I must disagree. Especially with non-heat treatable alloys like 5052
and 5086 used in marine applications. These alloys are work hardened.
You are confusing bent strength with fatigue cracking. If you bend any
metal back and forth it will crack but if you bend aluminum once it gets
stronger. Aluminum can be bent and stretched more than almost any
metal. A beer can starts of as a flat disk.

Aluminum sheet usually comes hardened to some degree. The hardness
comes primarily from the rolling process. The amount is indicated by
the H number that follows the alloy number. For example H0 is anealed,
the softest and weakest. H1 is hardened only. H2 is hardened and
partially anealed. H3 is hardened and then stabalized. The second
number is the amount of hardening and the third number defines hardnes a
little colser. H116 is between 1/8 and 1/4 hard only. H34 is half hard
and stabalized. When you bend them the hardness and therefore the
strenght goes up slightly. When you weld any of them they drop back to
the anealed H0 condition and are up to 20% weaker.

Also if the weld is not done exactly right or it is a little windy when
it is done blowing the shield gas away you run the risk of hydrogen
enbrittlement which results in cracking.

Stephen Baker wrote:

Brian says:


Is there any issue with bends becoming weak?



No, there is an issue with bends BEING weak. ;-)
Take a sheet of aluminum, bend it 90 degrees, then bend it straight. Now try
to rip it.
See what I mean?
Welding will lose you a lot of strength, yes, but it is a well-documented loss,
and folks will generally use only strength figures for the welded condition.
If you use bent plate, and calculate for the un-welded strength, you _will_
suffer for it.

Steve "not an aluminum expert...."

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com