318 DOI: 10.5545/sv-jme.2025.1381
Strojniški vestnik - Journal of Mechanical Engineering   ▪   VOL 71   ▪   NO 9-10   ▪  Y 2025 © The Authors. CC BY 4.0 Int. Licencee: SV-JME
Fusion Behavior of Pure Magnesium  
During Selective Laser Melting
Snehashis Pal
1,2 
 − Matjaž Finšgar
1
 − Jernej Vajda
3
 − Uroš Maver
3
 − Tomaž Brajlih
2
 − Nenad Gubeljak
2
 − Hanuma Reddy 
Tiyyagura
4
 − Igor Drstvenšek
2
1 Faculty of Chemistry and Chemical Engineering, University of Maribor, Slovenia
2 Faculty of Mechanical Engineering, University of Maribor, Slovenia
3 Faculty of Medicine, University of Maribor, Slovenia
4 Institute of Optoelectronics, Military University of Technology, Poland
 snehashis.pal@um.si.
Abstract This study examined the melting behavior and flowability of pure magnesium during selective laser melting. The potential to increase product density 
was also investigated. Various combinations of manufacturing parameters were considered. The laser power was gradually increased in different machine 
runs, with different scanning speeds for each run to vary the energy density (ED). The laser power ranged from 10 W to 75 W, and the scanning speed ranged 
from 100 mm/s to 800 mm/s. Lower laser powers resulted in poor melting, while higher laser powers produced better melting, with significant differences 
even when the ED was the same. High EDs between 3.50 J/mm² and 4.30 J/mm² led to a lack of melting at low laser power and to an unstable melt pool with 
significant spattering at high laser power. In contrast, moderate EDs in the range of 1.40 J/mm² to 2.90 J/mm² resulted in better density at high laser power. 
Higher scanning speeds helped to avoid the formation of a dense smog cloud and provided sufficient energy in a short time with the aid of higher laser power. 
Therefore, increasing both laser power and scanning speed improved melting performance and increased product density. The relative product density ranged 
from 80 % to 96.5 %. Reducing the layer thickness from 50 µm to 25 µm at a laser power of 40 W resulted in the formation of a well-formed melt pool in some 
areas and significant melt spattering in others, which led to a deterioration in density.
Keywords magnesium, melt pool, laser power, scanning speed, layer thickness, support structure, laser powder bed fusion
Highlights
 ▪ The fusion and pore formation of Mg during the selective laser melting process were investigated.
 ▪ Higher energy density (ED) may cause a lack of melting than lower ED due to the high smog formation.
 ▪ Higher scanning speed with higher laser power can avoid the smog cloud and perform better fusion.
 ▪ Reducing the layer thickness from 50 µm to 25 µm led to improved melting or massive spattering.
1 INTRODUCTION
Lightweight materials are essential for a range of applications, 
particularly in the automotive, aerospace, and electronics industries 
[1,2]. Reducing component weight can significantly improve 
overall performance and fuel efficiency [3]. In medical implants, 
especially for orthopedic applications, lightweight and biodegradable 
materials are vital [4,5]. Their lightness aids patient mobility, 
while biodegradability eliminates the need for a second surgery by 
allowing the implant to dissolve naturally in the body over time 
[6,7]. Magnesium (Mg) and its alloys are increasingly favored due to 
their properties, which meet these stringent requirements [8,9]. Mg 
is not only very light but also offers promising biodegradability and 
high biocompatibility [10,11]. Mg and Mg-alloys allow regulation 
of mechanical and corrosive properties, making them suitable 
for biomedical applications [12]. Furthermore, the mechanical 
properties of magnesium alloys are similar to those of bone, which is 
advantageous for orthopedic implants [13].
Despite these benefits, Mg has certain drawbacks, such as a 
lower melting point and higher reactivity to oxygen and moisture 
compared to other metals [14,15]. In various applications, proper 
handling and alloying are required to address these challenges 
[16,17]. Traditional manufacturing processes have limitations in this 
regard [18]. However, additive manufacturing (AM) processes offer 
much greater flexibility than conventional methods [19,20]. AM 
provides a protective environment for the manufacturing process and 
enables in-situ alloying, which is crucial when working with reactive 
materials like magnesium. It can transform complex computer-aided 
design (CAD) models into single or multiple products, supporting 
customization and intricate designs [21]. Selective laser melting 
(SLM), also known as laser powder bed fusion (LPBF), is one of 
the most popular metal AM technologies for manufacturing metal 
products [22]. 
SLM uses an inert gas to reduce the oxygen content in the process 
chamber, requiring a continuous flow of this gas to maintain the 
desired oxygen levels [23]. In this process, a laser melts the metal 
powder track by track and layer by layer [24,25]. The powder 
particles, typically with diameters of several dozen micrometers, 
build up the product layer by layer, with each layer usually being 20 
to 100 micrometers thick [26,27]. Rapid heating, melting, mixing, and 
solidification occur during the fusion process in SLM [28,29]. Using 
Mg in SLM presents significant challenges due to its low melting and 
boiling points and high flammability [30]. Rapid heating can lead 
to vaporization and combustion of Mg [2]. The small temperature 
difference between the melting and boiling points causes the melt 
pool to become unstable [31]. Additionally, the lightweight nature of 
Mg poses a problem as it can be easily carried away by inert gas, 
leading to material loss and the formation of smog that obstructs 
the laser’s operation [16]. These issues significantly affect the SLM 

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process, as material loss from the action zone and smog formation 
hinder the laser’s ability to function effectively [32].
