Aluminum 6061T6 vs 5086H116 1

[kmer]

We have an existing tank constructed of 5086H116 Aluminum Alloy. The material is a week away from the US. Cracks have developed in the welds of a 10 year old water filtration unit. Welders are prepared to make the repairs to the welds, however, they need permission to utilize 6061T6 (readily available) for reinforcing and lining the tanks.

I haven't found any good literature on 5086H116 regarding the compatibility with 6061T6. Can anyone provide some direction to this information? My gut feeling is that its okay, I would just like to have a more reliable source to base it on.

Regards,

Kmer

 

[kenvlach]

According to the Aluminum Filler Alloy Chart,

http://www.alcotec.com/atasap.pdf

the filler alloys 5183, 5356 & 5556 are rated 'A' for corrosion resistance and either 'A' + 'B' or 'B' + 'A' for strength & ductility in this application.

 

[kmer]

Thank you. This is exactly what I'm looking for. Very helpful.

Cheers,

Kmer

 

[gfbotha]

What worries me a bit is that this all started with cracking... Now, you are using a heat-treatable alloy 6061 which is likely to be even weaker after welding than a nonheat-treatable alloy like 5086. Also elongation will be lower.

Hopefully the fact that it is reinforcement (additional thickness/material) will see you trough here.

Regards

 

[kenvlach]

The filler metal selection charts consider the effects of alloying during welding upon cracking, ductility, etc. The 3 fillers listed above, 5183, 5356 & 5556, are all rated 'A' versus weld cracking.
[Whereas, 5%Si 4043 reacts with 4%Mg 5086 to form lots of Mg₂Si plus excess Si; the 2 solid phases during solidification of the aluminum matrix results in voids & cracking.]

Also, strengthening due to cold work (H116 of the 5086) & heat treatment (T6 of the 6061) is lost. Generally, one uses the annealed property values for each alloy.

For more info, Elia E. Levi and

http://www.welding-advisers.com

have collected a list of on-line resources on aluminum welding. The ALCOTEC site is best IMHO, but others are good, too:

http://www.welding-advisers.com/PRACTICAL_WELDING_LETTER-PracticalWeldingLetterNo41B.html

 

[gfbotha]

Kenvlach, I agree about alloying in the weld zone... actually I'm referring to the HAZ.

And, yes, true about the strength losses, but still the remaining/annealed properties will be better for the 5086. My data come from an AWS publication on welding of Alu.

As I said, hopefully it might not be critical for this repair job.

Cheers

 

[gfbotha]

Forgotten to say - I am also referring to in-service cracking not weld cracking.

 

[kmer]

This is what I'm counting on...

"Also, strengthening due to cold work (H116 of the 5086) & heat treatment (T6 of the 6061) is lost. Generally, one uses the annealed property values for each alloy."

5356 filler-alloy will be utilized, first to repair the cracks. Then to add 1/4" plate reinforcing (6061T6).

It appears that 5356 gets a better grade for ductility, which seems to be the governing factor. The only portion of the tank showing these cracks is the in the compartment that gets drained, agitated and refilled every 30 to 40 hours (cyclical cleansing of the filter media).

From visual examination of the weld inside the tank (which is leaking at the weld joint) I can see that the weld is 'undercut'. Particles of the media (anthracite) have collected (interlocked) together which led me to this observation.

As you may well appreciate, the 6061 will be here Monday, the 5356 would be here 'next Monday'. I honestly don't know if I want to wait that long.

I am considering lining the tank as well (pitted for some yet unknown reason... another thread I guess) and for this, we will wait for the 5086H116.

Thanks for your time and your thoughts.

 

[gfbotha]

Kmer, time and money also counts; due to the reinforcement you should be OK. Merely wanted you to be aware that the substitute material will be weaker right next to the weld.

Thanks for sharing the web sites, Kenvlach.

Regards