No myth, it's only a myth to those who own aluminum bikes because they don't want to think about it; kind of like saying your Hyundai is going to break more often than my Lexus...I have insulted your buying decision now your upset. It's common knowledge that AL always has some threshold in fatigue cycles beyond which it will fail. First you have folks right here on this post saying they had failures. There have been many post over the past year on the bicycle.com forum of failures. I have a friend who back in 1986 bought a Vitus AL and it failed about 7 months after buying so his LBS allowed him to move up into a Klien stating that due to his 245lb weight he stressed out the smaller tube Vitus. Over the next 12 years he broke 3 of the Kliens; then someone said Cannondale was better so he bought one and 9 months went by and it broke but it took 8 months to get Cannondale to replace it so he bought a steel Gios in 1999 to ride in while waiting. He got the Cannondale back and less then a year later it broke except this time he threw in the dump! He still rides the Gios today and so far no problems. But he likes steel so much better that he bought a Rivendell for touring last year.
By the way, glue bonded lugged AL frames are actually stronger than welded tubes. The reason the glue bonded lugged frames of days gone past failed was due to the use of the smaller diameter tubing which flexed to much causing the glue to eventially fail-which on welded tubes of the same diameter the failure rate was more than 4 times as much! The reason they stayed with the welded tube was cost.
see for more info:
http://www.exploratorium.edu/cycling/frames1.html
Also a book by: Hayduk, Douglas. Bicycle Metallurgy for the Cyclist. Says this about AL frames: "Aluminum is light and cheap and always large-diameter because, like a presto log or a block of pink popcorn, it doesn’t stand up to repeated flexing. Aluminum has a short fatigue life, so the smarter makers eliminate fatigue-inducing flex by using huge diameter tubes. There are some fine aluminum frames out there—notably, the ones made by Charlie Cunningham and Gary Klein. They at least, have some flesh and blood and brains behind them. But today’s cheap-labor imitations have nothing to offer beyond their function, and if you can warm up to one of them, you can likely warm up to anything. Consider yourself lucky?"
VeloNews last summer (on page 42) had a product guide issued and made some disparging comments about AL framed bikes: "VeloNews dated 6/10/03, page 42. “As anyone familiar with beer cans can tell you, al is softer and less stiff than steel. Al is easy to draw and form into shapes, easy to machine and relatively easy to weld. Its density is about a third of steel and half of ti, so it is not hard to build a light bike with it. It will oxidize, and should be painted, powdered coated or anodized to prevent corrosion, but it does not rust away rapidly. Al has downsides too. Its tensile strength, yield strength and elongation are far less than those of high strength steel and ti alloys. Al is more vulnerable in a crash. Al has no fatigue limit, a property steel possesses, often expressed as a % of its tensile strength. Below this limit, the material can be cycled indefinitely without breaking. This means that al can be less predictable than steel as to when it will fail after long use. Back to our beer can: compare a can of beer to a metal can of olives and it’s apparent that he al container has much less stiffness than a steel can of similar thickness and diameter. Yet many al bikes feel stiff. Why? It’s because al’s density is so low; tubes can be made large and thick for stiffness and light weight. Al can be alloyed with other elements to enhance its properties. Scandium for instance is an element that can help make a very strong al alloy."
I could go on but why?
This whole issue of AL being used to construct bike came about in the early 80's when cycle manufactures where losing money on bike frames because of all the hand work it took to build a bike. So they found that with AL they can have mass production robotic machines weld the tubes saving labor cost; PLUS they can use recycled AL and save on material cost. The average AL frame made in Asian plants cost $45 (a little bet less in China and little bit more in Thailand)...that includes labor and material! Why do you think Nike builds shoes in China? So they can get the shoe for $5 and sell it to you for $120, the reason: PROFIT! And all that profit does not have to pay for insurance or lawyers for workers here in the States. No wonder 90% of the crap in WalMart is now made in China.