To address these challenges, this study investigated the 
interactions between the laser and Mg, as well as the thermophysical 
properties of the melt pools and solidification during the SLM 
manufacturing process. There are several results in the literature 
on the density of Mg-alloys fabricated by SLM, but only a few 
studies focus on improving the density of pure Mg products. To our 
knowledge, and according to the report by Zeng et al. [33], there is 
no literature in which a relative density of 98 % was achieved for Mg 
parts produced by the SLM process. Therefore, in this study, the laser 
powers and scanning speeds were initially selected based on previous 
studies by Hu et al. [34] and Yang et al. [5]. Hu et al. [34] obtained 
the best relative height density of 96.13 % at a high energy density 
(ED) with a laser power and scanning speed of 90 W and 100 mm/s, 
respectively. On the other hand, Yang et al. [5] obtained useful results 
at laser powers and scanning speeds between 20 W to100 W and 
100 mm/s to 900 mm/s. Therefore, this study started with a scanning 
speed of 100 mm/s and a laser power of 10 W to keep the ED within 
a suitable range. Observations and analyses from this initial phase 
served as a basis for selecting different combinations of laser power 
and scanning speed to further investigate these phenomena and 
achieve better metallurgical properties.
This comprehensive approach aimed to optimize the SLM process 
for Mg, focusing on understanding and mitigating issues related 
to rapid heating, material loss, and smog formation. By exploring 
the effects of different combinations of laser powers and scanning 
speeds, the study sought to enhance the metallurgical properties of 
the produced components, paving the way for more effective use of 
Mg in SLM processes.
2 METHODS AND MATERIALS
2.1 Material
The samples were produced using pure magnesium powder from 
Nanografi Nano Technology (Germany), and the manufacturing 
characteristics were analyzed. The spherical powder particles ranged 
in size from 35 µm to 50 µm, with 5 % of the particles outside this 
range. After production by centrifugal atomization, the powder was 
packaged in an inert gas environment. The powder was unsealed to 
fill the filling chamber after the oxygen concentration was reduced to 
less than 0.01 % using argon.
2.2 Machining Chamber
The manufacturing behavior was studied using the Arrow Metal 
Printing – LMP200 SLM machine supplied by Dentas, Slovenia. 
Argon was used to reduce the oxygen content in the chamber and 
to keep the O2 level below 10 ppm during sample production. An 
O2 sensor monitored and automatically adjusted the O2 level by 
adding argon to the machining chamber when it exceeded 10 ppm. 
As magnesium is very light, the processing environment contained 
Mg powder and its fumes. To remove these, the chamber gases 
were circulated and passed through a filter at a flow rate of 280 L/
min. Before production runs began, the laser system was calibrated 
and a sensor monitored the current laser power. To maintain heat 
conduction and the material bond between the build plate and the 
support, the build plate was made of magnesium.
2.2 Support Structure
Several cubic test specimens measuring 6 mm × 6 mm × 6 mm were 
produced for each test condition. As magnesium has good thermal 
conductivity and a very high coefficient of thermal expansion 
(CTE of 26 × 10⁻⁶ K⁻¹), large thermal stresses and volume changes 
occur during the SLM process, causing the part to shrink, bend, and 
eventually self-destruct. Therefore, three types of support structures 
were used to hold the samples firmly. As shown in Fig. 1, fabrication 
of the specimens began with 2 mm high supports. In this study, a 
support structure typically used for the fabrication of stronger 
materials such as Ti-6Al-4V and AlSi10Mg was employed (see Fig. 
1a). This support beam has a smaller diameter neck that facilitates 
separation of the fabricated part from the support beams. Twenty-five 
(5 × 5) support beams were placed under the 6 mm × 6 mm base of 
the cubes.
Cubic sample
Cubic sample
Contour scanning
Core 
scanning
Support 
beams
Support beams
Y
Z
X
Z
X
Y
Z
X
Y
Z
X
a)
c)
b)
d)
Neck
Y
Fig. 1. Supports and scanning patterns; a) support beams with necks, b) cylindrical support 
beams, c) samples with different orientations, and d) scanning pattern
In this study, the effects of laser parameters at different layer 
thicknesses and their melting properties with existing supports were 
investigated. The manufacturing process is costly due to the use of 
argon and the risk that the failure of a single sample can cause the 
failure of several samples in the same build. If one sample fails, it can 
hinder the movement of the recoater, requiring the entire process to be 
stopped and restarted from the beginning. This research aimed to find 
a solution to the manufacturing problem when supports are present, 
as supports are often necessary for the actual production of the part. It 
is easier to remove samples from the build plate and prepare a smooth 
build plate again than to produce samples without support. Therefore, 
in addition to analyzing melting properties, the effect of support, 
including different support designs, is also examined and reported in 
this article.
Since the support beam with a neck was not able to prevent the 
piece from bending, cylindrical beams were used, as shown in Fig. 
1b. The beams had diameters of 0.4 mm, with a 6 × 6 array of beams 
under the 6 mm × 6 mm base of the cubes. Although this support 
structure was sufficient to prevent most specimens from bending, 
some specimens still bent or detached from the supports after a few 
layers were fabricated.
