Optimization and mechanism of precise finishing of TC4 alloy by plasma electrolytic polishing

Abstract

A plasma electrolytic polishing (PEP) technique was used to yield high-quality, precise surfaces of a TC4 alloy to ensure high reflectivity. An orthogonal experiment was carried out to investigate the multiple factors affecting the surface quality of the alloy during the polishing process. The factors that affect the surface roughness are ranked as follows based on the extent of the effect: temperature > time > voltage > depth. The surface crest and trough area decreases by an order of magnitude, and the average roughness of the alloy is reduced to approximately 1/27 of its original magnitude after PEP. The vapour gaseous envelope (VGE) ascends as the bubble expanded under the buoyant force of the electrolyte, causing the thickness of the plasma-gas layer close to the electrolyte-air interface to increase. Further, it is proposed that the mechanism of surface smoothing during the PEP process involves a combination of discontinuous discharge, electrochemical reactions, and dissolution, thereby finishing the surface of the TC4 alloy. This work provides an alternative to the surface finishing of TC4 by PEP, which is expected to be a promising technique for polishing complex structures, especially porous structures (such as 3D printed Ti, Cu, Al, Nb, Mg, and their alloys).