Originally Posted by Flak
In a practical scenario, what does this mean? An alu bike exposed to too much salt will become brittle and snap? What about fresh water?
Nice post btw.
It means really, that your alloy frame will become pitted and dull and crusty looking. It's very hard to make it go as far as the crusty stage, though. It's most dangerous at welds, because were the curve of the fish-scale is a tiny stress raiser. This, coupled with the preferential attack of reagents at zones of higher stress (it's called stress-corrosion cracking or SCC), will cause the weld strength to degrade, but worse, the toughness to drop substantially. Remember! Clean your frame regularly. It'll help you see corrosion sooner.
Originally Posted by LongIslandTom
Yeah Titanium is not easy to weld..
I grew up on Long Island near where Grumman built F-14 Tomcat fighter jets for the U.S. Navy in the 1970's. A friend of mine worked on the production line and he tells me the titanium assemblies for their particular application can only be welded using a computer-controlled electron-beam welder. Apparently that method of welding does make quite a strong joint-- So strong in fact that the titanium load-bearing wing boxes on the F-14's swing wings has never had a failure during the fighter jet's service life (the Tomcat's motto: "...Anytime, baby!" yeah!).
I guess bicycle manufacturers can't be bothered to invest in electron beam welder tooling for making titanium frames.
The part you're talking about is the variable-geometry anchor box. It's 6/4 Titanium alloy, and back then, in the '70's, titanium alloys were neither as clean, nor welding technologies as refined as they are today. A high end TIG torch can satifactorily purge the weld zone for bike frame assembly.
One of the reasons they've never had a failure on them is the enormous over-engineering of the joint system. That and the wing exits the body some inches from the axle through the wing root.
Pity they couldn't say the same for the powerplants
