working with titanium

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I am in the process of designing a titanium mountain bike frame. I have welded titanium before but I'm not sure what type of titanium to use for my frame ? One other manufactures uses 3AL-2.5V, and i have also heard of companies using 6AL- 4V. Does anyone know the characteristics of these materials in tube form and plate form ? Also can these two materials be welded together ? thanks
Reply:I'm no expert... but I have found some online resources that may help you (these are clickable links):A primer on titanium tube and pipeChallenges and considerations in joining exotic materialsDelta repair welders aim highTitanium—You can weld it!TITANIUM METALS CORPORATION TIG for titanium tubingHope that helps some....  and Good luck.-----------------------Carmen Electrodewww.CarmenElectrode.comand the boss blogs at  www.JoeWelder.comall powered by  www.Arc-Zone.com
Reply:There are 13 grades of titanium.The first 3 (one of the ones you mentioned) are called commercial grades.Basically the first ones on the 1-13 list are more prone to cracking and as you get towards 13 it is softer. The best grade is 6ALV6 because it has the best balance between stiffness and ductility. The three manufacturers of titanium say there was not enough demand for the sizes used for bicycles but that was 10 years ago Some of the sizes you need may now be available in 6alV4. The bicycles being sold that have the sticker on the frame that say 6alV4 are often ONLY the bottom bracket.You can TIG the round tube without shielding if there are no drafts in the room. The gas flows around a round tube very well. The weld should look very shiny like mercury, If there is coloration the weld is not getting the gas sheilding needed.They make plastic bubbles to use for welding bicycles and small parts.I feel like the whole exercise is pointless because a well made chromoly frame can compete with titanium and not be prone to cracking. The weight difference is not great.AWS certified welding inspectorAWS certified welder
Reply:Hey Art,3Al2.5V is grade 9, 6Al4V is grade 5. Googling 'titanium grades' will get you loads of links giving the properties of these (and a lot more than 13 others) alloys which are usually split into groups- alpha, alpha-beta and beta alloys + comercially pure. Very basically 6/4 is stronger and harder than 3/2.5 so wall thickness can be reduced a (very) little to save a bit of weight. It used to make a bigger difference some years back when all that was around was plain gauge tube, virtually always 3/2.5- places like Litespeed would form their own tube from 6/4 sheet as there wasn't much in the way of alternatives. Now that Reynolds are mechanically butting Ti tube the weight reductions are less obvious, for example a typical 3/2.5 butted tube may have wall thicknesses of 0.9/0.7/0.9mm versus 0.85/0.7/0.85mm for 6/4Both 3/2.5 and 6/4 are alpha-beta alloys and are easily welded to each other. There's a choice of fillers, not sure what's commonly used in the bike industry but 3/2.5 filler will result in tougher, more ductile joints- 6/4 filler works but welds are apparently less ductile than the parent material. Not 100% sure but IIRC Litespeed used to produce their own filler from 6/4 sheet offcutsA lot of the fittings such as bottle bosses and cable guides are available in CP grade 2 as well as grades 5 and 9I've not worked with 3/2.5 but i would guess it would be a little easier to work with than 6/4 which (although lovely to weld, as is CP) is a real bitch to fabricate withPersonally i always preferred the ride of a steel frame but the latest maraging steels being used are getting silly now- UTS in excess of 2000MPa, wall thicknesses around 0.3mm with an increase in OD to get the stiffness back. A lot of the nice characteristics are disappearing imo
Reply:Ive had a good amount of working with Ti,  i don't know the specific grade of Ti, but it sure does weld differently,