LAUSR

Abstract Selective laser melting (SLM) is a powder bed based additive manufacturing (AM) technology which is expected to fabricate parts with complex structure. Top surface roughness, a key quality index for SLM which strongly affects the lifetime of the recoater blade, changes due to the complex thermal history during SLM. This paper systematically studied the top surface roughness evolution during selective laser melting (SLM) of an Al-Cu alloy, which is widely employed in aerospace, automotive, and military industries. Single-track, single-layer, multi-layers, and cubic samples were fabricated. The fluid flow intensity affected both the roughness along the scanning direction and the roughness perpendicular to the scanning direction whereas the roughness perpendicular to the scanning direction was also affected by the overlapping of the molten pool. As the layer number increased, the increases in the fluid flow contributed to the spreading of the molten pool. However, the increases in the powder thickness harmed the top surface quality in both directions. Besides, the top surface roughness led to the fluctuation of the powder thickness in the subsequent layer, which resulted in the instability of the molten pool. As a result, for most of the tested processing conditions, an initial increase in the surface roughness was observed followed by a reduction before reaching saturation when the layer number increased. Larger hatch spacing weakened the effect of the thermal accumulations, which reduced the growth rate of the fluid flow intensity and limited the reduction in the surface roughness. This study can bring insights into the understanding of the top surface roughness evolution during SLM.