Applications, types, and characteristics of galvanized steel sheets SECC (electrogalvanized steel sheets), SGCC (hot-dip galvanized steel sheets)

Galvanized steel sheet with high rust resistance

Galvanized steel sheet, as the name implies, is a material made by applying “galvanizing” to “steel sheet”. First, let’s introduce the manufacturing method and basic knowledge.

Manufacturing method

Galvanized steel sheet is a material made by applying zinc to SPCC (cold rolled steel sheet). SPCC is a relatively cheap and easily available steel sheet with excellent workability, so it is often used for forming processes such as bending and drawing. However, SPCC is very easy to rust, so surface treatment is basically required. There are various methods for surface treatment of SPCC, such as painting and plating, among which galvanized steel sheet is galvanized.

Features

Plating is a surface treatment that forms a metal film on the surface of metal or resin. Among them, forming a zinc film is called galvanizing. Zinc combines with oxygen in the air to form a passive oxide film. Therefore, it has a very high rust prevention effect.
In addition, zinc has a higher ionization tendency than iron, so it also has the characteristic of oxidizing faster than iron. Therefore, if iron (steel) is galvanized, even if a small scratch is temporarily generated on the electroplated surface, the internal iron is exposed, and the surrounding zinc will be corroded preferentially, thereby having the effect of preventing iron corrosion. This phenomenon is called sacrificial corrosion protection. Therefore, galvanizing is mainly performed on iron (steel).

Types

Galvanizing is classified according to the plating method and metal.
There are two methods: hot-dip galvanizing and electro-galvanizing.

Hot-dip galvanizing is a method of dipping steel plates and parts into heated and molten zinc. Think of fondue, chocolate fondue, etc. It is also called hot dip galvanizing or hot dip galvanizing. In addition to being able to obtain a thicker electroplated layer, an alloy layer of zinc and base metal can be obtained between the electroplated layer and the base metal layer, so it is very strong and can obtain a long-term corrosion resistance effect. This is its characteristic. On the other hand, since the product and parts are immersed in high-temperature molten zinc, deformation due to heat may occur.

Electro-galvanizing is a method of placing zinc and the material to be plated in a solution and passing electricity to cause the zinc dissolved in the solution to precipitate on the surface of the material to be plated. There are many methods of electroplating, such as zinc ammonium bath using acidic solution, potassium zinc chloride bath, and cyanide bath and zincate bath using alkaline solution. Its characteristics are uniform thickness and excellent decorative properties. On the other hand, unlike hot-dip galvanizing, electrogalvanizing cannot be used directly. Chromate treatment is usually applied to improve corrosion resistance and prevent white powder from being generated due to corrosion. Chromate treatment is a treatment that makes zinc plating more durable by using a solution with a composition similar to that of the treatment solution used in chrome plating. Chromate treatment can be used for decoration, such as adding a color close to yellow (gold), black, or gloss.
In the past, hexavalent chromium was the mainstream for chromate treatment. However, hexavalent chromium is toxic, so trivalent chromium is now used. Although trivalent chromium is non-toxic, the use of nickel alloys and molybdenum instead of trivalent chromium is increasing due to the global trend towards chromium-free. In recent years, from the perspective of environmental issues, restrictions are sometimes imposed on metals used in the manufacturing stage, and electroplating methods and treatments may also change. Be sure to check the latest information frequently.

The following table shows a comparison of the characteristics of hot-dip galvanizing and electrogalvanizing.

type	Plating thickness	advantage	shortcoming
Electrogalvanizing	About 2 to 25 µm	Uniform coating thickness and excellent decorative properties	Chromating required
Hot dip galvanizing	About 50~100µm	Strong corrosion resistance	Deformation due to heat

There are pure zinc plating and zinc alloy plating by metal classification. In zinc alloy plating, the types of metals added are different between hot-dip galvanizing and electro-galvanizing. Lead is often used in hot-dip galvanizing, and the addition of aluminum and magnesium has also increased in recent years. On the other hand, in electro-galvanizing, alloy zinc plating using nickel or iron is performed.

Electrogalvanized steel sheet, SECC

Features of SECC

SECC is a steel sheet that has been electroplated with zinc. It is also called Steel Electrolytic Cold Commercial in English. It is also called Bond Steel Sheet, which is the trade name when Nippon Steel first sold SECC.
The CC at the end of SECC is the same as the base material of SECC before electroplating, SPCC (cold rolled steel sheet), indicating that it is a general material that has been cold-rolled.
Since the base material is SECC, it has the same characteristics of excellent workability as SECC. And because it is electroplated, it has a beautiful and shiny appearance, but it has good paintability and can be painted in various colors.
It is the most circulated steel sheet among the treated steel sheets.

Uses of SECC

Because it is a general steel material, it cannot be expected to have too high strength. And the zinc coating is thinner than hot-dip galvanizing, so it is not suitable for use in harsh environments. It is mostly used for housings of home appliances and indoor electrical equipment.

Hot dip galvanized steel sheet, SGCC

Characteristics of SGCC

SGCC is a steel sheet that has been hot-dip galvanized. It is written in English as Steel Galvanized Cold Commercial.
Since it is hot-dip galvanized SPCC, its basic properties are almost the same as SPCC. It is also called galvanized sheet. The coating is thicker than SECC, so it has the characteristics of high corrosion resistance. Among SECC’s partners, there are also alloyed hot-dip galvanized steel sheets and aluminum-zinc-coated steel sheets.

Uses of SGCC

It is not a material with particularly high strength, but it has excellent corrosion resistance, so it is used in many places. In addition to the materials and guide rails for power transmission towers, it is also used for vehicle running parts. It also has many uses as a building material. In addition to being used as a material for rolling shutters and window guards, it is also used in the form of galvanized sheets for the exterior walls and roofs of buildings.

Summary
Plating is a process of forming a metal film on the surface of metal or resin. Among them, galvanizing is characterized by high corrosion resistance, so it is often used for surface treatment of iron products.
SECC is a material that has been electroplated with zinc on SPCC (cold-rolled steel), and SGCC is a material that has been hot-dip galvanized on SPCC. Because it is an easy-to-process steel sheet that has corrosion resistance due to galvanizing, it is widely used in housings of electrical products, building materials, etc.