metalurgical question-6069 aluminum



the blur

New Member
Apr 15, 2004
27
0
0
i just bought a new mountain bike frame.
near the top tube/head tube junction is a vertical bulge about 1 cm long in the top tube. i think its from heating when the tubes were welded.
there's no defect inside the tube (you can't feel it), just a bulge on the outside.
the manufacturer says it's no risk, but they're willing to exchange it. i don't really want to wait for a replacement, but i will. any opinions on whether 6069 aluminum is weakened by heating? i think some metals need controlled heating/cooling to be strong, but not sure about this aluminum.
thanks
 
Many frames go though a process of being baked in a furnace at various temperatures for various lengths of time after being welded together to relieve any stresses produced by the high temperatures used in the welding process. You shouldn't need to worry about welding weakening the frame - this kind of thing will have been thought of.

If the LBS says they'll replace it though, that might mean that the bulge shouldn't be there, i.e. it may be a defect of some sort. If this is that case, I'd have it exchanged. Even though the LBS says it's not a risk, they might not be qualified enough to say this for certain.