Ressourcenschonendes Recycling von Aluminiumspänen zu hochwertigen Produkten

Due to the high demand for aluminum products within many different applications and high energy demand, being related to its primary production from ores, secondary production of aluminum based on scrap gains in popularity. As conventional recycling based on melting results in high amounts of losses during processing, alternative processes for recycling are investigated to increase resource efficiency. Therefore, metal forming and powder metallurgical approaches, collectively called “Solid State Recycling”, aim to directly convert scrap to new products, surpassing melting metallurgy and associated losses. To compare both conventional and direct recycling approaches, a complete overview on the processing chain for recycling EN AW 6082 aluminum alloy chips is presented within this research work. Further, main steps regarding preparation and consolidation are investigated in laboratory scale and evaluated based on feasibility. As a first processing step, cleansing of residue cutting and cooling fluids from mechanical processing is investigated. Subsequently, the dried chips are briquetted with high compressional forces to facilitate handling and ensure a uniform starting material for further experiments. To investigate the consolidation behavior and main parameters, two metal forming processes, cold extrusion and high pressure torsion and an additional powder metallurgical approach, pulsed electric current sintering, are examined. As results of this thesis prove, after cleansing and compaction, a consolidation of aluminum chips is possible under severe plastic deformation, even at room temperature. Elevated processing temperatures help to lower necessary amounts of deformation for a connection between particles and additionally, reduce problems with blistering after subsequent heat treatment. An application of pulsed current over the specimens and dies also promotes a connection amongst adjacent chips and may be used in combination with high temperatures and deformation for better consolidation. For an industrial application, a step by step optimization throughout the whole processing chain will be necessary, to ensure clean and well sorted scrap. The results will be beneficial for improving efficiency of the conventional recycling route as well and enable an industrial application of solid state recycling routes after further research. Through existing process knowledge and possibilities to control the induced deformation with variation of die designs, particularly hot extrusion presents a promising option for future implementation of solid state recycling in existing production plants.