Improvement on surface quality of 316L stainless steel fabricated by laser powder bed fusion via electrochemical polishing in NaNO3 solution

Poor surface quality necessitates polishing of the parts manufactured by laser powder bed fusion (LPBF) to meet the requirements of use and service. Electrochemical polishing is one of the effective post-treatment methods to reduce the surface roughness. In this manuscript, polishing behavior of 316L stainless steel fabricated by LPBF in the eco-friendly NaNO3 solution was investigated. Different electrochemical tests including current efficiency, open circuit potential, and polarization behavior were carried out in this solution to investigate the influence of section orientation on the electrochemical polishing behavior. Test results indicated that electrochemical dissolution of the transverse section is more difficult than the longitudinal section because of the near-equiaxed dendrites and smaller grains diameter. The electrochemical polishing experiments showed that the polished surface presents hollowed-out retiform structure which is not conducive for the reduction of surface roughness value at low current density and the roughness value significantly decreases with the increase of total quantity of electricity at high current density. The weight loss of the transverse section is smaller than that of the longitudinal section at all current densities and electric charges, but the difference decreased with increasing current density. The electrochemical polishing at the current density of 40 A·cm−2 resulted in maximum reduction of the surface roughness with minimum weight loss. Finally, interior surfaces with longitudinal section and transverse section were polished successfully. The roughness values decreased from 17.3 and 18.3 μm to 2.4 and 2.6 μm, respectively. © 2022 The Society of Manufacturing Engineers