Additive friction stir deposition for aluminum alloys in aerospace applications

Humanity and engineering are facing great challenges in every aspect of life. Engineers have been chasing innovation in finding superior materials and manufacturing techniques to be able to spend less energy and get more performance by considering the living ecosystem. Additive manufacturing (AM) techniques have been in our lives for more than a decade. The main motivation of these techniques brings flexible and light geometric design, zero or less waste, on demand manufacturing, excellent scalability, reduction in lead time and storage, fast adaptation to digitalization, and economical to make prototypes. Challenges are the excessive cost of equipment and materials; the need for new materials in different forms; processes are slow; and need for designing new postprocesses. In aerospace applications, aluminum alloys have been utilized because of these flexible and wide range of mechanical properties for designers. Great competition and designing new vehicles for the aerospace sector have been pushing the limits of materials and processes to have light and strong components. Plus, maintaining the products needs these novel solutions. Aluminum alloys are one of the best candidates for additive friction stir deposition (AFSD) feedstocks due to their deformation capabilities and their potential to be strengthened via deformation and/or precipitation hardening. Among all the other AM techniques, this chapter focuses on summarizing the state of the art in the AFSD process and as applied to aluminum alloys for aerospace applications. AFSD is a novel developing solid-state technique based on a thermomechanical stirring of rotating materials resulting in layer-by-layer deposition via high rate and severe plastic deformation. With the help of rotating feedstock of solid rods or chips, a solid and a fully dense homogenous refined layer having a fine microstructure, low levels of residual stress and distortion can be achieved with a high yield and low cost. Furthermore, in comparison to fusion-based processes, the absence of melting and solidification makes this process free from shrinkage, porosities, and cracks providing superior strength and ductility. This chapter summarizes state-of-the-art in AFSD of aluminum alloys, most of which have significant usage in the aerospace industry. Being capable of building near-net shape large parts in relative short process times, AFSD has a substantial application potential in production.