On morphological surface features of the parts printed by selective laser melting (SLM)

Among the most popular additive manufacturing processes for metals, Powder bed fusion technology involves a layer by layer manufacturing approach utilizing a high power source, such as a laser or an electron beam, interacting with the metal powder on selected surfaces. Beam-powder interaction brings up a handful of phenomena affecting the quality of the final part in its volume and surface. In this study, different surface features generated by Selective Laser Melting of an Al-Si7-Mg alloy are investigated and interpreted based on their morphology, microstructure and hardness to improve the general understanding of defect genesis. Ballings, spatter particles and partially melted metal powders are distinguished by their morphology, size and microstructure. It is shown that these differences arise from different cooling rates during their generation. Ballings share the same microstructure with the bulk material both experiencing cooling in conduction mode. Spatters and partially melted powders show coarser microstructure driven by solidification mainly ruled by convection and radiation during their flight in the inert atmosphere of the process chamber.