Electrogalvanized galvanizing and its alloy coatings are widely used in the engineering field due to their excellent corrosion resistance and cost-effectiveness. The following is a detailed analysis of electrogalvanizing and its alloy coating, including its properties, formation mechanism, preparation process and post-treatment.
Electrogalvanized coating properties
Corrosion resistance
Electrogalvanized coatings provide protection primarily by forming a zinc layer on the surface of the base steel. The zinc layer exhibits excellent stability in dry environments, while in humid environments, a protective film (mainly composed of alkali and zinc carbonate) forms on the surface of the zinc, which effectively prevents corrosion from occurring. The potential of zinc is more negative than that of iron, so the zinc layer, as the anode, is preferentially corroded during electrochemical corrosion, thus protecting the base steel from damage. However, the corrosion resistance of the zinc layer in acidic and alkaline environments and high temperature and humidity conditions is relatively poor, and it needs to be used in specific environments.
Aesthetics and shelf resistance
The electro-galvanized layer is passivated to take on different colors, which not only enhances the appearance, but also enhances the corrosion resistance. In particular, the rainbow-colored passivation film has a "self-healing" ability and can recover quickly after minor scratches, thus maintaining its protective properties.
Cost-effective
The coating thickness of the electro-galvanized layer is usually thinner than that of the hot-dip galvanized layer, and the amount of zinc used is relatively small, which makes the electro-galvanized coating advantageous in terms of economy. Electrogalvanizing is currently the most widely used technology in protective coating for steel workpieces.
Electro-galvanized alloy coating properties
Electrogalvanized alloy coatings significantly improve the corrosion resistance and mechanical properties of the coating by adding different alloying elements.
Zinc-nickel alloy –Zinc-nickel alloy coatings perform well in terms of corrosion and wear resistance, typically 3 to 5 times that of pure zinc coatings. In addition, the zinc-nickel alloy coating has high hardness and excellent heat resistance, making it suitable for high-temperature working environments.
Zinc-iron alloy –The zinc-iron alloy coating contains a moderate amount of iron, which significantly improves its corrosion resistance compared to the pure zinc coating. The coating has good ductility and low production costs, making it a very practical protective coating.
Zinc-nickel-iron alloy –The zinc-nickel alloy coating is similar to the zinc-copper alloy in terms of corrosion resistance, exhibits excellent wear resistance, and has good decorative properties, which is suitable for subsequent chrome plating treatment.
Zinc-iron-cobalt alloy –The alloy coating has a low electrode potential, is an anodic coating, exhibits good corrosion resistance, is suitable for decorative coatings, and enhances the aesthetics of the material.
Formation and structure of electrogalvanizing and its alloy coating
The formation process of electrogalvanizing and its alloy coating is closely related to its chemical composition.
Cyanide galvanized layer
The formation of cyanide galvanizing involves the complexation of zinc ions with cyanide, resulting in a fine and glossy coating on the surface of the substrate. This coating has high current efficiency and good coverage, but due to the toxicity of cyanide, the environmental risk is greater.
Zinate galvanized coating
The formation mechanism of zincate galvanized layer is similar to cyanide galvanization, which has good uniformity and is suitable for use in most steel substrates. Its passivation film is stable and provides good corrosion resistance.
Chloride galvanized layer
The chloride galvanized coating is highly galvanic efficient and suitable for coating complex shapes, but its passivation film may be discolored during long-term storage.
Sulfate galvanized layer
The preparation cost of sulfate galvanized coating is low and the current efficiency is high, but the dispersion ability is relatively poor, resulting in a rough surface structure of the coating.
Preparation process of electrogalvanizing and its alloy coating
Preparation of cyanide galvanized layer——The process has good uniformity and is suitable for complex parts, but has a large polluting impact on the environment.
Preparation of zincate galvanized layer——The zincate galvanized layer has high stability and strong adaptability, but it is sensitive to impurities and requires strict control of operating conditions.
Preparation of chloride galvanized coating——The process of chloride galvanizing is simple and the current efficiency is high, but it needs to properly treat the wastewater to avoid environmental pollution.
Preparation of sulfate galvanized coating——This process is highly economical, easy to operate, and suitable for large-scale production, but it is difficult to control the quality of coatings.
Post-treatment of galvanized coating
Dehydrogenation
To prevent hydrogen embrittlement, the galvanized layer undergoes heat treatment after plating to eliminate hydrogen from the coating.
Passivation
Passivation improves the corrosion resistance of the zinc layer and increases its durability. The formation process of passivation film includes the dissolution of zinc and the regeneration of the film, and the thickness and composition of the formed film directly affect the corrosion resistance of the coating.
conclusion
Electrogalvanized galvanizing and its alloy coatings play an important role in various engineering applications due to their excellent corrosion resistance, economy and aesthetics. By selecting the right alloy composition and preparation process, the coating properties can be optimized for specific needs, thus enhancing its wide applicability in practical applications.
