Solid state recycling of aluminium chips: Multi-technique characterization and analysis of oxidation

Solid-state recycling of metallic alloys is a promising alternative method which avoids remelting and reduces significantly the CO2-emission compared to remelting. Contamination being critical for solid-state recycling, the objective of this study is to quantify and localize oxygen contamination at each step of the process. Pre -compacted AA6060 aluminium alloy machining chips were hot-extruded. The oxygen intake and the forma-tion of oxides were quantified and localized through a multi-technique characterization, including X-ray photoelectron spectroscopy and transmission electron microscopy. The overall oxygen content is found to in-crease at every step of the recycling process. Analyses reveal that the initial thin Al2O3 layer on the chips gets covered by a MgO layer during pre-annealing and hot extrusion. Thus, alloying elements, as Mg, are involved in oxidation. It results in a tenfold increase of the oxygen content in the extrudate accompanied by a complex network of oxides with an average thickness of 290 nm and a low density. Thus, tuning processing parameters is a promising leverage to limit oxidation and improve chip welding, which will probably depend on the alloying elements.