As some specimens bent and moved away from the cylindrical 
support beams, the orientation of the specimens was changed, as 
shown in Fig. 1c. However, this orientation increased the bottom 
surface area, leading to a more uneven surface at the start of 

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fabrication. Although this support structure held the part firmly in 
place, the uneven shape and surface formation of the specimens led 
to the decision in this study to align the cubic specimens so that their 
base surface remained horizontal. Ultimately, cylindrical support 
beams are best suited to hold the part when the base of a cubic sample 
is horizontal.
2.3 Scanning Patterns
The scanning pattern consisted of four successive contours and 
a checkerboard core scanning pattern, as shown in Fig. 1d. As the 
area to be scanned for each layer was approximately 6 mm × 6 mm, 
four sub-squares were scanned in a checkerboard arrangement. 
Each square was scanned with multiple laser scan tracks, with a 50 
% overlap between tracks. The diameter of the laser spot was 70 
µm; therefore, the hatch spacing was 35 µm. A larger hatch spacing 
resulted in a lower product density. Two consecutive scanning 
tracks were scanned in opposite directions. The scanning tracks 
were rotated by 60° for successive layers during manufacture. The 
Yb:glass fiber laser was always focused perpendicular to the powder 
bed using a telecentric F-theta lens. The telecentric F-theta lens 
combines the flat-field focusing of a conventional F-theta lens with 
the vertical positioning of a telecentric lens for object space, ensuring 
the emerging laser beam is always perpendicular to the target surface 
across the entire scan field.
Since the diameter of the laser spot is 70 µm and the laser moves 
at high speed during scanning, which is typical for the SLM process, 
the space between successive hatches must be considered when 
measuring the ED. Therefore, the ED [J/mm²] can be defined as 
defined in Eq. (1), where P, v, and h denote the laser power [W], 
scanning speed [mm/s], and hatch distance [mm], respectively.
ED
P
vh


. (1)
2.4 Manufacturing Parameters
Laser power, scanning speed, and layer thickness were varied to 
investigate their effects on the fusion of pure Mg and the potential 
for sample fabrication. As Mg has low melting and boiling points, 
the experiments began with low laser power combined with four 
different scanning speeds. Thus, the ED varied with scanning speed, 
while laser power remained constant. Subsequently, the laser power 
was gradually increased from 10 W to 40 W, as shown in Table 1, 
and combined with four different scanning speeds. Consequently, 
the ED also changed, ranging from 0.95 J/mm² to 4.29 J/mm². The 
ED played a significant role in the melting process of Mg and was 
therefore considered an important fabrication parameter. The hatch 
distance and layer thickness were kept constant in the initial stage 
of the study at 35 µm and 50 µm, respectively. Three samples were 
fabricated for each testing condition.
The most important factor in determining the useful range of 
parameters is the density of the samples. The proportion of smog 
formation is also considered. With some parameters, a higher 
density product can be achieved, but smog formation can cause 
deterioration in melting at higher scan ranges. A high level of smog 
in the processing chamber causes the laser rays to be reflected more 
strongly by the airborne powder particles. Increased vapor also 
absorbs more of the laser energy, which ultimately prevents the laser 
beams from reaching the powder bed.
After observing and analyzing the fusion behavior and density 
results in the first step of the study, the laser power was increased in 
the second step while maintaining the scanning speeds listed in Table 
2. Since higher laser power led to better fusion results and product 
densities, higher laser powers were selected to analyze their effects. 
However, scanning speed can also have a significant influence. 
Therefore, in the second step of the study, the most effective scanning 
speeds were combined with the increased laser powers. Although 
scanning speeds of 400 mm/s, 600 mm/s, and 800 mm/s at 40 W 
resulted in good densities, 400 mm/s, 500 mm/s, and 600 mm/s were 
chosen at laser powers of 55 W, 65 W, and 75 W, respectively, due to 
the high ED induction.
Table 1. Manufacturing parameters in the first step of the study
Sample 
number
Laser 
power
[W]
Scanning 
speed
[mm/s]
Hatch 
spacing
[mm]
Layer 
thickness
[mm]
ED
[J/mm
2
]
Product 
density 
[g/cm
3
]
Relative 
density 
[%]
I-1 10 100 0.035 0.050 2.86 - -
I-2 10 200 0.035 0.050 1.43 - -
I-3 10 300 0.035 0.050 0.95 - -
I-4 10 400 0.035 0.050 0.71 - -
I-5 20 150 0.035 0.050 3.81 - -
I-6 20 200 0.035 0.050 2.86 - -
I-7 20 300 0.035 0.050 1.90 - -
I-8 20 400 0.035 0.050 1.43 - -
I-9 30 200 0.035 0.050 4.29 - -
I-10 30 300 0.035 0.050 2.86 - -
I-11 30 400 0.035 0.050 2.14 - -
I-12 30 500 0.035 0.050 1.71 - -
I-13 40 300 0.035 0.050 3.81 - -
I-14 40 400 0.035 0.050 2.86 1.65 94.91
I-15 40 600 0.035 0.050 1.90 1.61 92.68
I-16 40 800 0.035 0.050 1.43 1.39 80.18
Table 2. Manufacturing parameters in the second step of the study
Sample 
number
Laser 
power
[W]
Scanning 
speed
[mm/s]
Hatch 
spacing
[mm]
Layer 
thickness
[mm]
ED
[J/mm
2
]
Product 
density 
[g/cm
3
]
Relative 
density 
[%]
II-1 55 400 0.035 0.050 3.93 - -
II-2 65 500 0.035 0.050 3.71 - -
II-3 75 600 0.035 0.050 3.57 - -
In the second step of the study, a large amount of smoke and 
smog was observed when using high laser power and relatively 
low scanning speed. The lower scanning speed resulted in a high 
ED. Consequently, the samples were not produced satisfactorily. 
