I read this and thought it was kind of intresting
I'm trying to get a set of my ASA IS6's repaired and have been reading up on powdercoating aluminum alloy rims. For those who aren't familiar with powdercoating, it involves baking the item in an oven for 400 F for 20 minutes. I was concerned about this heat process affecting the hardness of the wheel's alloy. After some research, I found that my fears are not unwarranted. There are a few threads on the NASIOC Subaru forums about cracked, bent and broken rims that many feel were the result of the powdercoating process softening up the rim. One forum member even contacted BBS (who makes the forged STi wheels) and they responded:
"The heat involved with stripping the finish and powder coating process will compromise the structural integrity of your wheel. If you change the color, paint it like you would paint your car. Thanks for asking first!!
Thanks again,
Michael Cox
BBS of America"
There's more:
"We always prefer the wheels not to be powder coated because of the heat involved. They're heat treated during the manufacturing process so reheating them isn't the best thing. Another reason is what if the finish doesn't come out right and the people powder coating it does it again to try to get the finish right....heated again....
It's kind of scary what people are doing to wheels out there these days. That's our position. Just be careful. If you have any other questions, please let us know. "
Apparently the issue lies within the heat treatment and the alloy of the rim. Re-heating the alloy hotter than it was heated during the heat treatment stage can apparently soften the rim. Luke at the Tirerack posts on many forums and has also advised strongly against powdercoating for the same reasons. I did contact him and found out that my rims were heat treated, low pressure cast, & shot peened when produced. The exact alloy used was AC4CH-T6 Aluminum alloy.
I understand that some OEM rims are powdercoated (although I'm not sure which ones). My understanding is that the powder is baked during the heat treatment stage and so this isn't an issue.
I know, there are thousands of people who have powdercoated rims without problems but I'm also aware of quite a few failures including a friend of mine who lives a block away. The last time I talked to him, he said something about cracking his BBS CH's. He just had them coated a few weeks ago.
Something to keep in mind, especially after seeing pictures like this (scroll down):
http://www.witchdoctormotorsports.com/wd-news-tde0607mar04.htm
I am sure there are different alloys, maybe lower bake temps and perhaps "safe methods" to coat rims. However, I don't think it's worth the risk. I understand that Tig welding is the approved method for welding damaged wheels because it doesn't transfer much heat to the rim during the repair. If that's an issue, I'm not sure why so many wheel repair places are quick to throw the rims in an oven. Food for thought; I'm interested in comments or opinions. I'm not a metallurgist but the information and the warnings that I've read were enough to sway me for now. I'm going to stick with paint when I repair these ASA's.