Shrinkage of Alum when heated

Hi,
I need to straighten a frame made of welded 6061-T6 4" square tubing. If it were made of steel I could use a torch to permanently bend the
tubing. As the heat is applied to one side of the tube it will initially expand, but the heat would be enough to cause a phase change that causes the metal to permanently shrink when it has cooled off.
My question is whether aluminum does the same thing?
Thanks in advance Bruce
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Bruce Lehmann wrote:

change
Don't try that with T6 alloys. T6 is a heat treating process to harden the alloy. Heating it again to significant temperatures results in a loss of strength. This cannot be repaired until the whole part is heat-treated again properly. Where T6 is applied, any loss in strength us usually not acceptable.
Aluminium has no phase change like steel, so the process won't work that well anyway.
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Exactly,
If you heat up any portion here you will end up anealing the area and will not be able to have that material come back up to strength without first anealing, and then re-heat treating the entire assembly where the damage has occured.
Paul
Andreas Rutz wrote:

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Thanks for the replies.
I'm not worried about strength in this case. The frame is to provide stiffness and is way over built. But it would be nice to have the frame straight for attaching other components.
Bruce
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snipped-for-privacy@thinkerf.com (Bruce Lehmann) wrote in message

Hi Bruce,
I think there may be a mis-understanding on flame straightening, although a phase change will distort steel (after all thats one of the ways heat treated parts get distorted in the first place) the operation of flame straightening is typically done below the phase change temperature of most steels (note phase change can be detected by a magnet). Generally a 100F temperature difference between tow adjaccent areas in a steel part will exceed the yield strength and distort steel. The same applies to aluminum - local change in T6 properties could be expecting depending on time and temperature used - when in doubt measure hardness.
Check out John P. Stweart Book "Flame straightening Technology for welders" ISBN 0-9692845-1-9
Ed Vojcak
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Ed,
The phase change concept didn't seem right to me either since the temperatures used in straightening didn't seem high enough.
So, the part to be straightened has to be contrained, either by it's own bending stiffness or an external structure, so that the thermal expansion can generate stresses above yield. Pre-stresses will also have to be considered. Also, I assume part of the effect comes from the reduction in yield stress with temperature.
Thanks for your reply
Bruce
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