What Is Aluminum-Zinc Coating? The Difference Between a Fence That Lasts and One That Rusts
Aluminum-zinc coating — sold as Galvalume® — is a mill-applied layer of about 55% aluminum and 43% zinc that protects steel two ways at once: the aluminum forms a barrier, the zinc protects cut edges sacrificially. Pre-painted, it is called PPGL. It is the reason a metal fence can go decades without rust or repainting.
The short definition
Aluminum-zinc coating is a metallic layer — roughly 55% aluminum, 43% zinc and 1.6% silicon — bonded to steel sheet at the mill before the sheet is painted or formed. Its best-known trade name is Galvalume®. When a panel is coated this way and then pre-painted, the industry calls the result PPGL: pre-painted Galvalume.
The coating is not paint and it is not a surface treatment applied after fabrication. It goes on as molten metal in a continuous line, so it is metallurgically bonded to the steel underneath.
Why two metals instead of one
Zinc protects steel sacrificially: where the coating is scratched or cut, the zinc corrodes first and the exposed steel does not. That is the whole idea behind galvanizing, and it works.
Aluminum protects as a barrier: it forms a stable oxide film that slows the reaction across the whole surface rather than giving itself up.
An aluminum-zinc alloy does both at once — barrier protection over the face of the panel, sacrificial protection at the edges and scratches. That combination is why the same thickness of coating lasts materially longer in humid, salt-carrying air than a zinc-only coating does.
What it means for a fence
A fence is a hard test for a coating. It has two faces, both exposed. It has cut edges at every panel. It sits in sprinkler spray, ground moisture and — in coastal Florida — salt. And nobody repaints a fence on schedule.
- No rust bleeding down the face of a panel
- No chalky patches where the paint has given up
- No peeling at cut edges and fastener holes
- No repainting cycle to budget for
ecFence panels use an AZ150 aluminum-zinc coating with an epoxy primer and a Silicone Modified Polyester (SMP) topcoat over it, on both faces. That stack is what the 25-year panel warranty is written against.
The terms you will see
If you are comparing metal fences, the coating is the first specification to ask about — before color, before gauge, before hardware. It is the part that decides how the fence looks in year fifteen.