Galvanized Steel Sheet
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I. Definition and Basic Composition of Galvanized Steel Sheet
Galvanized steel sheet is a composite material coated with zinc using a hot-dip or electrochemical process on a plain carbon steel substrate. Zinc has a low melting point (approximately 419.5°C) and forms a dense protective layer with iron, effectively isolating it from oxygen and moisture, thereby slowing down rust. According to international standard ISO 3575, the zinc coating thickness for galvanized steel sheet typically ranges from 10 to 275 g/m² (approximately 1.4 to 38 microns), depending on the intended application. For example, galvanized steel sheet for construction requires a zinc coating of ≥100 g/m² (approximately 14 microns) to ensure long-term outdoor weathering resistance.
II. Two Main Types of Galvanizing Processes
1. Hot-Dip Galvanizing (Hot-Dip Galvanizing)
The steel sheet is immersed in molten zinc (approximately 450°C), where a metallurgical reaction forms a zinc-iron alloy layer. It features a thick zinc layer (typically 50-300 g/m2) and strong adhesion, making it suitable for structural components exposed to harsh environments, such as high-voltage power pylons and bridge guardrails. According to Chinese standard GB/T 2518, the zinc layer thickness tolerance for hot-dip galvanized steel must be controlled within ±15%.
2. Electrogalvanizing (Cold Galvanizing)
This process deposits a thinner zinc layer (typically 3-20 g/m2) onto the steel surface through electrolysis, resulting in a more uniform and smooth surface. It is often used in applications requiring high aesthetic standards, such as appliance housings and automotive interior panels. Electrogalvanized steel offers superior processability compared to hot-dip galvanizing, but has a shorter corrosion lifespan (typically 5-10 years, compared to 20-30 years for hot-dip galvanizing).
III. Core Performance Advantages of Galvanized Steel Sheet
-- Corrosion Resistance: Zinc has a lower electrode potential than iron, making it a preferred corrosion target (sacrificial anodic protection). Even if the coating is partially damaged, it still protects the substrate. Salt spray tests show that hot-dip galvanized steel sheets can withstand rust for over 500 hours under standard conditions (5% NaCl solution).
-- Cost-effectiveness: The galvanizing process only increases the original price of the steel sheet by 10%-30%, but extends its service life by 3-5 times, significantly reducing maintenance costs.
-- Machinability: The galvanized coating does not affect the sheet's ability to be stamped or welded. Some models (such as the DX51D+Z) can pass a 180° bend test without cracking.
