Corrosion, weight, machinability, cost. How a coastal Jeddah project picks differently from a Riyadh inland one, and the math you should run before specifying.
To match a 1.5 mm steel panel's bending stiffness, you need ~2.4 mm aluminium. The weight savings shrink as the wall gets thicker, and cost rises with it.
The native oxide self-heals scratches at 4–8 µm. In Saudi coastal air it beats any factory coat on bare steel for long-term protection.
Carbon steel material is one-third the kg-price of aluminium. For an inland MV cubicle in a substation, painted steel wins decisively on capex.
An aluminium door on a steel frame at the coast becomes a battery. Use nylon isolators or pick one metal end-to-end. A handful of bolts decides the lifespan.
Weight, strength, corrosion, cost, what changes when you swap material.
| Property | Steel (S235) | Aluminium (6063-T5) |
|---|---|---|
| Density | 7.85 g/cm³ | 2.70 g/cm³ (~1/3) |
| Yield strength | 235 MPa | 145-185 MPa |
| Young's modulus | 200 GPa | 69 GPa (~1/3) |
| Thermal conductivity | 50 W/m·K | 200 W/m·K (~4×) |
| Corrosion (untreated, coastal) | Fails in months | 20+ years (self-passivates) |
| Material cost per kg | 1.0× ref | 3-4× ref |
| Coating required outdoors | Always | Optional (anodise for premium) |
Aluminium is not always lighter, cheaper or better. Match it to the job.
To match a 2 mm steel panel's stiffness you need ~2.9 mm aluminium. The weight savings shrink from 65% to ~50%. The cost savings disappear. Buy aluminium for corrosion, not weight.
LED heatsinks, electronics chassis, anything thermally critical, aluminium's 4× thermal conductivity is decisive. A steel LED heatsink runs 25-35°C hotter than aluminium under the same load.
Aluminium + steel + Saudi humidity = a battery. The aluminium becomes the sacrificial anode and dissolves. Isolate with nylon washers, EPDM gaskets, or zinc-rich primer. Never bolt bare aluminium to bare steel outdoors.
The 6XXX series welds with TIG/AC, but the heat-affected zone drops from T5 temper to T0 (anneal). Designs must assume as-welded strength, not parent metal. Steel welds are forgiving in comparison.
It's a controlled oxide layer 5-25 μm thick, integral to the substrate. Type II (decorative) lasts 15-20 years. Type III (hard anodise) wears like ceramic. For outdoor luminaire bodies, Type II at 20 μm gives sea-front durability.
Aluminium luminaire bodies, steel enclosures, mixed-metal assemblies with proper galvanic isolation. 6063-T5 extrusions stocked locally; steel from DKP to 316SS.
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