welding an already heat treated aluminium frame

[Juhan]

so, all deng frames are made of aluminium and heat-treated after the welding, now what would happen if for example my zoo python would develop a crack at some place or i wanted to put a rear disc mount on it? i know i could just have it welded, but what are the results of welding an aluminium frame that has already once been heat-treated? I know Tomac had a bt5.0 and he had a rear disc mount welded onto it and in the beginning he promised it would be his last frame, but recently i saw a post from him somewhere(can't seem to find it now) where he said the disc mount wasn't as good as he thought in the beginning and he ditched it some time later(that's what i think i read, in reality it might not have been so), it would be really nice to hear what tomac has to say about this because he has the most impressive e-engineering skillz in this forum and seems to know just about everything about bicycles.

[RomanC]

long story short his disc mount was too soft as it wasn't heat treated and got deformed.

[Juhan]

it's probably a stupid question, but could that be avoided in any way ?

[manimal]

http://www.key-to-metals.com/Article7.htm
http://www.matsci.ucdavis.edu/MatSciLT/Other/Files/HT-Aluminum.pdf
http://www.heattreating.ca/resources.htm

some stuff to read.

[Juhan]

i have to say, that even after reading through all that text you gave me i still don't see the answer to my question(maybe because english isn't my mother tongue and reading a bunch of text filled with specific scientific phrases didn't really help too much), so still can that "softness" be avoided in any way or if it can't, well, maybe tomac could tell what exactly happened to his disc mount?

[manimal]

to be honest, I didn't know if it would help you answer the question, but more give you an understanding of heat treatment. (basically googled for info)

the way it looks, you could re weld it, but if you want the disc tab to hold, you'd have to reheat treat your frame. which might get pricey.. so would it be worth it? highly doubt it.

best to stick with the original mounts, and then if you want to run rear disc, get a frame that has the mount already.

[tomacropod]

oh just noticed this thread - sorry Juhan.

The frame wasn't re heat treated after welding and the disc mount material, although thick, was too soft. If it's soft it's less likely to fracture/crack (to a certain extent) but will deform. The bolts deformed the holes and they simply stretched out of alignment.

I would suggest getting a frame re heat treated if you're having a contact point worked on. Such as a disc mount, other brake mount, bottom bracket shell, headtube etc.

- Joel

[loffa]

Ühesõnaga Juhan, kas ei oleks olnud lihtsam küsida kellegi käest, kelle jutust sa tegelikult aru ka saad? :momaru: Ise kettakinnituse raami külge keevitamine on suhteliselt mõttetu üritus, sest nagu juba eespool mainiti, alumiiniumi peab karastama pärast keevitamist.

See, kas su raam on juba eelnevalt karastatud või mitte, ei oma mingit tähendust, sest kogu see kuumus, mis keevitamisest tekib nullib selle ära, ning keevitus ja selle ümbrus, kuhu see kuumus levib, jäävad ikka pehmed ja lähevad katki. Kõik raamid, mis Metagrupis keevitatud on, lähevad uuesti katki, kas siis sealt samast keevitusest või selle lähedalt. Huvitav küll, miks? (minulemmik, vilega smaili)

Ning ma ei oska ka soovitada ühtegi usaldusväärset kohta, kus saaks lasta alumiiniumi uuesti U6-ks karastada. Seega ära riku oma korralikku raami ära, vaid müü ta parem maha ja osta khmm.. MONTY.

---Translation, for all of you, who didn't understand a word what I was saying :bigthumb: ---

Welding a disk mount to your frame would be pretty pointless, because as it was mentioned before you have to heat-treat aluminium after welding, otherwise it won't be as strong as it should be.

It doesn't particullary make any difference if your frame was heattreated before, because the heat coming from welding will soften the areas around the weld and it will become soft again. All the frames that have been re-welded at our local workshop have cracked again pretty quckly, and all of them have cracked at the same weld or near it. Wonder why?

And I can't recommend you any decend place at our area where you could get your frame heat-treated, so don't ruin your otherwise perfectly fine frame, better just sell it and get a Monty instead.

[hydroboy]

an oven to fit a frame in is large, and expensive.

[Juhan]

loffa siia tegin ma selle teema sellepärast, et tomac tegi seda ükskord oma bt 5'ega ja ma tahtsin just tema käest kuulda mida ta selle kohta ütleb. ja siis veel see kaa, et biketrialsist oleksid aint sina vastanud midagi ja ülejäänud teema oleks trukk ära nussinud + ma katsun oma plaanidega madalat profiili hoida :D

thank you all for your answeres, i got everything i needed to know. i'll try and find out if i could get the frame heattreated after the welding and what it would cost me ( i already have the possibilities to cnc machine whatever i need and also i know a few places where i could get it welded by professionals so heattreating is the only obstacle atm)

again, big thanks for everyone who bothered to answer.