Types of hot dip galvanized

The hot-dip substrate can be either hot-rolled or cold-rolled. In some foreign trade inquiries, the abbreviation HX or HC is used to refer to the hot-rolled or cold-rolled substrate. This is derived from the naming rules of the Europa sign, and of course it is not standardized.

In addition, in some industries, GI is often used to refer to hot-dip pure zinc coating, GA to hot-dip galvanized iron coating, and ZAM to refer to zinc-magnesium coating.

What are the mainstream hot-dip coatings?

There are many types of hot-dip coatings for steel plates and steel strips, and the classification rules in major standards such as American, Japanese, European, and national standards are also similar. We take the European standard EN 10346:2015 as an example to analyze.
The mainstream hot-dip coating is divided into six categories, namely:

1. Hot-dip pure zinc (Z)

2. Hot dip galvanized iron alloy (ZF)

3. Hot-dip galvanized aluminum (ZA)

4. Hot dip aluminum zinc (AZ)

5. Hot-dip aluminum-silicon (AS)

6.Hot-dip galvanized magnesium (ZM)

Definition and characteristics of various hot-dip coatings

The pretreated steel strip is immersed in a molten bath, usually different molten metals in the molten bath will obtain different coatings (except zinc-iron alloy coatings).

1. Hot-dip zinc coating (Z) hot-dip zinc coating

The zinc content in the molten pool metal liquid should not be less than 99%.

The hot-dip pure galvanizing process can generate spangles of different sizes. The spangles affect the surface feel, but do not affect the corrosion resistance.

2. Hot-dip zinc-iron alloy coating (ZF) hot-dip zinc-iron alloy coating

The main difference between hot-dip pure zinc coating and hot-dip pure zinc coating is that an alloying treatment process is added to make iron diffuse in zinc to form a zinc-iron alloy layer. The iron content in the alloy coating is usually 8~12%.

The welding performance of the zinc-iron alloy coating is good, the color of the coating is matte gray-white, and it appears dark gray after oiling, and the zinc-iron alloy coating has no spangles.

For hot-dip pure zinc and zinc-iron alloy coatings, the relationship between thickness and weight is basically the same: 1μm≈7.1g/m2.

Note 1: For hot-dip pure zinc and zinc-iron alloy coatings, although the zinc content in the zinc pot is the same, the use characteristics of the coatings are different, and the corrosion resistance is also different.
3. Hot-dip zinc-aluminium coating (ZA)

The molten metal in the molten pool contains about 5% aluminum (Al) and a small amount of rare earth elements, and the remainder is zinc.

The surface of zinc-aluminum coating is brighter than that of pure zinc coating, and its corrosion resistance is stronger than that of pure zinc coating, but it is rarely used in China and is occasionally mentioned in foreign trade inquiries.

The relationship between coating thickness and weight: 1μm≈6.6g/m2.
4. Hot-dip aluminium-zinc coating (AZ)

The molten metal in the molten pool contains approximately 55% aluminum (Al) and approximately 1.6% silicon, with the remainder being zinc.

Aluminum-zinc coating has excellent corrosion resistance, but also has a certain high temperature resistance.

The relationship between the thickness of the coating and the weight: the thickness of the coating is 1μm≈3.8g/m2.

Note 2: Hot-dip galvanized aluminum (ZA) and hot-dip galvanized aluminum (AZ) are two completely different coatings. Although there are few hot-dip galvanized aluminum products in domestic trade, they are still mentioned in foreign trade enquiries. , need to be carefully confirmed.

5. Hot-dip aluminum-silicon alloy coating (AS)

The molten metal in the molten pool contains about 8% to 11% silicon (Si) and the rest is aluminum.

The aluminum-silicon coating will form an obvious aluminum-iron-silicon alloy layer on the surface of the steel plate, which is characterized by excellent high temperature resistance and can be used in some high temperature processing and high temperature working environments.

The relationship between the thickness of the coating and the weight: the thickness of the coating is 1μm≈3g/m2.

Note 3: Hot-dip aluminum-silicon-coated steel sheets and strips are a type of “aluminized sheet” mentioned in trade. In the European standard, pure aluminum plating requires a separate agreement to supply, while in the JIS standard, it is classified according to different applications such as corrosion resistance and high temperature resistance.
6. Hot-dip Zinc-magnesium alloy coating (ZM)

Hot dip galvanized magnesium coating is also known as zinc aluminum magnesium (ZAM), the composition of the molten metal in the molten pool is the sum of aluminum and magnesium usually 1.5~8% (must contain at least 0.2% magnesium), and the rest is zinc.

The hot-dip galvanized aluminum-magnesium coating is characterized by extremely excellent comprehensive corrosion resistance, especially the protection of the shear fracture of the steel plate.

This kind of coating is relatively special, and each manufacturer has its own formula, so there is a large adjustment space for the content of aluminum and magnesium in the standard, and there is no fixed value for the conversion relationship between the thickness and weight of the coating, which is about 1um≈6.2-6.6g/ m2.

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