Surface passivation and brightening of titanium-based AM materials using a robotic electrochemical mechanical polishing system

Since titanium alloy parts produced by the additive manufacturing (AM) method often have rough and complex curved surfaces, surface polishing is relatively difficult and time-consuming. Therefore, this study integrates a robotic arm into the electrochemical mechanical polishing (ECMP) process of AM titanium alloys to improve its surface quality and corrosion resistance, and to meet the needs of automated polishing. The parameters and process for ECMP with a multi-axis robotic arm were determined, resulting in an automated ECMP system that could effectively and rapidly reduce the roughness of a curved AM surface. The performance of system was tested. With a novel bias grinding brush head and jet electrolyte flow, the surface roughness of the AM titanium can be greatly improved from Ra 16 µm to Ra 0.227 µm. Moreover, microstructural observation revealed that a dense passivation film approximately 10 nm in thickness was formed on the surface after polishing, improving corrosion resistance of the material. Electrochemical impedance spectroscopy investigation also revealed that the absolute impedance (|Z|_f=0.01 Hz) of the material was promoted from 9788 Ω*cm² to 27292 Ω*cm² after ECMP.