# Processing of AZ91D Magnesium Alloy by Laser Powder Bed Fusion
## 3 Results and Discussion
### Bulk Samples I  
In the following step, cube samples were produced in three series to minimize the negative effects of the sample position of the platform. Using DoE, a total of 20 process parameters were used, which are listed in Table 3. _LP_ and _LS_ from the previous single-track test were chosen as the DoE input marginal parameters (Section 2.1). Furthermore, the distance between the individual tracks ('Hatch distance'--_HD_; Figure 6) and the percentage of overlap of individual tracks ('Overlap'--_OL_) are included in DoE. _HD_ is calculated using _OL_ and the width of the tracks from the single-track weld test. In addition, the table shows the values of the input energy density \(E_{\
u}\), which is determined according to Equation (2), and the resulting values of relative areal density (_RD_) of the material:  
\[E_{\
u}=\frac{LP}{LS\cdot LT\cdot HD}\left[J/mm^{3}\right] \tag{2}\]  
Figure 5: Metallographic images of single tracks for the entire experimental area. Green border represents parameters used for follow-up testing. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Group** & **Sample** & _LP (W)_ & _LS (mm/s)_ & _OL (\%)_ & _HD (mm)_ & \(E_{\
u}\) (J/mm\({}^{3}\))_ & _RD (\%)_ \\ \hline \multirow{8}{*}{1} & 1-1 & 150 & 750 & 50 & 0.098 & 40.8 & 99.2 \(\pm\) 0.02 \\  & 1-2 & 150 & 475 & 30 & 0.151 & 41.8 & 99.0 \(\pm\) 0.02 \\  & 1-3 & 180 & 612.5 & 40 & 0.133 & 44.2 & 99.2 \(\pm\) 0.12 \\  & 1-4 & 210 & 475 & 50 & 0.126 & 70.2 & 98.0 \(\pm\) 0.02 \\  & 1-5 & 180 & 612.5 & 40 & 0.133 & 44.2 & 98.9 \(\pm\) 0.11 \\  & 1-6 & 210 & 750 & 30 & 0.153 & 36.6 & 98.8 \(\pm\) 0.01 \\  & 1-7 & 180 & 612.5 & 40 & 0.133 & 44.2 & 99.1 \(\pm\) 0.01 \\ \hline \multirow{8}{*}{2} & 2-8 & 150 & 475 & 50 & 0.108 & 58.5 & 98.4 \(\pm\) 0.03 \\  & **2-9** & **210** & **475** & **30** & **0.176** & **50.2** & **92.8 \(\pm\) 0.05** \\  & 2-10 & 210 & 750 & 50 & 0.110 & 50.9 & 98.4 \(\pm\) 0.02 \\  & 2-11 & 150 & 750 & 30 & 0.137 & 29.2 & 94.8 \(\pm\) 0.11 \\  & 2-12 & 180 & 612.5 & 40 & 0.133 & 44.2 & 98.8 \(\pm\) 0.04 \\  & 2-13 & 180 & 805 & 40 & 0.120 & 37.3 & 97.2 \(\pm\) 0.06 \\  & 2-14 & 138 & 612.5 & 40 & 0.120 & 37.6 & 97.6 \(\pm\) 0.08 \\ \hline \multirow{8}{*}{3} & 3-15 & 180 & 612.5 & 26 & 0.164 & 35.8 & 99.0 \(\pm\) 0.01 \\  & 3-16 & 222 & 612.5 & 40 & 0.135 & 53.7 & 99.0 \(\pm\) 0.01 \\ \cline{1-1}  & 3-17 & 180 & 612.5 & 54 & 0.102 & 57.6 & 99.3 \(\pm\) 0.21 \\ \cline{1-1}  & 3-18 & 180 & 420 & 40 & 0.144 & 59.5 & 97.7 \(\pm\) 0.04 \\ \cline{1-1}  & **3-19** & **180** & **612.5** & **40** & **0.133** & **44.2** & **99.4 \(\pm\) 0.02** \\ \cline{1-1}  & 3-20 & 180 & 612.5 & 40 & 0.133 & 44.2 & 99.0 \(\pm\) 0.02 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Overview of process parameters and measured values of area relative density (_RD_) of cube samples with standard deviation, XY plane. Representative images of the samples with the lowest and highest relative densities are shown in Figure 7. The highest relative density was achieved in sample 3-19 with the process parameters \(LP\) = 180 W, \(LS\) = 612.5 mm/s, \(HD\) = 0.133 mm and \(OL\) = 40%. These process parameters are used several times to avoid calculation and measurement errors in production of only one sample. On the other hand, sample 2-9 shows extensive porosity (Figure 7a) mainly consisting of spherical pores and voids with a size of 10-200 \(\upmu\)m. The pores and voids are irregularly distributed throughout the sample volume. Local line alignment of the cavities can be observed, indicating the correlation of their formation with the laser beam track as a consequence of high input energy density [21,22]. The porosity of sample 3-19 is minimal (Figure 7b). Spherical pores with a size of about 10 \(\upmu\)m occur mainly in the subsurface region of the sample. The AZ91D alloy investigated in the study by [PERSON] et al. [23] shows a similar result with a relative density of 99.52% and an input energy density \(E_{v}\) = 166.7 J/mm\({}^{3}\).