Galvanized vs. Galvalume®: What's the Difference?

The short version

Galvanized steel is coated with zinc. Galvalume® steel is coated with an aluminum-zinc alloy — roughly 55% aluminum, 43% zinc, 1.6% silicon. Both are applied at the mill; both protect the steel underneath. They fail differently, and that difference is the entire decision.

How each one protects

Zinc is sacrificial. It corrodes preferentially, so bare steel at a scratch or a cut edge is protected by the zinc beside it. This is why galvanizing has been the standard for a century, and why it handles rough handling and cut edges gracefully.

Aluminum is a barrier. Its oxide film is stable and slows corrosion across the whole surface, but it does not throw itself in front of exposed steel the way zinc does.

The alloy gets both behaviours: barrier protection over the face, sacrificial protection where the panel is cut or scratched — with the barrier slowing the rate at which the sacrificial reserve is spent.

Neither is universally better

• Humid, coastal, high-UV air — the alloy holds up longer at the same coating weight. This is the Florida case, and it is not close.
• Heavily cut, drilled or field-modified work — zinc's sacrificial behaviour at raw edges is an advantage.
• Contact with wet concrete or mortar — strongly alkaline conditions are hard on aluminum-zinc; zinc-only coatings are the conventional choice there.
• Interior or dry inland exposure — the gap narrows enough that price and availability usually decide.

The naming, decoded

So the honest answer to "which is better" is: better for what, and in what air. For a fence that lives outdoors in heat, humidity and salt spray and will never be repainted, the aluminum-zinc alloy is the one built for the job.

Galvalume® is a registered trademark of BIEC International.