Precision Machining of Different Metals by Plasma Electrolytic Polishing: A Review for Improving Surface Smoothness and Properties

The surface quality of metal materials is closely related to their service life and performance. Appropriate polishing techniques can significantly reduce surface roughness and the coefficient of friction, thereby enhancing properties such as wear resistance and corrosion resistance. However, traditional polishing methods have certain limitations. For instance, mechanical polishing has low processing efficiency and fails to ensure consistent product quality; chemical polishing can cause environmental pollution; and electrolytic polishing may result in severe corrosion. In contrast, plasma electrolytic polishing (PEP) has attracted considerable attention for its ability to achieve high-quality surface finishes, its use of environmentally friendly aqueous electrolytes, and its rapid processing speed. It has been successfully applied to the finishing of various metal materials. Hence, this review firstly introduces the basic principles of PEP from two perspectives of macroscopic structure and microscopic mechanism, and summarizes the typical features appearing in the polishing process. Secondly, the key parameters affecting the quality of the polished surface are discussed, including voltage, electrolyte composition and electrolyte temperature, and polishing time. Subsequently, the application of PEP on various metals was discussed, along with considerations regarding the polishing efficiency and removal characteristics of coatings and non-metallic substances. Finally, the challenges and potential future development prospects of PEP are summarized.