Aluminum Weld Safety
 

I should have searched the forums before I had work done to my frame. I cut the dropouts of my old Aluminum Trek 1100 about 3/8 from the tubes at an angle and had a machine shop tig weld in forkends. The welds look great but tempering or re-tempering was not an option.

Now I have two worries:
That the weld will fail
or that the bond will fail (frame is bonded aluminum).

I'm at the end of the conversion from geared to fixed and am worried that I blew it. The bike looks beautiful you would never know that it started as a geared bike.

What do you guys think? Should I hang it on the wall and call it art? Or ride it and see?

Thanks

you'd have to find out what kind of aluminum it is

Yeah, because some of it heat treats by sitting around, and some of it needs an oven. It would also mater what the new pieces were, and the filler material. ftwelder has the aluminum welding experience here.

Both pieces were 6061, the machine shop works with aluminum a lot (boats) and provided me with the 6061 as I had 7005 and he didn't want to mix the metals. He quized me on the metal type and actually only believed the metal type when I was able to show him the sticker on the frame. At that point he said he would be willing to weld it up as long as I used 6061 and then he provided me with the 6061 plate (1/4") to shape.

So, perhaps it will hold up? I know it is kind of late, luckily this is going to be a play bike on smooth pavement.

I'm no expert, but I'm pretty sure you are going to have problems. The article at wikipedia says that 6061-T0 has yield strength of 8ksi vs. 35ksi for T-6
My guess is that they heat treated the tubes to T-6 before gluing, so that the design loads assumed the higher yield strength.

That is the article that caused me to panic. Aluminum transfers heat like crazy so the tubes may have lost their temper as well as the plate.

Oh well, it has been fun. I'll see how it fits and ride it around a bit and then buy a steel frame.

Thanks for the replies.

I wouldn't panic yet. I think the heat treat is like 400 degrees, you might be able to go to use a heat gun to get up there, or do a deal with a powder coater, or stick the back end in your stove. The other issue is how loaded that area is. Anything out by the drops is at the easy end of the spar. That is why the tubes taper on steel bikes out there, and the triangle comes to a point. I'm not saying you are good to go, but it may be salvageable. One nice thing about 7075 is it does not need all this.

I think it's 7005 that doesn't need heat treating, but don't quote me. 7075 is definitely heat treated

I'm pretty sure that there is some point on the stays that went through a heat cycle closely approximating an annealing step.

Shop for a back up frame just in case..

did they heat sink the tube with a cold wet rag or something,
to keep the welding heat from moving to the epoxied end?

I wasn't there to see but the paint was still on the tubes. The weld itself is about 3/4 of an inch from the tubes as I kept as much of the drop out as possible.

Some of the bonded frames used 7075 (easton EA70) which can be welded but will crack. If trek welded anywhere on the rear at any time, it's a weld-able alloy. I think the main problem will be damage to the dropout from tightening the axle nut. The tubes will be fine if the material was clean when welded and only 3/4" of paint is lost. The normal "weld happy" alloys are 6061/7005

Welding aluminum really doesn't leave the part in "0" condition unless it goes over 700 degrees and is allowed to saturate the material.

It is OK to weld 7005 and 6061 to each other. In your case, it may have been a good thing as the dropout might harden a bit over time quicker than 6061.

ftwelder: that sounds promising. The two pieces that were welded together were both 6061. No paint was lost as I had it sanded back the dropout plate to the tubes which were 3/4 inch away.

I should have the new wheels and BB by the 14th and I'll finish assembly and see what happens. If anythings gonna happen it'll happen out there...

Thanks for all the replies. I am no longer panicked and if it fails I'll chalk it up to learning.

Can you throw the frame or at least the welded section into a tub of boiling water for a few hours and do a slow cool down? I think that is a standard procedure for tempering 6061 in other industries. What about a vat of cooking oil (HomeDepot Turkey boiler!)??

If heat treating Alu were so simple I doubt that companies would spend many thousands on special ovens. Andy.

First you aren't *tempering* 6061. Second, it needs to be a lot warmer than boiling water for aging 6xxx series. Third, I doubt tapwater in your area is clean anough to allow you to boil aluminium in it without some unpleasant, structure-weakening corrosion (and no, saucepans are hardly a loaded structure that you'd notice it in, and they *should* be coated anyways).

Frank: There are ways to weld 7075 now, but not in any practical, home engineering way...