Galvanized steel is steel that has been coated with a thin layer of zinc. A galvanizing process is used to apply a zinc coating to the surface of steel or iron sheets to prevent corrosion. In this process, the steel is cleaned and then submerged in a bath of molten zinc. As the steel is drawn up from the bath, the zinc coating forms and bonds to the surface through metallic bonding. When exposed to air, the zinc coating develops a protective patina that shields the steel below from corrosion. The zinc acts as a sacrificial anode that corrodes in place of the steel. Galvanized steel is widely used for constructing fences, pipes, outdoor structures, and metal roofing because the zinc coating provides long-term corrosion resistance in many environmental conditions.
What Is the Difference between Galvanized Steel and Regular Steel?
Galvanized steel resists corrosion much better but has a slightly higher cost, while regular steel is cheaper but more prone to rusting.
- Galvanized steel has a thin coating of zinc applied to the surface, while regular steel is uncoated. The zinc coating is what provides galvanized steel with enhanced corrosion resistance.
- Corrosion resistance: Thanks to the zinc coating, galvanized steel has much higher corrosion resistance than bare or regular steel. The zinc coating protects the steel underneath from rusting or corroding. Regular uncoated steel is more prone to corrosion when exposed to moisture, acids, salts, etc.
- Appearance: Galvanized steel has a silver-gray, shiny appearance right after the galvanizing process. As it weathers, it develops a duller, flaky patina. Regular steel typically shows signs of rust or corrosion over time when outdoors.
- Strength: The zinc coating does not significantly affect the mechanical or structural properties of the steel. So galvanized and regular steel has comparable strength, hardness, etc. The zinc layer is very thin.
- Cost: Galvanized steel costs more than regular steel due to the additional galvanizing process. But it provides enhanced durability and lifespan that can offset the higher initial price.
What Are the Types of Galvanized Steel?
Hot-dip galvanizing is the most common and provides the best all-around corrosion performance for structural and outdoor applications. The main types of galvanized steel are:
- – Hot-dip galvanized steel: This is the most common type. It involves dipping steel into a bath of molten zinc. This results in a uniform zinc coating on all sides of the steel for superior corrosion protection.
- – Electrogalvanized steel: In this process, steel is electroplated with a thin zinc coating. It provides less corrosion resistance than hot dip. Often used for parts that can’t be submerged or for aesthetic/decorative purposes.
- – Galvannealed steel: The zinc-coated steel is then annealed to form an alloy layer between zinc and steel for added corrosion protection and paintability. Used in automotive, appliance, and construction industries.
- – Painted galvanized steel: For applications needing color coating, hot-dip galvanized steel can be painted for both corrosion protection and aesthetics. The zinc acts as a primer promoting paint adhesion.
- – Zinc-aluminum alloy coated steel: Contains small amounts of aluminum added to zinc coatings. Provides enhanced corrosion resistance, formability, and weldability over standard hot-dip galvanized.
- – Amalgam method: Zinc and other metals like aluminum, tin, or lead are electro-deposited on steel to form a corrosion-resistant alloy coating. Used in some critical fastener applications.
What Are the Properties of Galvanized Steel?
| Property | Details |
| Chemical Composition | Base Material: Iron alloyed with carbon (steel)<br>Coating: Zinc |
| Structure | Base: Ferrous, body-centered cubic crystal structure<br> Coating: Hexagonal close-packed crystal structure of zinc |
| Corrosion Resistance | High – Zinc coating protects the steel through galvanic corrosion where zinc atoms sacrificially corrode first |
| Tensile Strength | Between 350-550 MPa depending on steel grade. Not significantly affected by thin zinc coating. |
| Ductility | The zinc coating layer is very thin so the density is the same as base steel at 7.75 g/cm3. |
| Hardness | Zinc coating is softer than steel (0.25 GPa vs typical steel of 2.5-4 GPa). |
| Density | The zinc coating layer is very thin so the density is same as base steel at 7.75 g/cm3. |
| Melting Point | Base steel: 1,500°C (2,632°F) |
| Thermal Expansion | Similar to base steel: 11-13 x 10^-6/K |
| Electric Conductivity | Slightly lower than steel but still electrically conductive. |
| Paintability | Zinc layer compatible with most paint types for additional corrosion protection & aesthetics. |
What Industries utilize Galvanized Steel?
1. Fences
Galvanized steel fences can last decades with minimal maintenance. Regular steel fences would require much more frequent repair/replacement due to rusting.
2. Pipes and ductwork
Galvanized steel is widely used for water pipes, ventilation ducts, and other outdoor plumbing applications since it protects against corrosion from moisture.
3. Construction beams and supports
For buildings and structures near salt water or in coastal areas, galvanized steel beams and columns are specified to prevent rust corrosion over time.