Therefore, higher scanning speeds were used in the third step of the 
study to reduce the ED, while the laser power remained the same as 
in the previous step. These parameters are listed in Table 3.
Table 3. Manufacturing parameters in the third step of the study
Sample 
number
Laser 
power
[W]
Scanning 
speed
[mm/s]
Hatch 
spacing
[mm]
Layer 
thickness
[mm]
ED
[J/mm
2
]
Product 
density 
[g/cm
3
]
Relative 
density 
[%]
III-1 55 700 0.035 0.050 2.24 1.65 94.96
III-2 65 700 0.035 0.050 2.65 1.67 95.95
III-3 75 750 0.035 0.050 2.86 1.68 96.51
Higher laser powers and their adjustable scanning speeds did 
not yield improved results. Therefore, the optimal laser power and 
scanning speeds identified in previous studies were used in the fourth 
step of the study, where a lower layer thickness was selected. As 
800 mm/s at a laser power of 40 W resulted in low product density, 
a reduced scanning speed of 700 mm/s was chosen for this step, 
as shown in Table 4. These parameters were selected to observe 

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the effects of different layer thicknesses and the laser absorption 
characteristics of the powder bed and its top surface.
Table 4. Manufacturing parameters in the fourth step of the study
Sample 
number
Laser 
power
[W]
Scanning 
speed
[mm/s]
Hatch 
spacing
[mm]
Layer 
thickness
[mm]
ED
[J/mm
2
]
Product 
density 
[g/cm
3
]
Relative 
density 
[%]
IV-1 40 400 0.035 0.025 2.86 1.54 88.66
IV-2 40 500 0.035 0.025 2.29 1.55 89.34
IV-3 40 600 0.035 0.025 1.90 1.55 89.16
IV-4 40 700 0.035 0.025 1.63 1.55 89.04
2.5 Analysis of Product Properties
The densities were measured on samples that were well fused and 
capable of providing accurate results. When ethanol was used 
as a liquid, Archimedes’ principle was applied to determine the 
densities. The weight of each sample was measured in air and then 
while immersed in the liquid, with an error margin of ±0.0001 g, to 
calculate the density. The measurement was performed six times to 
improve the accuracy of the results. Three-dimensional images of the 
solid and pore zones of the materials were obtained using a ZEISS 
Xradia 620 Versa nano-computed tomography (nano-CT) scanner 
(Germany). The porosity of the samples was also observed with a 
scanning electron microscope (SEM) from Carl Zeiss (Germany), 
after the samples had been ground 1 mm from the vertical surface and 
then polished.
3 RESULTS AND DISCUSSION
3.1 Effect of Lower Laser Powers
The powder particles were not well fused at the low laser powers of 
10 W and 20 W, even though the energy density was sufficient at 
lower scanning speeds. At a laser power of 30 W, the particles were 
adequately fused at scanning speeds of 200 mm/s and 300 mm/s; 
however, some layers were distorted and delaminated, as shown in 
Fig. 2. With a further increase in scanning speed to 400 mm/s and 
500 mm/s at 30 W laser power, fusion did not occur. Therefore, the 
samples fabricated using 10 W to 30 W laser power were unsuitable 
for further studies such as density and porosity measurements.
There are several possible reasons for these results with 10 W 
to 30 W laser powers. The main reasons may be the low absorption 
of laser rays by the powder bed and the obstruction of the rays by 
the dense smog cloud. In laser–material interaction, most laser rays 
are typically reflected from the top surface of the powder layer [35]. 
Furthermore, magnesium is a shiny grey metal, which increases this 
reflection. The process is illustrated by the schematic diagram in 
Fig. 3a. Therefore, although the power was sufficient, only a small 
fraction of the laser rays was absorbed by the powder bed. After 
entering the powder bed, the rays are reflected multiple times within 
it [36]. The reflection and absorption are shown schematically in Fig. 
3b. However, the low laser power of 10 W to 20 W was not sufficient 
to heat and melt the powder particles.
As the laser power increased to 30 W, the laser rays were sufficient 
to raise the temperature of the powder bed above 650 °C and melt 
the powder. Scanning speeds of 200 mm/s and 300 mm/s at 30 W 
laser power allowed enough time to melt the particles. Although 
melting occurred due to the greater number of laser rays penetrating 
the powder layer, as shown in Fig. 3b, the melt pool did not form 
sufficiently to agglomerate the layers and scan tracks. Therefore, it 
can be assumed that some areas were melted while others were not. 
As a result, some plate formation and shifting were observed, as 
shown in Fig. 2. The plates were shifted by the recoater movement. 
With a further increase in scanning speed, sintering among the powder 
particles occurred. Consequently, soft cubic samples were formed at 
scanning speeds of 400 mm/s and 500 mm/s. These were destroyed 
during powder removal and detachment from the support structures. 
