deformation structure was retained in the material. Also, much lessporosity was observed for this material. Only small band on the peripheryof this extrudate was recrystallized after extrusion. This was reected by the mechanical properties, i.e. this material showed the overall highestultimate tensile strength. At feed rates of 300, 400 and 500 g/min, theamount of recrystallized grains was observed to increase, as well as theporosity. A decrease in ultimate tensile strength, yield stress and elongationat fracture was consequently observed at increased feed rates.By varying the rotation speed of the screw, a decrease in the amount ofrecrystallized grains was observed as the rotation speed was increased. Theamount of retained deformation structure was gradually increasing, and as aconsequence, the ultimate tensile strength and yield stress was increasingcorrespondingly.Compared to material extruded conventionally by direct extrsion from abillet, the general observation is that the microstructure in the screwextruded material favors the retardation of the deformation structure. Thematerial produced from the billet had equiaxed recrystallized grainsthroughout the whole mass.Investigation of the material after heat treatment showed that the screwextruded material overall had a fairly good response to heat treatment. Theheat treatment procedure used did not yield material with mechanicalproperties that was expected from the alloy content. Further investigationof a specic heat treatment procedure for the screw extruded material isneeded.Particle analysis in SEM and TEM showed that the material containediron rich particles. Wear was observed in the metal parts of the setup, butdue to their composition and presence in the structure, the particles can beassumed to be fragmented primary particles containing AL-Mg-Si-Fe. Oxideparticles from the surface layer of the particles was not found in the currentinvestigation.