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International Journal of Bioprinting Versatile pomelo peel-inspired structures

Figure 6. (A) BPPS component with a VF of 40%. (B) SEM of surface morphology at an intersection portion. (C) OM of the molten pool. (D) LSCM of the
3D surface topography. (E) SEM of the surface topography on the same surface. (F, G) Local SEM magnification detail of the holes.

droplets away, leading to the formation of spatters. Due to gravity and surface-tension, resulting in the formation of
the low boiling point (1170°C) and high saturated vapor dross . The length of the overhanging surface in Figure 6F
[51]
pressure of the Mg element, the Mg in the Al-Mg-Sc-Zr was significantly shorter than that in Figure 6G, and the
powders were easily prone to evaporation in the forming inclination angle of the overhanging surface in Figure 6F
process, leading to the recoil pressure [45-47] . This may was about 30°, which was obviously higher than the 0°
intensify the occurrence of spatters by further destroying inclination angle of the horizontal overhanging surface in
molten pool stability. The presence of Mg in the Al-Mg-Sc- Figure 6G. This not only contributed to a smaller volume of
Zr spatter particles led to more oxides, further weakening dross in Figure 6F than in Figure 6G, but also may lead to a
forming quality [48,49] . Moreover, Al-Mg-Sc-Zr alloys were smaller molten pool size of overhanging surface in Figure 6F
susceptible to hot cracking, and the average crack density compared with Figure 6G . In Figure 6F, the molten pool
[52]
improved with increasing Mg content . The presence of was mainly supported by the underlying solidified layers,
[50]
dross in the as-fabricated structures was attributed to the which possessed a higher thermal conductivity compared
lack of solid support at the overhanging surfaces, where to the loose powder. This allowed for the dissipation of heat
the powder bed was in direct contact with the molten pool. energy through the solidified layers, thereby accelerating
A significant amount of heat was accumulated under the the cooling rate and reducing the size of the molten pools.
combined influence of the laser beam and powder bed, However, in Figure 6G, the loose powder with lower
due to the lower thermal conductivity of the metal powder thermal conductivity was used as a support, which led
compared to the solid substrate material. Consequently, to the accumulation of heat energy at the laser exposure
the large molten pool above the powder bed caused the points and limited heat dissipation to the surrounding
molten pool to sink into the lower powder layer owing to regions. This resulted in a slower cooling rate that favored

Volume 9 Issue 6 (2023) 421 https://doi.org/10.36922/ijb.1011