Friction stir extrusion to recycle aluminum alloys scraps: Energy efficiency characterization

Solid state recycling refers to a group of processes allowing direct recycling of metals scraps into semi-finished product. Their main advantage lies in avoiding the molten state of the material which badly affects the environmental performance of the conventional (remelting based) recycling routes. It is expected that such process category would lower the environmental performance of metals recycling. In this paper, the friction stir extrusion process for aluminum alloy AA 2050 wire production is analyzed under the primary energy demand perspective. The process electrical energy demand is quantified with varying process parameters. An empirical modelling approach was applied and an analytical model able to expresses the specific energy consumption as a function of the extrusion rate was carried out. Finally, the primary energy demand of the whole recycling route was quantified and compared with both conventional and Equal Channel Angular Pressing (ECAP) based routes. Results revealed that Friction Stir Extrusion approach allows substantial primary energy savings for the case of wire production. To be more specific, FSE allows a reduction in energy demand up to 74% and 63% with respect the conventional and the ECAP routes, respectively. This is mainly due to avoided permanent material losses as well as to the absence of intermediated process steps (wire drawing).