# Heat treat a must after a small weld repair on the frame?



## SingleTrackHound (Jul 29, 2003)

I have a 4 year old rear chain stay that I just noticed a small hair line crack. About 1/4" wide and 1/4" deep. It's on the CNC'd part of the chainstay near the BB on the solid part of the aluminum, not the tubing piece. Frame is made out of 6061 aluminum alloy.

I have a friend who is a welder and he said he can weld it after clean off the crack. He doesn't think heat treat will be needed. He is not a bicycle frame welder, however. My guess is one pea size weld bead is all that is required based on the size the crack. 

Question: heat treat required after this small weld repair? If so at what temp and for how long? If I am lucky, I may also have access to industrial furnace that does nothing but heat treats manufactured various hand tools, albeit for steel stuff. Or, heat treat is not necessary based on the size of the small weld?


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## DeeEight (Jan 13, 2004)

I myself wouldn't worry if its just a spot weld over a small crack to keep it from growing. So that one spot isn't as strong as the rest of the frame, it'll still be better than had you let the crack keep growing.


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## BrendanC (Aug 11, 2005)

Yes, you _should_ h/t the frame. That will also mean alignment... The size of the weld doesn't matter so much as the fact that the metal will get VERY hot in that area.

There are garage mechanics who quench it with water & let it dwell for a few days... This isn't a good idea if for no other reason than the area you've damaged is already prone to stress. Having a suboptimal weld in this area will likely invite failure again.


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## D.F.L. (Jan 3, 2004)

Is the crack on the drive side?

If you had sid that it was 7005, then I'd be less concerned, but 6061 becomes extremely soft after welding and does require heat treating.

A trick shown to me...

...that may be completely insufficient and unsafe...

...is to cover the still-extremely-hot part in ash. The ash is is a great insulator and it will slow the cooling rate of the part, retaining some of the desired hardness. Enough? I don't know, but the part we made was quite a bit stiffer than if it hadn't been covered.

Maybe someone else will know more about this.

(I don't work in aluminum and I don't do aluminum repairs)


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## SingleTrackHound (Jul 29, 2003)

D.F.L. said:


> Is the crack on the drive side?


No, non-drive.


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## TortugaTonta (Jun 14, 2004)

Your frames already broken so you aren't going to break it worse by welding it.

Yes 6000 series turns to butter when you anneal it, so you should heat treat but for most that is not an option.

Order a new part and weld the old one to keep you riding until the new one comes in. Just don't try any wheelie drops to flat. 

Edited to add a link to some light reading you might enjoy...

http://www.amazon.com/gp/reader/1400047609/ref=sib_dp_pt/103-3361087-8366245#reader-link


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## BrendanC (Aug 11, 2005)

FWIW, I use the water quench technique for tooling & other odds & ends around the shop. It works pretty well from I've done. Still can't wholeheartedly recommend it for your frame, but...


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## jeffscott (May 10, 2006)

The quench will convert 6061 to is most workable state, very soft.

Natural aging at room temp to elevated temps say 200 F will allow the alloy to harden and regain its strength to the T4 condition.

the T6 condtion is achieved with 18 h at 320 F.

T4 strength is 13,000 psi and T6 strength is 40,000 psi.

Since it cracked already you know you need the T6 strength.

More important is the temp than the time, so a powder coat bake job is pretty dam good.


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## BrendanC (Aug 11, 2005)

Again, garage mechanic stuff here- like jeffscott says, the quench will bring the alloy to a workable state. But as I'd mentioned in my first post you'll want to age it it back to T6.

Typical quench/age in the bike industry is 980* for long enough to get everything up to temp, 1-2hrs. Then quench in water/gycol, then age 320 for 8 hours.


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## dnlwthrn (Jan 26, 2006)

Here's kind of a side question, with some similar issues. I want to modify my frame (change the dropouts) on an older AL bike. Its 7005 aluminum, and I can get the new dropouts in the same material. Do I need to heat-treat after welding the new dropouts on?


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## jeffscott (May 10, 2006)

7005 is very similar to 6061 and 7050 7075, wrt to queching and age hardening.

