Influence of re-melting on surface roughness and porosity of AlSi10Mg parts fabricated by selective laser melting

Re-melting strategies with same and opposite directions to the first scanning routine were performed in AlSi10Mg parts by selective laser melting (SLM) technology. Surface roughness and porosity were investigated with confocal microscopy, micro-computed tomography (CT) and optical microscopy (OM). Re-melting facilitates the top surface finish with Ra value decreasing from 20.67 μm to 11.67 μm (same direction) and 10.87 μm (opposite direction), almost at the same level. On side surface there is a contradictory trend. Pores at SLM parts include spherical pores due to entrapped gases, irregular pores for lack of fusion, and keyhole pores because of laser movement. The former two kinds form in the central areas while the latter one is located at edges of melting tracks and exhibits different distribution at both sides. Re-melting allows more chances for pores (spherical and keyhole pores) to escape from the melting pools. Irregular pores decrease because smoother surface allows powders to be fully melted. Porosity decrease of both re-melting strategies in central areas of the SLM parts is almost on the same level while same directional re-melting exhibits superior ability to release porosity at edges because of the porosity distribution difference at the head and wake of the melting tracks.