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Fabricating & metal temper

KatieB

KatieB

Well Known Member
As I'm fabricating parts from both 6061 and 2024, the metal will often heat up to the point where I can't hang on to it. This happens mainly with the band saw and the disc sander for cutting and final-shaping. I've been holding my elevator hinge brackets with a vise-grip during cutting and grinding so I don't burn my fingers.

How hot can these alloys get before I have to worry about screwing up the temper? Is it bad to stick them in water to cool them, then put them back on the grinder? I read that the initial heat-treat temperature was like 900 degrees, but how will 200-300 degree temperature fluctuations affect the strength?
 
I seem to remember being taught (years and years and years ago) that if you can keep aluminum under 350 degrees, it doesn't even know it has been heated. Cylinder heads are usually god up to 500 degrees before you start worrying about immediate damage (I like to keep mine under 400, consider 450 to be red line, and take immediate action to reduce them above about 420.

I often wear gloves when holding aluminum parts to a wheel, sander, or saw. If I can't hold on to it with leather work gloves, I stop until it cools down. I doubt those temps are above 200 degrees, and often dip them in a pan of water to get the temps back down to start workign again.

I'm sure Gill will be along soon with an actual reference document...;)

Paul
 
Thanks Katie and Paul, I've wondered the same thing over the last few years but never tracked down an answer. Seems like I did read once that if metal is too hot to touch with your bare skin, it's over 140 degrees F.

Dave S
 
Hot!

I've had water drops boil off of pieces of 6061, so they were above 212F.

Gil!! We need some data!! :confused: I guess if people normally do this while they build their planes, then go out and do aerobatics without the wings falling off then it's OK, right? :rolleyes:
 
If you know the temperature you are trying not to exceed, there are temperature tapes and paints.

If you just want to know how hot you are getting the piece you can purchase a temperature gun, just point it at the work and it will read digital temperature. These can be had for as little as $20 but most you will find are $50-100. Radio control airplane suppliers carry them as do Amazon.com and Sears.

Jordan
 
AC 43-13-1B para 4-54 (b)

says it all. Keep it below 212. My experiance with actually heat treating is this range of temperature is in the artificial aging range as in "tends to impair". I personally wouldn't worry about it unless you are grinding on a spar or other highly stessed part for an exending time.
Andrew
A&P I.A.
 
Data!!

Thanks!! I read that AC last year, but now have Chapter 4 bookmarked. Time to review it.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/list/AC%2043.13-1B/$FILE/Chapter%2004.pdf

Here is a quote:

b. Reheating at Temperatures Above
Boiling Water. Reheating of 2017 and
2024 alloys above 212 ?F tend to impair the
original heat treatment. Therefore, reheating
above 212 ?F, including the baking of primers,
is not acceptable without subsequent complete
and correct heat treatment.
 
Mike S said:
IIRC, quenching in water is how you soften rivets----of course the temp is a lot higher before the quench, but ???
Click to expand...

Just to be clear - I am talking about getting a piece down to touch temp - and I am pretty much a wimp when it comes to burning my fingers. I never get anything hot enough on a wheel where it creates steam or bubbles when I dunk it in a pan - well below the 212 degree limits, and I can't imagine the materials properties are changed.

Paul
 
Paul, my concern is that the rapid cooling of the rivets from a high temp, is how you soften them-------

Now, by a bit of left handed logic, it seems to me that a rapid cooling of alum from a lower temp is going to cause a softening also, but less due to the heat of the material in the first place???

I really dont know, just using extrapolation based in ignorance to create speculative confusion here :confused::confused::confused:

We really need a metals engineer to jump in on this one.
 
We bend, shape, stretch and form complex aluminum parts at work. Depending on the part, we sometimes purchase 2024 and 6061 aluminum in the O (soft) condition. The parts are subsequently cut and formed. We then heat treat it to the W condition (working) and restrike or re-form the part. The parts will then change to the T42 temper over the next 96 hours. However, the parts will remain in the W condition if they are stored in a freezer.
The O to W process involves 900 degree F ovens and water tank quenching. Our parts won't get quite that hot by contacting a belt sander.
 
