## 3 Results and Discussions  
### Relative Density and Microstructure  
The optimized laser energy density imparted to the Al4047 powder material resulted in near fully-dense parts with a remnant porosity of less than 0.4%. These calculations were carried out only for the pure Al4047 material. An exemplary micrograph is shown in Figure 4 for batch A, the as-built condition, which shows that the dominant type of defects is the gas porosity. Table 3 quantifies the resulting percentage of remnant porosity where the as-built condition resulted in a remnant porosity of 0.26%. After post-process stress-relief, it is increased to 0.38%, which can be attributed to the extended duration of the applied temperature during the stress-relief procedure thatwould have developed an internal pressure in the pores, and a slight expansion of these pores would be possible resulting in a marginal expansion in porosity volume. Similar observations were reported in SLM processed materials in [43; 44]. For the base-plate heated and stress-relieved configuration, batch C, 0.29% remnant porosity was calculated, which is less as compared to similar conditions without base plate heating. batch B. This improved relative density can be attributed to the reduced thermal gradients by heating of the base plate, thereby helping the melt pool to stabilize, increasing the density of the melt pool itself as compared to the released gases and allowing more time for these gases to escape the melt. The microstructure of SLM-processed Al4047 alloy has been reported in the literature that it consists of ultrafine grains in terms of dendrites developed in the matrix. As the process is localized in nature, so is the microstructural development, which consists of fine and relatively coarse regions. Coarser regions are existing at the places, e.g., hatch overlaps receiving more laser energy per unit area. However, the most important aspect of microstructure observed was the average width of the dendrites in the prevalent single melt regions. The size of these dendrites was found to be dependent on the cooling rate during the process as well as on the thermal treatment after the process. Dendritic width was measured across six images for batches A-C and exemplarily shown in Figure 4b,c for the batches B and C and plotted in Figure 4d in relation to the measured residual stresses. For the as-built condition, batch A, the average dendritic width of 0.29 \(\upmu\)m was calculated, which increased to 0.35 \(\upmu\)m after stress-relief treatment (batch B), and 0.56 \(\upmu\)m for the batch manufactured with base plate heating (batch C). Though there is an increase in dendritic width after stress-relief, 0.35 mm from 0.29 \(\upmu\)m, the increase due to base plate heating is much higher reaching to 0.56 \(\upmu\)m. Results of residual stresses that were measured at the surface of the specimens are shown in Figure 4d as a function of the dendritic width. The as-built condition, batch A, has developed the highest value of tensile residual stress at the surface, i.e., 36 MPa. After stress-relief treatment, batch B, the residual stress reduced to 13 MPa, and the combination of base plate heating and stress-relief, batch C, resulted  
Figure 4: Part parameters of SLM-processed Al4047: (**a**) part morphology; (**b**) microstructural features for batch B; (**c**) microstructural features for batch C; and, (**d**) residual stresses as a function of the dendritic width. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Batch** & **A** & **B** & **C** \\ \hline Remnant porosity [\%] & 0.26 & 0.38 & 0.29 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Percentage remnant porosity in batches A, B, and C.  
in a very small value of 4 MPa. These values are worth discussing based on the microstructural features, Figure 4d. The highest value of tensile residual stress of 36 MPa is observed in the batch with the least value of dendritic width, 0.29 \(\upmu\)m, which is previously attributed to the highest thermal gradient in the SLM process.