scotts300

iTrader: (46)

As long as said reputable shop doesn't fuse the PC over 500F or doesn't do some crazy chemical treatment to remove the previous finish, I agree.

I've read statement before stating that forged wheels shouldn't be PC'd, and think it's more manufacturer CYA than anything else. Just like modifying your 350Z, it has warranty implications. Has anyone had a Volk representative tell them this directly? I ask because Volk wheels are powdercoated directly from Rays Engineering, followed by powder coating. I've read that Rays has a proprietary process for the powdercoating application, but unless they have a way of fusing the coating by locally heating the wheel surface only, then I don't see an issue with having them powdercoated from a qualified outside source.

I've also read that any aftermarket PC process anneals the wheels, which would alter the structural integrity of the metal; however, T6061 aluminum is annealed at about 800F - well above conventional PC processing temps. Aging, which Rays does do for long periods (probably 8-12 hours), is done on T6061 aluminum around 350F. It's done on purpose to control the grain characteristics. One hour at 350F for powdercoating should have little, if any, effect on the aluminum's properties - see info below. I should do a pre and post-PC hardness test to give some data to this discussion. . .

Disclaimer: I'm not talking about stripping a wheel's powdercoat first, just adding PC.

Here is some data to back up the argument:

ASM Handbook Volume 2, Properties and Selection: Nonferrous Alloys and Special-Purpose Materials has the following information:
For cast wheels (356 alloy):
356-T6: aging at 305 to 315 °F for 2 to 5 hours
Yield stress = 185 MPa
Ultimate stress = 262 MPa
Fracture strain = 0.05

356-T7: aging at 435 to 445 °F for 7 to 9 hours
Yield stress = 165 MPa
Ultimate stress = 220 MPa
Fracture strain = 0.06

Metals Handbook 9th Edition, Vol 4, Heat treating:
For forged wheels (T6061 alloy):
T6 temper 6061 has an ultimate tensile strength (UTS) of about 310 MPa and yield strength of about 24 MPa after a 10hr cure at 340F. The data suggests that an additional hour at 340F would have little effect on the UTS (it's about linear at that portion) and the yield strength would actually go up slightly. Aging is much more sensitive to the temperature than the time at temperature. The strength data are log functions of time. Grain elongation at 340F does not occur until the hold time is over 24 hours, and it's still a log function of time.

Based on these data, treatment for less than 1 hour shouldn't reduce the fatigue strength significantly enough that Joe Average would notice it or be effected by it. I will say, however, that these data go through an inflection point at the 500F heat-treatment mark. A quality PC shop should know this, and be fusing their coatings in the 350F range.

Again, I think it boils directly down to the manufacturers covering themselves, just like anyone else would if you "modify" their product.