Galvanized zinc-aluminum-magnesium steel coils, officially known as continuously hot-dip galvanized aluminum-magnesium alloy coated steel sheets and strips, are steel sheets or strips made from cold-rolled or hot-rolled pickled steel sheets as the base material, with a zinc-aluminum-magnesium ternary alloy coating formed on the surface through a continuous hot-dip galvanizing process. Internationally, they are often simply referred to as ZAM steel (Zinc-Aluminum-Magnesium). Galvanized aluminum-magnesium steel coils are a new generation of high-performance coated steel products following galvanized sheets and aluminized zinc sheets. By adding magnesium to the coating, they achieve a significant improvement in corrosion resistance and a unique self-healing function at cut edges, and are recognized as the future direction of coated steel technology globally. They are gradually becoming an ideal substitute for traditional galvanized steel sheets and aluminized zinc steel sheets.
Coating Composition and Classification
1. Basic Coating Composition
The coating of galvanized aluminum-magnesium sheet/coil is mainly composed of three elements: zinc (Zn), aluminum (Al), and magnesium (Mg), with trace amounts of silicon (Si) and other alloying elements added.
2. Classification by Aluminum Content
Based on the different aluminum contents in the coating, galvanized aluminum-magnesium sheet/coil can be divided into three main categories.
3. Classification by Substrate Type
Galvanized zinc-aluminum-magnesium steel coils are produced using a continuous hot-dip galvanizing process, which is basically similar to the production process of galvanized steel sheets.
Core Process Flow:
Substrate (cold-rolled/hot-rolled coil) → Uncoiling → Cleaning (alkaline spraying, electrolytic cleaning) → Annealing (controlling furnace pressure, dew point, and residual oxygen) → Hot-dip galvanizing (immersion in a zinc bath containing aluminum and magnesium) → Air knife control of coating thickness → Post-galvanizing cooling → Passivation treatment (chromium-free passivation) → Oiling → Coating → Finished product
Comparison of zinc-aluminum-magnesium sheet/coil and pure zinc sheet/coil
Key features and advantages of Galvalume Zinc-Aluminum-Magnesium Steel Coil:
1. Enhanced Corrosion Resistance: The most outstanding performance of Galvalume magnesium steel sheet & coil is its superior corrosion resistance. Numerous studies have shown that its corrosion resistance is 5 to 20 times that of traditional galvanized steel sheets:
Flat-surface corrosion resistance: 5 to 10 times better corrosion resistance
Red rust resistance: Generally 10 to 20 times better than traditional galvanized steel sheets
Salt spray test: Up to 4000 hours without red rust
Corrosion resistance varies by product type:** 6 to 15 times better corrosion resistance than traditional pure zinc-coated steel sheets (specific multiples vary depending on the product type).
The addition of magnesium promotes the formation of a dense oxide film (such as magnesium hydroxide), effectively inhibiting corrosion diffusion. The corrosion products of aluminum are dense, stable, and insoluble in water, effectively blocking the intrusion of corrosive The improved corrosion resistance of the zinc-magnesium coating helps reduce steel corrosion losses and safety hazards caused by corrosion, contributing to the achievement of the national "dual carbon" target.
Zn-Al-Mg steel coil provides excellent corrosion resistance, making it suitable for use in coastal regions, industrial environments, and areas with high humidity or pollutants.
2. Self-Healing Properties:
This is the most significant feature that distinguishes galvanized aluminum-magnesium steel coils from traditional coated steel sheets. When the steel sheet is scratched, cut, or the cut edge is exposed, the magnesium element in the coating preferentially dissolves, forming a stable, dense, and strongly adhering protective corrosion product (basic carbonate double salt) on the scratch and cut edge surface. This automatically covers and repairs the damaged area, thereby preventing the spread of edge corrosion.
This characteristic allows galvanized aluminum-magnesium steel coils to maintain good corrosion resistance even at cut edges after cutting, punching, bending, and other processing, overcoming the fatal defect of "cut edge corrosion" in traditional galvanized sheets. In highway guardrail applications, zinc-aluminum-magnesium products with a coating of 120g/m² can replace traditional galvanized products with a coating of 800g/m².
3. Excellent processing and forming performance:
The coating hardness of zinc-aluminum-magnesium sheet/coil is high (40-160HV), and its scratch resistance is three times that of traditional galvanized sheets. The high coating hardness facilitates stamping and improves stamping efficiency. At the same time, magnesium improves the adhesion and processability of the coating.
4. High Heat Reflectivity:
The reflective properties of Zn-Al-Mg Steel Coil contribute to reducing heat absorption, which can be beneficial for energy efficiency in buildings and applications where heat management is crucial.
5. Lightweight:
Despite its enhanced performance, Zn-Al-Mg Steel Coil steel remains lightweight, making it easier to handle and transport.
