Powder coating a flex fan?

That`s the same fan i run..hard to beat it`s ability to pull air and cool...

I had 2 done.   70 AMX 390 & 78 CJ5 Golden Eagle with a 304 and it looks great and no peal at all.  The powder coat place said they do lots of fans with no problems.  This was a commercial size operation.   Huge place.  They do car frames etc.  and endless  stacks of aluminum railings for buildings.

Powder coating ovens won't take the temper out of the blades. You'd have to go to around  500 degrees to do that. From Wikipedia:

"Tempering quenched-steel at very low temperatures, between 66 and 148 °C (151 and 298 °F), will usually not have much effect other than a slight relief of some of the internal stresses. Tempering at higher temperatures, from 148 to 205 °C (298 to 401 °F), will produce a slight reduction in hardness, but will primarily relieve much of the internal stresses. Tempering in the range of 260 and 340 °C (500 and 644 °F) causes a decrease in ductility and an increase in brittleness, and is referred to as the "tempered martensite embrittlement" (TME) range."

Quenched steel is a hardened steel. This is a critical statement:
"One-step embrittlement usually occurs in carbon steel at temperatures between 230 °C (446 °F) and 290 °C (554 °F), and was historically referred to as '500 degree [Fahrenheit] embrittlement'."

So stay below 400 degrees and you should be fine as far as affecting steel strength. The hard powder coating could still crack and flake off.

Frank.....not temper in the sense of Heat Treatment (I think I misused the term for this discussion and agree that Powder Coating Temps are far from having any negative effect on the blade materials), but rather using abrasive blasting will Stress Relieve each side of the thin Stainless Blade and change it's shape. The problem is you can not equally abrasive blast the blade on both sides, so each blade will have "effectively" a different pitch (or bite of air)..making a 7 blade fan act like a 6 or 5 or 4 or less blade fan. I see this happen at times when Shot Peening materials that are too thin and the compressive stresses damage the part, rather then strengthen it. Think of Shot Peening and Glass or Sand Blasting as a like technique, just with different mediums......you are using set air pressure to move a particle (Sand, Glass bead or Steel Shot) at a fixed object. This is illustrated by how Shot Peening intensity is measured, usually via a Almen Test Strip. The test strip is has a known thickness, hardness, size and flatness.....when the test strip is struck with a specific media size for a specific time, intensity (velocity) it will bend from compression of the metal on one side. That "arc" is measured to determine if the proper values are being used....or need adjusted..such as longer time or higher intensity. Sorry to ramble on here, but since we can not be so exact with Glass or Sand on a thin fan blade, the amount of "arc" is very non-precision. The glass/sand media breaks down and is never consistent, air pressure varies....even the angle that the particle hit the surface can make large variances. I have personally had several customers bring me fans "ready" for paint...or have already painted and all the blades are not on the same plane....will not lay flat on work bench.

Here is a picture of the Almen Test Strips before and after Peening.

I just did the fan on my 390, and instead of blasting it I immersed it in a container of apple cider vinegar and let it sit for a day. Took it out, rinsed it off, and watched the rust fall off in sheets. Then I soaked it in a water/baking soda mix, and POR15 metal prepped it. Then I sprayed it with the POR15 chassis black. Looks awesome. Next step with be a satin clear for added durability.