The quenched strength of 7075 is 33,000 psi and the age hardened stregth is 83,000 psi.

So you "should do it" even just a powder coat bake.

I have worn out one set of dropouts (on my chain stays) already. I just got a new one from Rocky.

One day I think I will machine in a stainless steel insert to eliminate any drop out wear.

Hopefully before I have to get another chain stay.


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## DeeEight (Jan 13, 2004)

7005 no, just let the thing sit around for a month or so and it'll naturally age. This is what most manufacturers used to do when sourcing asian frames. They'd skip the artificial aging step knowing that between welding and delivery to the customer the bikes would have been unused for a couple months (hell the boat ride across the pacific alone would take a couple weeks).


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## dnlwthrn (Jan 26, 2006)

jeffscott said:


> 7005 is very similar to 6061 and 7050 7075, wrt to queching and age hardening.
> 
> The quenched strength of 7075 is 33,000 psi and the age hardened stregth is 83,000 psi.
> 
> So you "should do it" even just a powder coat bake.


So if I plan on getting the frame powder-coated, that might be enough? I was discussing this with an engineer here at work (Ph.D in Materials, specialized in aluminum alloys) and he recommended heat-treating (high temp, short duration, quench, low temp, long duration) for 7005. I guess I'm trying to decide if its worth it, or if I should just pony up the $$ for a new frame.


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## DeeEight (Jan 13, 2004)

jeffscott said:


> 7005 is very similar to 6061 and 7050 7075, wrt to queching and age hardening.
> 
> The quenched strength of 7075 is 33,000 psi and the age hardened stregth is 83,000 psi.


Nobody makes frames from 7075.... except Trek in the early 90s and then those were bonded. The zinc content is too high to allow welding unless its had scandium added to the alloy mix.

Straight 7005 without any treatment is 28,300psi UTS, and 7005-T6 is 50,800psi UTS.


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## jeffscott (May 10, 2006)

Tha will get you close to T4 the a powder coat bake out will get you closer to T6.

Dropouts are highly stressed.

Don't you want to clean the thing up after welding?


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## dnlwthrn (Jan 26, 2006)

The real issue is whether its more economical for me to replace the dropouts (since I have the ability to, kind of) or just replace the frame. If it will cost me nearly as much to change dropouts, heat treat, and powdercoat as it would to buy a new frame, I'll just get a Santa Cruz Chameleon ($549 for the frame).


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## jeffscott (May 10, 2006)

New frame sounds good, but don't they sell those chainstays anymore.

Rocky can replace chainstays (dropouts) for really old bikes, I payed like $130 and waited two weeks, for a powdercoat matched chainstay.


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## SingleTrackHound (Jul 29, 2003)

BrendanC said:


> Typical quench/age in the bike industry is 980* for long enough to get everything up to temp, 1-2hrs. Then quench in water/gycol, then age 320 for 8 hours.


Three step process to achieve T6 level?

1. HT at 980 degree for 1-2hrs.
2. Quench in water...for how long and at what H2O temp?
3. Then HT again for 320 degree for 8hrs?


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## jeffscott (May 10, 2006)

Cool water, to cool to the touch and then 320 F for 18 hours by the book.

Check out the Easton site they have furthur info.


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## SingleTrackHound (Jul 29, 2003)

Thx a bunch!


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## dnlwthrn (Jan 26, 2006)

oops, I realized that jeffscott's reply about chainstays was directed at SingleTrackHound, not me. Carry on.


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## Yardstick (Jan 10, 2007)

I haven't seen mentioned one of the most important things when dealing with cracks... Drill the end of the crack to prevent any further growth. Just a very small drill is all that would be required. You should do this even if you plan to weld it to make sure you've taken care of the crack tip. The weld might get it, but don't count on it. 

Personally, I'd get a new frame.


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## SingleTrackHound (Jul 29, 2003)

It will not be a surface weld job. Crack is on the solid part of alumimun piece that has been CNC'd by mfg. Crack will be cleaned off to its depth and refilled with weld bead. Then nicely filed and buffed down. HT process will follow if I have access to furnace at work. 

