How many types of galvanized steel are there?

Galvanized steel is an indispensable anti-corrosion material in modern industry. It can be divided into many types according to production process, coating composition, and application. Common types include hot-dip galvanizing (HDG), electrogalvanizing (EG), alloyed galvanizing (GA), and high-performance aluminum zinc (Galvalume) and zinc aluminum magnesium (ZAM) coated steel. Each type has its characteristics in corrosion resistance, strength, cost, and applicable environment, and is widely used in construction, automobiles, home appliances, and other fields. This article will detail the characteristics of various types of galvanized steel to help you choose the most suitable material.

Classification by production method

Although the galvanized sheets we see have almost the same surface and are smooth, bright, and durable, there are many processing methods for them. According to the process, they are divided into the following 4 categories.

(2)Alloy galvanized steel sheet

It is also hot-dip galvanized, but the difference is that it is immediately heated to 500℃ after leaving the zinc tank to form a zinc-iron alloy film. Therefore, its coating adhesion and weldability are strong.

Classification by coating composition

• Pure zinc coating: more than 99% pure zinc (Zn), medium (15-25 years) corrosion resistance, such as G235, Z120, Z275, are all pure zinc coatings.
• Aluminum-zinc alloy: coating composition 55% aluminum + 43.4% zinc + 1.6% silicon, such as AZ150, extremely strong (30-50 years) corrosion resistance, can be used as color-coated substrates and roofs.
• Zinc-aluminum-magnesium: coating composition Zn + 5-11% Al + 2-3% Mg, has excellent self-repairing properties, super long (40-60 years) life, and  can be used for high-end buildings and marine engineering.
• Zinc-nickel alloy: coating Zn + 10-15% Ni, high chemical corrosion resistance, belongs to special anti-corrosion, used in military industry and petrochemical equipment.

Classification by substrate type

Substrates with different processes

• Cold-rolled substrate: cold-rolled to 0.3-3.0mm, smooth surface (Ra≤0.8μm), strong coating adhesion, suitable for color coating (PPGI).
• Hot-rolled pickled substrate: hot-rolled plate pickled to remove oxide scale, low cost, used for thick-gauge structural parts (such as steel beams).
• Black annealed substrate: annealed after cold rolling, dark gray surface, improved stamping performance, mostly used for electrogalvanizing.

Commonly used galvanized substrates

• DX51D: specially designed for hot-dip galvanizing, silicon content ≤0.05% (to prevent excessive growth of zinc layer).
• SPCC: SPCC-SD, cold-rolled low-carbon steel: smooth surface, high precision, suitable for parts with high surface quality requirements (such as home appliance panels) after galvanizing.
• SGCC: Japanese galvanized substrate, divided into ordinary grade (SGCC) and deep drawing grade (SGCD).
• DC01 low-carbon steel: excellent stamping performance, suitable for complex formed parts (such as automotive accessories) after galvanizing.
• CS Type B: American galvanized substrate standard, carbon ≤ 0.10% + manganese ≤ 0.60% (balanced strength and coating adhesion).
• Q195 low carbon steel: low carbon content, good plasticity, easy processing and forming, suitable for galvanized products with low strength requirements.
• Q235 low carbon steel: balanced comprehensive performance, moderate strength, wide application, often used in galvanized scenes such as construction and structural parts.
• St01Z low carbon steel (European standard): low carbon content combined with the galvanizing process, both corrosion resistance and processing adaptability, commonly used in machinery manufacturing.

China Carbon Structural Steel Grades

• Q195: Yield strength ≥195MPa, good plasticity, used for thin plates, steel wires, galvanized substrates, etc.
• Q215: Yield strength ≥215MPa, slightly higher strength than Q195, used for tie rods, hooks, etc.
• Q235: Yield strength ≥235MPa, the most widely used, divided into A/B/C/D grades (impact toughness increasing), used for building structures, mechanical parts, galvanized products, etc.
• Q275: Yield strength ≥275MPa, high strength, used for sprockets, shafts, light rails, etc.
• Q345: The old standard was classified as carbon structural steel, now it is low-alloy high-strength structural steel, GB/T 1591-2018.

Classification by use

(1) Industrial steel

Construction steel can usually be divided into steel for steel structures and steel for reinforced concrete structures. Steel for steel structures mainly includes ordinary carbon structural steel and low alloy structural steel. Varieties include section steel, steel pipe, and steel bar. Section steel includes angle steel, I-beam, and channel steel.

(2) Decorative steel

Galvanized steel generally used for decoration, handicrafts, and sculptures is mostly made of galvanized wire mesh, galvanized iron wire, galvanized grille, and galvanized perforated mesh. Because these scenes generally do not involve load-bearing, huge impact, stretching and torsion, high heat and humidity, etc., the most commonly used process is electro-galvanizing, which is more economical.

(3) Agriculture, roads, vehicles, boats, and electricity

These fields mostly require outdoor galvanized steel, especially in the field of vehicles and ships, which may wade in the water. Therefore, a hot-dip galvanizing process is required, and the coating thickness is selected according to the environment. It will not fade even if it is washed by wind, snow, and rain.

Surface spangle classification

In addition to the above classification methods, galvanized steel sheets can also be classified according to the quality of the zinc layer (such as the size of the zinc flower and the thickness of the zinc layer), and specific performance requirements (such as fingerprint resistance, corrosion resistance, processability, etc.).

How to make galvanized steel?

Commonly used zinc coating models

By coating weight (g/m²)

• Z60: coating weight per square meter is 60 grams, suitable for mildly corrosive environments.
• Z100: coating weight per square meter is 100 grams, suitable for general industrial environments.
• Z200: coating weight per square meter is 200 grams, suitable for highly corrosive environments.
• Z275: coating weight per square meter is 275 grams, suitable for marine or chemical environments.

By coating thickness (μm)

• 5μm: suitable for mildly corrosive environments.
• 10μm: suitable for general industrial environments.
• 20μm: suitable for highly corrosive environments.
• 35μm: suitable for extremely corrosive environments.

Other common models

• G30: coating thickness is about 0.3 mil (7.6μm), equivalent to Z21.
• G60: coating thickness is about 0.6 mil (15.2μm), equivalent to Z42.
• G90: The plating thickness is approximately 0.9 mils (22.9 μm), equivalent to Z60.
• G115: The plating thickness is approximately 1.15 mils (29.2 μm), equivalent to Z80.
• G165: The plating thickness is approximately 1.65 mils (41.9 μm), equivalent to Z115.

Summary

Galvanized steel has become an ideal choice for construction, manufacturing, transportation and other fields due to its excellent corrosion resistance and diverse types. Whether it is economical and practical hot-dip galvanizing or high-performance zinc-aluminum-magnesium (ZAM), it can meet different environmental and usage requirements. Choosing the right type of galvanized steel and the right zinc layer can significantly extend the material life and reduce maintenance costs.

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