Exploiting the SPH meshless approach potential for Tube Friction Stir Extrusion: insights into process mechanics, grain size, and micro-mechanical properties

Friction stir-based manufacturing processes have recently attracted increasing attention due to their ability to process aluminum without melting, potentially reducing energy consumption compared to conventional routes. Among these, Friction Stir Extrusion (FSE) has emerged as an effective technique for producing metal wires, and more recently, its potential has also been explored for tube manufacturing applications. This paper aims to provide an insight into tube production through the FSE process by developing a dedicated numerical model using the Smoothed Particle Hydrodynamics (SPH) technique. The model was first validated against experimental temperature and load measurements and then used to (i) investigate the complex material flow occurring during the process, through the analysis of dissimilar three-material tubes; (ii) investigate the effect of tool rotation on the main microstructural and micro-mechanical properties of the tubes, i.e., grain size and microhardness. The results indicate that two regions can be identified across the tube thickness, namely an inner one, characterized by higher deformation, smaller grain size, and higher microhardness, and the outer one, where elongated grains and lower microhardness values are observed. Overall, the FSE process proved to be a valid, sustainable alternative for tube manufacturing, while SPH modelling offers high accuracy and effectiveness on microstructure and hardness prediction.