Do you have access to the material certs and/or supplier test reports for the material lot that you are testing?

Are you welding to a code?

If so, what is the CTQ (Critical to Quality) requirement for tensile strength?

Typically, specimens that break outside of the weld zone are preferred.

Your issue of concern might require the designer to evaluate the suitability for service, or a process change to improve the results.

Hi Jordan,

-I understand spending too much time welding can weaken the base metal.

While I wouldn't be brave enough to say thats the case with out a reasonable doubt, I would say yes in the spectrum of the statement. From the view of a welder, I can say in most instances, the longer you sit and play with the puddle the more trouble you'll get into. On its most basic level, solid to fluid to solid.

Sound like you have a very wide haz in the material. Maybe two of them? Over heating during the welding process could bring this about. Think protected by shielding and heat transfered outside the shielding. These areas will both be cooling? Who know for sure reading and guessing?

And the person doing the welding, some pass with a 65% some with a 85%. Some pass because the coupon didn't break that day. And some do it because they can. So I can't speak to that either except to say it gets complicated.

The posting of the gas mixture was good. Adds to the possibility of a lengthy educational response but no sense in boring you to death either. Suffice to say, the gas mixture does effect welding heat input and travel speed.

If nothing changes picture this and think what is the outcome?

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I'm not able to offer more then welding advice on the matter. But from what you mentioned, think about how the heat is being placed into the material, could it be placed in quicker if the welder was more skilled?   In my experience yes. Blame him for your poor results.

You mention tensiles on thinner sheets...case in point. Thinner the material the greater skills needed.
Tell you what, you find that welder, give him a slap on the helmet and tell him to smarten up or you will replace him with a banana eating chimp...Then run like hell.

As much as I blame the welder, its because he is in this instance an easy target. The problem is actually in education of the welder, and those learning the welding trade as part of their job duties and functions.
But I like the way your thinking on the matter.

Best regards.

I honestly can't think of any engineering practices applied to welding that would have the expectation of a welded 6061 T6 coupon retaining it's original T6 condition (mechanicals) post weld... 

Plasma said "Suffice to say, the gas mixture does effect welding heat input and travel speed."

I will say... gas mixture *CAN* effect heat input and travel speed.

If you add or increase %He in your shield gas the energy at the arc increases....  Does the operator use to his advantage?  Or does the operator do the same thing he did before hoping that a different result will occur because the gas was changed.

Stopwatch required for trials...  Both GMAW and GTAW can increase travel speed, and by doing this reduce HAZ and improve tensiles.

From a weld management or QC standpoint... Getting through the trials mean nothing beyond pencil whipped compliance if the practices on the floor don't change....  So what if the tensiles pass when you are in the lab..  The welded joints will NOT be as engineered if the shop floor does not employ whatever worked in the lab.

If it's hit and miss in the lab.... Think hard before moving toward production.

I understand that Al, The question was more directed to how close can you get it to its normal sheet tensile.  Since its "as welded" Could you in theory get so much higher in strengh if you were more careful?