Galvalume coil looks a lot like galvanized coil at a glance. Same silvery surface, same coil form, same general use in roofing and cladding. But the coating underneath is completely different, and that difference is worth years of service life.

Galvalume, also called aluzinc or GL, is steel coated with a 55% aluminum-zinc alloy instead of pure zinc. The aluminum forms a stable oxide barrier that resists corrosion far longer than zinc alone. In most environments, galvalume lasts 2 to 4 times longer than galvanized steel with the same coating weight.

This guide covers the coating grades, when to choose GL over GI, and how to verify what you are actually buying.

Step 1: Understand What Galvalume Is

Galvalume coating is roughly 55% aluminum, 43.4% zinc, and 1.6% silicon. The aluminum provides a long-term barrier against corrosion. The zinc provides sacrificial protection at cut edges and scratches. The silicon improves adhesion.

This combination gives galvalume several practical advantages over galvanized coil.

Step 2: Choose the Right AZ Coating Weight

The coating is designated by AZ followed by the coating weight in grams per square meter. This is the single most important spec for corrosion life.

What most buyers should do: For standard roofing and cladding, AZ100-AZ150 is the practical range. For coastal projects or solar mounting structures that need decades of service, AZ150-AZ185. AZ50 and AZ70 are budget options for sheltered applications.

Step 3: Galvalume vs Galvanized, When to Choose Which

Both are valid products. The choice depends on the service environment.

• Choose galvalume when: the roof or panel will face long-term outdoor exposure, coastal salt, high heat, or high UV. The longer life and better heat reflection more than pay back the 5-12% price premium.
• Choose galvanized when: the part will be heavily bent or welded, the cut edges will be protected, the environment is mild and sheltered, or budget is the absolute priority. GI is also better for buried or soil-contact applications where maximum sacrificial protection matters.

Cost reality check: galvalume costs 5-12% more than equivalent galvanized coil. But for roofing, it lasts 2-4 times longer. On a 20-year horizon, galvalume is usually the cheaper material per year of service.

Step 4: Know the Applications

Galvalume coil is used across construction, solar, agriculture, and appliances.

Step 5: Verify the Supplier

Galvalume and galvanized can look nearly identical in a photo, which makes substitution a real risk. Your checklist.

• Confirm AZ designation on the MTC. The mill test certificate must state the AZ coating weight (e.g., AZ150) and the silicon content. Never accept a certificate that only says "galvanized."
• Standard check. Galvalume is governed by ASTM A792 (US), JIS G3321 (Japan), and EN 10346 (Europe). Confirm which standard your certificate references.
• Third-party coating weight test. SGS and BV offer coating-weight pull-through tests. Specify this at order stage, not after shipment.
• Base grade. Confirm whether you need commercial (DX51D+AZ), drawing (DX52D+AZ), or deep drawing (DX53D+AZ) quality.
• Surface finish. Options include regular spangle, zero spangle, anti-fingerprint, chromated, and oiled. For roll-forming or painting, anti-fingerprint is a good choice.