Eventually, an increase in scanning speed resulted in better melting.
Powder spreading direction
Departed part
Scan 
areas
Fig. 2. A photograph during scanning
A large amount of smog was observed in the processing chamber 
during laser scanning. Although the smog was not detected by any 
sensor, only the observations made during production are discussed 
here. Smoke and particle detectors could provide more quantitative 
results and better control over the melting process. Therefore, it can 
be assumed that this smog also affects the amount of laser power 
reaching the powder bed. The smog formed from evaporated and 
combusted materials and powder particles [37,38]. As Mg has a low 
melting point and is prone to oxidation, it evaporated and burnt 
significantly. In addition, due to the cyclone effect above the action 
zone and the significantly low mass of Mg, the powder particles 
were easily lifted and mixed into the cyclone, as schematically 
represented in Fig. 3d. Moreover, powder explosions occurred in the 
powdered zone due to the expansion of inter-particle inert gas [37]. 
Consequently, a dense cloud formed above the action zone, with a 
high probability of impeding the laser from reaching the powder bed. 
At this point, higher laser power could escape this smog cloud. As a 
result, higher scanning speeds led to the formation of soft cubes at 
30 W laser power.
A further increase in laser power to 40 W enabled the fabrication 
of some samples, whereas the lowest scanning speed of 300 mm/s did 
not produce any samples. At higher scanning speeds, however, some 
good cubes were formed with measurable densities. The laser power 
of 40 W delivered sufficient energy into the powder layer for good 
fusion to begin, as shown in Fig. 3c. As discussed, the lower scanning 
speed did not allow sufficient time to move forward to avoid the 
smog cloud. When the scanning speed increased to 400 mm/s, better 
melting occurred. Gradually increasing the scanning speed to 500 
mm/s and 600 mm/s resulted in better melting than at 300 mm/s, even 
though the energy density was higher at the lower scanning speed. 

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particles in the subsequent layer at that location, resulting in a higher 
powder layer height. Consequently, the subsequent layer could not 
fuse well or form a uniform melt pool, as shown in the SEM images 
in Fig. 4. This led to insufficient bonding with the previous layer and 
the formation of a pore. To observe this phenomenon, the sample 
fabricated with 60 W laser power, 700 mm/s scanning speed, 0.035 
mm hatch spacing, and 0.050 mm layer thickness is shown in Fig. 4.
Figure 4 shows that some layers are affected by the phenomena 
described above. These layers are significantly influenced by highly 
irregular melt pool and pore formation. Several of these layers are 
marked by two parallel lines in Fig. 4. These pores also influenced 
Preceding layer
Penetrated ray
Powder particle
Scanning layer
Top surface
Reflecting ray
Laser beam
No fusion occurrence
a)
Preceding layer
Penetrated ray
Powder particle
Scanning layer
Top surface
Reflecting ray
Laser beam
Partial fusion occurrence
b)
Preceding layer
Powder particle
Scanning layer
Top surface
Reflecting ray
Laser beam
Melt pool occurrence c)
Heat affected zone
d)
Fig. 3. Fusion characteristics; a) fusion with low laser power, b) fusion with medium laser power, c) melt pool formation with high laser power, and d) smog formation
However, the product density decreased at higher scanning speeds 
from 400 mm/s to 800 mm/s due to the significantly lower energy 
density.
There is also a possibility of high ED formation in the melt pool 
at a low scanning speed of 300 mm/s, which may cause instability in 
the melt pools and result in melt spattering [39], as shown in Fig. 3d. 
Additionally, trapped gas bubbles and metal vapor caused explosions 
in the melt pools [40]. This resulted in significant metal splashes, 
causing the action zones to lose material. Conversely, the splashed 
material fell onto the scan area and created some bumpy zones. 
The loss of material in one area led to an accumulation of powder 
200 µm 40 µm a) b)
50 µm
A layer
50 µm (a layer)
50 µm
Connected 
pore between 
layers
Connected pores in a layer
Pores in a layer
Connected pores
Balling
Fig. 4. Common pore characteristics of the samples; a) overall pore formation, with some layers exhibiting high pore content,  
and b) higher magnification image of the pores in a layer with high pore content

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pore formation in subsequent layers. Some pores extended across 
several layers, forming connected pores between them. Additionally, 
part of the last scanned layer may exhibit uneven areas due to the 
deposition of spattered particles and the formation of spheres caused 
by the balling effect, as shown in Fig. 4a. As a result, this part had to 
be removed and displaced from the specific manufacturing location 
by the recoater movement. Ultimately, the combination of 40 W laser 
power and 300 mm/s scanning speed produced disorganized samples. 
Therefore, density was not determined for samples produced with 
these manufacturing parameters.
Comparing the effects of laser power between samples I-5 and 
I-13, it can be seen that despite the same high ED of 3.81 J/mm², 
no melting occurs in I-5, while high temperatures and significant 
spattering of molten metal occur in I-13. The heating rate (scanning 
speed) played an important role in the fusion mechanisms. Since the 
ED was very high, there is a high probability that strong vaporization 
began at the top of the powder bed. After the onset of vaporization, 
the penetration of the laser beam decreased due to obstruction by the 
vapor cloud, resulting in insufficient melting of sample I-5. When the 
scanning speed was increased at the same ED, the laser left the action 
zone after supplying higher energy in less time. This allowed for a 
higher probability of melting and a greater energy content in the melt 
pools. Therefore, a high ED led to high temperatures and a reduction 
in the viscosity of the melt pools, resulting in spattering of molten 
metal in sample I-13. To investigate these phenomena in more detail, 
the part with the lowest density was analyzed using a nano-CT scan 
and explained with the help of Fig. 5.
