Framebuilders - ATI 425 Titanium
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12-24-05, 10:05 PM
I was just wondering if any of you framebuilders or past frame building students out there have had any experience with ATI 425 Titanium tubes yet? All the features of this metal that Allegheny/Wah Chang lists indicate that it should be a better alloy for forming and butting bicycle tube sets.
I had the same thoughts when reading about this alloy. Strength similar to 6Al4V but ductility like 3Al2.5V, should be cheaper than 6Al4V since less vanadium needed.
The major cost of a an alloy is usually the processing and alloy surcharges, not the raw cost of the alloying elements. You'll find all sorts of ridiculous costs dependant on the volume of supply, and seeing as 6/4 is one of the highest tonnage titanium alloys in any dimensions, it'll be unusually cheap for it's theoretical cost.
There's already a huge body of butted 6/4 about, but most aerospec stuff remains plain gauge and that's the major use of Grade 38 at the moment. Framebuilders, unless there’s a supplier pushing tubes in the sizes they want, aren't really in a position to just go get tubing from somewhere.
So is 3Al2.5V generally used because it is easier make tubes from this alloy?
3/2.5 and 6/4 are both used because, well, they've been used forever. Their initial application was aerospec structural tubing, forgings, hydraulic lines. As a result the industry had access to a large number of different sections of drawn tube. The difference between 3/2.5 and 6/4 is transformability. The leaner alloy is all alpha, with the working characteristics of a strong hexagonal metal. To get the best of out of it you really need to know how slip systems and texture behave in hexagonal metals, but it is a high volume alloy so it's commensurately lower cost by comparison to 6/4. 6/4 is very forgiving of misunderstanding of the foibles of titanium working because it contains a fraction of BCC phase, and cubic metals are lovely to roll and draw. It's stronger, tougher and can be heat treated, unlike 3/2.5, but it's also a little more expensive per tonne.
The volumes available in certain shapes argument rears its head for the cost of tubes. There's many more much stronger titanium alloys than 6/4, much stronger and tougher, but they tend to be forged solid shapes, so you might see them in BB axles, bolt stock, even rings or cassette sprockets, but very unlikely in tube.
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