Any special tricks to tig weld Alphja ZX aluminum

By Lawrence (*****)

Date 06-19-2008 11:03

I think ZX Aluminum may just be a trade name the bike maker uses for their assembly process.

I might hazard to *guess* that the tube is 7005.

Right or wrong about the guess, I wouldn't touch a cracked aluminum tube on a mountain bike. Those frames are heat treated after welding.

A repair weld is going to soften a spot that has already proven to be weak by breaking in the first place.

So I don't think the frame needs to be welded.. I think it needs to be replaced.

If you do fix it, be prepared to buy your customer new teeth.

By Ringo

Date 06-19-2008 11:49

He said the frame was guaranteed for life,but since it was in an area where the chain rubbed (possible carbon embedded) that it was his fault for not replacing the chain,therefore they would not replace the frame.

I agree with you that it would soften the area of interest.I told his this,and said it was his call.I'll let you know

Thanks,Ringo

By DaveBoyer (*****)

Date 06-20-2008 03:44

I think if it were Mine I would make a sleve in 2 halves probably 4x-5x tube diameter in length with the ends rounded or pointed, and epoxy it in place with West System epoxy following their suggestions on epoxying metals. It might not work, but it wouldn't cost much to try.

By Ringo

Date 06-20-2008 10:26

He said he wants it welded.I told him it would be a weak spot since there would be no PWHT.He's still trying fight it out with the manufacturer over the warranty.

By DaveBoyer (*****)

Date 06-21-2008 03:20

Ringo, what type of joints did the manufacturer use, fittings or fillet welds?

By Ringo

Date 06-24-2008 11:38

Fillet welds,Lap joints

By DaveBoyer (*****)

Date 06-25-2008 05:24 Edited 06-25-2008 05:26

This sounds like an item that just doesn't lend itself to reliable repair. I wonder if these frames are really heat treated after fabrication, and how they keep them in shape during the process [or restore them to shape after] if they are.

By Ringo

Date 06-25-2008 10:39

I'm not sure,they may be left in the fabrication fixture.The welds look pretty slick.

By ason1965 (*)

Date 06-25-2008 15:55

Ringo, man I used to race mtn bikes in my younger days and know the stresses those things are put through. I wouldn't weld or ride on an repaired aluminum mtn bike frame due to the stress those things go through and the potential for liability. The chances of correctly welding on an aluminum bike frame and getting it 'as strong or stronger' as it was originally made is slim simply due to the fatigue characteristics of aluminum.

What was the brand and model?

Good Luck though!

By Ringo

Date 06-25-2008 18:09

I agree with you,and told him it would be weak in the area of interest.Also it's very chaffed along that side (where the chain rubbed) that's cracked.He said he would rather have it welded and hope for the best than buy a new frame (Trex frame).

By Lawrence (*****)

Date 06-25-2008 18:44

Just because he would rather his broken frame to be welded, it does not make it a wise thing for you to do.

Sometimes you just need to say no.

I encourage you to take the advice offered here.

By Ringo

Date 06-25-2008 18:51

Yea,I think he is just too tight to buy a new frame.Even if it was welded,I don't think it would last much longer anyway.It's in pretty rough shape.

By rlitman (***)

Date 06-25-2008 19:40

From what I can find, Alpha ZX is a process, not alloy. It refers to a seamless drawn aluminum tube with custom butting (butting refers to a geometry, where the tube wall is thickest at the ends, and thinnest in the middle, to save on weight, without sacrificing strength).
All of the aluminum Trek frames I could find online were 6061-T6, but it could be a 7000 alloy like 7005.
There's a fantastic writeup about the differences in 6061 vs 7005, for bike frames here:
http://www.mtbr.com/files/data/250.html
The gist of the article, is that if it is 6061, it will need full heat treatment after welding, as the heat from welding will certainly anneal it to mush.
If it is 7005, it is MUCH more resistant to annealing, and so is often heat treated before welding, followed by artificial aging, post welding (which is at a much lower temp, possibly low enough to not even damage paint), and you might even get away without any treatment at all.

You say it failed where the chain rubbed. Was this in the middle of the right chainstay, or on the downtube right over the bottom-bracket (I can't think of another area that could get rubbed by the chain)?
Knowing the nature of the break will help in estimating both the amount of heat needed for the weld (weakening the surrounding area), and the amount of stress the tube will receive in use. Protecting the tube from the chain the future would also be a good idea.

By Ringo

Date 06-25-2008 20:27

That's an interesting article,thanks.I'm not a bike guy,but it looks to be in the middle of the chain stay near the fwd bracket by the sproket hub.I would hate to weld it and send the guy bouncing down the trail,the frame looks like it has taken some abuse 9(ridden hard).I don't have any method of PWHT like a furnace or anything.He's still pissed that the company won't honor the lifetime warranty,but I guess they can only warranty so much.

By rlitman (***)

Date 06-26-2008 19:21

Well, I would be pissed too. Unfortunately, all I can find on Trek aluminum frame alloys, is 6061-T6 (and a few that are 6013-T6).
Without being sure its 7005, I wouldn't consider welding it.
Although I hate to mention glue on this board, if it were my bike, I would open up the side of the chainstay tube, and fit in as long and large a piece of aluminum I could squeeze in, bedded in epoxy, with a minimum of four inches of glued surface on each side of the break (preferably 6" or so).
Unfortunately, if its near the front of the chainstay (near the bottom-bracket end, where the pedal arms connect to the chainring), the tube is usually bent, and may be hard to reinforce.

By Ringo

Date 06-26-2008 19:48

Most of the advice I've been given has been to NOT weld it.The cracked area is in that bend area you spoke of,and I will tell the guy he might want to epoxy it (we have tons of it here).I'll try to get the model # from him just to see exactly what type of aluminum it is.I'll let you know.

Thanks,Ringo