COMPUTER AIDED ENGINEERING FOR SOLID BONDING RECYCLING PROCESSES

In most sectors of the automotive and aerospace industries, a combination of high strength and low weight is essential to meet the requirements of modern products. In this context, aluminium and its alloys are increasingly replacing conventional steels thanks to their low density and superior strength-to-weight ratio. However, despite the mechanical advantages, aluminium’s primary production has a significant environmental impact. The extraction and synthesis of aluminium from ores result in extremely high greenhouse gas (GHG) emissions and high energy consumption compared to other traditional metals. To mitigate GHG emissions, several international frameworks have been established. For instance, the United Nations Framework Convention on Climate Change (UNFCCC) led to the Kyoto Protocol (2005–2012), which imposed emission reduction targets for participating nations, and the Paris Agreement (2015), which set the goal of limiting the global temperature rise to well below 2 °C by the end of the century. In response to the growing need for sustainable goals, recycling strategies have gained increasing attention. Among these, the conventional remelting process has been developed to enable the reuse of aluminium scrap generated during industrial manufacturing, bypassing the high energy-intensive stages of auminium production (primary production). Nevertheless, remelting has significant drawbacks: it requires substantial energy input, and oxidation of the molten metal leads to unavoidable losses, often reaching 15–20% of the processed material. To address these drawbacks, researchers have developed innovative recycling methods that avoid melting the metal scraps, known as solid-state recycling (SSR) processes. These methods are capable of recycling machining swarf through the combined action of pressure, temperature, and contact time, thereby reducing both energy demand and material loss. Based on this background, this dissertation provides a comprehensive investigation of aluminium alloy recycling using a specific group of solid-state recycling (SSR) techniques: friction stir-based processes. Specifically, friction stir consolidation and friction stir extrusion were employed to turn machining chips into consolidated billets and extruded tubes, respectively. Particular focus was given to understanding the solid bonding phenomena governing friction stir-based recycling, through a dedicated methodology combining experimental investigations, numerical simulations, and analytical modelling within the MATLAB environment. Furthermore, the study examined process dynamics and their influence on the resulting microstructure and mechanical properties, thereby enhancing the understanding of these processes. Finally, the main challenges associated with FSC and FSE were critically assessed, and innovative solutions were developed to overcome their current limitations.