4. Hardware and fasteners
Bolts, nuts, screws, nails, etc. used in outdoor applications are often galvanized for longer lifespans.
5. Electrical transmission towers
The high strength need for these supports is fulfilled by galvanized steel which also withstands weather exposure.
6. Shipping and storage containers
The galvanized coating protects containers even during overseas transport exposure to elements.
7. Agriculture equipment
Implements, gates, and other machinery used in wet, muddy fields perform better with galvanized steel.
8. Roofing and siding
The coatings on metal roofing and steel house siding are typically galvanized for decades of use without maintenance.
What Are the Pros and Cons of Galvanized Steel?
Galvanized steel offers significant longevity benefits through corrosion resistance, though it has a small cost and weight penalty over plain carbon steel. With proper handling, its risks are generally manageable.
| Pros | Cons |
| High corrosion resistance – Zinc coating protects steel from rusting for decades. | More expensive than plain carbon steel initially due to galvanizing process. |
| Low maintenance – Once installed, galvanized steel requires little ongoing upkeep. | Zinc coating is slightly softer than steel, so may dent or scrape more easily. |
| Recyclable – Both the steel and zinc can be recycled at the end of life. | Thermal conductivity is lower than plain steel, reducing heat transfer properties. |
| Facilitates rust-proofing and rain drainage. | Sensitive to over-thick coatings which can crack and peel over time. |
| Forms strong bonds for welding and painting. | Zinc coating provides some weight penalty vs plain steel. |
| Widely available as a construction/industrial material. | Imperfections in hot-dip galvanizing leave marks and may reduce corrosion protection. |
| More expensive than plain carbon steel initially due to the galvanizing process. | More toxic than plain steel if galvanized materials are burned without emission controls. |
| Compatible with most environments and structures. | Can present inhalation risks if (hot-dip) galvanizing fumes are inhaled without protection. |
FAQs about Galvanized Steel?
To help you get a better knowledge about galavanised steel, here we present more frequently asked questions about it:
Does Galvanized Steel Rust?
Is galvanized steel rust-proof? Galvanized steel sheets have very strong corrosion resistance and generally do not rust. However, in some special corrosive environments, rust may still occur. To effectively extend the service life of galvanized steel sheets, regular inspection, cleaning, and maintenance are necessary. It is also important to choose high-quality raw materials and pay attention to the environmental conditions during use.
Can You Weld Galvanized Steel?
Galvanized steel can be welded. Common welding methods such as manual arc welding, gas shielded welding, and submerged arc welding can all be applied to galvanized steel. However, due to the presence of the zinc coating, special conditions arise during welding, and corresponding measures must be taken to ensure welding quality.
How To Weld Galvanized Steel?
When welding galvanized steel, it is best to use MIG (Metal Inert Gas) welding or TIG (Tungsten Inert Gas) welding methods. Both methods can melt and join metal materials at high temperatures while avoiding the evaporation of zinc oxide, which can release toxic gases during welding. Electric arc welding or gas welding can also be used on galvanized sheets but require extra caution to prevent damage to the zinc layer.
Key points to note when welding galvanized steel:
- The zinc coating must be thoroughly cleaned before welding to avoid toxic gas generation. Solvents or other cleaners can be used.
- Select the correct welding current and voltage to ensure weld quality and stability.
- Minimize welding time to avoid overheating the zinc layer and causing damage or oxidation.
- Avoid concentrating large amounts of heat in the same spot during welding to prevent zinc layer damage and corrosion.
- When performing gas welding or arc welding, use low-temperature welding rods and avoid directing the flame or arc directly onto the zinc layer.
- After welding, rust removal and anti-corrosion treatment should be applied to the welded area to ensure quality and corrosion resistance.
- Check the surface of the galvanized sheet for cracks, bubbles, or other defects before welding to avoid quality issues.
- When using MIG or TIG welding, choose appropriate shielding gases such as argon or carbon dioxide to ensure welding stability and quality.
- Because galvanized sheets are relatively thin, control welding current and voltage carefully to avoid excessive welding.
- During gas or arc welding, pay attention to the direction of sparks and flames to avoid direct contact with the zinc layer, preventing damage and corrosion.
Can You Paint Galvanized Steel?
Galvanized steel can be painted, but specialized coatings must be used, and strict surface treatment and application processes must be followed. Because the galvanized surface is smooth and can chemically react with ordinary paints, direct application usually results in poor adhesion or paint peeling. Special primers such as epoxy zinc-rich primer or phosphating primer must be used along with appropriate topcoat systems.
How To Paint Galvanized Steel?
