Understanding the impact of additive friction stir deposition on the production of 7xxx aluminum alloy parts

As an alternative to current additive manufacturing (AM) techniques, additive friction stir deposition (AFSD) is a solid-state process that has been recently explored and does not require melting or remelting of the feedstock, which is a challenge in fusion AM processes. Once its yield point is reached, the material is deposited under elevated temperatures-a similar mechanism to that of friction stir welding (FSW), producing fully dense parts with more equiaxed and finer grain structures, potentially not requiring postheat treatment. Compared with direct energy deposition (DED) technologies, it benefits from reduced heat input and high build rates. It also allows for open-air deposition of reactive metals such as aluminum alloys. These alloys are used extensively in the aerospace industry, and demand is expected to double over the next decade. The 7XXX series is the hardest and strongest commercial grade among the aluminum alloys, making them useful for aircrafts, high-speed trains, and parts under high stress. Although research on AFSD development has mostly focused on aluminum alloys, advancements using 7XXX series have been either limited or nonexistent. In this paper, we analyze 7XXX series aluminum parts produced through AFSD by the introduction of different combinations of torque, deposition rate, and tool speed. Tensile and hardness tests are performed in different directions, including the interface between the baseplate and deposited material, assessing the overall strength of all AFSD parts carried out. Despite AFSD's potential, it is demonstrated that there is an opportunity for improvements, and further work (e.g., Charpy test, microstructural characterization, heat treatment) is required to comprehend the technologies' impact and benefits.