Lightweight Alloys Recycling and Processing through Innovative Friction Based Direct Technologies

In the last decades, the use of lightweight alloys has been spreading in almost any industrial field thanks to the relevant weight reduction allowed by the use of such materials. On the other hand, aluminium alloys are characterized by high-energy demands primary production cycles that are responsible for a relevant share of the global CO2 emissions. In order to limit and reverse such phenomenon, putting in place strategies to keep the material in the circle over multiple life cycles is mandatory and the concepts of circular economy, closed loop society and industrial symbiosis are progressively gathering more and more pace. Nevertheless, metal scraps are often mainly composed of chips resulting from machining operations and sheet metal coming from trimming after forming processes. This kind of wastes is between the most difficult kind of scraps to be recycled as they are characterized by high surface/volume ratio and they are usually oxidized and covered by different types of contaminants. Due to these features, conventional melting recycling technologies may lead to different drawbacks the overall energy efficiency is quite low and, more importantly, permanent material losses occur during remelting because of oxidation. In order to overcome such issue, researchers started investigating solid-state recycling approaches; in fact, by avoiding the remelting step, both energy and material can be saved. In this dissertation, the Friction Stir Extrusion and Friction Stir Consolidation processes capabilities for lightweight alloys recycling and processing are investigated with a particular focus on the influence of the process parameters on the mechanical properties of the processed materials. Numerical models to predict the processes evolutions are described and the environmental impact of these technologies are evaluated.