1. Galvanized Sheet - Sacrificial Protection
The surface of galvanized steel sheet is evenly coated with zinc, which plays the role of anodic protection for the base material: the substitution corrosion of zinc protects the base material, and only when all the zinc is corroded can the inner base material be damaged. On cut edges and drilled holes, the zinc layer continues to protect the exposed steel - the decisive advantage of GI in cutting-intensive fabrication.
2. Aluzinc (Galvalume) Sheet - Honeycomb Coating
The surface coating of aluzinc sheet is composed of 55% aluminium, 43.5% zinc and small amounts of other elements (per ASTM A792 / EN 10346 AZ series). Under a microscope the coating appears as a honeycomb structure with zinc enclosed in the "honeycombs" formed by aluminium. Anodic protection is greatly reduced - less zinc content, and the zinc is wrapped by aluminium and not readily electrolysed. Once the aluzinc sheet is cut, the edges, which are basically unprotected, rust quickly. Therefore aluzinc should be cut as little as possible; once cut, the edges should be protected with anti-rust paint or zinc-rich paint to extend the service life.
3. Other Differences
| Item | Galvanized (GI) | Aluzinc (AZ) |
|---|---|---|
| Coating | Pure zinc | 55% Al + 43.5% Zn |
| Cut-edge protection | Sacrificial (excellent) | Very limited - treat edges |
| Heat resistance | Moderate | Better (suits ovens, chimneys, roofs) |
| Appearance | Standard | More attractive |
| Price (same spec) | Lower | Generally higher |
Note: price mainly follows the coating specification (e.g. AZ150 vs Z275) and the base material, not the spangle size.
4. Selection Guide
Choose galvanized sheet where extensive cutting and drilling occur - profiles, fabrication, grating.
Choose aluzinc where intact-surface corrosion resistance, heat resistance or aesthetics matter - roofing, cladding, appliance housings.
Confirm the coating designation and three-point test values on the MTC.
