Electropolishing for AlSi10Mg Alloy Manufactured by Powder Bed Fusion

The irregular and highly rough surface of AlSi10Mg alloy parts fabricated by metal additive manufacturing technology can result in dimensional instability, poor surface quality and fluid turbulence. Therefore, post-treatments are needed to adjust the surface roughness and irregular surface morphology to satisfy industrial requirements. One of the most promising candidates is electropolishing, which dissolves the metal surface by electrochemical reactions. In this study, we investigated electropolishing processes to effectively reduce surface roughness while minimizing deformation of the shape and dimensions of additively manufactured AlSi10Mg parts. Sodium carbonate-trisodium phosphate (STP), perchloric acid-ethyl alcohol (PEA), choline chloride-ethylene glycol (CEG), and perchloric acid-ethylene glycol (PEG) solutions were employed. Then, electropolishing was conducted on AlSi10Mg specimens fabricated by Powder Bed Fusion (PBF). Changes in surface roughness and thickness with respect to the applied voltage and time were explored in the four types of electrolytes. The STP electrolyte was not suitable for electropolishing the AlSi10Mg alloy, while the other three types of electrolytes showed significant reduction in the surface roughness of the AlSi10Mg alloy. Surface roughness and the difference in roughness between up-skin and down-skin of additively manufactured AlSi10Mg were significantly reduced in the PEA electrolyte, but was accompanied by a serious reduction in thickness. In the CEG electrolyte, the dissolution rate during electropolishing was quite slow, taking more than 30 min. to achieve a surface roughness similar to PEA and PEG. However, the CEG solution had the advantage of minimizing dimensional change during electropolishing. The PEG solution was more chemically stable than PEA, since it contains less volatile ethylene glycol instead of highly volatile ethyl alcohol. In addition, the performance of the PEG solution was similar to that of the PEA solution for electropolishing additively manufactured AlSi10Mg alloy, so the PEG solution is considered more suitable for real applications for surface finishing.