I want to completely refurbish all five 18' alloy wheels. After discussing with a local shop the process is done in three main steps:
- blasting with a fine compound to remove the old paint
- coating with electrostatic paint
- baking the coated wheels in an oven at 200 Celsius to allow the paint to polymerize

My concern is about baking the wheels at 200 C, it seems that some alloys used in wheels are sensitive and this temperature can affect the alloy structure. At this temperature the alloy annealing can take place.

Does anybody have any experience with this ?

Thanks.

This all depends what type of alloy and how long the set is baked in 200 degree celcius.

I copy this from internet:

Quote:

ASM Handbook Volume 2, Properties and Selection: Nonferrous Alloys and Special-Purpose Materials has the following information:

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

Based on these data, a 400 °F treatment for less than 1 hour shouldn't reduce the fatigue strength significantly.

I've decided to not do the powder coating, it's too risky. I've found another local shop where they will do refurbishment followed by a normal painting.

That convinced me:
http://www.ferrarichat.com/forum/technical...eaker.html

Quote:

With the greatest respect, this is an engineering question. It is not for refinishers or chrome platers to decide. Many forged wheels have been weight optimized for a specific load on a specific vehicle. That is, the weight is reduced to the absolute minimum required by the vehicle load, otherwise why bother? Therefore, any loss of strength compromises the reliability of the part and its load carrying capability as well. And potentially, the safety of the driver.The chroming process reduces the ductility and strength of the forged alloy to varying degrees, depending upon the methods used and the specific plating alloy used. This phenomenon, known as hydrogen embrittlement, is well documented scientifically and carefully tested for in aircraft/aerospace components.Wheels can certainly be designed with chroming in mind. Excess material and mass can be added during manufacturing to compensate for losses in the chroming tank. This thread, however, deals with REFINISHING.It is our opinion that there are simply too many unknowns in these processes to risk weakening the alloy. Therefore, for forged, heat treated alloys, we do not recommend powder coating except by trained expert facilities with quality systems and Brinell hardness testing systems.And we do not recommend chroming forged wheels, unless the wheel was designed for this finish. A cure temp of 375 degrees fahrenheit for 30 minutes will overage the alloy and begin the annealing process. This is not recommended by us, HRE, OZ, Champion Motorsports (who forbids powder coat entirely), BBS and most other forged wheel companies. This also includes the 50 or so forged wheel companies worldwide for which we supply the blank forgings.Many of these companies will void the warranty for any refinish not done under their control. We don't blame them.As far as the OEs are concerned, if you refinish or plate a factory wheel and ANYTHING goes wrong, you are on your own: ZERO warranty.Safety and liability are the issues. We don't know anything about your company, its processes, quality systems or technology. But if a wheel is refinished and then fails in service, or someone gets hurt, we all know who gets served with a lawsuit. The USA has 4% of the world's population and over 50% of the world's lawyers.

I had a look on the inner side of the wheels and the alloy composition it is marked, is AlSi7Mg. Because Magnesium exist in the alloy composition I believe this make the heating to 200 C even more problematic.

I think you're right to be careful. On the normal road condition the stress is fairly constant; but in off-road situation enormous stress exerts on the wheels of the vehicle. The baking of the wheels may remove all safety margin which has been built into the wheels.

Around here we have so many holes in the roads... is like driving off-road.