## 3 Results
As shown in Figures 7 and 8, grain size can vary dramatically in certain regions of the build, with relatively large grains still present in the substrate, and very refined grains observed at the edges of the flash material. For this analysis, grain size was investigated in the dynamically recrystallized deposition material near the overlap interface but excluded the flash material which would be machined away in practical applications. Figure 11 displays the relationship between the grain size and the deposition overlap distance, measured in mm, with the recorded scatter included for each cross-section. A negative overlap distance corresponds to a gap of the same magnitude. Although some of the tested regions have a relatively wide range of scatter, with the largest range being slightly larger than 1 \(\upmu\)m, the average grain size remains consistently between 4 and 4.5 \(\upmu\)m across all cross-sections. Similar to the collected hardness data, there is no observed trend  
Figure 3.4 (a) Cross-section of the 6.4 mm AFSD overlap sample with selected regions for grain size analysis. (b,c) High magnification images used for grain size analysis. \begin{table}
\begin{tabular}{c c} \hline \hline
**Overlap Region Width (mm)** & **Average Deposition Hardness (Hv)** \\ \hline \(-\)6.4 & 123.0 \\ \(-\)3.2 & 128.9 \\ 0.0 & 127.9 \\ 3.2 & 126.0 \\ 6.4 & 132.5 \\ 9.5 & 128.6 \\ 12.7 & 127.3 \\ 15.9 & 135.0 \\ 19.1 & 121.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Average Vickers hardness of the deposited AA 7075.  
relating grain size to overlap region width. This is expected, as all process parameters aside from the overlap region width were held constant between depositions. The observed range of grain sizes is also within the expected range for a 7 XXX-series aluminum alloy processed with AFSD [39]. Table 4 details the experimental results of tensile testing including the yield strength and ultimate tensile strength, measured in megapascals, and the elongation to failure, measured in percentage, for each tested AFSD overlap specimen. Additionally, Figure 12 shows the engineering stress-strain results for each tested AFSD overlap specimen. As expected, since the as-deposited materials were no longer in the T6 condition, the feedstock material exhibited higher yield and ultimate strength compared than the as-deposited material specimens. As the AFSD build is deposited, the material experiences relatively high temperatures for an extended period of time. This causes the feedstock material to undergo precipitate coarsening, which effectively removes the benefits of the T6 heat treatment from the material during the deposition process [39]. Because the completed builds were not heat-treated before the mechanical testing was conducted, this difference in tensile strength is expected. Due to geometric constraints, specimens could not be collected for every deposition, and two tensile specimens were collected from each tested build. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Specimen** & **YS (Mpa)** & **UTS (Mpa)** & **EF (\%)** \\ \hline \(-\)3.2 mm overlap (A) & 247 & 405 & 9.8 \\ \(-\)3.2 mm overlap (B) & N/A & N/A & N/A \\
0.0 mm overlap (A) & 229 & 258 & 1.5 \\
0.0 mm overlap (B) & 249 & 346 & 5.0 \\
3.2 mm overlap (A) & 266 & 360 & 3.8 \\
3.2 mm overlap (B) & 264 & 387 & 6.6 \\
9.5 mm overlap (A) & 299 & 434 & 7.2 \\
9.5 mm overlap (B) & 290 & 426 & 7.8 \\ Feedstock & 525 & 583 & 19.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Numerical data for quasi-static results. Figure 11: Grain size as a function of overlap distance in the AFSD builds. The yield strength, ultimate strength, and ductility all show favorable improvement as the overlap width increases across almost every specimen tested. The exceptions to this trend are the specimens taken from the 3.2 mm gap (\(-\)3.2 mm overlap) build. Specim B from this build shows no measurable performance that can be compared to the other tested specimens due to its nearly immediate failure.