[totalmechanic]

Hey, been a visitor to the site for a while and had a question:

I came across this article about the strength and durability of weld joints in 6061-T6:

http://www.intrepidequipment.com/handcy ... rials.html

In summary, a quote:

"The most important thing when considering aluminum is the ease with which they can be welded, and the strength of the weld.

When aluminum is welded, the weld zone becomes annealed. The key difference between the alloys is that 7005 recovers some of its strength after welding in a process known as age hardening (or low temperature precipitation hardening), while 6061 requires an expensive high temperature heat treating process to regain strength and temper.

• 7005 has approximately 60% of its original strength after welding and age hardening.

• 6061 has approximately 30% of its original strength after welding."

Two questions:

1) Is the writer correct about the post weld condition of 6061 and does it require as much treatment as described?

2) Would using a slightly more flexible filler rod such as 4043 reduce such a problem or not?

Thanks,

Scott

[Canuck]

Most agree that welding T6 will reduce it to just 6061-0 no heat treatment or at the very least an unknown degree of the strength would remain (some suggest it gets some strength over time). I've done a bunch of work on this lately as a part that I'm making for a project would have required post weld heat treatment if made with 6061-T6. The filler rod specified was 4643. I convinced them that steel was fine in this application. It's not like I can find that filler at the local weld supply center.

[totalmechanic]

Canuck,

Thanks for the input, great point! The author of the article then goes on to state:

"For this reason it is vital that all bicycles and handcycles that are made from 6061 aluminum need to be heat treated. If they are not heat treated they are dangerous."

Would anyone have any insight into such a claim?

My reason for questioning the claim: The typical big box store sells a lot of bikes made of 6061 or similar alloy. I am not saying that such frames don't go through any post treatment, only that given the prices of such bikes I wonder how much post weld treatment the frames might receive.

If the big manufacturers don't post treat then how valid are the writer's claim about safety?

I like 6061-T6 for many reasons: easy to machine, light and weldable but if the above strength claims are true then I might be looking to use 4130 for the stuff I do in the future.


Scott

[Canuck]

Hi Scott,

It totally depends on the application. I was welding up a frame and when the engineers did the calculations the strength of the part was 2.5 times more than any calculated stresses even at 6061-0, at T6 it was 11 times stronger than required. This part had welds in stressed positions - so we opted to go for steel as it is more predictable. 99/100 times you're going to be fine and the weld and weld affected zone is fine as the materials used for the cheap Walmart bikes are ticker and most likely subject to less stress (jumping over curbs, not real off road stuff). 6061-0 is still pretty strong, T6 is very strong. The post weld heat treatment is complicated and I don't understand all the in's and out's - but I doubt many do it for things like a bike frame.

Craig

[g234me]

heat treating is not that complicated. Stick it in an oven at 990 degrees until its thoroughly heated (depends on thickness) quench it. Then stick it in another oven at 320 for 18hrs. Here read about it


http://www.suppliersonline.com/propertypages/6061.asp

big manufactures would have ovens.