As-welded strength of 6061-T6 AL

[dirtft]

Just received the 2005 Aluminum Association Design Manual and there has been a major change to the listed as-welded yield strengths for just about all the weldable AL alloys. The explanation we received from the Alum Assoc was that they changed the test sample gage length from 10" to 2" so the .2% offset yld strength would more accurately represent the yld strength of the welded material. The reduction in strength for 6061-T6 was 25%, 20KSI to 15KSI! This is a major issue for our products (welded AL structures) and drops our safety factors from 2.5:1 to under 2:1. Our products have not had any structural issues in the field, but dealing with the lowered safety factor is going to be a major pain.

Anyone else run into this issue and what have you done or are doing about it?

dirtft

 

[WagEng]

Just a thought, but could you heat treat your entire structure after welding it up? If you keep it in the fixture during heat treat, it would probably be OK.

 

[dirtft]

WagEng,
We have thought about heat treating after welding, but that would be a major capital expense to install a furnace large enough to handle weldments that are up to 30' long. Currently we are doing our own testing to determine as-welded strength of our weld joints which are not identical to the standard ones in the ADM. We are also looking at substituting 7005 for some of the most highly stressed members. We shall see.

 

[MikeHalloran]

The real safety factor of your product didn't change.

An inaccuracy was removed.

It would be still more accurate to use a gage length that just spanned the weld in the test article, but the numbers might scare you more.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[dirtft]

Mike,
You are correct that the real safety factor has not changed and we have 25+ years of product in the field with no structural issues at all so we are not in fear of something falling to the ground. The issue is more of a marketing one where we have said for years that our safety factor was 2.5:1 based on a 20KSI yld strength and now it drops to below 2:1 because of a reduction in the listed yld strength to 15KSI.

I am trying to see if anyone else has run into this issue and how are they handling it. Changing a listed mechanical design property by 25% with no warning is a pretty major deal and surely we are not the only ones who have been affected.

Thanks for your input.