An Investigation into the Deterioration of Copper Surface Quality in Plasma Electrolytic Polishing

Abstract

Plasma electrolytic polishing (PEP) is widely used in the finishing process of metallic parts. Some parts with narrow structures always suffer from surface quality deterioration in the PEP process. In this paper, the deterioration of surface quality was studied to reveal the vapor film evolution mechanism during the polishing. The conditions for the bump defects generation were investigated with the comparison of polished surface morphology under different voltages and immersion depths. The reasons for the bump defects generation were analyzed through the compositions, the chemical states of the elements, and the microstructure of bump defects. The relationship between the current density, the thickness of the vapor film, and the heat to maintain the vapor film was discussed. The vapor film was maintained by Joule heat generated by itself. During the PEP process, excessive current density on the anode surface made the vapor film thickness greater than the critical value of heat could maintain, leading to the collapse of the vapor film. The anode then came into partial contact with the electrolyte, resulting in bump defects. As a result, it is suggested that the thickness of the vapor film be reduced to prevent the surface quality of narrow structures from deteriorating.