Solid-state recycling of AA6063 aluminium alloy chips into L-profiles by hot extrusion

Machining chips of AA6063 aluminium alloy were solid-state recycled into equilateral L-shaped profiles via cold compaction into briquettes followed by hot extrusion at 600 K with extrusion ratios of 10 and 21. Two chip morphologies, namely long coiled turning chips and short irregular milling fragments, were examined to clarify the influence of chip geometry on consolidation, microstructure and mechanical performance. Stable extrusion was achieved in all cases without fracture or incomplete die filling. The relative density of the extrudates reached approximately 97%–99%, while tensile strength ranged from 112 to 120 MPa, falling between those of AA6063-O and AA6063-T1 alloys. Increasing the extrusion ratio improved strength and hardness but slightly reduced relative density and ductility. Surface roughness measurements showed pronounced anisotropy, with Ra values of approximately 0.4–1.1 μm parallel to the extrusion direction and 1.6–5.6 μm in the perpendicular direction, with higher roughness observed for milling-derived materials and at higher extrusion ratios. Microstructural observations revealed that residual chip boundaries and voids, particularly in materials recycled from turning chips, decreased markedly with increasing extrusion ratio, suggesting enhanced metallurgical bonding despite limited densification. A positive correlation between relative density and fracture strain highlights the importance of void elimination for ductility recovery. Finite element analyses predicted highly non-uniform strain distributions, with maximum deformation near the outer bend of the L-section, consistent with improved bonding at higher extrusion ratios. These findings demonstrate that hot extrusion following briquette compaction offers a viable and sustainable route for converting aluminium machining chips into structurally usable profiles.