A novel approach to enhance mechanical properties during recycling of aluminum alloy scrap through friction stir consolidation

Solid state recycling (SSR) is a new approach for making metals recycling more efficient with respect to remelting-based approaches. Friction stir consolidation (FSC) is a new solid-state process that is employed to recycle metallic scraps. Until now, a single-step FSC process was applied to recycled metal chips. During the single-step approach, critical processes parameters, especially processing time and rotational speed, are considered vital to control the quality and mechanical properties of the billet. However, the effectiveness of process parameters is highly restricted by challenging masses of recycling chips and machine competency. The present study first highlights the issues of the single-step FSC process, such as unconsolidated billet and poor mechanical properties at the bottom of the part, i.e., far away from the stirring action. Then, for the first time, three different two-step FSC methods were introduced as new approaches to overcome the existing challenges of the single-step method. The effectiveness of these methods was evaluated through the Vickers hardness measurements, and microstructure analysis. The results showed that two-step FSC methods successfully led to a fully consolidated billet and considerably improved mechanical properties.