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Old 04-14-2020, 09:44 PM
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Default Cracking aluminum

Bending up some 6061 1 1/4” aluminum sch 40 pipe and I start having problems with cracking all of the sudden. 700 linear foot over the last few months and a couple different lot#’s of pipe. Not a problem until Saturday morning when a joint cracks about 40 degrees into a 45 degree bend. Try again on the same piece and bam! 30 degrees in and another crack... try a new piece and it cracks within 20 degrees, rinse repeat and I have 4 20’ sticks left. As I go out to the trailer to compare lot #s on the remaining pieces I notice one pipe is split down the middle almost its entire length. Has anyone seen this before?

I tried annealing the pipe that was cracking and have had mixed results. One bent a full 180 and the other bent about 160 degrees before breaking.

NOTE: the piece split down the middle has not been bent or modified at all. It is in the condition that it was delivered in.
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Old 04-14-2020, 10:11 PM
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What temper? 6061-T6 is the most common and it's definitely NOT a bendable alloy. Over the years we've made thousands of bends using 6063 but on the odd occasion that we've been sent the wrong material we've rarely been able to make it to 45 degrees before the material breaks...
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Old 04-14-2020, 10:29 PM
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Bad seams in your pipe.
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Old 04-15-2020, 08:42 AM
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Quote:
Originally Posted by Shade Tree Welder View Post
Bad seams in your pipe.
+!. Time to return the whole lot.
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Old 04-15-2020, 09:12 AM
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I concur with Shade.


But I will add, in my previous job I had to bend some Alum Pipebfir a handrail. I found some old stuff in the rack that was probably 4-5 years old at least. It would start cracking at about 20- 30 degrees. Tried heating it up slightly, and got one or two done. But had to ok order new material to finish job, and the new material bent without a problem.

Somewhere I had read that aluminum will harden with age, and I attribute the older stock for most of the problems.


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Old 04-15-2020, 10:52 AM
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Originally Posted by toprecycler View Post
Somewhere I had read that aluminum will harden with age, and I attribute the older stock for most of the problems.
6061 does age harden, but you are getting cracks along the weld seam, so I
think it is more an issue of a bad lot and not so much aging.

I would have suggested extruded aluminum tubing, no seam. Also as mentioned
above 6063 is a more formable alloy and have better corrosion resistance.
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Old 04-15-2020, 11:12 AM
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I asked my two local suppliers last year about 6063 and they didn’t have it and couldn’t get it.

Only one piece is cracked down the middle. The others cracked across the pipe.
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Old 04-15-2020, 12:34 PM
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Quote:
6061 does age harden, but you are getting cracks along the weld seam, so I
think it is more an issue of a bad lot and not so much aging.
Agreed. It looks like your supplier got rid of the stuff he found in the back of the shed.

I guess I'm lucky down here as with the differing manf's that use Al in large qty's, I have had no problems getting any alloy properties I need.

6063 is a common variety in my neck of the woods. FWIW, I use the same suppliers as NG when necessary.

A local supplier helps me out with the drop shipping to his place. He usually gets a bit as well considering cost.
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Old 04-15-2020, 01:16 PM
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Are using any lube? If not oil the dies.
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Old 04-15-2020, 02:18 PM
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If you have been getting any 6061-T6 to bend without catastrophic failure consider yourself fortunate. As previously mentioned it is age hardening and that could play into why you got some (newer) pieces to bend and the older ones didn't. You definitely need to take that cracked piece back to your supplier - that's just bad material.

Any chance you can get a Mill Test Report from your supplier for the different heat numbers you have? That may give us more of a clue as to what's happening as well.
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