Study on improving the inner surface quality of laser powder bed fusion-fabricated Hastelloy X by electrochemical polishing

Although laser powder bed fusion (LPBF) exhibits significant advantages in forming complex structures, its application in precision engineering is severely constrained by poor surface quality. This study aims to enhance the surface quality of LPBF-fabricated Hastelloy X through electrochemical polishing (ECP) using eco-friendly NaCl-aqueous and NaCl-ethylene glycol (NaCl-EG) electrolytes. The effects of electrolyte composition and current density on electrochemical dissolution behavior were experimentally investigated. ECP parameters were optimized through a comprehensive evaluation of surface roughness, material removal rate (MRR), and thickness reduction. The results indicate that the formation of a supersaturated salt film in the NaCl-EG electrolyte can suppress the uneven dissolution of carbides and matrix, but its improvement on roughness is limited. Compared with the NaCl-EG electrolyte, the NaCl-aqueous electrolyte achieves comparable surface roughness while increasing the MRR by at least 336.21 %. Furthermore, to address the challenge of polishing internal cavity surfaces of LPBF parts, a conformal tool electrode design strategy is proposed. Through this approach, partially melted particles on the inner surface of curved channels were successfully removed, reducing the surface roughness Sa from 7.16 to 11.91 μm to 1.63–1.95 μm. This extends the application potential of ECP for polishing complex internal channels in LPBF components.