Comparing samples I-1, I-6, I-10, and I-14, which have the same 
ED (2.86 J/mm²) but different laser powers (10 W, 20 W, 30 W, and 
40 W), it can be observed that while 10 W to 30 W could not produce 
a good sample, 40 W resulted in the highest density. Even the 
significantly low ED of 1.43 J/mm² was sufficient to fabricate a good 
sample with a laser power of 40 W. In contrast, the same ED of 1.43 
J/mm² and higher EDs could not produce a sample when the laser 
powers were below 40 W. It is therefore clear that lower laser powers 
perform worse due to insufficient absorption of the laser rays by the 
powder bed. Here, a good sample refers to one that is well formed 
with a cubic structure and whose product density can be measured, 
while other samples are not well formed or fused and do not form a 
cube.
Since I-16 has the lowest product density among the well-formed 
samples, this research has taken this sample into account to study the 
formation and behavior of melt pools. To investigate the effects of the 
laser parameters and the formation of melt pools, the product with 
the lowest density was selected. This can provide an indication of the 
melting mechanism, even if the product was not well manufactured. 
Therefore, this sample was analyzed with nano-CT scanning and is 
shown in Fig. 5. The light grey and dark grey areas represent the 
solid and porous regions, respectively. Successive images are taken at 
intervals of 5 µm through the vertical direction, which is the build-up 
direction of the sample. Examining these images, it can be seen that 
the pores are interconnected. It is also clear that they have irregular 
shapes, and their sizes vary accordingly. 
Based on the pores of sample I-16 and the consolidated patches, 
certain melting characteristics of this sample can be determined. This 
indicates that the track was not laid down evenly throughout. There 
are occasional fluctuations in the melt pools of the track [25]. The 
pores also varied in size in each direction. Consequently, the density 
varied both between the layers and between the tracks. For example, 
the three strips -1, -2, and -3 marked in Fig. 5 can be considered to 
investigate their melting properties. The width of the stripes is 100 µm, 
and these stripes can be visualized in all images. However, the region 
in strip-1 has a higher density than the region in strip-3, indicating 
that fusion was better in some areas, while in others less material 
was obtained, and pores were formed. Although this is one possible 
cause for such melting properties and the formation of porosity, other 
factors may also contribute. It is an inherent characteristic of SLM 
that some action zones melt well and form a good melt pool, while 
others may suffer from lack of melting or spattering of molten metal. 
This can also be influenced by the different size distribution of the 
powder particles and the varying powder packing from place to place.
The shape of a melt pool can be understood from any dot (with 
a small surrounding area) placed on a figure panel in Fig. 5. For 
example, a red dot is placed on each panel representing the same 
scan area. Since the following images represent the 5 µm above in 
the build direction, the same area or location shows the variation 
of the melt pool in the vertical direction. However, the red dot 
originated from a pore area that eventually filled with material as 
it moved in the vertical direction. Similarly, one can visualize and 
examine the pore and solid zones, which provides insight into the 
melting properties. As mentioned earlier, these porosities result from 
evaporation, combustion, material loss, material spattering, and laser 
shielding by smog [32]. On the other hand, a large number of round 
patches of solid material in the cross-section of the sample match the 
section size of the powder particles and could indeed be unmelted 
powder particles. Better stabilization of the melt pools is required to 
maximize density. A higher laser power may be preferable to achieve 
the desired melt pool properties.
100 µm
Metal
Pore
Dot
Strip-1
Strip-3
Strip-2
100 µm 100 µm 100 µm 100 µm
100 µm 100 µm 100 µm 100 µm 100 µm
Fig. 5. Nano-CT scanned images showing pores and metallic zones 

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3.2 Effects of High Laser Powers
As the increase in laser power supported an improved fusion process 
during manufacturing and resulted in higher product density, the 
laser power was further increased in the second stage of the study. 
However, since scanning speed significantly affects the fusion 
process, the speeds were selected based on findings from the previous 
study. High ED also led to increased fume and smog generation 
in the manufacturing chamber. Therefore, to maintain the ED, a 
scanning speed of 400 mm/s to 600 mm/s was chosen for the second 
stage. It was observed that higher laser power produced better melt 
pools; for example, 40 W was more effective than 30 W, although 
both generated considerable smog. Additionally, although increased 
vaporization from the top of the powder bed is possible, the resulting 
vapor also impedes effective laser penetration. Therefore, higher 
laser power at the outset can lead to excessive energy deposition. 
The proportion of laser rays reaching the powder bed decreases as 
vaporization begins. Accordingly, higher laser power can result 
in improved melt pool formation. With this in mind, a higher laser 
power was selected for further investigation.
The densities of some samples in the second stage are lower 
than those prepared with 40 W laser power for samples I-14 to I-16, 
and some are not well fabricated. Therefore, the densities of these 
samples cannot be reported. The second stage of the experiment 
showed strong smog formation in the fabrication chamber. The smog 
reflected the laser rays even above the intended scanning layer. As a 
result, insufficient energy was delivered in many areas, which also 
contributed to a high level of pore formation. However, due to the 
high laser power, a significant amount of Mg was burnt and vaporized. 
