Aluminum vs. galvanized steel: when to use each and what the equivalent part weighs

Switching a part from galvanized steel to aluminum, or the other way around, changes the gauge, the weight, the die, the corrosion protection and the cost per part. This guide compares the two metals with public sources, works out the equivalent aluminum thickness gauge by gauge and says, application by application, when each one makes sense. Almexa makes aluminum, not steel: the steel data are here for comparison.

Quick answer: aluminum or galvanized steel?

• Weight: at the same thickness, aluminum weighs one third as much; at the same bending stiffness it needs 1.42 times the thickness and still weighs about half.
• Stiffness: steel is about 2.9 times stiffer; for thin parts that must not flex, steel wins.
• Price: per pound, galvanized steel usually costs less; per part the gap narrows.
• Corrosion: aluminum forms its own oxide layer; galvanized steel is protected while its zinc lasts, and G90 sheet carries 19 µm of zinc per side.

Difference between aluminum and galvanized steel: properties with sources

Sources are listed at the end. The carbon steel in the sheet is not in NIST's conductivity tables, so pure iron stands in as the reference.

What the equivalent part weighs

• Same thickness: weight drops in proportion to density, 2.71 ÷ 7.85 = 0.35. Aluminum weighs one third, but the part is about 2.9 times more flexible.
• Same bending stiffness: this is the comparison that matters for a panel, a roof sheet between supports or a duct wall. Plate stiffness grows with modulus times thickness cubed (E × t³), so t aluminum = t steel × ∛(200 ÷ 69.6) = t steel × ∛2.87 = t steel × 1.42. Weight ends up at 1.42 × 2.71 ÷ 7.85 = 0.49 times the steel.

At equal stiffness, aluminum sheet is 1.42 times thicker than steel and weighs about half.

Galvanized thickness and weight: American Steel & Aluminum gauge chart (October 2026), the one in the gauge chart guide. Aluminum at 0.0979 lb/in³ (2.71 g/cm³); at equal stiffness the calculated thicknesses are 0.0392, 0.0478, 0.0563 and 0.0734 in, rounded up to the next 0.005 in (1.02, 1.27, 1.52 and 1.91 mm). All fit Almexa's range of 0.0177 to 0.148 in (0.45 to 3.76 mm); at 0.148 in, aluminum matches up to 13 gauge galvanized (0.0934 in × 1.42 = 0.133 in).

What this calculation does not tell you: it matches stiffness, not strength or dent resistance, which depend on alloy and temper (Almexa reports them on each lot's mill test report). If the part works in tension or compression in its own plane, like a tie, stiffness grows with E × t: aluminum would need 2.87 times the thickness and weigh about the same. The final gauge is set by the part's engineer with the load, the span and the project's code.

Does aluminum rust? Corrosion of each metal

Aluminum. On contact with oxygen it forms an aluminum oxide film that protects its surface and re-forms if scratched (Australian Aluminium Council). It does not produce the red rust of iron. For harsher environments, such as the coast, 5005 or 5052 is used.

Galvanized steel. Zinc protects the steel while it lasts. The American Galvanizers Association (AGA) estimates time to first maintenance, when 5% of the steel shows rust, for five environments (rural, suburban, temperate marine, tropical marine and industrial), and protection grows in proportion to zinc thickness: with 3.9 mils (100 µm), in an industrial environment, about 72 years (AGA, 2010). That chart covers after-fabrication hot-dip galvanizing. G90 sheet is galvanized continuously and carries 19 µm per side, less than one fifth: by the same proportion, about 14 years in an industrial environment (our calculation, not the AGA's). The AGA warns that this coating does not give long-term outdoor protection without paint and that sheared edges and punched holes are left without zinc (AGA, 2013).

Galvanized steel is protected while its zinc lasts; aluminum does not depend on a coating, and its sheared edge is the same metal.

Galvanic corrosion: aluminum and steel in the same assembly

When two different metals touch with moisture between them, the more active one corrodes faster; the farther apart they are in the galvanic series, the stronger the tendency (ASTM G82). In seawater, the AGA lists zinc at -1.10 V, aluminum -0.86 V, carbon steel -0.68 V and copper -0.43 V.

• With galvanized steel: low risk, because zinc and aluminum sit close together (AGA, 1995); the zinc protects the aluminum while it lasts (Hydro, 2020).
• With bare steel, stainless steel or copper: aluminum is the one that corrodes (Hydro, 2020).
• Area matters: a large cathode with a small anode can cause a severe reaction (AGA, 1995): an aluminum rivet in a steel plate is a bad idea; a stainless screw in a large aluminum sheet carries far less risk.
• No moisture, no galvanic corrosion: it does not happen indoors or in dry atmospheres; on the coast, with chlorides, always consider it (Hydro, 2020).

To prevent it, separate the metals with an insulating barrier (AGA) or bond breaker tape (STRUCTURE), or paint the more noble one, here the steel (Hydro). Outdoors and on the coast, use stainless steel fasteners, not black or galvanized steel (STRUCTURE).

