My roommate (who I trust very much) told me that powdercoating wheels can/will degree the wheels over time and can potentially lead to cracking a wheel.

Is there any truth to this? and what other methods are there to have wheels painted besides powdercoating

thanks

 

it's not over time, it does it right away by heating the wheels up to the point where the metal will lose some of its original strength properties(from annealing). Most people have been fine with a powder coat and if you are worried you should talk to your p-coater about getting a powder that can bake at a lower temp, the lower temp (I think its 350) seems to be fine. I personally have never had a problem with powder coated wheels so I guess it depends on many variables.

 

I don't get it. I'm sure the hub of the wheel gets close to that temperature or beyond on track days.

You can age/heat treat aluminum to make it stronger by heating it to a relatively low temp and letting it cool. I think the aluminum used to make car wheels is non annealable. It's heat treated after manufacturing to artificially age and strengthen it. I :think: wheels are made from 60 series aluminum since I know that most car wheels have an aluminum/copper mix...among other things. Copper alloyed aluminums are usually a 60xx, IIRC.

Non heat treatable aluminum needs like 650-775 degrees F to anneal anyway....

Besides, annealing makes the metal softer and easier to bend...not more brittle and prone to cracking. Annealing is done to PREVENT cracking.

 

just a thought:

it's the method and duration of heat transfer. i suppose the oven gives a more constant, uniform heat through all forms of heat transfer

versus a track situation where the heat source isn't constantly being applied and is mainly through conduction.

 

sorry I was wrong, the only reason it would weaken the metal of the wheel is by over-aging the aluminum:

http://www.eng-tips.com/viewthread.cfm?qid=151053

You would think I would know this considering I'm in a material science class

 

There was a long thread about this in the r&c forum.

The conclusion was that, just to be safe, you should powdercoat wheels as the lowest temperature possible. Also, be sure to ask how they prep the wheel before the PC.

 

Lots of variables, but I've been in the wheel business for a while now and honestly, there's a lot of opinion and extreme cases, but there's really nothing solid.

Lower temp is better, but too low won't do the job. The right temp is somewhere around 375 degrees, but there's people that will tell you that's too high, and there's people who'll say you can go much higher.

The point is, around 375 degrees WILL alter the wheel at the molecular level. But guess what? Alter =/= weaken. In some cases it does, but not in all.

I've had several wheels powder coated with no problems. Race cars and even NASA space shuttles have powder coated parts, and no problems. The U.S. Air Force seems to get a lot of jollies out of powder coating various things. No issues.

Alternate approaches include PVD processes in a vacuum environment (mostly used in a new form of chroming), or simply painting the wheels with spray paint made specifically for wheels. One thing to remember no matter what you do to refinish a wheel is that the proper preparation will work wonders ;-) If you see a place that powder coats for less than $50 a wheel, you're probably looking at a place that cuts corners on the prep process, and that's bad.

 

Interesting to note. So if it's able to be baked at 350 you think that's generally a safe temp?

I'm just kicking around the idea, because I do wanna see my car sitting on something different. Thing is the ap2v2's look great, but the stock alloy color or w/e you want to call it just looks so bloise.

I met a neighbor of a guy on our local forums who quoted me $60 a wheel (which I think was a slightly discounted price). I appreciate the insight guys

 

Some alloys are heat-treatable, yes. But wheels will have already been heat treated. Further exposure to temps above ~350F will overage the material and degrade properties.

Most forged wheels will be 6061-T6 (heat-treated) and most cast will be A356-T6 (also heat-treated).

Heat-treating for strength and annealing to soften are two different things.

You wouldn't want to run wheels that had been ANNEALED! Soft, yes. Ductile, malleable, yes. Also VERY weak, they would absolutely crack and fail despite not being as brittle simply due to lack of tensile strength.

You might anneal heat-treated aluminum in order to be able to form/bend it into the desired shape without cracking the material, but in any kind of structural application you would then want to heat-treat it again to get strength properties back.


Long/short: As long as the powdercoat process doesn't expose wheels to temps above ~350F for forged (6061-T6) or ~325F for cast (A356-T6), you have absolutely nothing to worry about, there won't be any loss of strength. Above those temps, there may be, dependent on temp and time of exposure.

Wheels improperly heat-treated have failed, so if you have it done make absolutely certain that it's a process guaranteed not to degrade strength properties of heat-treated aluminum.

 

Also worth noting that the preparation process has to be compatible with aluminum alloys as well. Apparently some caustic pre-powdercoat cleaning/degreasing processes that are commonly used for prepping steel aren't compatible with aluminum and may also lead to problems/failure.