BHBiker

Can a broken aluminum frame be repaired/welded back into place? If it can be reapired, would the costs be prohibitive?

ElJamoquio

Yes, it can be repaired; yes, the cost is generally prohibitive.

Impulse666

welding aluminum is difficult, because the aluminum oxide (surface layer) melts at 3500*F while the actual aluminum is around 1200*F, so the oxide must be removed (it doesn't stay gone very long) and welding it can be a pain the but. if you can find a local shop that would do it, it shouldn't cost much.
if the break is at a joint, it can probably be fixed, but if a tube is cracked, i wouldn't ride it.

pcad tossed a seven (right?) frame out in the trash because it cracked and its too hard to weld ti.

edit: cost: if you get a bike shop to repair it, it'll be loads, but if you go to a small fabricator or auto shop they can do it in a couple minutes.

ElJamoquio

Do not get a small fabricator. The small wall thicknesses of an aluminum frame, combined with the high stresses, require proper pre/post heating, and heat treatment.

If you get it welded, it'll work... for a while.

Impulse666

touche.

sstorkel

Guess you've never heard of Alternating Current (AC) TIG welding? It handles the aluminum oxide problem rather nicely, in my experience. The real problems with aluminum are: 1) it conducts heat very well; you need a lot more power to weld aluminum than to weld steel and you have to move quickly when you do it, and 2) there's a very, very fine line between having the metal hot enough to weld and so hot that you burn through it. This is especially true with thin aluminum; one second it looks fine, the next you've burned through it and you're looking at nickel-sized hole in your tubing.

To the OP: I would expect that having an aluminum bike repaired would be expensive. Not many people know how to weld aluminum well. Of those people who do, there's a smaller number who have the skill to weld thin aluminum. Those people are usually in demand and their services don't come cheap. In addition, as ElJamoquio points out, you may need to have the frame heat-treated after welding. Finally, alignment is critical for a bike frame. A general-purpose welder may not have the jigging necessary to properly align the frame while the repair is being completed.

Retro Grouch 

Not a good idea. Aluminum bike frames are made from 6061 T6 aluminum or 7005 T2. The T6 and T2 are the issue. After welding you will have lost the heat treatment. I doubt a small fabricator or auto shop will have the facilities to restore that.

Capt_phun

I sold a cracked Moser aluminum frame cause there was no way I was going to bother with it. i spoke with the guy one night & had a welder friend fix it for him. I do think he is a serious racer/rider type & he has been riding it, but for me, it was not worth the hassle & the ever lingering thought that the frame would blow out from under me.

You can pick up a frame on ebay pretty cheap versus dealing with the welding hassle.

Val23708

if you have a cracked alu cervelo, go get it warrentied

ken cummings

There are bikes with metal bonded (glued) to other metals or to composites. Could our OP have the bad section cut out and a replacement bonded in? Given that you would need a wizard of a frame builder to do it.

Fastflyingasian

if i still worked at my former shop i could have fixed it for you. i run a shop in a different field now but a shop like my old one could have accommodated your needs. a tig welder would fix it fine. also we had a large oven (1 car garage size) which we mostly used for power coating which would have taken care of the heating or tempering issues.

and yes, unless if you had a friend that worked at a place like this. cost would be pretty high if you wanted anything more than just a weld. the weld alone is cheap enough.

ElJamoquio

Yes, this could be done. The cost of custom making the composite will likely be higher than the cost of a replacement frame.

AngryScientist 

onto the important question : how'd you crack the alu?

Homebrew01

Got any details or pics ?? You say "broken" .... that's a lot different than a small crack, so some specifics might get you a better answer.

rmfnla

I'm guessing you have never really done this before since it is such a bad idea.

OP: Take the hint; scrap the frame and leave the aluminum to beer cans as God intended.

sstorkel

Heat-treating aluminum until it reaches optimal strength is a bad idea? That's news to me...

AngryScientist 

^^^ heat treating particular metals isnt like cooking a turkey. there is a science involved to correctly heat treat AND stress relieve structural welds in materials such as aluminum.

welding alters the crystaline structure of metals, and cooling must be done at a controlled rate. heat treating in itself must be done in a strictly controlled environment, not in a garage sized oven generally speaking.

as mentioned, aluminum frames are easy and cheap to come by, scrap the broken one, finding someone with the correct equipment AND knowledge to fix your frame will not be cheap, fast, or easy.

sstorkel

Fortunately, heat-treating aluminum properly is a well-understood science. Doing it properly has nothing to do with the size of your oven and, for most alloys, there's quite a bit of latitude in terms of the temperatures and cycling. Garage-sized ovens for heat-treating definitely do exist. Not sure I'd use a heat-treat oven for powder-coating, but it could certainly handle the job...

SushiJoe

science makes me

rmfnla

No, heat treating an assembled frame unless you know what you are doing is a bad idea.

The owners of this oven use it for powder coating; would you trust them to re-heat treat your frame?

sstorkel

Maybe you should have said this in the first place?

If I wanted an aluminum frame heat-treated, I'd do one of two things: 1) contact my frame-building mentor and ask him who to call, or 2) call a friend who's a machinist at NASA and ask him to find out who they use. If either answer turned up fastflyingasian, then I would certainly get a quote from him...

rmfnla

...except he no longer works at that shop so he can't do the job.

Why don't you ask your two friends if they would suggest a powder coating shop for heat treating an aluminum frame; I suspect they would come back with a lot of questions that neither you nor fastflyingasian could answer.

sstorkel

Fortunately, I know a lot more about the welding, machining, and heat treatment of aluminum than you, apparently, do...