Galvanized steel is a material formed by combining steel and zinc. Galvanized steel combines the advantages of both materials, resulting in a material with the strength and plasticity of steel and a corrosion-resistant coating that is used in a wide range of industrial applications, including construction, home appliances and automobiles. In this issue, we will first introduce hot-dip galvanized products.
Protective effect of strip galvanization and galvanizing method
Mechanism of zinc plating to protect steel plates
In the atmosphere, zinc is much more resistant to corrosion than steel, and under normal conditions zinc is several times more resistant to corrosion than steel.
1), physical effect.
Zinc plating on the surface of the steel plate, blocking the contact between the steel plate and the corrosive medium outside, so that the steel plate is exempt from the corrosive effect of the corrosive medium.
2) Electro chemical effect.
When galvanized steel substrate and zinc plating exposed to corrosive media environment (such as galvanized scratches and cuts), due to the electrode potential of zinc (-0.726V) is lower than the electrode potential of iron (-0.44V), zinc is anodic and steel is cathodic, so the zinc priority corrosion and protection of the substrate, which is called the sacrificial anode protection of zinc.
The main processes for galvanizing strip steel
Hot-dip galvanizing and electroplating are the two main processes for galvanizing steel sheets, and today we will mainly talk about hot-dip galvanizing.
Hot-dip galvanizing: The difference between the melting points of steel and zinc is large. The melting point of pure iron is 1534°C, while that of zinc is only 419°C. The method of dipping the treated strip steel directly into the molten zinc solution for galvanizing is called hot-dip galvanizing.
Continuous hot-dip galvanizing of strip steel: The production process of joining the steel coils, after the necessary pre-treatment and annealing, the strip steel is directly galvanized through a zinc pot with molten zinc solution is called continuous hot-dip galvanizing of strip steel.
Product classification and features
Classification: According to the type of plating, it is divided into GI (pure zinc plating), GA (zinc-iron alloy plating), 55% Al-Zn (aluminum-zinc plating, GALVALUME), 5% Al-Zn (zinc-aluminum plating GALFAN), Aluminizing (aluminum plating), Zn-5Al-3MG (zinc-aluminum-magnesium plating).
Hot-dip galvanized Products (GI)
Features: beautiful surface, good corrosion resistance, good processability.
Normal zinc spangle
By adding elements such as lead or antimony to the zinc solution, large and beautiful zinc flowers can be obtained.
Minimal ( None) zinc spangle
Hot-dip galvanized alloyed products (GA)
Features: good adhesion of painted zinc-iron alloy coated steel sheet, good corrosion resistance after painting, and good weld ability.
Hot-dip galvalume products (GALVALUME)
Features: good corrosion resistance, 2-6 times that of hot dip galvanizing, which is the conclusion of exposing the specimen to different environments for more than 15 years and comparing it with galvanized steel; good temperature resistance, can be used at 300°C without discoloration, such as allowing discoloration using temperature up to 700°C. It has excellent heat reflective surface.