Although hot-dip galvanized surfaces have certain rust and corrosion resistance, they have limitations such as limited color choices and vulnerability to localized rust if the zinc layer is damaged. Therefore, many users choose to paint galvanized steel structures for both corrosion protection and decoration. However, a common problem is paint peeling. The following painting solutions can effectively paint galvanized steel.
Steps to Paint Galvanized Steel:
- Clean the surface – Before painting, clean the surface thoroughly to ensure good paint adhesion. Cleaning methods include using detergents, scraping rust, and removing loose coatings. If the surface has grooves or other damage, repair and sand to smooth it.
- Choose appropriate paint – Selecting the right paint is crucial. Use paints specially designed for metal surfaces, such as baked enamel for galvanized steel, epoxy coatings, or acrylic paints. Choose paint colors to meet different occasions and needs.
- Painting technique – Shake the paint well and add thinner if required before application. Follow the manufacturer’s guidelines and product instructions. Use brushes, rollers, or sprayers as appropriate. For curved or hard-to-reach areas, prepare and mask properly before painting.
- Protection and maintenance – After painting, protect the coating from sunlight and rain during drying. Regularly inspect and maintain the coating to ensure it remains intact.
Best Paints for Galvanized Steel:
- Epoxy Zinc-Rich Primer: Designed for alloy surfaces such as aluminum and zinc with high decorative and weather-resistant anti-corrosion requirements. Used as a rust-proof primer for galvanized steel and paired with corresponding topcoats like polyurethane or fluorocarbon paints. Single-component epoxy ester zinc-rich primers are also available for moderate corrosion protection with decorative needs. Compatible topcoats vary for indoor, heat-resistant, solvent-resistant, or decorative uses.
- Phosphating Primer: Intended for galvanized steel structures to provide a versatile surface treatment, allowing various paints to be applied without traditional phosphating steps.
- Lead-Calcium Primer, Zinc Powder Primer, and other non-oxidizing oil-based coatings such as epoxy asphalt coatings and chlorosulfonated polyethylene coatings are also suitable. Acrylic water-based paints also show good adhesion.
Can You Powder Coat Galvanized Steel?
Galvanized sheets cannot be powder coated directly; surface treatment is required before powder coating. The choice of surface treatment before powder coating depends on the specific usage environment and expected service life. During powder coating, environmental and parameter controls are also necessary to achieve a uniform, durable coating, making galvanized sheets more durable in use.
Surface treatment before powder coating galvanized steel:
- Surface cleaning – Remove grease and impurities using chemical cleaning, mechanical cleaning, or water washing to ensure a clean surface.
- Remove oxide layer – Use phosphoric acid cleaning or pickling to remove the oxide layer and achieve a smooth surface.
- Shot blasting – Increase surface roughness via shot blasting to improve coating adhesion.
Galvanized Steel vs Stainless Steel: What are the Differences?
Galvanized steel and stainless steel are two common metal materials with significant differences:
Material characteristics: Galvanized steel is an iron-based material coated with a zinc alloy layer for corrosion protection. Stainless steel is an alloy steel mainly composed of iron, chromium, and nickel, known for its rust resistance.
Corrosion resistance: Stainless steel has excellent corrosion resistance due to chromium and nickel content, maintaining performance in various environments. Galvanized steel has good corrosion resistance as long as the zinc coating is intact but deteriorates sharply if the coating is damaged.
Applications: Galvanized steel is widely used in construction, manufacturing, and piping, especially in environments at normal temperature without frequent water or chemical exposure. Stainless steel is used in high-end fields like kitchen equipment, medical devices, and chemical industries due to its high strength, corrosion resistance, and appearance.
Cost: Galvanized steel is relatively inexpensive, while stainless steel is more costly due to alloy composition and manufacturing complexity.
How to distinguish galvanized steel from stainless steel:
- Appearance: Galvanized steel has a silvery metallic sheen, while stainless steel is shinier and smoother, making it easier to clean.
- Magnetism test: Generally, stainless steel is non-magnetic or weakly magnetic, whereas galvanized steel is magnetic. A magnet can easily differentiate the two.
- Corrosion resistance test: If conditions allow, expose to corrosive environments to test. Stainless steel will show higher corrosion resistance.
Is Galvanized Steel Magnetic?
Galvanized steel is made by coating carbon steel or similar substrates with zinc. Its magnetism mainly comes from the steel itself. Since carbon steel is ferromagnetic, ordinary galvanized steel is usually magnetic. The zinc coating has minimal effect on the steel’s magnetic properties and cannot fundamentally change its magnetizability.
Using vacuum high-temperature technology, alternating or constant current demagnetization processes, non-magnetic galvanized steel pipes can be produced. These are mainly used in subway, high-speed rail, and other environments sensitive to magnetic fields to avoid interference with signal transmission.