Material selection
Aluminum 6061 vs Stainless 304
Both machine well and both are stocked everywhere, so the choice usually comes down to two things a datasheet states plainly: how much the part can weigh, and what it has to survive in service. The numbers below are the same published values used on each material's own page, set side by side.
| Aluminum 6061 | Stainless 304 | |
|---|---|---|
| Density | 2.70 g/cm³ | 8.00 g/cm³ |
| Tensile strength | 310 MPa (T6) | 515 MPa |
| Yield strength | 276 MPa (T6) | 205 MPa |
| Elongation | 12 % | 40 % |
| Hardness | 95 HB | 201 HB max |
| Melting range | 582–652 °C | 1400–1450 °C |
| Relative cost | Low | Medium |
Published values for standard grades at 23 °C unless stated, taken from each material's own datasheet page. Confirm against the supplier datasheet for the grade you specify.
The short answer
Choose 6061 aluminum when weight and machining cost matter most: it is about a third the density of 304 and cuts without work hardening. Choose 304 stainless steel when the part must survive wet, washdown or chemically mild service with no coating, or when it will be welded and cannot be heat treated afterwards.
Worked example: the same bracket in each metal
Take a solid block 100 × 50 × 10 mm, a volume of 50 cm³. In 6061 it weighs 50 × 2.70 = 135 g. In 304 it weighs 50 × 8.00 = 400 g, close to three times as much for the same shape.
Per unit of weight the gap is wider still. Dividing yield strength by density gives about 102 for 6061-T6 (276 ÷ 2.70) against about 26 for 304 (205 ÷ 8.00), in MPa per g/cm³. So where a part is sized by yield strength, 6061 carries roughly four times the yield load per gram. Where it is sized by ductility or impact, 304 stretches to 40 % before breaking against 12 % for 6061.
What Aluminum 6061 is
6061 is a magnesium-silicon aluminum alloy and the most widely machined aluminum in the world. In the T6 temper it has roughly the yield strength of mild steel at a third of the weight, and it cuts at high spindle speed without work hardening. It anodises cleanly to a uniform finish, welds without difficulty, and is stocked everywhere in plate, bar, and extrusion.
What Stainless 304 is
304 is the default stainless grade for washdown, hygienic, and general corrosion-resistant hardware, and at roughly three times the density of 6061 it is the heavier of the two by a wide margin. Chromium in the alloy forms a passive oxide layer that self-heals when scratched, so a part needs no plating or anodising to hold up in wet or chemically mild service. The real trade-off against aluminum shows up on the machine: 304 work hardens under the cutting tool, so a feature that finishes in one pass in 6061 can take several slower passes in 304, and that labor time usually outweighs the gap in raw material price.
Aluminum 6061 against Stainless 304
| Aluminum 6061 | Stainless 304 | |
|---|---|---|
| Weight | 2.70 g/cm³, roughly a third the density of stainless | 8.00 g/cm³, close to three times heavier for the same volume |
| Strength | 276 MPa yield in T6, comparable to mild steel at a third the weight | Higher ultimate tensile at 515 MPa, but lower yield at 205 MPa, and far more ductile at 40 % elongation against 12 % |
| Corrosion resistance | Needs an anodised or plated finish for salt spray or continuous wet exposure | Passive chromium oxide film reforms on its own if scratched, no coating needed for most environments |
| Machinability | Cuts fast at high spindle speed and does not work harden | Work hardens aggressively with dwelling in the cut; machining time runs several times longer than an equivalent aluminum part |
| Weldability | Welds by TIG or MIG, but the heat-affected zone loses temper and needs post-weld heat treatment on structural joints | Welds readily without special procedure; use 304L on welded assemblies to avoid carbide precipitation at the joint |
| Relative cost | Low, and the fastest of the two to machine | Medium material cost, but the work-hardening penalty on machining time raises the finished-part cost well above the material-cost gap alone |
Which one, for which part
- A part where weight is a real constraint, portable equipment, robotic end effectors, anything carried or moved by another mechanism, favours 6061 at roughly a third the density.
- Food, beverage, pharmaceutical, or medical equipment is 304's case: the passive oxide film needs no coating and the alloy is the industry default for washdown and hygienic environments.
- A part exposed to salt spray, cleaning chemicals, or continuous wet service without a protective coating favours 304; uncoated aluminum will pit and stain in the same environment.
- Heat sinks, machined housings, brackets, and jigs made in volume on a machining budget favour 6061: it cuts fast without work hardening, and the finished-part cost gap over stainless is larger than the raw material cost gap alone.
- A welded assembly that must not lose strength at the joint without a post-weld heat treatment step favours 304, which welds readily without special procedure; 6061's heat-affected zone loses its T6 temper and needs that extra step to restore it structurally.
Our status
Trumould machines and forms both aluminum 6061 and stainless 304 in-house across CNC machining and sheet metal fabrication; neither runs through injection molding or 3D printing here. Send the part, its service environment, and target volume, and the quote states which of the two is recommended and why, not just a price for whichever one you asked about first.
Questions
Frequently asked
What buyers ask when choosing between the two. Each answer comes from the figures above.
Ask an engineerIs 6061 aluminum stronger than 304 stainless steel?
It depends on which strength you mean. 304 has the higher ultimate tensile strength, 515 MPa against 310 MPa for 6061-T6, but 6061-T6 has the higher yield strength, 276 MPa against 205 MPa. Per gram, 6061 is far stronger: 304 is close to three times as dense.
Which is cheaper to machine, 6061 aluminum or 304 stainless?
6061. Its raw material cost is lower, and it cuts fast at high spindle speed without work hardening, while 304 work hardens under the tool and takes several slower passes on the same feature. The machining time gap usually outweighs the material price gap.
Can 6061 aluminum replace 304 stainless in wet or food contact service?
Only with a protective finish. Uncoated 6061 will pit and stain under salt spray, cleaning chemicals or continuous wet exposure, so it needs anodising or plating. 304 forms a passive chromium oxide film that reforms when scratched and is the default grade for washdown and hygienic equipment.
More
Related guides
Aluminum 6061 material page
Full datasheet, processing notes, grades, and design rules.
Stainless 304 material page
Full datasheet, processing notes, grades, and design rules.
Mild steel (CRCA)
The cheaper alternative when the part will be painted and neither weight nor corrosion resistance is the deciding factor.
Specifying this part?
Send your CAD and target volumes. We come back with a price, a lead time, and any material or design notes that would reduce either.