Improving the Industrial Efficiency of Recycling Aluminum Alloy Chips Using Friction Stir Extrusion: Thin Wires Production Process

Abstract Friction stir extrusion is one of the most promising solid-state chip recycling techniques because of its relative simplicity and high efficiency. One of the most straightforward applications for the process is the production of recycled wires to be utilized as filler material in welding or welding-based additive manufacturing processes, in order to create an industrial symbiosis link, fostering a circular economy and enhancing the technology readiness level of the process. The scalability of the process to the thin wires needed for such applications has not been investigated so far. In this paper, an experimental and numerical analysis was developed. A dedicated numerical model was first validated and then used to design the tool geometry. The effect of tool rotation and tool force on both “standard” mechanical properties, as Ultimate Tensile Strength and microhardness, and specific properties for the envisaged application, as the wrapping around reels with different radii, was investigated. The numerical model results were used to explain the influence of the process parameters on the material flow as well as on the distribution of the primary field variables, namely temperature, strain, and strain rate. Finally, the energy demand was measured, and the specific energy consumption (SEC) was evaluated. It was found that a conical shoulder surface favors the conditions for effective solid bonding. Low values of the extrusion force have detrimental effects on the wires properties as they result either in insufficient strain, or hot cracking defects. High values of extrusion force results in lower SEC, unlocking the potential of the process as symbiotic link enabler.