As previously mentioned, this also created a cyclone above the 
powder bed, which drew in many Mg powder particles and formed a 
protective shield. This shield prevented the laser from penetrating the 
powder layer. Many sparks were observed with the increased number 
of powder particles in the cyclone, as shown in Fig. 3d. It can be 
assumed that the laser struck the particles and caused the sparks. As 
a result, the amount of melting was insufficient to form a good melt 
pool. Additionally, the formation of smoke, the vaporization of the 
metal, and the removal of powder particles caused metal loss from 
the action zone [38]. Consequently, the density decreased, and the 
samples were damaged during production.
3.3 Effects of High Laser Powers with Higher Scanning Speeds
Since lower scanning speeds combined with higher laser powers 
resulted in a high ED, the scanning speed was increased in the third 
step of the study. As a result, the samples were well prepared, as 
shown in Fig. 6a. Additionally, the densities of the samples increased 
in this step, as shown in Fig. 6b. When the laser power was lowest at 
55 W (in sample III-1) in the third step, the resulting density was low 
(1.62 g/cm³). However, when the laser power was increased to 65 W 
and the scanning speed was kept constant at 700 mm/s, the resulting 
density in sample III-2 increased to 1.63 g/cm³. In sample III-3, 
which was fabricated with a higher laser power (75 W) and scanning 
speed (750 mm/s), the density was even higher.
Since a high ED occurred in sample II-1 due to the lower 
scanning speed compared to sample III-3, a large amount of smog 
was generated. When the scanning speed was increased at the same 
laser power, the ED decreased, and fusion and melt pool formation 
improved. This resulted in successful sample fabrication with high 
density. The smog and fumes were much lower compared to the 
1.40
1.42
1.44
1.46
1.48
1.50
1.52
1.54
1.56
1.58
1.60
1.62
1.64
1.66
1.68
1.70
1.72
1.74
Density [g/cm
3
] Speed [mm/s]   700 700 750
Power [W]          55 65 75 b)
a)
Build-tray Cubic samples
III-1 III-2 III-3
Sample Sample Sample
Fig. 6. Samples and density results in the third step of the study; a) photograph of the cubic samples on the build tray; and b) densities
200 µm a) b) 200 µm
Fig. 7. Difference in porosity; a) sample fabricated with a laser power of 70 W and a scanning speed of 750 mm/s;  
and b) sample fabricated with a laser power of 80 W and a scanning speed of 800 mm/s

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1.40
1.42
1.44
1.46
1.48
1.50
1.52
1.54
1.56
1.58
1.60
1.62
1.64
1.66
1.68
1.70
1.72
1.74
Density [g/cm
3
]
a)
Speed [mm/s] 400 500      600       700
Power [W]       40             40                 40                40
IV-1 IV-2 IV-3 IV-4
Sample Sample Sample Sample
100 µm
100 µm
100 µm
b)
c) d)
Metal
Pore
Edge of the sample
Pore
Metal
Metal
Pore
Fig. 8. Densities and porosities of the sample fabricated in the fourth step of the study; a) densities; b) low-porosity site; c) medium-porosity site, and d) high-porosity site
second step of the study. However, increasing the laser power from 
55 W to 65 W improved the quality of the melt pools, as indicated by 
the increase in density. This was confirmed by SEM examinations of 
other samples produced with a laser power of 70 W and a scanning 
speed of 750 mm/s, and with a laser power of 80 W and a scanning 
speed of 800 mm/s, while keeping the other parameters constant. 
The SEM images of the vertical cross-sections of these samples are 
shown in Fig. 7.
The SEM images in Fig. 7 clearly show that the quality of the melt 
pools improved as the laser power increased, reducing gaps between 
tracks and decreasing pores. Therefore, higher laser power combined 
with a slightly higher scanning speed helped to melt the powder more 
effectively and form a better melt pool in sample III-3 compared to 
sample II-3. As the EDs in the third step of the study were within an 
appropriate range, less fume and smog were observed.
3.4 Effect in Decreasing the Layer Thickness
By reducing the layer thickness to 25 µm, the density results were 
slightly lower than those for samples with a higher layer thickness 
of 50 µm. In the fourth step of the study, the densities were almost 
the same for all samples, as shown in Fig. 8. Smog formation was 
almost identical to that of samples fabricated with the same laser 
power (40 W) in the first step of the study, except at the lowest 
scanning speed (300 mm/s). As the scanning speed in the fourth 
step was within the optimal range, smog formation was low. This 
was due to the uniform effects on the top of the powder layer. As 
the layer thickness decreased, the total energy input to the powder 
layer increased, which also increased the thermal energy in the melt 
pools. This led to a lower viscosity of the melt, resulting in instability 
of the melt pools and spattering of molten metal [39]. Therefore, the 
action zone lost more material than the previous samples produced at 
50 µm. As a result, the overall density of the samples decreased.
