T6 aluminum fatigue
T6 aluminum fatigue
(OP)
Hello all. First of all, I apologize for asking what I expect may be a simple question to you. I am not an engineer, but would like to ask those who are and versed in what the issue is
I am a powder coater. I have a set of motorcycle wheels cast in T6 aluminum. Since they are cast, SOP says they should be outgassed above the powder cure temp, in this case 400* F, prior to powder application.
The wheels have been outgassed and saw a PMT of 430* F for about an hour. My customer is very uneasy about the wheels seeing these temps in this grade of aluminum. Monday I hope to have them Rockwell tested.
If their integrity has been compromised, is it possible to anneal them and return them to where they should be?
Apologies for coming here like this, but you go where the water is!
Thank you.
I am a powder coater. I have a set of motorcycle wheels cast in T6 aluminum. Since they are cast, SOP says they should be outgassed above the powder cure temp, in this case 400* F, prior to powder application.
The wheels have been outgassed and saw a PMT of 430* F for about an hour. My customer is very uneasy about the wheels seeing these temps in this grade of aluminum. Monday I hope to have them Rockwell tested.
If their integrity has been compromised, is it possible to anneal them and return them to where they should be?
Apologies for coming here like this, but you go where the water is!
Thank you.





RE: T6 aluminum fatigue
They will probably not be very round after the SHT.
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: T6 aluminum fatigue
RE: T6 aluminum fatigue
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: T6 aluminum fatigue
take a look over here, there is some discussion, : http://sl
found some more discussions without a real answer... and another quote; "The discussion usually ends up with the general consensus that The coating process will not harm the aluminum enough to matter, as most any aluminum structure is over engineered by enough of a margin that the heat treating process is not compromised to a degree of eminent failure. "
I think i have to agree with that quote.
RE: T6 aluminum fatigue
I believe you are right to question the 6061, owner believes they are 365 after all. Going tomorrow to have them Rockwell tested to get some clear data as to what has happened. Owner also has some unlomested factory wheels he is having tested on his end. As long as teh wheels are from the same few years of peoduction, is is safe to assume they are of similar alloy? 90's Honda motorcycle?
Really appreicate the info and help here. As messed up as this has become, its a little comforting to get educated info and leads such as that link.
RE: T6 aluminum fatigue
Riders depend on those wheels to stay alive.
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: T6 aluminum fatigue
RE: T6 aluminum fatigue
RE: T6 aluminum fatigue
http://w
Not large enough to get any kind of a good reading on the wheels as they really could not be held still. Professor has a PhD in Metalurgy. Smart guy. We talked for ~30 minutes and his general concensus was that the wheels have not been rendered useless but only a hardness test could validate anything. Spent a good amount of time pouring through ?ASM? books and charts.
I am going to look into buying 365-T6 bar stock, doing some controled bakes at varying temps and times and have those tested. This seems to have piqued his curiosity a bit and is eager to help out and get concrete data. I can report back with results if anybody is intereted.
RE: T6 aluminum fatigue
RE: T6 aluminum fatigue
The Brinell test uses a 10mm ball, which measures the hardness over a far larger area than the 1/16" ball of an Rb test. This can be a factor on castings.
BTW, the alloy is 356, not 365. If you buy any for testing, make sure you do not get 355, which is stronger than 356.
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: T6 aluminum fatigue
"Standards for Aluminum Sand and Permanent Mold Castings" from the Aluminum Association if you contemplate continued business powder coating aluminum wheels. The standard costs $60 and lists the ageing times/temperatures for all of the common cast alloys.
RE: T6 aluminum fatigue
Is this actually the process of eutectic seperation?
There are some situations where this is desireable but I would like a better understanding of which alloys are susceptible to this, and see if someone with knowledge of this process will comment on these wheels.
I have run into this issue while coating a cast aluminum piece that is not too different than this wheel in size/mass and found that it could not be re-treated. But the temperatures involved were over 700 degrees.
RE: T6 aluminum fatigue
~Metalguy, we are looking into obtaining a sacrificial wheel right now. Of course no one wants to put up a good wheel but bent/unusable ones should pop up before too long. That would be the ideal candidate for testing.
~swall, That book sounds like a perfect addition to what I do, but with ym very limited knowledge, I'd have next to no idea what alloy I am dealing with. What little I have gathered so far, 356 seems to be the alloy of choice in an application like this?
