Aluminum vs Stainless Steel
Aluminum is a third the weight of stainless steel and machines three to four times faster, but stainless is roughly three times stiffer, stronger per unit volume, and holds up to heat, abrasion and cleaning chemicals that aluminum does not. Both resist corrosion, in different ways: aluminum by a thin oxide that anodizing thickens, stainless by a chromium oxide that passivation restores.
The representative grades here are 6061-T6 and 304, the two most stocked alloys in each family. Choose aluminum when weight, machining cost or thermal conductivity drive the design. Choose stainless when the part sees heat above about 150 °C, wear, sanitary cleaning, salt exposure without a coating, or must be strong and thin.
| Property | Aluminum | Stainless steel |
|---|---|---|
| Representative grade | 6061-T6 | 304, annealed |
| Density | 2.70 g/cm³ | ~8.0 g/cm³ |
| Yield | 276 MPa (40 ksi) | 205 MPa (30 ksi) min |
| Tensile | 310 MPa (45 ksi) | 515 MPa (75 ksi) min |
| Modulus | 69 GPa (10 Msi) | 193 GPa (28 Msi) |
| Specific stiffness (E/rho) | Similar | Similar |
| Thermal conductivity | ~167 W/m·K | ~16 W/m·K |
| Max service temperature | ~150-200 °C before strength loss | ~800 °C intermittent |
| Machinability | Excellent, fast | Fair; slow, work-hardens |
| Corrosion | Good; anodize for salt | Good; 316 for chlorides |
| Relative cost (per part) | Lower machined; similar per volume | Higher machined; 3x heavier per volume |
Typical values for the stated conditions. Confirm against the mill certificate and your spec.
Need a Aluminum or Stainless steel part made?
- Welding & Fabrication companies that work with aluminum · 593
- Machine shops that work with aluminum · 572
- Finishing & Heat Treating companies that work with aluminum · 546
- All U.S. manufacturers working with aluminum · 2,300
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- Welding & Fabrication companies that work with stainless steel · 540
- Machine shops that work with stainless steel · 412
- Finishing & Heat Treating companies that work with stainless steel · 345
- All U.S. manufacturers working with stainless steel · 1,635
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Attach a drawing (PDF or STEP) or describe the part; a U.S. shop that fits quotes it.
Decision matrix
A check marks the side with the edge on that dimension.
| Dimension | Aluminum | Stainless steel |
|---|---|---|
| Machining | ✓ Excellent; high speeds, low tool wear | Fair; slow speeds, work-hardening, rigid setups |
| Welding | Good; TIG/MIG, HAZ softens heat-treated alloys | ✓ Excellent; any process, distortion from low conductivity |
| Forming | Excellent in O and 5xxx; fair in T6 | Excellent; deep draws, springback higher |
| Strength | High strength-to-weight; low absolute stiffness | ✓ Higher absolute strength and stiffness; 3x heavier |
| Corrosion resistance | Good; pits in chlorides, galvanic with steel | ✓ Good; 316 or duplex for chlorides |
| Finishing | Anodizes, powder coats, chem films | Passivates, electropolishes, brushed and mirror |
| Material cost | ✓ Lower per part in most machined work | Higher material and machining cost |
| Availability | ✓ Every form, plus extrusions | Every form; no extrusions |
Choose Aluminum when
- Weight matters: enclosures, brackets, frames, anything carried or flown
- Machining cost dominates: complex pockets, thin walls, high part counts
- Heat sinks and thermal parts that need conductivity
- Custom extrusions are the cheapest way to make the shape
Choose Stainless steel when
- Service temperature above about 150 °C or exposure to open flame
- Sanitary, food, pharmaceutical and medical equipment that is cleaned aggressively
- Wear surfaces, threads and fasteners that would gall or strip in aluminum
- Thin, strong, stiff sections: springs, shafts, fasteners, structural sheet
Frequently asked questions
- Is aluminum stronger than stainless steel?
- Per pound, 6061-T6 and 304 are close and 7075 beats 304 handily. Per unit volume, stainless is stronger and three times stiffer. For a given envelope stainless carries more load; for a given weight aluminum usually does.
- Which is cheaper, aluminum or stainless?
- For most machined parts, aluminum: the material is cheaper per volume and machines several times faster. Stainless is cheaper only when the part must be thin and strong, when it eliminates a coating, or when its life in a hot or corrosive environment avoids replacement.
- Does aluminum rust?
- No. Aluminum forms a protective oxide instead of rust, but it can pit in salt water and corrode galvanically when bolted to steel or stainless. Anodizing, chem film or a coating and isolated fasteners handle both.
- Which is easier to weld?
- Stainless, for most shops. It welds with every common process and the joint keeps its strength. Aluminum needs a clean surface, AC TIG or spool-gun MIG, and heat-treated alloys lose strength in the heat-affected zone.
