Solid bonding criteria design for aluminum chips recycling through Friction Stir Consolidation

Decoupling economic growth from resource depletion is an urgent target to achieve. Adopting circular economy paradigm is the only way to address such challenge. Manufacturing scientists have to make a research effort addressed to find and design proper manufacturing processes enabling circular economy strategies such as remanufacturing, repairs, recycling, etc. This paper aims at enhancing the knowledge concerning Friction Stir Consolidation (FSC) process, a solid state innovative and resource efficient aluminum alloys scrap recycling process that directly turns a batch of chips into a consolidated billet. In this paper, FSC process is used to recycle AA7075 chips and different solid bonding criteria, already presented in literature, have been tested through an experimental and numerical approach. All of them failed to predict the chips solid bonding in FSC processes. Therefore, a new criterion, specifically designed for FSC, is presented. The performance of conventional criteria has been compared to that provided by the new criterion on two validation tests. For the analysis of the bonding prediction performance, an innovative procedure is proposed for the threshold values identification. The proposed approach is based on experimental data collection, numerical simulations and an optimization procedure implemented in MATLAB environment. The new, and here presented criterion, provided the best results with at least 90% of prediction accuracy compared to the conventional Plata – Piwnik criterion characterized by an average accuracy equal to 55%, instead. The proposed procedure, and the new identified solid bonding criterion, represent a powerful tool for understanding and designing aluminum alloys recycling through FSC