Zinc-Aluminum-Magnesium (ZAM) coated steel is a type of steel that has been coated with a specific alloy consisting primarily of zinc, aluminum, and magnesium. This coating is applied to the steel surface to enhance its corrosion resistance and durability.
Composition of Zinc-Aluminum-Magnesium steel
Zinc-Aluminum-Magnesium (ZAM) steel is a type of coated steel that offers enhanced corrosion resistance compared to traditional galvanized steel. The coating composition typically includes:
Zinc (Zn): The primary component, usually comprising around 90-96% of the coating. Zinc provides the primary corrosion protection.
Aluminum (Al): Generally makes up about 1-8% of the coating. Aluminum helps to improve the adhesion of the coating and enhances corrosion resistance.
Magnesium (Mg): Typically present in the range of 1-4%. Magnesium further enhances corrosion resistance, especially in harsh environments.
These elements work synergistically to provide a durable, long-lasting protective layer that is more effective than traditional zinc coatings alone. The exact composition can vary depending on the specific requirements and manufacturer formulations.
Corrosion resistance mechanism of ZAM steel
ZAM’s corrosion resistance mechanism is due to its coating layer of aluminum and magnesium. The blend of Mg and Al creates an enduring protective film on its zinc base, giving protection against corrosion.
Compared to hot-dip galvanized coating layers, ZAM offers a finer and tighter adhesive property on the substrate. ZAM’s coating surfaces block the corrosive action over a long period of exposure to harsh environments.
In a salt spray test that lasted for four hours on both ZAM and hot-dip galvanized steel, ZAM formed a protective film on the coating surface. Take a glimpse at the figure below:
The cut-edge parts of the ZAM steel have superior corrosion resistance. The ends are covered with a fine base that contains a protective film comprising aluminum and magnesium leaching on its coating layer.
The corrosion resistance on the cut edge was based on a test on the steel substrate. The initial exposure period took several weeks, during which there was an initial rust on the exposed cut edge. The rust formed due to oxidation from condensation and rain.
The intermediate exposure period took several weeks to years. During this period, the cut edge resists corrosion due to the fine zinc-based protective film, which has a leaching of zinc, aluminum, and magnesium coating layers. The substrate turns darker to gray-black over the years of exposure to the elements.
Weldability
The coating layer of ZAM steel affects its weldability performance due to its zinc base. Zinc has a low melting point, which is not ideal for arc welding. This application leads to weak joints and deformation compared to cold- and hot-rolled steel sheets.
ZAM is prone to splashing, hole formation, and cracking. ZAM performs better if you weld it into joints, provided the structure has adequate strength and is under proper conditions.
Experts recommend conducting tests when welding ZAM steel to achieve greater strength and maximum welding parameters. The weld quality depends on the type of welding machine and the shape of the joints.
Defective joints are avoidable if you follow the right conditions when welding ZAM steel. The joints should have enough welding strength and adequate internal sectional structure before welding the steel.
ZAM Steel vs. Galvalume Steel
| Feature | ZAM Steel | Galvalume Steel |
|---|---|---|
| Composition | Zinc, Aluminum, and Magnesium | 55% aluminum, 43.4% zinc, and 1.6% silicon |
| Corrosion Resistance | Superior due to the inclusion of magnesium | Very good, but slightly less than ZAM |
| Coating Thickness | Typically thinner due to higher efficiency | Generally thicker for similar performance |
| Durability | High, with excellent edge protection | High, but edges may be more susceptible to corrosion |
| Surface Appearance | Smooth and shiny | Smooth and slightly spangled |
| Cost | Generally higher due to advanced properties | Generally lower compared to ZAM |
| Applications | Roofing, siding, automotive, appliances | Roofing, siding, construction |
| Environmental Impact | Uses less zinc, potentially more eco-friendly | Standard zinc-aluminum coating |
| Paint Adhesion | Excellent | Very good |
| Heat Resistance | Good | Good |
Both materials offer excellent performance in terms of durability and corrosion resistance, but ZAM steel tends to provide enhanced protection, especially at the edges, due to its unique composition. Galvalume steel, on the other hand, is widely used and cost-effective, making it a popular choice for many applications.
Standards
EN 10346: Specifies the technical delivery conditions for continuously hot-dip coated steel flat products, including zinc-aluminum-magnesium coatings.
JIS G 3323: Specifies the requirements for hot-dip zinc-aluminum-magnesium alloy-coated steel sheets and coils.
ASTM A1046/A1046M: This specification covers the requirements for steel sheet, zinc-aluminum-magnesium alloy-coated by the hot-dip process.
Applications
ZAM is a versatile steel brand that is useful in various applications. ZAM is a popular choice in the building and construction sector. It is used for making refrigerant ducts, ceiling crosspieces, indoor baseball fields, sound barrier louvers, heavy-duty shutters, and house frames.
In road and civil engineering, its uses include bridge reinforcing plate, soundproof wall (ZPG treatment), wind barrier panel, sound barrier, sound barrier member, snow fence, guardrail, bridge railing, pipe for joining bolts of concrete block, rock bolt, windbreak screen, drain reinforcement pipe, handrail in tunnel, steel pipe pile, and fireproof protection for optical fiber.
ZAM is ideal for making automobile parts such as wiper linkage, filter cases, radiator fan motor cover, starter motor yoke, hood lock, horn, pulley, splash guard, window regulator motor yoke, tank heat protector, constant velocity joint cover, and lower sash.
ZAM steel is also used in making electric power and electric equipment, farming structures, railroads, housing, and construction.
Conclusion
In summary, Zinc-Aluminum-Magnesium (ZAM) coated steel represents a significant advancement in coating technology, offering superior corrosion resistance, durability, and versatility. Its wide range of applications, combined with cost-effectiveness and sustainability benefits, make it an attractive choice for various industries.
References:
https://www.nipponsteel.com/product/catalog_download/pdf/U110en.pdf
ZAM Case Study. Nipponsteel
