Thanks for finding that. I'm no scientist but it seemed pretty obvious that heating heat treated aluminum compromised the heat treatment and weakened the metal itself.
Read: Turns a stiff and strong fantastic frame into something brittle and noodly (or rather noodlier as much as aluminum can actually be), and something, perhaps, dangerous.
Rep-worthy stuff, Taco!
Makes me wonder about PC-ing other stuff like rims, which is quite popular these days. I'm considering it myself, but I do not know what alloy they use for such parts, and it occurs to me to wonder first or risk wasting money. Do they use non heat treated alloys like 3003 or 5052, and count on the forming process for work hardnening them? Seems regardless of the alloy used, the PC process stands to anneal the metal if done improperly.
Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
- John Hajny, a.k.a. TrailMaker
[QUOTE=3. The effect of 1, 3, and 5 cycles of low-temperature
(121C for 30 min) heat treatment was almost negligible
on the mechanical and electrical properties of 6061-T6,
2024-T3, and 7075-T6 alloys.
4. The effect of 1, 3, and 5 cycles of high temperature 204C
for 12 min was significant: 6061-T6 and 7075-T6 showed
overaging trends (7075-T6 showed more pronounced overaging)
while 2024-T3 showed age hardening trends.[/QUOTE]
I don't fully understand point 4 of their conclusion. Looking at the provided data the only material with significant degradation of properties was 7075. The results for 6061 and 2024 changed very little. You are looking at less than 3% change in ultimate and a 9% increase in yield after cycling the part five times. From the data provided I see no reason to not powder coat the aluminum part.
You can find more data on it. I learned the hard way, so the risk is up to you. Took a while for me to gather information about it back then since the internet had not begun yet. Much easier now. I just know I will never heat a critical part over 325F.
If the PC shop uses the low temp cure, then you should be ok.
This paper shows how 6061-T6 goes from tensile/yield of 45/40 at 350F to 29/21 at 450F, strength drops the longer it is heated.
Millions of aluminum frames get powdercoated every year, as do millions of crank arms.