I am doing this more so for DIY project to understand the process and see if repair job like this will hold up to normal riding. I will stay off of 4'+ flat landing drops like I have done in the past...it is XC frame after all. Actually, I already bought a rear triangle and swaped it over couple of months ago. 

I got plenty of bikes. I just get kick out of reviving once thought dead bike stuff.


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## swift (Apr 3, 2007)

I missed whether or not it was a FS frame. If 'yes', I'd just hit the manufacturer up for a new rear triangle/chainstay as appropriate. Most manufacturers will sell items like this at a reasonable cost (my friend replaced a Rocky Mountain chainstay for $230 and it came powder coated in the original color). If it's a hardtail, I'd just shop for a replacement frame. 

Aluminum frames are not really cost effective to repair on the scale of one-offs. By the time it's welded, heat-treated, and refinished you're going to be into it more money and time than it'd be worth IMO. ...And if the repair is not done properly, keep in mind that healthcare costs are prohibitive as well.

Good luck!


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## DeeEight (Jan 13, 2004)

I don't think the whole frame needs to be heat-treated for a pea-sized weld. Its not like the heat from the welding in that one tiny spot is going to magically conduct thru the ENTIRE frame and ruin the strength of the rest of it.


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## swift (Apr 3, 2007)

DeeEight said:


> I don't think the whole frame needs to be heat-treated for a pea-sized weld. Its not like the heat from the welding in that one tiny spot is going to magically conduct thru the ENTIRE frame and ruin the strength of the rest of it.


This isn't going to read very well, so please understand that before proceding.

With all due respect, it doesn't really matter what anyone "thinks". Metals responds in a predictable manner when worked. If the repair is not done properly, the bike will be substandard at best and potentially unsafe. I wouldn't ride it unless the repair were done proper and the reality is that a proper aluminum repair is cost prohibitive unless you have access to the necessary tools. Furthermore, I wouldn't knowingly ride with any friends in this situation unless their frame was fixed properly because I don't need to be packing anyone out, over my shoulder, when we're 10+ isolated miles from the car. ...Talk about Buzzkill!

To the OP; It's not my health we're talking about and I'm not likely to ride with you since I don't know you, so feel free to do as you see fit. You posted the question in an effort to get educated on the topic, so now that you've read through various opinions, you'll ultimately make the decision that's right for you.

Yeah, that doesn't read very well at all. ...Sorry 'bout that.

Best Regards


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## Thylacine (Feb 29, 2004)

All this chitchat is useless without a picture of the crack.


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## SingleTrackHound (Jul 29, 2003)

Chain stay is on my welder friend's hand. He will be welding it once he gets a chance. Picture of crack was so small (1/4") it was barely detectable to naked eye so I didn't even bother taking pix. I had to squeez the chain stay with both my arms to barely see the hairline crack. I suppose I could've had someone take the picture while I was flexing the chain stay.

I will HT it as other OPs have suggested if I get accessed to furnace at work. Whether it gets HT or not, it will become spare to my current chain stay I have on my bike.

Unfortunately fame mfg has stopped making this model since 2004 and don't carry spare parts used or new. IMO, it's better to have repaired spare than none. No? Especially when repair will cost zero and minimal time on my behalf while learning the process.


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## SingleTrackHound (Jul 29, 2003)

*Here's the finished product!*

Finally rear chainstay is repaired. It will become my spare for now.

I Sharpie marked the repaired area with dotted line on the picture. Surprisingly similar size crack was discovered on the opposite chainstay (near same area) during repair.

Went thru the exact HT process (T6) suggested by OP. Thx!:thumbsup:

Now all I got to do is polish it to make look nice!


