Galvanized vs Galvalume vs ZAM Steel — What’s the Difference?
When sourcing steel coils for roofing, cladding, or structural applications, you’ll often come across three coated steel products: galvanized steel (GI), galvalume steel (GL/AZ), and ZAM steel (Zn-Al-Mg).
They look similar but perform very differently. Choosing the wrong one can cost your project thousands in early replacement. In this guide, we break down the differences in coating composition, corrosion resistance, price, and best-use scenarios, so you can make an informed decision.
1. What Is Galvanized Steel (GI)?
Galvanized steel, also called hot-dip galvanized (HDG) or GI (galvanized iron), is steel coated with a layer of pure zinc (Zn).
Coating composition: 99%+ Zinc (Zn)
How it’s made: Steel sheet is passed through a bath of molten zinc at around 460°C. The zinc bonds to the steel surface, creating a durable protective layer.
Key characteristics:
- ✅ Excellent sacrificial protection — zinc corrodes first, protecting the steel
- ✅ Lower cost — most economical option
- ❌ Shorter service life in harsh environments
- ❌ Cut-edge corrosion can occur at sheared edges
Best for: Indoor applications, mild outdoor environments, budget projects, general sheet metal work.
2. What Is Galvalume Steel (GL / AZ)?
Galvalume steel (also known as Aluzinc, Zincalume, or GL) is coated with a zinc-aluminum alloy — roughly 55% aluminum, 43.5% zinc, and 1.5% silicon.
Key characteristics:
- ✅ 2–4× longer service life than GI in the same environment
- ✅ Superior heat reflection — excellent for roofing in hot climates
- ❌ No sacrificial protection at cut edges (bare steel exposed)
- ❌ Cannot withstand highly alkaline or acidic environments
Best for: Roofing and wall cladding, high-temperature environments, coastal areas (with edge treatment).
3. What Is ZAM Steel?
ZAM (Zinc-Aluminum-Magnesium) is a next-generation coated steel containing 93% Zn, 5% Al, 2% Mg.
Key characteristics:
- ✅ Best cut-edge protection — magnesium compounds seal exposed edges
- ✅ 8–15× longer life than GI in the same environment
- ✅ Excellent resistance to red rust and white rust
- ❌ Higher cost than GI and GL
Best for: Coastal/industrial environments, cut-edge exposed applications (purlins, decking), 20+ year projects.
4. Side-by-Side Comparison
| Property | Galvanized (GI) | Galvalume (GL/AZ) | ZAM (Zn-Al-Mg) |
|---|---|---|---|
| Service Life | 1× (baseline) | 2–4× longer | 8–15× longer |
| Cut-Edge Protection | Excellent | Poor | Excellent |
| Heat Reflectivity | Low | High | Moderate |
| Price | Low | Medium | High |
5. Which One Should You Choose?
Choose Galvanized (GI) if:
- Your project has a tight budget
- The environment is mild (inland, low humidity)
- Cut edges will be painted or sealed
Choose Galvalume (GL/AZ) if:
- You need roofing or cladding in hot climates
- You want 2–4× longer life than GI
- Cut edges are not exposed to moisture
Choose ZAM if:
- The project is in a coastal or industrial environment
- Cut edges remain exposed (purlins, deck sheets)
- You need 20+ year service life without maintenance
6. Summary
There is no single "best" coated steel — only the right one for your project.
- GI — budget-friendly workhorse for general use.
- Galvalume — excellent longevity for roofing in hot climates.
- ZAM — premium option for harsh environments and long-term projects.
All three products are available from Qiaosi Steel as coils, sheets, and roll-formed profiles.
Need coated steel coils? We supply GI, GL, and ZAM with full mill test certificates.
📧 inquiry01@qiaosi-group.com | 📱 +86 135 2663 0668