6069 aluminum and welding

[the blur]

does uncontrolled heating/melting of this aluminum weaken its "structure"? does aluminum have a structure? can welding weaken a tube if it's deformed a bit?
why do i ask? i have a new mountian bike frame and there's a bulge near one of the welds. the tube is not thin there, as there is no defect on the inside of the tube. just a 1 cm by 3-4 mm slight bulge on the outside of the tube. the manufacturer will exchange it but i don't want to bother if it's just cosmetic. any opinions? i have pictures if necesary. thanks

 

[Vintage]

Absolutely. Pic's will help but I think you must accept the
replacement offer!! It gets serious especially on certain
areas of the frame where the stresses are at the max such as
the joint between downtube and headtube where many
manufacturers add gussets at the bottom. In addition, the
joints on the tubes frames go through not only tensile or
compressive stresses, but also TORSIONS! The bulge reduces
the tube strength to withstand torsions. Remember how
fatique aluminum mat'ls are.

the blur <[email protected]> wrote in message
news:<[email protected]>...
> does uncontrolled heating/melting of this aluminum weaken
> its "structure"? does aluminum have a structure? can
> welding weaken a tube if it's deformed a bit? why do i
> ask? i have a new mountian bike frame and there's a bulge
> near one of the welds. the tube is not thin there, as
> there is no defect on the inside of the tube. just a 1 cm
> by 3-4 mm slight bulge on the outside of the tube. the
> manufacturer will exchange it but i don't want to bother
> if it's just cosmetic. any opinions? i have pictures if
> necesary. thanks
>
>
>
> --

 

[the blur]

it's not really close to the actual weld-it's on the side of the top tube about an inch from the head tube. it's below a gussett weld on top of the top tube. i think its minor-probably cosmetic only. you can feel it and see it if the lighting is right. there's no defect on the inside of the tube(-i can feel through the head tube)

 

[Jim Beam]

the blur wrote:
> does uncontrolled heating/melting of this aluminum weaken
> its "structure"?

yes

> does aluminum have a structure?

yes

> can welding weaken a tube if it's deformed a bit?

yes

> why do i ask? i have a new mountian bike frame and there's
> a bulge near one of the welds. the tube is not thin there,
> as there is no defect on the inside of the tube. just a 1
> cm by 3-4 mm slight bulge on the outside of the tube. the
> manufacturer will exchange it but i don't want to bother
> if it's just cosmetic. any opinions? i have pictures if
> necesary. thanks

its not cosmetic, it's structural. take advantage of the
manufacturers generous offer & have it replaced. to
perform a safe repair requires substantial work, time &
expensive equipment making it most unlikely to be an
economic exercise.

 

[JøRn Dahl-Stamn]

In article <[email protected]>, jim beam <[email protected]> wrote:
>the blur wrote:
>> does uncontrolled heating/melting of this aluminum weaken
>> its "structure"?
>
>yes
>
>> does aluminum have a structure?
>
>yes
>
>> can welding weaken a tube if it's deformed a bit?
>
>yes
>
>> why do i ask? i have a new mountian bike frame and
>> there's a bulge near one of the welds. the tube is not
>> thin there, as there is no defect on the inside of the
>> tube. just a 1 cm by 3-4 mm slight bulge on the outside
>> of the tube. the manufacturer will exchange it but i
>> don't want to bother if it's just cosmetic. any opinions?
>> i have pictures if necesary. thanks
>
>its not cosmetic, it's structural. take advantage of the
>manufacturers generous offer & have it replaced. to perform
>a safe repair requires substantial work, time & expensive
>equipment making it most unlikely to be an economic
>exercise.

Just wanted to add my comments. 2 years ago I discovered a
crach in my Cannondale bike in the right chain-stay. The
crach was about 3/4 around the tube about 4-5 cm from the
dropout, and was caused by an accident 5 years before that.

I got the frame welded by a friend, who works with metals at
the university in town. I know that the fram will never be
as strong as before, but it is a lot stronger compared it's
state when I discovered the crack. After all, I have been
riding the frame with that crack... and not noticed it.

I now use the bike as a spare one when training in bad
weather. The new bike is only used during competition and
training in good weather.

--
Jørn Dahl-Stamnes
http://spiderman.novit.no/dahls/