On the role of laser in situ re-melting into pore elimination of Ti-6Al-4V components fabricated by selective laser melting

Laser re-melting is a potential technique performed during the selective laser melting (SLM) process to improve the quality of Ti-6Al-4V alloy, especially the density. In this study, a transient mesoscale model with a packed powder-bed is proposed by a simulation to reveal the pore elimination mechanism during the laser re-melting process intuitively. The effect of the laser re-melting on the temperature distribution, molten pool dynamics and resultant surface morphology is investigated. The results show that the re-melting scanning speed played an essential role in controlling the elimination effect on pores. A higher re-melting scanning speed does not eliminate most of the pores due to the limited energy input. In contrast, a lower re-melting scanning speed introduces new types of pores caused by the unstable molten pool. At an appropriate re-melting scanning speed, most of the pores are eliminated attributing to the sufficient spreading of the molten material due to the drag force of melt flow and the escape of the entrapped gas driven by thermocapillary force. The density and surface quality are determined experimentally. The relative density after laser re-melting at a scanning speed of 300 mm/s is improved 99.2% and the surface roughness reduced to Ra 1.9 mm. The simulation results can serve to provide guidance for parameter optimization and improve the density in high effectiveness and efficiency finally. (C) 2020 Published by Elsevier B.V.