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...
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...