Tempering 6061? (was: Welding 6061 weakens it?)

Some in these groups have opine'd that welding 6061-T6 would make it lose its treatment and result in T1. Aging at room temps would bring it to, maybe, T2 after a month.
TIG welding will bring the area of interest up to 600-plus F(?). If quenched immediately, would this help bring it back to temper? Or will this risk damaging the weld if it's cool so fast?
Usual quench bath is iced brine, I read...
I've got no access to an oven large enough to bake it per proper procedure (it's a bike frame) and beside, most of the frame is just fine (T6).
Comments? Suggestions?
Thanks.

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No. There is a caveat here, that a proper heat treatment for 6061 involves a heat-and-quench step to maximize the hardening *potential* of the aluminum, but the actual hardening occurs later and has nothing directly to do with quenching. The purpose of quenching aluminum alloys is to "freeze" alloying elements in the metal, in a solid solution. The actual hardening is accomplished by precipitation hardening, which occurs naturally by room-temperature aging, or more quickly with a low-temp heat-soak process known as artificial aging. Most heat-treatable aluminum alloys can achieve a moderate or even a large fraction of their potential hardness without the heat-and-quench step. IIRC, 6061 is one of those that achieves most of its potential hardness without quenching, but I haven't refreshed my memory on this for a while.
If this is a critical job, you'd do well to study it a bit. 6xxx-series aluminum that's randomly heat-treated, as by welding, continues to age for years and is never really stable. 2xxx aluminum, in contrast, will stabilize within a week. But 2024, for example, is risky to weld, usually producing high-stress areas and even cracks. 6061 is much less trouble and is far better for welding.
Few applications require the highest levels of strength or long-term stability, so welding 6061 usually is not a problem. Just weld and wait. Within a week or so it will have recovered a substantial percentage of its strength. I wouldn't try quenching it because the required heat-and-quench to achieve maximum hardness is time-and-temperature sensitive. If you can't control both and know exactly what values of time and temperature you need, heating and quenching can make things worse.
Don't try to relate it to hardening carbon steel. The hardening mechanisms are entirely different.
-- Ed Huntress
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Thank you very much, Ed, for the benefit of your experience. I'll tell the welder to just let it cool and give it back to me.
It's not *real* critical (my mountain bike frame). I'll watch for any obvious changes as time goes by.
Thanks again, Dave

Ed, one more question:
When prepping the weld area, any grinding wheels (to taper the edge where the weld will go) or stainless wire wheels the welder uses should be either new or if used, only used on aluminum previously, yes?
I think I remember an issue of contamination of ferrous material getting imbedded into the aluminum if precautions are not taken.
Is this right?
Dave

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I don't know what best practice is on this. This is something else for the welding experts to answer. From a materials standpoint, contamination of aluminum is a serious problem if you're joining it.
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That's definitely right, but again, you want the voice of welding experience on that.
-- Ed Huntress

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Oops. I didn't know it was a bike frame. That's a job I'd consider to be fairly critical. In fact, it will be interesting to see what the welding experts say.
I'm a materials guy, Dave, but only a klutzy weldor. If it were me I'd check with the people at the welding NG, which is a source of some real welding expertise. Also, there is a bicycling NG that's been home to some bike-building experts. That may be the best place of all. Bicycle-frame tubing is tricky stuff and joining it is a real specialty.
In any case, I hope you get it done successfully.
-- Ed Huntress

Ed Huntress wrote:
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Seconded...
Highly stressed truss frame with small contact areas. And little if any redundancy.

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The mechanism for hardening aluminum is nothing like that for hardening ferrous materials, you're growing or regrowing a specific microstructure and the instructions for the specific alloy for achieving the specific hardness HAVE to be followed. You can't wing it on this stuff and get good results. Commercially, the whole welded structure would be stuck in an oven and run through a specified heating and cooling cycle, time vs. temp. This speeds up the natural growth of the microstructure, which would normally take weeks or months at room temperature. One reason that adhesives are popular for joining heat-treated alloy pieces, no post-heat treat needed. When we were running motor home chassis extrusions, they'd be in the oven for a couple of days.
Stan

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Thanks, Stan.
I'm not experienced enough to make the decision whether or not it's recommended to have this weld done or to instead look into bolting the piece to the frame rather than welding it.
This is the location and a template of the part:
<http://tinypic.com/r/i4lszt/3
The aluminum "hump" on the frame is not important and can probably be leveled and the fabricated part made without a notch. (Note: holes are 7/32, not 7/16 as shown.)
Note the proximity of other welds in the area where the tube meets the plate aluminum.
Opinions & suggestions about whether this is recommended (as well as how best to minimize any risk) or whether it's too risky are welcome.
Thanks, Dave

On 09/16/2009 09:06 PM, DaveC wrote:
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it's not just the temper, or lack thereof, that results from welding, but the structural considerations also. "retrofitted" frames are often seen to bend because the stay to which the tab is welded is not strong enough for the resultant bending force of the disk brake.
in view of both the welding temper and the bending, i say it's simply not worth trying this experiment. simply spend $99 on a new frame that's designed for the job from the outset and be done.
http://www.nashbar.com/bikes/Product_10053_10052_173009_-1_201511_10000_201512

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Jim, Thanks for your comments.
Can you provide some references? I'd be interested in seeing detailed accounts, photos, etc. of such occurrences.
Thanks, Dave

On 09/17/2009 10:56 PM, DaveC wrote:
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d.a.g.s.

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?

"DaveC" wrote in message d.a.g.s.
?
DO A GOOGLE SEARCH !!!!!!!!

DaveC wrote:
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http://geekdictionary.computing.net/define/dags
--Winston

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So that would be "no".