Galvanized Steel Guide: Types, Grades, Benefits, and Applications for Corrosion Protection

Galvanized steel refers to steel that has been coated with a layer of zinc to shield it from corrosion. This zinc coating acts as a protective barrier, preventing moisture and other corrosive agents from coming into contact with the steel beneath. The process of applying the zinc layer is known as galvanization, which is usually carried out through two primary methods: hot-dip galvanizing (dipping steel into molten zinc) or electrogalvanizing. 

Here’s a closer look:

Origin of the Term "Galvanized":

The term "galvanized" originates from Luigi Galvani, an Italian scientist who made significant discoveries in bioelectricity, particularly the effects of electrical currents on muscle contractions. Although the term now refers to zinc coating, its early association was tied to electrical applications.

Protective Mechanisms of Zinc Coating:

The zinc layer safeguards steel through two key mechanisms:

- Barrier protection: The zinc coating provides physical separation between the steel and its environment, blocking moisture and corrosive substances from directly contacting the steel.

- Sacrificial protection: Zinc is more chemically reactive than iron, the primary constituent of steel. In corrosive conditions, the zinc corrodes first, "sacrificing" itself to protect the underlying steel.

Methods of Galvanizing Steel:

Steel can be galvanized using the following approaches:

- Hot-dip galvanizing: The steel is submerged in a pool of molten zinc.

- Electrogalvanizing: A layer of zinc is applied onto the steel through electrochemical means.

Common Applications:

Due to its excellent resistance to corrosion, galvanized steel finds widespread use across various industries:

- Construction: Used in roofing, framing, guardrails, and structural components.

- Automotive: Commonly featured in body panels and numerous vehicle parts.

- Agriculture: Utilized for fencing, storage tanks, and animal enclosures.

- Outdoor structures: Seen in handrails, canopies, and supports for solar panels.

Galvanized steel remains a versatile and highly durable material, valued for its ability to withstand challenging environmental conditions. 

Galvanized steel is differentiated by its coating process and grading system, which defines the zinc coating weight and mechanical characteristics. The most common types include hot-dip galvanized (HDG), electro-galvanized (EG), galvannealed (GA), and zinc-aluminum-magnesium (ZAM). The grading standards, such as G30, G60, G90, and G235, specify the coating thickness, which directly impacts both durability and cost. Additional classifications, including commercial, structural, and drawing qualities, are tailored based on strength and forming requirements.

Types of Galvanized Steel:

Hot-Dip Galvanized (HDG)

This process involves immersing steel into molten zinc, creating a thick, durable layer for general corrosion protection. It is widely used due to its reliability.

Electro-Galvanized (EG)

Steel surfaces are electroplated with zinc, yielding a thinner, precisely controlled coating better suited for applications requiring accuracy.

Galvannealed (GA)

This method combines galvanizing with annealing to produce a matte finish that offers increased weldability and a uniform appearance.

Zinc-Aluminum-Magnesium (ZAM)

A specialized coating made from zinc alloyed with aluminum and magnesium provides superior corrosion resistance compared with traditional zinc-only coatings.

Grades of Galvanized Steel:

G30, G60, G90, G235

Utilized mostly in hot-dip galvanizing, these grades indicate the zinc coating thickness per square foot. Larger numbers signify thicker layers, offering heightened corrosion resistance and durability.

Commercial, Structural, Drawing Qualities

Steel is further categorized by its designated use and mechanical attributes. Examples include CS-A, CS-B for commercial applications; DS, DDS for drawing needs; and EDDS for extra deep-drawing purposes.

DX51D, DX52D, DX53D, DX54D Series

These European designations define galvanized steel grades tailored for specific forming processes such as bending or drawing, aligning with standards set by the European Steel Business Group.