T6 Aluminum vs Powder Coating 1

[LukeG11]

Seeking someone who knows more about T6 aluminum and heat treating than I do.

I recently had a set of racing wheels powder coated. I had no idea that the powder coating would do anything to the T6 annealing process and found out after the fact. Now I am trying to figure out if the wheels are still usable, or if I have ruined them and made them unsafe.

How much strength reduction as a percentage would heating T6 Annealed Aluminum to 390F for 1.5 hours cause? I spoke with the powder coater and they confirmed that was the temp and duration.

I have studied the linked chart below and from what I can tell it appears to be very minimal. Assuming they annealed the wheels to maximum tensile strength at 400F, another 1.5 hours at 400F appears to be a <5% change.

Thanks for any help!!!

Link

 

[WKTaylor]

LukeG11...

Suggest contacting the wheel manufacturer [or vendor] to clarify/resolve Your question.

Reason.

'T6' is an aluminum-alloy temper state. Without knowing the specific aluminum alloy Your wheels are made from [3-digit number for castings; 4-digit number for wrought], the term 'T6 aluminum' is meaningless... and NO ONE... except the manufacturer... can answer Your question.




Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[tbuelna]

As WKTaylor noted, -T6 is a temper designation indicating a solution heat treated and artificially aged condition, and not an annealed condition. The -T6 temper would indicate the aluminum material is some form of heat treatable alloy. But without knowing the specific alloy composition and form (wrought, forged, cast, etc), it would not be possible to determine the effect on mechanical properties of the elevated temperature exposure you described.

Just for your reference, here is a paper with some graphs (figs. 12c & 12d on p.16) showing the effect of exposure at 390degF vs time on the RT tensile properties of 6061-T6 aluminum in the context of a painting operation. You can also take a look at MMPDS-01. Figures 3.6.2.2.1(c) & (d) show the effect of exposure at various times/temps on RT mechanical properties of 6061-T6.

 

[swall]

356 is a common cast aluminum alloy for wheels. The heat treatment schedule calls for aging at 310F. So, a powder coat cure temp of 390 would overage this alloy and degrade the tensile strength. To fully answer how much degradation you might have would require obtaining some test bars of the alloy used for the wheels and running them through the powder coat cure oven, then performing a tensile test.

 

[SwinnyGG]

Call the wheel manufacturer.

Your use of the term 'racing' leads me to believe you may be talking about a 3-piece wheel with a cast or forged center, which will likely have very different properties than 6061-T6 depending on the specific alloy used.

You are not the first person in the world to powdercoat an aluminum wheel, that I can guarantee.

 

[drawoh]

jgKRI,

If the wheel were forged, the code would be H, followed by a number, e.g. 5052-H32.

--
JHG

 

[WKTaylor]

Hmmmm...

LukeG11 hasn't replied/commented on any element of this thread. I personally dislike that behavior.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[LukeG11]

Thanks for the responses guys.

Per the manufacturer... flow formed monoblock construction, low pressure cast (one piece)

The manufacturer told me the wheels are ruined and to throw them away, literally. Although I respect them, I believe that is more of a legal response to cover their ass and not respective of the actual situation.

I am trying to determine how much degradation they would have seen from the powder coating process. A 5% or less change is not one I would be worried about. I'm trying to determine a rough estimate of the facts behind this and make an educated decision based on that of whether or not to use the wheels.

 

[BrianE22]

It's also possible the part wasn't at that temperature for 1.5 hours. They might have put it in the oven and let it sit there for 1.5 hours but of course it takes awhile for the part to get to 400 deg F. The power coat paints I've seen only require the part to be at 400 Deg F for 10 minutes or so.

I went through what you did with our 356-T6 castings years ago. I didn't find any published data that said the strength would decrease by more than about 3% (400 Deg F for 1/2 hour).

 

[LukeG11]

Thanks for the info Brian! Very true about the temp and time. From what I have seen, I would expect a strength decrease of less than 5%. Just checking though to make sure, I figured you guys would know best.

 

[djhurayt]

On another thought path, unless these wheels are some super exotic alloy, people powder coat wheels all the time . . ., yes I realize that these are for a competition vehicle, but still, even racers powder coat wheels all the time. I have powder coated motorcycle wheels in the past and they get pushed pretty hard.

I also tend to agree with the manufacturer doing a CYA in tell you to scrap them.

One other thought is that I would run them. Particularly since being on my race car these things will have the opportunity to be inspected after each event. Unlike on a street vehicle where at best the may get looked at during a 5000 mile tire rotation, maybe.

 

[LukeG11]

Very true and I agree. Just got a bit nervous with the manufacturer telling me they are now dangerous and need to be destroyed.

 

[WKTaylor]

LukeG11...

Did the wheel OEM ever tell you specifically what alloy the wheels were made from?

"Per the manufacturer... flow formed monoblock construction, low pressure cast (one piece)." ... is a very obscure/obtuse reply from the OEM. They still didn't tell You what the wheels were made from.

Was there any apparent warpage or distortion after this baking process [still round/true]?

Perhaps there is an auto racing components forum on another website that this can be discussed...?!


Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[SwinnyGG]

The other thing to consider is that if this wheel is actually on a race car, you're less likely to cause a failure than if you drive this car and this wheel set on the street.

Unless you're traveling back in time and racing at Lime Rock Park when it was still full of potholes and chop. In that case throw them away.