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Should I use stainless steel or aluminum?
Use 6061-T6 aluminum when weight, machining cost or heat transfer matters: it is about one-third the density of 304 and machines several times faster. Use 304 stainless for food contact, caustic wash-down, heat above about 300 °F (150 °C), and bare surfaces that must stay clean without coating. Yield strengths are close: 40 ksi (276 MPa) versus 31 ksi (215 MPa) annealed.
Stainless steel 304
Aluminum 6061-T6
By the numbers
Priced on the same representative part: plate, cnc machining, 50 pcs.
Tensile strengthMPa
304 SS
505
6061-T6
310
Yield strengthMPa
304 SS
215
6061-T6
276
Densityg/cm³
304 SS
8
6061-T6
2.7
Max service temp°C
304 SS
925
6061-T6
150
Elongation%
304 SS
70
6061-T6
12
Raw material cost$/kg
304 SS
6
6061-T6
7
Which should you pick?
Pick 304 SS when
- The part is food, dairy, medical or wash-down equipment
- Caustic or chlorinated cleaners contact the part
- Service temperature is above about 300 °F (150 °C)
- Thin panels must be stiff: about 28 Msi (193 GPa) versus 10 Msi (69 GPa)
Pick 6061-T6 when
- Weight matters, as in brackets, frames and robot arms
- Machine time drives part cost
- The part moves heat, such as a heat sink or cold plate
- You want anodized color or a hard anodized wear surface
Key differences
| 304 SS | 6061-T6 | |
|---|---|---|
| Machining | Slow; work-hardens | Fast with good chip control |
| Corrosion protection | Passive chromium oxide; passivate after machining | Natural oxide; anodize or chem film for harsh service |
| Cleaning chemicals | Handles most food and sanitizing chemistries; chlorides can pit | Attacked by strong alkaline (caustic) cleaners |
| Welding | Welds easily; 304L for welded parts | TIG or MIG; the heat-affected zone loses T6 strength |
| Galvanic behavior | Cathodic to aluminum | Corrodes first when wet-coupled to stainless; isolate joints |
| Finish options | Passivation, bead blast, polish, powder coat | Type II and III anodize, chem film, powder coat |
Questions
Is stainless steel stronger than aluminum?
Not by the pound. Annealed 304 has higher tensile strength, about 73 ksi (505 MPa) versus 45 ksi (310 MPa), but 6061-T6 has higher yield, 40 ksi (276 MPa) versus 31 ksi (215 MPa), at one-third the weight. Stainless wins on stiffness, heat and wear.
Is aluminum or stainless cheaper for a machined part?
Usually aluminum. For the same blank size, 6061 bar weighs about a third as much and typically costs well under half as much as 304, and it machines several times faster. Stainless earns its cost where corrosion, heat or sanitation rule out aluminum.
Can I use stainless fasteners in aluminum parts?
Yes, and it is common. In wet or salty service, the aluminum around the fastener corrodes galvanically, so use anti-seize or a barrier coating, isolating washers, and anodized or chem-filmed aluminum.
Try both on your part.
The builder prices the same geometry in every suitable process and material, with DFM for each.