Electropolishing is the anodic erosion of metal parts under specific conditions. This process can improve the micro geometry of metal surface and reduce the micro roughness of metal surface, so as to make the surface of parts bright.

Electropolishing is often used for decorative finishing of steel, stainless steel, aluminum, copper and other parts or coatings such as copper and nickel, surface finishing of some tools, or for making highly reflective surfaces and metallographic specimens.

In many cases, electropolishing can be used to replace heavy mechanical polishing, especially for parts with complex shape and difficult to be machined by mechanical methods.

However, electropolishing cannot remove or mask surface defects such as deep scratches and deep pits, nor can it remove non-metallic inclusions in metals. In multiphase alloys, when one phase is not easy to be dissolved by anode, the quality of electropolishing will be affected.

Chemical polishing is the chemical etching of metal parts under specific conditions. In this etching process, the metal surface is etched and leveled by solution, so as to obtain a relatively bright surface.

Chemical polishing can be used for surface finishing of instruments, aluminum reflectors, and decorative processing of other parts or coatings.

Compared with electrolytic polishing, the advantages of chemical polishing are: without external power supply, it can process parts with more complex shapes and high production efficiency. However, the surface quality of chemical polishing is generally slightly lower than that of electrolytic polishing, and the adjustment and regeneration of solution are also difficult. Harmful gases such as nitrogen oxide will be precipitated in the polishing process.

At present, the electropolishing fluids used in production mainly include:

① Polishing liquid composed of sulfuric acid, phosphoric acid and chromic anhydride;

② Polishing liquid composed of sulfuric acid and citric acid;

③ A mixed polishing liquid composed of sulfuric acid, phosphoric acid, hydrofluoric acid and glycerol or similar compounds.

Electrolytic polishing of aluminum and aluminum alloy is widely used in production. If the polished parts are oxidized for a short time, they can not only get a flat and bright appearance, but also form a complete oxide film, improve corrosion resistance and maintain their surface luster for a long time.

Chemical polishing is the process of etching and leveling parts in a specific solution. Chemical polishing equipment is simple and can handle parts with complex shapes.

Disadvantages: the quality of chemical polishing is not as good as that of electrolytic polishing. It is also difficult to adjust and regenerate the solution, which is limited in application. Especially in the process of chemical polishing, nitric acid emits a large amount of yellow brown harmful gas, which is very serious to the environment.

Source: Changjiang nonferrous metals network