Material selection
Aluminum Fabrication vs Steel Fabrication
Aluminum fabrication works 2.70 g/cm3 alloys like 6061 that cut fast, resist corrosion bare, and weigh a third of steel. Steel fabrication works 7.85 g/cm3 grades like A36 that cost far less per pound and weld forgivingly. The trade is weight and corrosion against material cost and stiffness.
| Aluminum Fabrication | Steel Fabrication | |
|---|---|---|
| Material cost | 6061-T6 at $2.50 to $4.00/lb | A36 at $0.50 to $0.90/lb |
| Density | 2.70 g/cm3 | 7.85 g/cm3 |
| Stiffness | 69 GPa modulus; 3x deflection at equal section | 200 GPa modulus |
| Welding | AC TIG or pulsed MIG, oxide prep, crater cracks | MIG, stick, flux-core; forgiving process window |
| Fatigue behavior | No endurance limit; welds crack under cycling | Endurance limit near 50% of tensile |
| Corrosion protection | Runs bare outdoors, self-passivating | Needs paint, powder, or galvanizing at $0.35 to $0.65/lb |
| Machining and sawing | 3x to 4x the feed rates of mild steel | Slower feeds; oxy-fuel and plasma cut cheap |
Choose Aluminum Fabrication when
- Weight-critical work: trailers, marine, transport payload
- Outdoor or wet service without a finishing operation
- High-volume machined parts where 3x feed rates pay
Choose Steel Fabrication when
- Cost-driven structural frames and weldments
- Fatigue-loaded welded joints under cyclic service
- Shops without AC TIG or pulse MIG equipment and skill
The verdict
Default to steel when cost and stiffness rule; A36 at $0.70 per lb with a 200 GPa modulus is hard to beat for frames and weldments. Switch to aluminum when every pound saved earns money back in fuel or payload, or when bare corrosion resistance deletes an entire finishing step.
Cost comparison
A36 runs $0.50 to $0.90 per lb against $2.50 to $4.00 for 6061-T6, but compare per part, not per pound: an equal-strength aluminum part weighs roughly half, compressing the penalty to 2x to 2.5x. Aluminum welding adds 30 to 80% labor for prep and skill, while steel adds $0.35 to $0.65 per lb for the coating aluminum skips. The crossover is operating weight: transport applications valuing saved pounds at $2 to $10 each flip the math to aluminum.
Common questions
Why does aluminum fatigue matter so much in welded structures?
Aluminum has no endurance limit, so every stress cycle consumes life, and welding knocks 6061-T6 heat-affected zones down to roughly 165 MPa from 310 MPa. Design welded aluminum to finite life with generous sections, or move welds out of high-stress regions.