What Is Galvanized Steel?

What is galvanized steel?

Galvanized steel means that to prevent the surface of the steel from being corroded and prolong its service life, a layer of metallic zinc is coated on the surface of the steel. This kind of zinc-coated steel is called galvanized steel.

Galvanized steel is chemically treated to prevent corrosion. This steel is coated with a layer of zinc because it is difficult for rust bacteria to corrode this protective metal material.

The main way to make steel resistant to corrosion is to add other metals, such as zinc. After the steel is immersed in zinc, the chemical reaction will cause the zinc to be permanently plated on the steel. Therefore, zinc not only covers the steel paint but has become a part of it.

Different methods of galvanizing

Surface galvanizing is one of the most commonly used methods in the surface treatment of steel products. Since its birth, it has been widely used in all walks of life. In practical applications, the main methods of galvanizing can usually be divided into hot-dip galvanizing and electro-galvanizing.

Electro-galvanized

Electro-galvanizing is also called cold galvanizing, which is the process of using electrolysis to form a uniform, dense, and well-bonded metal or deposition layer on the surface. The workpiece is placed in the electrolyte, and the current flows through the electroplating solution so that the electroplated metal is deposited and deposited on the workpiece to form a coating.

The thickness of the coating is usually 4-12 microns, which is much smaller than the thickness of the coating produced after hot-dip galvanizing.

Hot-dip galvanized

Hot-dip galvanizing is currently the most widely used galvanizing method. It can make the workpiece get a thicker galvanized layer. Generally, the average thickness of the zinc layer can reach 50 microns or more, and the coating is uniform and coated.

Hot-dip galvanized steel has the advantages of strong strength and long service life.

The process of galvanizing 

Electro-galvanized

Cold galvanizing is also called electro-galvanizing. It uses electrolysis equipment to degreasing and pickling the workpiece into a solution of zinc salt, and connects the negative electrode of the electrolysis equipment.

Place a zinc plate on the opposite side of the workpiece and connect it to the positive electrode of the electrolysis equipment, turn on the power, and use the directional movement of the current from the positive electrode to the negative electrode to deposit a layer of zinc on the workpiece.

The electro-galvanization process is used to protect metals from corrosion. For this purpose, zinc filler coatings are used. Any coating method is used to apply them to the protected surface. After drying, a zinc filler coating is formed. The dry coating has The content of zinc (up to 95%).

Hot-dip galvanized

The traditional hot-dip galvanizing process is mainly to remove the dirt on the surface of the workpiece. Then the workpiece is pickled to remove rust, washed with water, then cleaned in a solvent, and then the workpiece is placed in a galvanizing tank for galvanizing treatment, which is completed after drying and renovation.

The application of galvanized steel

Galvanizing can effectively improve the corrosion resistance of steel, so it is widely used in electric power, transportation, automobile, construction, chemical, and other industries.

In most use environments, the corrosion resistance of galvanized steel is significantly better than that of ordinary steel. The use environment of galvanized steel includes indoor and outdoor atmospheric environments, freshwater, seawater, soil, and concrete.

Galvanized steel can be found in many places. For example, you may live in a house that uses a steel frame. The car undoubtedly uses steel parts to avoid collision damage. In addition to being cheap and effective, the reason this metal is so popular is that it can be recycled multiple times.

How does galvanizing protect the base metal below?

Zinc reacts with iron molecules in steel to form a galvanized layer. Most of the outer layer is zinc, but the successfully galvanized layer is a mixture of zinc and iron, while the inner layer is pure steel. These protective layers can well resist environmental corrosion such as seawater and moisture.

Zinc also protects the steel by sacrificing the activity of the layer. If in some cases rust adheres to the surface of galvanized steel, zinc will be corroded first. Therefore, it is possible to prevent rust from coming into contact with the steel pipe.

Galvanized steel properties

Galvanized steel has been widely used in major industries such as construction and home appliances since its introduction. Due to the continuous expansion of the scope of use, the product’s formability and various properties of the steel plate continue to improve.

The following is a brief introduction to the properties of galvanized steel.

  • Corrosion resistance
  • Abrasion resistance
  • Formability
  • Durability
  • Excellent surface appearance
  • Weldability
  • Paintability
  • Recyclable

Surface of Galvanized steel

Surface condition: The surface condition of galvanized sheet is different due to the different treatment methods in the coating process, such as ordinary spangle, fine spangle, flat spangle, zinc-free spangle, and phosphated surface.  

The galvanized sheet should have a good appearance and must not have defects that are harmful to the use of the product, such as no plating, holes, cracks and scum, excessive plating thickness, scratches, chromic acid dirt, white rust, etc.

The surface of the galvanized layer should be continuous, complete, and practical and smooth. The galvanized color is generally bright silver, gray or dark gray.

Galvalume vs Galvanized vs Aluminum

Galvalume steel is based on cold-rolled steel coils. After annealing, a layer of Al-Zn alloy coating is coated on both sides by hot-dip coating. The coating is produced by a continuous hot-dip production line and is composed of aluminum-zinc alloy. , The mass percentage of aluminum in the coating is about 55%, the mass percentage of silicon is about 1.6%, and the rest is zinc.

The comparison of galvanized products and hot-dip pure galvanized products shows that the material properties of products of the same level are the same, but the substrate grades of galvanized zinc are relatively fewer. The difference in product characteristics is mainly reflected in the protective effect of the coating. The aluminum-zinc coating combines the excellent characteristics of aluminum and zinc.

Aluminum alloy has the characteristics of lightweight, good strength, easy processing and beautiful appearance, suitable for various surface treatments, good thermal and electrical conductivity, good reflectivity to light, heat and electric waves, no magnetism, and low-temperature resistance.

Galvanized steel vs Stainless steel

The mechanism is different. Galvanizing is mainly to plate a dense layer of zinc on the surface of the steel to prevent it from being oxidized; while stainless steel is the addition of other gold elements inside the steel, but the internal structure changes so that the product does not rust (oxidize).

In the manufacture of galvanized steel, a piece of ordinary carbon steel is coated with rust-resistant and corrosion-resistant zinc. Stainless steel is made by mixing molten steel with chromium, which prevents rust.

Does galvanize steel rust?

Whether galvanized steel will rust or not has a lot to do with the environment.

If the galvanized steel sheet is left outdoors for a long time, the metal zinc on the surface will oxidize in a short time and rust will appear. Generally speaking, It will not rust if it is stored indoors without damp.

Disadvantages of Galvanized Steel

  1. If galvanized steel is exposed to a humid environment, it will produce white rust over time.
  2. When mixed with brass, galvanized steel triggers dezincification
  3. When combined with non-ferrous metals, it will cause electrolysis.
  4. Obvious defects are usually hidden under the zinc coating of steel.
  5. The costs associated with galvanized steel are high and maintenance costs are high too.

 

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