To decrease greenhouse gas (GHG) emissions by at least 40 % by 2030 as targeted by the European Union, all sectors are involved, including that of metallic alloy processing and recycling. Currently, metallic alloys are recycled by re-melting, which already decreases greatly GHG emissions. In order to decrease them even more, an alternative recycling route, solid-state recycling consists in a pre-compaction of machining chips followed by a heat-treatment and hot extrusion. By avoiding the re-melting step, the energy consumption and thus the GHG emissions are decreased [1], but removing contaminations, mainly oxygen, becomes complex. Indeed, it was shown in a previous work on AA6060 that oxygen contamination increases at each step of the process, resulting in an sub-micronic oxide network [2], which is deleterious for mechanical properties.
The objective of this work is to identify the optimum processing parameters to minimize oxidation while maintaining a complete densification. To do so, oxidation kinetics of AA6060 was studied at various temperatures by thermogravimetric analysis and X-ray photoelectron spectroscopy. The maximum temperature and applied force during extrusion was modelled for various conditions. Based on those results, new conditions for the heat treatments and hot extrusion were selected and some chip-based extrudates were subsequently produced and characterized. The evolution of the microstructure and mechanical properties will be described. Finally, a life-cycle analysis will assess the environmental impacts of varying processing conditions. The strategy to find the best compromise between oxidation, mechanical resistance and environmental impacts will be discussed.      

References:
[1] Duflou, J.R., Tekkaya, A.E., Haase, M., Welo, T., Vanmeensel, K., Kellens, K., Dewulf, W., and Paraskevas, D., CIRP Annals, 2015. 64(1): p. 37-40
[2] M. Laurent-Brocq, L. Lilensten, C. Pinot, A. Schulze, A. Duchaussoy, J. Bourgon, E. Leroy, A. E. Tekkaya; Materialia 31 (2023) 101864