Galvanised coil, formally known as galvanised steel coil, refers to a metal composite material with exceptional corrosion resistance. It is produced by uniformly coating the surface of a cold-rolled or hot-rolled steel substrate with a layer of metallic zinc through a specific galvanising process, typically supplied in coiled form.

I. Core Composition and Production Process

The performance of galvanised coil hinges fundamentally on the substrate and zinc coating. Its production involves multiple precision processes to ensure uniform coating distribution and strong adhesion:

Substrate Selection:

Mainstream substrates include cold-rolled steel (thinner gauge, smooth surface, suitable for applications demanding high aesthetics and precision) and hot-rolled steel (thicker gauge, higher strength, suitable for heavy-duty or structural components).

Specialised applications may utilise low-carbon steel substrates (excellent ductility) or high-strength steel substrates (superior impact resistance).

Key Production Processes (using mainstream methods as examples):

Hot-Dip Galvanising (HDG): The most prevalent process, accounting for over 80% of applications.

Substrate Pre-treatment: Involves degreasing (removing oil residues), pickling (removing surface iron oxide scale), rinsing (neutralising acid solutions), and drying to ensure a clean substrate surface.

Hot-dip galvanising: The pre-treated substrate is immersed in molten zinc at 440–460°C, where a chemical reaction forms a composite coating comprising an ‘iron-zinc alloy layer + pure zinc layer’;

Post-treatment: Zinc layer thickness is controlled using an air knife (high-pressure nitrogen). The substrate is then cooled, passivated (optional, enhancing fingerprint resistance and white rust prevention), oiled (for rust prevention), and coiled into rolls.

Electro-galvanising process (EG): Deposits a pure zinc layer onto the substrate surface via electrolysis. Characterised by a thin zinc layer (typically 5–20 g/m²), smooth finish, and high precision, though offering inferior corrosion resistance compared to hot-dip galvanising. Primarily employed in indoor applications such as household appliances and electronics.

II. Core Performance Advantages

The widespread adoption of galvanised coils stems from their unique dual advantage of ‘protection + workability’:

Superior corrosion resistance: The zinc layer isolates the substrate from air and moisture. Even if locally damaged, zinc protects the substrate from rust through the ‘sacrificial anode effect’.

Excellent workability: Direct processing such as shearing, stamping, bending, and welding is feasible, accommodating diverse product forming requirements;

Cost-effective durability: Compared to stainless steel or aluminium alloys, galvanised coils offer lower costs and extended service life (10-20 years in outdoor settings), with minimal maintenance expenses;

Environmentally sustainable and recyclable: The steel substrate and zinc coating contain no harmful substances, enabling 100% recyclability post-use in compliance with environmental standards.