## 3 Results
### Microstructural Characterization  
The microstructural evolution of a secondary phase over time is shown in Figure 5. For 0 NA, two distinct regions are present: Region 1, where there are very small phase particles, and Region 2, where these same particles exist but are larger. Examination of the particles in Region 1 also indicates that a greater number of phase particles are present. The opposite holds for Region 2, where a smaller number of the larger particles exist. Figure 5 and Table 4 show that as natural aging time increased prior to artificial aging at 325 \({}^{\circ}\)C for 4 h, particle evolution occurred such that the size increased while the number of particles decreased. Figure 6 shows the distribution for each case and highlights the overall increasing size of the phase particles. Figure 4: Tensile property evolution relative to natural aging time prior to artificial aging: (**a**) Representative tensile stress vs. strain curves for 4 NA. (**b**) YS. (**c**) TS. (**d**) Elongation at fracture. Trendlines present in (**b–d**) highlight the decreasing trend of median values. Note: For the box and whisker plots, the 25 th percentile is represented by the orange block, the 75 th percentile by the gray block, and the median value by the interface between the orange and gray blocks. Figure 5: Secondary phase particle evolution over natural aging periods: (**a**) 0 NA, (**b**) 6 NA, (**c**) 12 NA. Boundaries are marked for (**a**,**b**), denoting regions with differences in particle formation. Through the use of EDS, as shown in Figure 7, and an analysis of the literature, the particle phase in Regions 1 and 2 in Figure 5 is primarily composed of aluminum, scandium, and zirconium. It is believed that these particles are Al\({}_{3}\)(Sc,Zr), which is characteristic of Scalmalloy(r) components for strengthening through grain boundary pinning [48]. This theory has been confirmed through the use of standardized EDS point analysis. XRD was performed to further confirm the results shown with standardized EDS; however, due to the resolution of the available XRD equipment and the small quantity of the phase present in relation to the matrix, a peak could not be detected for the phase. The undetected peak has been noted in the literature for other studies performed on Scalmalloy(r)[31; 35; 49]. Analysis of the XRD results and standardized EDS results indicates that the matrix phase is an aluminum solid solution with the remaining alloying elements that did not precipitate out. \begin{table}
\begin{tabular}{c c c c} \hline
**Sample** & **Median Feret Diameter (\(\upmu\)m)** & **Range (\(\upmu\)m)** & **Area (\%)** \\ \hline
0 NA & 0.17 & 5.1 & 5.1 \\
6 NA & 0.17 & 4.5 & 4.0 \\
12 NA & 0.27 & 5.0 & 2.7 \\ \hline \end{tabular}
\end{table} 
Table 4: Secondary phase particle size measured via Feret diameter for 0 NA, 6 NA, and 12 NA cases. Figure 6: Particle size distribution for secondary phase particles showing the overall increase in size with longer natural aging prior to artificial aging. Figure 7: Energy dispersive spectroscopy (EDS) elemental maps depict the elemental concentration in the micron and sub-micron sized particle phase in DED-fabricated Scalmalloy®: (**a**) SEM micrograph showing a micron sized particle phase. (**b**) Aluminum. (**c**) Magnesium. (**d**) Scandium. (**e**) Zirconium. (**f**) Manganese. The characteristics of the nanoscale Al\({}_{3}\)(Sc,Zr) precipitates are shown in Figure 8. Figure 8a shows a representation of the precipitates seen in the microstructure. Using ImageJ thresholding, the nanoprecipitates were measured using Feret's diameter. Examination of the plot in Figure 8b details the evolution of the nanoprecipitates relative to longer natural aging time prior to artificial aging. The 0 NA case exhibited the smallest distribution of precipitates. At the same time, 0 NA exhibited the largest number of precipitates. As natural aging progressed, an increasing trend was noted for the precipitate size, see Figure 8c.