- Aluminum is about 34% of steel's weight by volume but deflects roughly three times as much at equal geometry.
- Carbon steel is cost-effective and fabrication-friendly but usually needs corrosion protection.
- Select stainless by exposure and aluminum by alloy/temper.
- Check galvanic corrosion, thermal expansion and life-cycle cost.
Values in this guide are practical starting points for RFQ, DFM and prototype validation. They do not replace load calculations, regulations, material certificates, qualified procedures or approved production drawings.
Start with Three Physical Properties
Typical density is about 7.85 g/cm³ for carbon steel, 7.9–8.0 for austenitic stainless and 2.70 for aluminum; equal-volume aluminum weighs roughly 34% of steel. Elastic modulus is about 190–210 GPa for steel/stainless and 69–72 GPa for aluminum, so identical aluminum geometry deflects roughly three times as much elastically. Yield strength depends on grade and temper and cannot be inferred from the material family.
Carbon Steel: Cost and Fabrication Efficiency
Low-carbon steel suits brackets, frames, bases and welded assemblies. Common families include Q235/Q355, S235/S355 and ASTM A36, but names alone do not make them interchangeable. Check yield strength, thickness range, chemistry, impact requirements and certificate standard. Indoor parts may use powder or zinc plating; long-term outdoor use usually needs a more robust coating or hot-dip galvanizing system.
Stainless: Select for the Actual Medium
Type 304 serves general indoor, food-equipment enclosure and mild environments. Molybdenum-bearing 316 generally performs better around chlorides and coasts, but it is not immune to every chloride, crevice or high-temperature condition. Where corrosion or appearance matters, remove weld heat tint and pickle/passivate as required. Prevent iron contamination from carbon-steel wheels, brushes and benches.
Aluminum: Redesign the Section Instead of Substituting Equal Thickness
5052-H32 is widely used for formed sheet because of its corrosion resistance and bendability. 6061-T6 offers higher strength and machinability but is less tolerant of tight bends, and welding reduces strength in the heat-affected zone. Recover stiffness with deeper flanges, closed sections, beads or local thickness rather than replacing steel with equal-thickness aluminum.
Check Galvanic Corrosion and Thermal Expansion
Aluminum coupled to stainless, copper or other dissimilar metals can corrode galvanically in an electrolyte. Use isolating washers, coatings, sealants and drainage. Typical thermal expansion is about 12×10⁻⁶/K for carbon steel, 17×10⁻⁶/K for 304 stainless and 23×10⁻⁶/K for aluminum; long parts and large temperature swings need movement allowance.
QUICK SELECTION
Low-cost welded frame: low-carbon steel plus an appropriate protective system.
Hygienic/cosmetic unpainted part: 304; evaluate 316 or higher grades for greater chloride exposure.
Lightweight enclosure or formed part: evaluate 5052-H32 first.
Higher-strength machined aluminum: evaluate 6061-T6 and recheck bending and post-weld strength.
REFERENCES
Use the material standards applicable to the project market, such as EN 10025-2, EN 10088-2, EN 485-2, ASTM A36/A36M, ASTM A240/A240M and ASTM B209/B209M; substitute grades require written approval.