When each one makes sense, by application

Roofing and gutters

Aluminum when the weight on the structure or proximity to the sea matters; galvanized steel on long spans that need stiffness at a thin gauge, or when cost per foot rules. Almexa suggests 3105 H14, or 3003 if the profile has heavy forming: 0.024 to 0.040 in (0.6 to 1.0 mm) for roll-formed profiles and 0.020 to 0.040 in (0.5 to 1.0 mm) for gutters, as a reference (roofing and gutters). Aluminum expands almost twice as much: a 10 ft run grows about 0.11 in with a 72 °F (40 °C) swing, against 0.06 in for steel; allow for it in fasteners and laps.

Facades

At equal stiffness aluminum weighs half, and the structure carries that weight. Order 3105 or 1100, H14 for bent parts and H16 for large flat panels, or 5005 or 5052 for more exposed parts: 0.080 to 0.118 in (2 to 3 mm) for solid panels and 0.020 to 0.050 in (0.5 to 1.3 mm) for light facades (facades). On a steel subframe, insulate the contact. Galvanized sheet on facades is usually painted (AGA, 2013).

Ducts

The AGA lists HVAC duct among the main indoor uses of galvanized sheet. Aluminum pays off when the duct hangs and its weight matters, or outdoors, where thin zinc does not protect without paint. As a reference, 0.024 to 0.040 in (0.6 to 1.0 mm); Almexa does not publish a duct alloy, and its general-purpose sheet is 3003.

Truck bodies and transportation

In dry vans, truck bodies and trailers, every pound of body is a pound of payload you cannot bill. The alloy of boxes, tanks and structural transportation parts is 5052, in O, H32, H34 and H36 tempers and up to 36 in (914 mm) wide; 3003 or 3105 in H14 work for transport bodies. As a reference, 0.1019 in (10 gauge) for boxes and 0.0808 in (12 gauge) for bodies and tanks. In frames and parts loaded in tension or compression, steel keeps its edge.

Stamped parts

Moving a stamped part to aluminum changes the gauge, means adjusting the die and calls for a tryout. For interior parts and brackets, 3003 or 3105 in H14; for structural parts, 5052 or 5754, up to 36 in wide; as a reference, 0.040 to 0.118 in (1.0 to 3.0 mm) depending on draw depth. Almexa does not make the 6000 series used for outer body panels. For drawn parts, see the deep drawing guide.

Is aluminum more expensive than steel?

Per pound, usually yes, but you pay for parts. To compare:

1. Work out the weight of each part: at equal stiffness the aluminum part weighs about 0.49 times the galvanized one; at equal thickness, 0.35.
2. Multiply by the price per pound of each sheet, in the same form and delivered to your plant.
3. Add paint, freight, installation, maintenance and the value of your scrap; Almexa buys recycled aluminum from its own customers.

At equal stiffness, the aluminum part costs less in metal if its pound costs less than about twice the galvanized pound.

We do not publish Almexa prices or galvanized sheet prices: we found no public source with both sheets on the same date and in the same form. What is public is the metal on the London Metal Exchange, with its monthly average on the aluminum price page; how a sheet price is built is in LME, premium and FAB.

What to send for a quote

The galvanized gauge or thickness you use today, the application, whether you will paint, width and tons per month. Almexa makes aluminum coil from 0.0177 to 0.148 in (0.45 to 3.76 mm) and up to 48 in wide (36 in in the 5000 series), sheet and plate in sizes up to 48 × 144 in and strip to your width, in mill finish with a mill test report per lot. It does not sell steel or painted sheet. Request a quote from the mill.

Sources

Accessed October 26, 2026.

• The Aluminum Association, Teal Sheets, August 2018: nominal density by alloy.
• ArcelorMittal, Orange Book, cold formed sections: steel at 7,850 kg/m³.
• Antonio De Luca, "Design Considerations for Aluminum Structures in South Florida," STRUCTURE magazine: 10,100 ksi modulus from the Aluminum Design Manual, stainless fasteners and bond breaker tape.
• FHWA, "Bridge Steels and Their Mechanical Properties," FHWA-HIF-16-002, December 2015: steel at 29,000 ksi.
• NIST, 1100 aluminum and 3003-F aluminum: conductivity and expansion, from their equations.
• Ho, Powell and Liley, "Thermal Conductivity of the Elements," 1972: pure iron, 80.2 W/m·K at 300 K.
• Wyoming Department of Transportation, Bridge Design Manual, chapter 1, January 2022: steel expansion.
• American Steel & Aluminum, gauge chart, October 2026: galvanized thickness and weight.
• AGA, "General Hot-Dip Galvanizing vs. Continuous Sheet Galvanizing," 2013: G90 at 19 µm per side, outdoor use, edges and ducts.
• AGA, "Time to First Maintenance Chart," 2010 and "Estimating the Life of Hot-Dip Galvanized Coatings," December 4, 2014: environments and years to first maintenance.
• AGA, "Galvanized Steel with Aluminum Parts," May 2, 1995: potentials, area and insulating barrier.
• ASTM G82-98(2021)e1, public summary: galvanic series.
• Hydro, "Galvanic corrosion in aluminum," August 21, 2020: more noble metals, zinc, environments and insulation.
• Australian Aluminium Council, "Properties": oxide layer and recycling energy.
• Eurofer, "Steel Recycling," 2013: steel recycling.