Comparisons / Aluminium
PEEK vs aluminium
This one is not a like for like swap, and treating it as one is how PEEK gets a reputation for being flimsy. The metal wins on stiffness and price. The plastic wins on everything the metal cannot do at all.
| Property | Unit | PEEK | Aluminium 6061 |
|---|---|---|---|
| Continuous service temperature | °C | 250 | 150 |
| Tensile strength | MPa | 90 - 100 | 290 - 310 |
| Tensile modulus | GPa | 3.5 - 4.0 | 69 |
| Thermal expansion | µm/m·K | 47 | 23 |
| Coefficient of friction | µ, dry vs steel | 0.30 - 0.40 | 0.40 - 0.60 |
| Water absorption | % at 24 h | 0.1 | 0 |
| Relative stock price | acetal = 1 | 10 | 1.5 |
The modulus row is the one that ends careers. 69 GPa against 3.5 to 4.0 means a bracket that deflected 0.1 mm in aluminium deflects nearly 2 mm in unfilled PEEK at the same section.
Stay with aluminium when
- The part is structural and stiffness sets the design
- Heat has to move through it rather than be stopped
- Threads are used repeatedly and inserts are unwelcome
- Cost per part dominates and nothing else on this page applies
Switch to PEEK when
- The part must insulate electrically, or must not disturb a field
- It must stop heat rather than carry it, as a thermal break
- Corrosion, acids or steam cleaning are in the picture
- It must not mark, scratch or gall the part it touches
- It must be radiolucent, non magnetic or free of lubricant in a cleanroom
- It slides without lubrication, where a bearing grade has no metal equivalent
Five changes every conversion needs
Do these before quoting the plastic version, or the comparison will be unfair to both materials.
- Grow the sectionMatch the stiffness, not the shape. Ribs and thicker walls, or move to a filled grade at 10 to 14 GPa.
- Replace tapped holesThreaded metal inserts where the joint is opened more than a few times.
- Recalculate every fitPEEK expands about twice as much as aluminium and four times more than steel. Use the fit calculator.
- Add radiiSharp internal corners are stress concentrations in plastic in a way they are not in aluminium.
- Plan the stress reliefThin walls and deep pockets need an anneal between roughing and finishing, which aluminium never asked for.
Questions people ask
Can PEEK replace aluminium one for one?
No. Aluminium is about seventeen times stiffer, so a part carried across unchanged will deflect visibly. Sections grow, tapped holes become inserts and the expansion doubles. It is a redesign, not a material swap.
Is PEEK lighter than aluminium?
Yes, roughly half the density at 1.30 against 2.70 g/cm³. A filled grade closes some of that gap, and the section usually has to grow, so the finished weight saving is smaller than the density ratio suggests.
When is PEEK cheaper than aluminium?
Almost never on the part alone. It gets cheaper at system level: no anodising, no corrosion, no insulator added, no galling of a mating part, no lubrication in a cleanroom.