Most of the world has already answered this question, and the answer differs by region for reasons that have nothing to do with engineering. A market-by-market reading, including where we lose.
Aluminium wins in most of Asia, the Gulf and coastal Africa; galvanised steel still wins in two places — South Africa, where a coated-steel supply chain and a theft problem favour it, and the GOST countries, where 0.8–1.2 mm double-folded steel is the inherited default. Everywhere else the decision is a fifteen-year cost calculation, not a preference.
| Market | Default substrate | Thickness | Why | Aluminium opportunity |
|---|---|---|---|---|
| Gulf / MENA | Aluminium 5052-H38 | 2–3 mm | Heat, UV, wind load, prestige specifications | Already aluminium — compete on flatness and film |
| Southeast Asia | Aluminium 3003/5052 | 1.2–2.0 mm | Humidity destroys steel edges; typhoon wind load | Aluminium is the default — win on price and lead time |
| Central Asia (GOST) | Galvanised steel, double folded | 0.8–1.2 mm | Inherited Soviet specification, local rolling capacity | Active substitution — the largest single opening |
| East / West / North Africa | Aluminium | 1.5–2.0 mm | Coastal corrosion, donor-funded specifications | Aluminium default; steel only for inland desert routes |
| Southern Africa | Chromadek coated steel | 1.4 mm | Local supply chain; aluminium resale value attracts theft | Weak — do not lead with aluminium here |
| United States | Aluminium 5052-H38 | 2–3 mm | MUTCD practice, Buy America on federally funded work | Private and non-federal work only |
Thickness figures are the ranges we see in tenders and in competitor shipments, not a standard. The governing document is always the national specification.
Take a 2 m² warning sign, 2 mm aluminium against 1.4 mm coated steel. Aluminium costs more per square metre at the factory — roughly a third more for the blank. But aluminium needs no painting, no edge protection and no re-coat at year eight, and it does not rust from a scratched edge inward. Over fifteen years the aluminium sign is usually the cheaper object even before you count the labour of taking it down.
Steel wins when the sign is large and the wind load is low, or when the buyer's own workshop can re-spray. It also wins when the buyer is the thief: in parts of southern Africa an aluminium sign has scrap value that a coated steel one does not, and that single fact decides the specification more often than any engineering report.
Moving a project from 1.2 mm steel to 1.5 mm aluminium is not a like-for-like swap. The panel gets stiffer but heavier per square metre, so the fixing spacing can usually stay and the channel can often go down one section. The post, however, may need re-checking — the wind load on the panel is unchanged, but the mounting hardware and the panel's own mass are not.
This is the point where a supplier who only sells one substrate is useless to you. We sell aluminium only, and we will say so when steel is the better answer for your road.
South African road work: the local coated-steel chain is cheaper than importing aluminium once duty and freight are counted, and the theft argument is real. Central Asian work that is still written around GOST steel: we can quote aluminium to the same dimensions, but the buyer's engineers have to accept a deviation. We would rather tell you that on day one than discover it at inspection.
No, and ours is never painted. Bare mill finish is standard; if a specification demands a coloured back, we supply film-laminated or anodised sheet rather than wet paint, because a painted back is the first thing to fail in a coastal environment.
In stiffness, roughly yes for sign-sized panels — aluminium is about a third of steel's modulus but the section is thicker. In strength, no: check the wind load case rather than assuming equivalence from thickness alone.
Because the failure mode of steel there is edge corrosion, and a sign is all edge. Once water reaches the cut edge of a coated steel panel, the coating lifts from the inside and the sign fails in two or three seasons.
Specification questions are answered by the same person who quotes the job.