Introduction
This article explains the advantages of galvalume steel coils, covering coating life, cut edges and applications. Galvanized and galvalume coatings protect steel in different ways, and the choice between them depends on the environment and the application. GI is a pure zinc coating, GA is a zinc-iron alloy coating, and galvalume AZ is a zinc-aluminum coating with longer life in many atmospheres.
Coating Systems Compared
GI, or hot-dip galvanized, is the standard zinc coating used for building and general fabrication. GA, or galvannealed, is produced by a post-dip heat treatment that converts the coating to a zinc-iron alloy, giving a dull surface that paints and welds exceptionally well. Galvalume AZ contains about 55 percent aluminum and 43.5 percent zinc, and its corrosion life is roughly two to four times that of an equal-mass zinc coating in most atmospheric exposures.
Performance Differences
GI resists corrosion by barrier and cathodic protection and is the lowest-cost durable coating. GA sacrifices some corrosion life for excellent paint adhesion and weldability, making it the choice for automotive and appliance panels. Galvalume offers the longest life in rural and industrial atmospheres and is preferred for roofing and wall cladding, but cut edges need protection because the aluminum-rich layer does not cathodically protect exposed steel.
| Coating | Composition | Best For |
|---|---|---|
| GI | Pure zinc | Economy, general use |
| GA | Zinc-iron alloy | Painting, welding |
| AZ galvalume | 55% Al / 43.5% Zn | Long outdoor life |
Applications
GI is used for roofing, cladding, purlins, pipes and general fabrication; GA for painted automotive and appliance panels; galvalume for roofing, wall panels, cooling towers and agricultural buildings where long life is required.
Selection Guidance
Match the coating to the environment, the finishing process and the design life: choose GI for economy and versatility, GA where painting or welding dominates, and AZ where the longest maintenance-free life is required.
Verification
Confirm the coating type and mass on the mill certificate, and verify the coating adhesion and surface treatment for the intended finish.