The melting mechanism and the effects of smog can be visualized 
by examining pore formation in one of the samples, which was 
produced with a layer thickness of 25 µm. Fig. 8b to d shows the 
nano-CT images of sample IV-1, which are vertical cross-sectional 
planes arranged sequentially at intervals of several hundred 
micrometers. The proportion of pores is visible in these images, 
indicating that they contain a low, medium, and high proportion of 
pores, respectively. The density therefore varied significantly within 
the same scanning layer. In some areas, there was good fusion and 
stabilized melt pool formation, while in others there was low laser 
energy or an unstable melt pool with high thermal energy. The smog 
obstructed the laser, resulting in low energy deposition on the powder 
bed. As the energy decreased, evaporation also decreased, causing the 
laser to fall onto the powder bed. When the melt pools accumulate 
higher energy, the viscosity of the melt may decrease, which can 
lead to destabilization of the melt pools. This can eventually result in 
spattering and material loss.

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4 CONCLUSIONS
This article investigates and describes the melting properties 
of magnesium during selective laser melting. The following 
characteristics are observed and demonstrated using density 
measurements, as well as images from nano-CT scans and SEM of 
the samples.
Low laser power is insufficient to melt the powder particles and 
connect the layers and tracks, even when the ED is the same as with 
higher laser power. At the same ED, the scanning speed must be 
increased, which is the main advantage in melting the powder and 
forming a melt pool. This is due to the ability to avoid the smog 
clouds formed by the vaporization of materials at the top of the 
powder bed. The forward movement after the penetration of sufficient 
energy within a short time results in better fusion. A slower scanning 
speed with lower power does not provide enough energy before a 
dense cloud forms and prevents the laser beams from reaching the 
powder bed.
A high ED causes melt pool instability due to the explosion of 
melt pools and spattering, resulting in insufficient material and 
the formation of voids or the inability to form a product. Although 
reducing the layer thickness enables better melting in some areas, in 
other areas there is instability in the melt pools, which also worsens 
the overall density.
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Acknowledgements The authors thank the Slovenian Research Agency 
for funding the research (Grant Nos. GC-0007 P2-0118, P2-0137, P2-0157 
J1-2470, J1-2471, J1-4416, J7-4636, J7-50226, J7-50227, J1-60015 and J7-
60120). The project is co-financed by the Republic of Slovenia, the Ministry of 
Education, Science and Sport, and the European Union through the European 
Regional Development Fund.
Received 2025-05-09, revised 2025-09-16, 2025-10-13, accepted 2025-
10-13 as Original scientific paper 1.01.
Data availability The data that support the findings of this study are 
available from the corresponding author upon reasonable request.
Author contribution Snehashis Pal: Conceptualization, Methodology, 
Formal analysis, Investigation, Visualization, Writing—original draft; Matjaž 
Finšgar: Formal analysis, Investigation, Writing—review and editing; 
Jernej Vajda: Formal analysis, Investigation; Uroš Maver: Formal analysis, 
Investigation; Tomaž Brajlih: Formal analysis, Investigation; Nenad Gubeljak: 
Formal analysis, Investigation; Hanuma Reddy Tiyyagura: Conceptualization, 
Formal analysis, Investigation, Writing—review and editing, Supervision; Igor 
Drstvenšek: Conceptualization, Formal analysis, Investigation, Writing—review 
and editing, Supervision.
Proces spajanja čistega magnezija  
med selektivnim laserskim taljenjem
Abstract V raziskavi smo proučevali obnašanje taljenja čistega magnezija 
in pretočnost njegove taline med selektvinim laserskim taljenjem. Raziskali 
smo tudi vpliv različnih kombinacij procesnih parametrov na povečanje 
gostote izdelka. Moč laserja smo postopoma povečevali in pri tem spreminjali 
hitrosti skeniranja za vsako serijo izdelkov, s čimer smo vplivali na vnos 
energije v talilni process (ED). Moč laserja se je gibala od 10 W do 75 W, 
hitrost skeniranja pa od 100 mm/s do 800 mm/s. Z nižjimi močmi laserja 
nismo dosegli zadovoljivega taljenja materiala, medtem ko so višje moči 
laserja povzročile boljše taljenje, z znatnimi razlikami tudi pri enakih vnosih 
energije - ED. Visoka energijska gostota - ED med 3,50 J/mm² in 4,30 J/mm² 
je povzročila pomanjkljivo taljenje pri nizki moči laserja oziroma nestabilen 
talilni bazen z znatnim pršenjem materiala pri visoki moči laserja. Nasprotno 
pa so zmerne ED v območju od 1,40 J/mm² do 2,90 J/mm² povzročile boljšo 
gostoto pri visoki moči laserja. Višje hitrosti skeniranja so pomagale preprečiti 
nastanek gostega oblaka smoga in s pomočjo večje laserske moči zagotovile 
zadostno energijo v kratkem času. Zato je povečanje tako laserske moči kot 
hitrosti skeniranja izboljšalo učinkovitost taljenja in povečalo gostoto vzorca. 
Relativna gostota vzorcev se je gibala od 80 % do 96,5 %. Zmanjšanje 
debeline plasti s 50 µm na 25 µm pri laserski moči 40 W je na nekaterih 
območjih povzročilo nastanek dobro oblikovanega bazena taline, na drugih 
pa znatno brizganje taline, kar je povzročilo poslabšanje gostote.
Ključne besede magnezij, talilni bazen, moč laserja, hitrost skeniranja, 
debelina plasti, nosilna struktura, lasersko taljenje praškastega sloja