Failing hardness testing

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Good afternoon all , I need some guidance  on this hardness issue i am having with some parts .We are welding to AWS D17.1  6061 -t4  .050thk parts  . I validated all T4 parts to be at the correct hardness however after welding they are aged to T6  and  most of the parts are failing hardness testing (due to being too low in hardness ). My theory is that between 3-4 guys who are welding these lots of parts someone is doing something incorrectly during the weld process  .What would cause an area to be softer  than the original hardness so much that after age they  don't meet  the hardness specification?any help is appreciated  . S/B: Harness Scale HREW 85 MinIS: 66 , 77 , 68
Reply:Interesting question.  Could you run a sample of T4 .050 material (without welding) through your hardness process along with a welded part.  If the non-welded part also failed, it would point to the hardness process.  If the sample tested T6, but the welded part failed, that would be an indication that the welding was related.  I do not have my AWS standards near me, so I have to ask, what filler material is being used?  4043 is known to pull silicon from the surrounding area, and will change the parent material properties.  Are you checking hardness very close to the weld, and away from the weld?  Do you see a difference?The above would be my first items to check.
Reply:6061 "hardens" when precipitates move to the grain boundaries,,,Well,,, if you heat the aluminum too long, the precipitates continue to come together,, abandoning the grain boundaries, and they basically form big useless blobs,,,(layman's terms)When the grain boundaries are abandoned,, the aluminum is softer than T4. (There is nothing to stop the grains from sliding past other grains)So, simply, somebody got the parts too hot.Sometimes, the parts can be heated so that the precipitate goes back into solution,, the re-precipitated, to get back to T6.That can be "iffy",,, as sometimes all the heating causes extensive grain growth,, then the precipitate can not adequately "harden" the aluminum,,,Next question,,,, LOL!!  




Reply:Seems like they were welded too hot, or allowed to cool way to slowly, or both.May try to use a water cooled chill block and see what happens from there.
Reply:Thanks guys , our processing house also pointed out way too much heat .Welding supervisor tells me everyone is welding the same  so that's a dead end . I'm going to hit them with a C.A.R and implement more traceability on who is welding what to see who is causing this issue  . Most of our experience welders quit due to management so that department is left with newbies . I will most definitely try  alternative welding wire  and suggest have a water cooled chill block . @ToolFanGeoffIts most definitely weld related  and I will ask the processing house to test the failing areas every quarter inch and see where it actually  stops failing(most likely outside the heat affected zone it might be ok  ) .