90% of the aluminum I powder coat does not bear a load, i.e. motorcycle valve covers, trim castings, etc.
The general standard in custom powder coating is to outgas for 60 minutes 50* F above the intended powder cure temp. In my case, 400*. This to ensure any pockets of gasses are released and oils/chemicals are burned to the surface. All to ensure this doesn't happen during the cure process ruining the finish mandating a complete strip and recoat. The professor I spoke to mentioned that 300* for 60 minutes should be sufficient to accomplish this. Opinions?
RE: T6 aluminum fatigue
RE: T6 aluminum fatigue
To share my experience. I heated a circular aluminum casting to apply a coating and it completely lost functional strength. This result surprised the engineer we consulted on material selection and the company applying the coating, as well as me. So my company tossed three highly finished, highly machined pieces.
But to just post that information to this thread without some explanation of how it may be different from his wheel situation would be irresponsible. So the person who can answer my question might have some insight as to whether this wheel might run into a similar problem.
RE: T6 aluminum fatigue
RE: T6 aluminum fatigue
I really appreciate the time/temp specs on the aging. Reading that, the problem begins to be time/temp requirements for powder. Typically 400* for most colors. Primers can require 460*. Soem can get as low as 325*. Its possible to 'slow bake' powders at 10%-15% lower temps fro longer times but then its possible to run into adhesion issues.
Fortunately, time requirements at those temps are usually just 10-15 minutes once the part reaches temperature.
RE: T6 aluminum fatigue
RE: T6 aluminum fatigue
Simulated teh original bake tonight and will get those parts retested tomorrow.
I was very suprised at the softness of that aluminum. Fully epxected high 40's to low 50's.
RE: T6 aluminum fatigue
Took that part back and tried to simulate the original bake. I wasn't able to start until late at night and didn't get the mass exactly right and wanted to err on the light side but got thigns fairly close. In retrospect I wished I'd not been as compliant in getting it done. I believe the ramp up was steeper and cool down was slower.
Retested the original sample piece and got a low of 19 and a high of 29. Another unbaked sample produced similar results but also showed a hit of 19. At teh same time a baked part showed a reading of 64. Both the professor and I believe those readings may/probaly have been skewed as the parts were not parallel and may have been the result of an imperfect sample surface (cast). We were both suprised at the results.
As much as the mass in the oven wasn't spot on and heat/cool ramps were not exact either, the temps remained spot on at 60 and 90 minutes. 430.
This has sparked a bit of interest in me and I hope to get another whole wheel I can chop up and run more detailed testing on.
Again, thanks for all the replies and guidance. Its been a great help to me!
RE: T6 aluminum fatigue
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: T6 aluminum fatigue
What does the Brinell do the Rockwell test does not?
RE: T6 aluminum fatigue
That should give a better reading than the "B" scale--bigger area being tested.
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: T6 aluminum fatigue
RE: T6 aluminum fatigue
http://www.carbidedepot.com/formulas-hardness.htm
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: T6 aluminum fatigue
RE: T6 aluminum fatigue
RE: T6 aluminum fatigue
Seeing what I have from all of this, I completely agree wtih swall. There is a lack of awareness on this. At teh same time, no one has any supporting data that load bearing items (wheels) have failed because of being powder coated. A few powder coaters (of whom I am now one :) ) will agree these is something to this and should be aware of and not abused.
Looking at previous posts I realize I haven't posted up any data. Testing a sample piece apporx. the size of a quater yielded results varying from 29-42. Again, this was the size of a quarter. Cycled that piece along with the rest of the sample piece through the oven which had a PMT of 430 after 30-45 minutes. total bake time was 90 minutes.
I had cut chunks out of the center (hub) part with a sawzall. Looking back, this may have created some heat and altered thigns a bit. Still, 2-3 different pieces and the results varied from 12 on an unbaked section from teh hub to 62 on a baked section.
Kedp in mind these parts were not perfectly flat, let alon parralel surfaces. Even the tested surfaces had casting flaws we had tried to file smooth.
The general results did show that parts that had tested around 36-37 dropped to low-mid 20's. That was really the most accurate we could get considering the shapes of what we had.
I believe we will do further testing after the holidays.
RE: T6 aluminum fatigue
RE: T6 aluminum fatigue
Excellent answers! That's why you got a red star.
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: T6 aluminum fatigue
Tell me exactly what you want tested and how and I'll do it!