7005 T6 - powder coating feasibility

[lukenew]

Hi everybody,

I'm about to have an aluminum bike frame power coated. The frame is made of 7005 T6 aluminum alloy. The T6 artificial aging has been achieved with a 6 hours @ 200 F followed by a 4 hours @ 320 F heat treatment.

The powder coat process will bake my frame for 20 minutes @ 350 F.

Will it overage the alloy too much?

The J. Gilbert Kaufman “PROPERTIES OF ALUMINUM ALLOYS” books says that 7005 T53 alloy (that is different from mine) has a:

Yield Strength @room temperature = 395 MPa
Yield Strength after 30 minutes @ 350 F = 380 MPa

It means that I would loose a 4% of the strengh of the material.

Do you think that the behavior of the 7005 T6 alloy would be similar to the 7005 T53 alloy?

Do you think that this loss is acceptable (it seems to be less than the difference between minimum and average yield values)?

A ten year natural aging of the alloy (the frame is 10 years old) could be significant and could add damage to the powder coating overaging effect?

Finally, would you powder coat the frame?

P.S. the frame was already powder coated by the manufacturer when sold.

Thank you.

 

[ornerynorsk]

You could contact the powder manufacturer to determine the minimum cure temperature. Many times, cure temps are expressed in duality - example: 375 deg F for 15 min or 400 deg F for 10 min. What composition is the powder, epoxy, polyester, hybrid, urethane?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[lukenew]

unfortunately local powder coaters can only treat my frame at 350F for 20 mins.

Anyway I've wrote to the tubing manufacturer asking an advice on the topic. Here is what he answered me:

"350F for 20 min should be fine, it's above the age temp so ultimate strength will decrease just a little bit but nothing to worry about. Bonus he will gain some SCC resistance. If this was Scandium and not 7005 RAD then it would be a no-no."

I think that actually I will have the frame coated.

 

[tbuelna]

You bike guys are sure sticklers for details. A 4% difference in the published min tensile yield strength properties of the aluminum alloy tube your bike frame was constructed from should be of no real concern. There are other factors that likely have far more effect on the fatigue life of your bike frame, such as stress concentrations at the weld joints. I would agree with what the tubing manufacturer said, putting the RT frame in a 350degF oven for 20 minutes should not significantly affect the mechanical properties of the 7005 aluminum tubing.

Just make sure the powder coater carefully controls the oven temp and process time.