Does anyone know of anywhere where I can get my wheels powder coated in Mississauga area for cheap?

 

You shouldn't powdercoat. Powdercoating process involves heating the rims and high heat can reduce the strength of cast alloy.
Get them painted professionally by a rim repair/restoration guy.

 

Metalcoaters in mississauga is great, around $200 for all four.

 

http://www.quyscoating.com/ in brampton I was going to powdercoat my rims but after reading the paint vs powdercoat debates I chose not to.

 

You are not entirely correct as the powder coating process involves curing and not high temperature heat treatment. The typical curing temperature is at 200°C (390°F) for 10 minutes. Nothing will happen to the rims at that temperature. People have been powder coating their rims for years with no issues related to structural regidity of the casting.

Powder coating is NOT a diffusion type of coating (no diffusion into the rim material), it's more similar to overlay coating, thus high temperature (that is used to diffuse coating material into the base material) is not required. Remember, the powder coating paints are based on epoxy of different types.

 

And 200c is enough to compromise the molecular structure of alloy. Basic cast smithing rules apply. Heat = weaken. Shock cooling it strengthen's.

 

metalcoaters is pretty decent, had mine done there

 

Metalcoaters has been very fair... and dont forget they will go lower.. had a few things done there!!

 

1. No one can "Quench" or “Shock” material in air furnace (which is used for curing the powder coat paint). It’s called air cooling and generally is a very slow process compared to true gas quenching. With gas quenching, you can get a hard and brittle material. Usually quenching takes place in vacuum furnace from high temperature at the rate of 20 – 30 Deg C per minute.

2. You are correct about basic rules, but they apply mostly at 600C and higher. There will be no phase transformations at 200C that could affect the material.

The picture you have posted shows a brittle fracture at the spokes. The location of the fracture is exactly at the weakest cross section of the spokes and in the location where there is a high chance of casting internal pores to exist, again, because it is the small cross section of the spoke profile and bubbles in molten material will tend to gather right there. There is a lack of info as to when did the fracture occur: right after coming out of the furnace or while the rim was already on the car. (The rim is very dirty on the picture - indicative of being on the car at the time of the fracture, then tire was taken off at the tire place, if tire survived). Fractures like that are always associated with stresses, either internal thermal stresses or dynamic mechanical stresses (like catching a pot hole while driving - I've seen in person on my friends Passat Mark III in Europe, but he was going 200 km/h and had caught a pot hole, his OEM WV wheel fractured exactly like on the picture you have posted). At the fracture surfaces we have found internal pores that were there from day one:

Also in this case on the picture, most probably there were internal (subsurface) pores in that casting. Even OEM casting process does not have a 0% scrap rate - impossible. The manufacturer does use Radiographic inspections, but like in every industry, there are acceptable limits for the found internal defects.
Even if the damage was resultant because of the improper powder coating curing cycle, I'd look into the furnace charts to prove that the rim was quenched/tempered.

I work for the company that repairs aeroderivative (land based counterparts of the engine on the planes we all fly on) and heavy duty industrial gas turbine components for living for more than 30 years now. We are direct competitor of GE, Siemens, Rolls Royce and Mitsubishi Heavy Industries (OEM) and such repair shops like WoodGroup, Masaood John Brown, Elbar and similar ones in other parts of the world. We deal with heat treatments 24/7 as we run three vacuum furnaces just in one of our facilities.

Gas turbine consists of the “cold” section - axial compressor, and a “hot” section - gas generator + power turbine. In a so-called "cold" section temperatures of the air goes from ambient (outside) to 300-450C depending on the size of turbine and a number of stages (up to 17 stages) in the axial compressor - because the air is being compressed. So, after repair, several stages of rotating blades in the compressor section receive a special coating (Al based with the organic binder), which is applied same way as powder coating. The curing temperature for that coating is 315 - 370C. The coating is applied for a different purpose, than on the rims of a car – to protect the blades from low temperature corrosion, yes SS does corrode at specific temperatures. The blades made out of Stainless Steel and never fail in service if repaired correctly with proper heat treatments. the coating is applied and cured AFTER stress relieve heat treatments were complete at around 500C. The blades are forged at manufacturing and the coating curing temperature does not affect their service life (material mechanical properties) in no way. Forgings are more susceptible to wrongful heat treatments than castings. So we have to be very carefull with what we do to those parts. Catastrophic engine failure (blade lets go by fracturing at the airfoil) would cost up to 10 mln $ on a heavy duty industrial gas turbine.

In reality in order to get hard material with ductile properties, it gets subjected to high temperature followed by gas quench (Argon or Nitrogen) – material becomes hard and brittle, then material is subjected to slightly lower temperature with controlled cooling rate (2 – 5 deg per minute), then material becomes hard and ductile.