Originally Posted by
Wogsterca
I think AL was a good material for bike manufacturers, it's cheap, fairly easy to work with and light weight, but I am not convinced it's a good material for bike riders, it's harsh riding, and does fail at welded joins, unless the welds are perfect and the heat treating (to add strength) is done perfectly, after the welding is complete. No matter what, the weakest point in any metal is the welded joint, and since Aluminum suffers from stress fracturing, it's most likely to fracture at a weld.
Now most sub $1000 frames come from China, and lately we have been seeing some big quality issues with Chinese manufacturing (just ask the folks at Mattel ), so maybe it's poor quality welds, or poor quality control at the Chinese contractor that welds the frames. This may not even be Treks fault, because, as typical in Asia you hire a company, they sub-contract out and you have no control over who they sub-contract out to.
+1
As en engineer (controls - not mechanical) my experience (with making brackets, etc.) is that, if you make a part out of aluminum that formerly was made out of steel, you make the aluminum part 25% to 50% thicker than the steel part. This is just a rule of thumb, and applied to non-critical parts. But I think it points towards some critical properties of aluminum.
Aluminum is softer than steel, so to get the same strength you have to make the part beefier. When you make the part beefier (thicker) you tend to loose some elasticity - just because a thicker part is less springy than a thinner part. That's why an aluminum frame has a "harsher" ride than a steel frame, so the manufacturers have to make forks and seatstays out of something that's springier to get an acceptable ride - carbon fiber, which is lightweight but has also comes with real-world durability issues.
Aluminum is harder to weld than is steel, and when you add the additional thickness of the part you get weld-penetration issues.
Then you go to a foreign country to get it done - with little or no government or regulatory oversight and a slave labor workforce - and what do you get?
Another less-desirable property of aluminum is that, again because of it's softness, you can't tap it for threads.
Add the problems of joining carbon fiber parts to aluminum - glue.
Also, it's necessary to make certain parts of an aluminum/carbon fiber frame out of steel - things like the dropouts - because neither aluminum nor carbon fiber is very good at carrying the concentrated loads inherently seen at the dropouts. Again, you have to figure out how to attach these dissimilar materials together - usually glue again.
Of course we are really living in the period of infancy regarding these technologies. As time goes by, the industry will learn how to apply these materials. For no, give me steel.