# Processing of AZ91D Magnesium Alloy by Laser Powder Bed Fusion
## 3 Results and Discussion  
### Single-Track Welds  
Based on the literature review described in Section 2.2, a map of the process parameters for the experiment is drawn up (Figure 4a). The map is divided into three areas depending  
Figure 3: **(a)** Bulk sample divided into the sections for metallographic processing, (**b**) image of porosity in the sample after metallographic processing and (**c**) image from ImageJ software for evaluation of relative density.  
on the energy range achieved for each single-track group. The energy value \(E\) is determined by Equation (1).  
\[E=\frac{LP}{LS\cdot LT},(J/\mathrm{mm}) \tag{1}\]  
where \(LP\) is the laser power (W), \(LS\) is the scanning speed (mm/s) and \(LT\) is the layer thickness (mm).  
The individual single-track welds were inspected to identify the parameters that resulted in high-quality single tracks. Such parameters were considered to be suitable for further investigation. They are characterized by the optimal shape of the cross-section and the continuity of the track. The continuity of the track is affected by significant contractions observed in the entire volume of the single-track series. Based on the inspection, the main characteristics of the single tracks in each area are identified as follows:  
* A--The region with a low value of input energy \(E\) = 3.7-4.7 J/mm shows a suitable depth of 179 \(\pm\) 25 \(\upmu\)m to connection with previous layers and a width of 204 \(\pm\) 11 \(\upmu\)m of the single track; however, the tracks in this region are not continuous. There are often areas where the material is not completely melted (unmelted powder particles occurred, Figure 4b--blue frame), which significantly affects both the continuity and the height of the track (32 \(\pm\) 14 \(\upmu\)m).
* B--The region with an average input energy \(E\) = 4.7-6.5 J/mm shows no cracks or pores around the weld (Figure 4b--green frame). The track depth is 218 \(\pm\) 21 \(\upmu\)m, the track height is 22 \(\pm\) 2 \(\upmu\)m and the track width is 215 \(\pm\) 6 \(\upmu\)m. Due to the relatively uniform dimensions of the track and the continuity of all tracks in this area, area B is evaluated as suitable for further testing.
* C--The region with a high value of the input energy value \(E\) = 6.5-12.7 J/mm shows an excessive depth of 338 \(\pm\) 81 \(\upmu\)m and a width of 233 \(\pm\) 20 \(\upmu\)m of single tracks. Metallographic analysis reveals the frequent occurrence of cracks and pores both in the deposit and in the surrounding material (Figure 4b--red frame), while the continuity of the deposit is not guaranteed.  
Based on the analyses and their comparison, 27 process parameters were evaluated as suitable for further testing (Figure 5). These are single tracks in the green area that show good cross-section shape and continuity. The balling effect, pores and cracking are not observed in them. These factors indicate a stable behavior of the weld tracks in their entire sample length. Similar results were obtained in the studies [17; 18; 19] for the magnesium alloys, where three areas that characterize almost identical defects in individual welds are also observed.  
Figure 4: (**a**) Map of process parameters for single-track test with defined areas and (**b**) representative single track for a specific area (metallographic image and 3D digital microscope image).