6. Paintability:
Zn-Al-Mg Steel Coil can be coated with additional paint or organic coatings to further enhance its appearance or provide specific functionalities.
7. Sustainable and Recyclable:
As with other steel products, Zn-Al-Mg Steel Coil is fully recyclable, contributing to sustainability and environmentally friendly practices.
8. Main limitations
Higher cost: The production cost of galvanized aluminum-magnesium coils is higher than that of ordinary galvanized sheets
Comparison with galvanized steel coils and Galvalume steel coils
The core advantages of galvanized zinc-aluminum-magnesium steel coils are: corrosion resistance is 5 to 20 times that of traditional galvanized sheets, a unique self-healing ability for cuts, excellent processing and forming performance, and environmentally friendly chromium-free passivation. Our products are widely used in building roofs and walls, photovoltaic brackets, automobile bodies, home appliance casings, agricultural greenhouses, highway guardrails, and power and communication fields. Currently, galvanized aluminum-magnesium sheet coils are continuously developing towards the implementation of international standards, inclusion in the national standard system, and rapid expansion of application fields.
There were no specific Chinese National Standards (GB/T) dedicated solely to Zinc-aluminum-magnesium (ZAM) steel coils in China. However, similar to the situations in other countries, the properties and performance of ZAM-coated steel typically fall under existing standards for coated steel products.
In China, the relevant standards for ZAM-coated steel would generally be covered by the Chinese National Standards (GB/T) related to continuously hot-dip coated steel products with various types of metallic coatings, including zinc, zinc-aluminum alloy, and aluminum-zinc alloy coatings.
The most common standard used for this type of coated steel in China is:
GB/T 2518-2019: Continuous hot-dip zinc-coated steel sheets and coils.
While GB/T 2518-2019 does not specifically mention ZAM steel, it covers the requirements for continuously hot-dip zinc-coated steel sheets and coils, which includes various types of zinc-aluminum alloy coatings. Zinc-aluminum-magnesium (ZAM) coating would fall under the category of zinc-aluminum alloy coatings in this standard.
There was no specific ASTM standard dedicated solely to Zinc-aluminum-magnesium (ZAM) steel coils in the United States. Instead, the properties and performance of ZAM-coated steel typically fall under existing standards for coated steel products.
The most common standard used for ZAM-coated steel in the US is ASTM A1046/A1046M - Standard Specification for Steel Sheet, Zinc-Aluminum-Magnesium Alloy-Coated by the Hot-Dip Process. This specification covers the requirements for steel sheet, in coils and cut lengths, coated by a hot-dip process with zinc-aluminum-magnesium alloy.
ASTM A1046/A1046M outlines the chemical composition, mechanical properties, coating weight, thickness, and other performance characteristics of ZAM-coated steel. It sets the standards for the quality and properties of this advanced coating technology and is used as a reference by manufacturers and users in the industry.
There were no specific British Standards (BS) or European Standards (EN) dedicated solely to Zinc-aluminum-magnesium (ZAM) steel coils in the United Kingdom. Similar to the situation in the United States, the properties and performance of ZAM-coated steel typically fall under existing standards for coated steel products.
In the UK, the relevant standards for ZAM-coated steel would generally be covered by European standards for continuously hot-dip coated steel products, which include zinc-aluminum-magnesium alloy coatings. The most common standard used for this type of coated steel in Europe is:
EN 10346: Continuously hot-dip coated steel flat products for cold forming - Technical delivery conditions.
EN 10346 covers the requirements for continuously hot-dip coated steel flat products with various types of metallic coatings, including zinc, zinc-iron alloy, zinc-aluminum alloy, and aluminum-zinc alloy coatings. The Zinc-aluminum-magnesium (ZAM) coating would fall under the category of aluminum-zinc alloy coatings in this standard.
While EN 10346 may not specifically mention ZAM steel, it provides the basis for the performance requirements and quality of ZAM-coated steel products in the UK and other European countries.
There were no specific Japanese Industrial Standards (JIS) dedicated solely to Zinc-aluminum-magnesium (ZAM) steel coils in Japan. However, similar to the situations in the United States and the United Kingdom, the properties and performance of ZAM-coated steel typically fall under existing standards for coated steel products.
In Japan, the relevant standards for ZAM-coated steel would generally be covered by the Japanese Industrial Standards (JIS) related to continuously hot-dip coated steel products with various types of metallic coatings, including zinc, zinc-aluminum alloy, and aluminum-zinc alloy coatings.
The most common standard used for this type of coated steel in Japan is:
JIS G 3323: Hot-dip zinc-aluminum-magnesium alloy-coated steel sheet and strip.
JIS G 3323 specifies the requirements for hot-dip zinc-aluminum-magnesium alloy-coated steel sheets and strips, commonly referred to as ZAM or ZAM-coated steel. The standard covers the mechanical properties, chemical composition, coating weight, and other performance characteristics of the ZAM-coated steel.
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