In acid monosalt plating bath, sulfate solution of galvanizing material is the most widely used, followed by fluoroboric acid solution. The characteristics of acid monosalt plating bath are small cathodic polarization and low dispersibility, but the allowable cathodic current density and current efficiency are high, and the plating speed is fast. Acidic monosalt bath is mainly used for zinc plating on simple parts. Organic additives are often used to improve cathodic polarization and deposition structure. In addition, brightener is added to zinc plating in sulfate solution. Fluoroboric acid solution is often used for continuous galvanizing of steel strips and steel wires because of its large buffer capacity and high current density.
Zinc exists in the form of zinc (CN) 42_complex anion in cyanide plating bath and zinc (OH) 42_complex anion in alkaline cocoon plating bath. Zinc electrowinning in cyanide bath has a high cathodic polarization, which increases with the increase of free cyanide content, and its current efficiency decreases with the increase of current density. Cyanide plating bath has the highest dispersing ability. Without special additives, zinc plating material can be widely used in the actual electroplating industry because of its good bonding with matrix metals and fine crystallization. However, in the presence of moisture in the air, free cyanide reacts with carbon dioxide to precipitate HCN, and the electrolyzer must be equipped with a special ventilation device. In addition, the composition stability of cyanide plating solution is worse than that of acid monosalt plating solution due to the carbonation process, which should be adjusted frequently. The serious disadvantage of cyanide zinc plating bath is that the plating bath is extremely toxic. Without special additives, obvious hydrogen permeation will result in poor mechanical properties of parts after zinc plating, such as reduced plasticity and increased brittleness.
