Unlocking the potential of friction stir extrusion as a sole manufacturing step for producing sustainable tubes from aluminum chips

Abstract Conventional remelting-based methods are widely used for recycling aluminium alloys scraps; however, these approaches come with significant drawbacks, including high energy consumption, permanent material losses, reduced purity, and low mechanical properties. To address these issues, solid state techniques have emerged over the last years as environmentally friendly recycling processes. Among them, friction stir extrusion (FSE) has proved to be a promising technique for producing wires/rods directly from metallic chips. In order to cover the market demand of semifinished product shapes, this study explores the possibility to produce aluminium alloys tube directly from chips without intermediate steps. This would save energy and resources, strengthening the environmental sustainability performance of FSE based recycling processes. An experimental and numerical approach is here proposed and the impacts of the main process parameters on the microstructural and mechanical properties of extruded aluminium tubes are analyzed. Results revealed that FSE could be used as sole process step to produce tubes from chips, and mechanical and microstructural analysis showed a substantial increase in hardness in correspondence to very fine and equiaxed grain structure. Moreover, numerical simulations were used to explain the small variations observed in grain size. Lastly, the electrical energy demand of this single-step approach was compared with that of conventional multi-step routes, demonstrating its superior energy efficiency.