PROCESS ENGINEERING OF SOLID STATE-BASED ADVANCED TECHNOLOGIES

In recent decades, the adoption of lightweight alloys has expanded across nearly all industrial sectors, driven by the significant weight reduction these materials offer. However, aluminium alloys, while advantageous in terms of performance, are associated with high energy demands during primary production, contributing substantially to global CO2 emissions. To mitigate and reverse these environmental impacts, implementing strategies that sustain materials within a circular lifecycle is imperative. Metal scraps characterized by a high surface-to-volume ratio, are often oxidized and contaminated. Conventional melting-based recycling methods encounter drawbacks such as reduced energy efficiency and permanent material loss due to oxidation during remelting.To address these issues, researchers have explored solid-state recycling techniques, which bypass the remelting step, conserving both energy and material. This dissertation investigates the capabilities of the Friction Stir Extrusion (FSE) process for recycling lightweight alloys, focusing on the influence of process parameters on mechanical, microstructural, and tribological properties of the extruded wire. The study also presents numerical models to predict process evolution and evaluates the environmental impact of these technologies. Additionally, it explores the incorporation of reinforcing particles such as SiC and Al₂O₃ to assess the feasibility of producing composite wires through FSE and the resulting enhancements in the extruded wire's properties.The research further delves into solid-state-based welding and processing technologies, such as Friction Stir Welding (FSW) and Friction Stir Processing (FSP) In the case of FSW, SiC-reinforced 2024-T3 aluminium composite joints were fabricated by embedding micro-sized SiC particles into sheets using a novel joint design to overcome powder dispersion issues commonly associated with conventional hole-based designs.For FSP, the study examines High-Pressure Die-Cast (HPDC) Al-4Mg-2Fe alloys, applying both single-pass and double-pass strategies to selectively alter the microstructure, eliminate defects, and minimize porosity. This approach establishes a defect-free processed zone, highlighting the potential of FSP as a powerful tool for improving the mechanical properties and microstructure of HPDC alloys.Overall, this research underscores the potential of solid-state recycling and processing technologies in promoting sustainable manufacturing practices and advancing material performance in alignment with circular economy principles.