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## rickthewelder (Sep 16, 2005)

SingleTrackHound said:


> It will not be a surface weld job. Crack is on the solid part of alumimun piece that has been CNC'd by mfg. Crack will be cleaned off to its depth and refilled with weld bead. Then nicely filed and buffed down. HT process will follow if I have access to furnace at work.
> 
> I am doing this more so for DIY project to understand the process and see if repair job like this will hold up to normal riding. I will stay off of 4'+ flat landing drops like I have done in the past...it is XC frame after all. Actually, I already bought a rear triangle and swaped it over couple of months ago.
> 
> I got plenty of bikes. I just get kick out of reviving once thought dead bike stuff.


If you want a pro repair, PM me.
RTW.


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## saga (Feb 12, 2005)

*Polishing welds down.*

I have the same Intense chainstay/seatstay that I just got polished at a industrial polishers.

I paid $40 and they've done quite a good job but my only concern is they've used quite heavy handed machines to polish and have ended up smoothing out those lovely welds by about 2mm max.

It's exactly the same as singletrackh's chainstay but welds don't have so much of an edge. Manufactures double weld these areas don't they so I'm sure it's ok but I'm wondering if heavy handed polishing can weaken the surface.

Will the smoothed out welds weaken my chainstay/steatstay?


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## gotboostedvr6 (Sep 1, 2008)

Ask Klein  
I would say no


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## lyndonchen (Nov 8, 2007)

saga said:


> I have the same Intense chainstay/seatstay that I just got polished at a industrial polishers.
> 
> I paid $40 and they've done quite a good job but my only concern is they've used quite heavy handed machines to polish and have ended up smoothing out those lovely welds by about 2mm max.
> 
> ...


No, smoothed out welds are theoretically stronger. Sanding/polishing removes the surface imperfections (that we like to call nice welds) and therefore removes stress concentrations. The material in those weld "puddles" add no strength on their own.

Probably no real difference, but like I said, theoretically stronger.


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## Burnt-Orange (Dec 10, 2008)

I modified my cannondale rear swing arm already to fit a longer shock 
the welding done was not near the drop outs or main pivot 
should I toss it in the kitchen oven at 325 for 18 hours 
would this restore most of the heat treatment 
just wanted to know if baking it would make it stronger 
or am I not understanding the process

thank you 
Joe


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## nilknarf_c (Sep 22, 2008)

Not that I have the capability to do the welding myself, but is it conceivable that once a weld is done, that you could fit a chainstay in the kitchen oven on the self-clean cycle (approx 900-degrees) on the 2-hr "speed clean" setting? Unfortunately, the automatic oven door lock wouldn't open until the oven temp had dropped to 600-degrees... would that mess up the process? One other dumb question: would a 50-50 mix of water and automotive antifreeze at room temp do the trick for quenching? After that, the 325 slow-bake would be a piece of cake... right?

_curt


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## Burnt-Orange (Dec 10, 2008)

this is what I got so far - I added extra metal to make up for any strength lost - I also decided not to use v brakes just to reduce the stress to the area of my modifications I want to know if there is anything to add the strength back after welding without a full heat treat - I might make the rear brake mount bolt on because I am not brave enough to make the rear drop out unsafe 

here is the rear arm 
any advice is welcome

joe


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## jeffscott (May 10, 2006)

Joe not sure about the pictures:

But wrt to heat treatment.

First check out the Easton site they describe heat treating for 6000 series alloys, and 7000 series alloys.

Next you are fundementally correct, the problem is that the temper of the entire, and repaired section of the part is unknown after welding.

The correct heat treatment would be full annealing to T0 lowest strength...

Then a tempering process back to the original temper (close to Easton reccomendations).

It is easily possible to "over temper aluminium" to a less stronger state by heating to long, or at too high a temp.

One can estimate temper by checking hardness, this can be done qualititively by striking a point with a calibrated (constant impact), on the metal before and after tempering).

Not sure you want to go there.

I would use Easton reccomendation for tempering but cut the time in half, for a gut feel job.


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## Burnt-Orange (Dec 10, 2008)

rite now my gut says macine a bolt on rear brake adapter so I do not take any temper out of the rest of the arm - watch ebay for a "new" rear triangle off a jekyll - and keep a very close eye on my new shock mount area for stress cracks - 

thanks Jeff
Joe


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