Shooting from the hip

Seems to me I remember that the alloying metals are "put into solution"? at 910 to 920 degrees. The quench in water from that temperature aligns the grain structure to make the material tougher. It comes out a little softer but immediatly begins to harden. 2024 "artificially hardens" in three days at room temperature, most of the hardening takes place in a few hours. This is why DD rivits are put on ice after quench (ice box rivits), to stop the hardening proccess from starting. The 7000 series alloys need an elevated temp to harden, I'm not familiar with the 6000 series. Annealling requires very slowly cooling down the metal.
I got to work on Nortern Air Cargos DC-6's, designing repairs from the Douglas SRM and making parts from the Douglas Standards Manual. Manuals aren't written like that anymore.
Andrew
A&P I.A.
 
Ironflight said:
I seem to remember being taught (years and years and years ago) that if you can keep aluminum under 350 degrees, it doesn't even know it has been heated. Cylinder heads are usually god up to 500 degrees
Paul
Click to expand...

Any hotter and then it could be the other place !!
 
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An excellent resource is found in the Alcoa Aluminum Technical Book Series such as "Riveting Alcoa Aluminum", "Welding Alcoa Aluminum" and "Forming Alcoa Aluminum."

These resources will answer all of the points (and more) raised above.

I'm reluctant to attempt an answer because there is so much information in these, and other works, that will provide a continuing benefit.

If you don't know the answer or do not have a suitable reference book (there are many) you really should get the exposure. Besides, I might get it wrong! :^)


Marc Bourget
TC#5436
 
Keepin Cool

I will look for the Alcoa books-- thanks!

One thing that reallly helps -- I replaced my bandsaw blade and sanding disc today. Holy cow, there is so much less friction, I can hold on to the pieces with bare hands now! :cool: The bandsaw blade I replaced was new a month ago, but ripping those long 3/16" 2024 doublers for the rear HS spar must have worn it out (16 feet total).
 
re shaping metal

Hi Katie,

Did you use the bench grinder to shape up or trim your stiffeners instead of a snip? is that what you did? i need to know becuase i am trying to do the same and i need to know if you had any issues wth is.

Thx
Omar.
 
Source for publications

Marc Bourget said:
An excellent resource is found in the Alcoa Aluminum Technical Book Series such as "Riveting Alcoa Aluminum", "Welding Alcoa Aluminum" and "Forming Alcoa Aluminum."
Click to expand...

Marc, I had a look on the Alcoa site and was unable to find these publications. Are they still available? Can you provide a web link?
Thanks
 
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We anneal 2024-T3 ribs and other parts at work in order to use thinner aluminum and we heat them to 925 degrees for that process. The are quenched in cold water after reaching temp and put in a freezer where they retain their annealed state for up to 30 days. We hydroform them while in the anealed state so that there are no cracks or grain issues. After forming they are allowed to come up to room temp and they self heat treat back to the T3 state.
 
2024 is a copper alloy and is known as a 'solid solution' of copper in aluminium (or aloominum if you prefer) that gets its strength from the copper precipitating out of solution at the aluminium grain boundaries. Heating to ~ 500C/900F and quenching immediately afterwards in water re dissolves the copper into solution and makes the alloy much more maleable (for a short time - about 2 hours). After a week at room temerature the copper precipitates out again and its back to its original strength - but that can be forced with further heat treatment. Freezing the parts (below -20C/-5F I believe) stops the re-hardening process.

So heating by working with the tools in your shop, for the time you would be applying the heat, is unlikely to do very much, but heating up to boiling point does seem a bit excessive! Perhaps more frequent dips in the water would be better? To bend a piece of 2024 through a tight radius it can be beneficial to soften the metal - but how do you know when it gets to 500C? Wipe some soap (carbolic is best) on the metal and heat gently from the back side until the soap turns black - and immediately quench in water. You will have a short period to work the metal - only works on thin sheet.

6061 is a magnesium/silicon alloy - I don't know much about its heat treatment.

Pete
 
osaleh said:
Hi Katie,

Did you use the bench grinder to shape up or trim your stiffeners instead of a snip? is that what you did? i need to know becuase i am trying to do the same and i need to know if you had any issues wth is.

Thx
Omar.
Click to expand...

Omar-- I rarely use snips for anything other than cutting largely oversized blanks for scratch building (did this with the parts for my CX4 tail). Snips leave serrated edges and cracks if you let them close all the way onto a piece. I've been using a band saw, disk sander, belt sander & hand files for most of the metal work so far.

Thanks for the new insight on heating, Pete and Randy-- I now try and keep everything to touchable temperature, just to be safe. I couldn't believe how much difference a new band saw blade made for keeping the temp down while cutting thick pieces--and they dull quickly while cutting thick 2024 bar stock so we now keep a few new ones "in stock."
 
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