Multi-step electrochemical polishing of additively manufactured 316L stainless steel components

Zhu, Haitao and Tian, Yingtao and Rennie, Allan (2021) Multi-step electrochemical polishing of additively manufactured 316L stainless steel components. In: 41st International MATADOR Conference on Advanced Manufacturing, 2021-09-152021-09-17, University of Manchester.

Abstract

Powder bed fusion (PBF) additive manufacturing has been recognised as an enabling technology for the upcoming industrial revolution, however, it still suffers poor surface finish due to the partially melted powders attached to the outer surface[1,2]. Electrochemical polishing (EP) treatment on laser PBF (L-PBF) additive manufactured components has attracted significant attention in recent years with the drive towards quality improvement for functional use[3,4]. However, single electrolyte and polishing conditions (temperature, agitation, and potential) have limited polishing capability, meaning that it is difficult to obtain a fine surface (roughness Sa < 1 µm) from a rough one (roughness Sa > 10 µm) using a one-step EP process[4,5]. In this work, an investigation was undertaken into the possibility of sequentially using commercial electrolyte A2 (Struers) and NaCl-based electrolyte to polish L-PBF 316L stainless steel. The polarisation curve of the polishing system with different electrolytes was measured using an Autolab potentiostat, and the areal roughness (Sa), surface morphology, height distribution of as-built and polished surfaces were characterised using an Olympus LEXT microscope. The results indicate that the commercial electrolyte, polishing at ambient temperature and 40 V potential, can reduce the surface roughness from 13.454 µm to 1.411 µm with high efficiency. The NaCl-based electrolyte can continue reducing the Sa to 0.824 µm after 20 mins polishing at 6 V, but can cause pitting corrosions on the sample surface. Figure 1 show the surface morphology and physical surface before and after two-steps EP proceses, where a smooth and mirror-like surface is given.The proofof-assumption process can guide the subsequent adjustment of the electrolyte composition and concentration, having the potential to improve the surface quality of L-PBF components in a low-cost, easy-to-handle and damage-free process.