Large-scale metal additive manufacturing (AM) provides a unique solution to rapidly develop prototype components with net-shape or near-net shape geometries. Specifically, additive friction stir deposition (AFSD) is a solid-state method for large-scale metal AM that produces near-net shape depositions capable of high deposition rates. As AFSD is utilized for a broader range of applications, there is a need to understand deposition strategies for larger and more complex geometries. In particular, components with larger surface areas will require overlapping deposition passes within a single layer. In this study, the AFSD process was used to create depositions utilizing multiple passes with a varying deposition path overlap width. The effects of overlapping parallel pass depositions on the mechanical and microstructural properties of aluminum alloy 7075 were examined. The grain size and microstructural features of the deposited material were analyzed to evaluate material mixing and plastic flow in the observed overlap regions. Additionally, hardness and tensile experiments were conducted to observe the relationship between the overlap width and as-deposited material behavior. In this study, an ideal overlap width was found that produced acceptable as-deposited material properties.

In this research, we explore the preliminary effects of processing conditions using a novel additive manufacturing (AM) process, known as additive friction stir deposition (AFSD), on resulting build direction (BD) mechanical performance. Using the AFSD process, a feasibility study of three AM builds of identical size are created using differentiating processing parameters. A relationship referred to as the deposition pitch, exhibiting similarities to weld pitch, is determined to be a simple but effective predictor of the interlayer bonding in AFSD processing of AA7020. The deposition pitch directly correlates the necessary temperature, time, and pressure required for effective solid-state bonding. Using this correlation, increased mechanical performance in the BD is achieved through an increase in deposition pitch. A reduction in the deposition pitch from 4.46 rev/mm to 1.08 rev/mm resulted in a significant decrease in failure strain from 24.4% to 0.82%, with the failure mechanism shifting from a ductile failure to brittle failure. The inverse relationship between grain refinement and BD failure strain at high deposition pitches suggests deposition pitch and heat input are the dominant factors in the resulting BD mechanical properties.