Green electropolishing treatment of Ti6Al4V EBM parts: effect on morphology and corrosion resistance

The surface finish of additively manufactured (AM) parts is an important drawback of the new technologies. High roughness value could trigger corrosion phenomena and cracks, decreasing mechanical properties. Thus, post-processing treatments able to significantly reduce surface roughness are needed. This work aimed to study the effect on morphology and corrosion resistance of Ti6Al4V cylindrical parts produced by Electron Beam Melting technology and post finished with an environmentally friendly electropolishing (EP) treatment. An anodic levelling and brightening of the surface have been obtained modifying the treatment duration time. Morphological, metallographic and crystallographic analyses were performed. The corrosion behaviour was tested by potentiodynamic polarisation technique and electrochemical impedance spectroscopy analysis in a 0.6 M NaCl aqueous solution. A significant modification of the surface morphology was obtained after the EP treatment. A smoothing of the surface reduced the high peaks, but an orange-peel skin aspect was yet to show. The complete brightening of the surface has allowed to level the peaks and valleys. The electrochemical measurements revealed an important improvement of the corrosion resistance of the samples electropolished compared to the untreated and wrought samples, used as benchmark.