On the Manufacture of Lightweight Alloy Tubes via Friction Stir Back Extrusion: Process Evaluation and Material Performance

A new manufacturing approach in which the friction stirring phenomenon is used as a vehicle for facilitating the deformation of bulk lightweight materials into manufactured components has been recently introduced under the general concept of “bulk friction stir forming”. In a preliminary work, the concept was applied to the back extrusion process, in what was referred to as “friction stir back extrusion” or FSBE; it was shown that the concept is practically valid and FSBE is capable of producing lightweight tubular specimens. Nevertheless, the FSBE process was claimed to have several merits over conventional processes, mainly: (i) unique process capabilities and energy efficiency (ii) significant grain refinement, and thus (iii) favorable mechanical properties in the formed tubes. None of these claims were adequately addressed nor quantified in earlier work. Therefore, this work presents a comprehensive study that aims to reveal the true merits of FSBE, validate the claims, and quantify its effects on the microstructure and mechanical properties of the deformed material. The outcomes of the study are presented in three major parts, each addressing one of the abovementioned claims. Force, torque and power measurements during FSBE experiments are used to address the first claim. Detailed optical microscopy and electron back scatter diffraction work is carried out in the second part to quantify the changes to the grain structure and texture of the material. Finally, the third part presents detailed mechanical characterization using digital image correlation to quantify the effects of FSBE on the performance of the produced tubes.