Titanium

  1. johnny99 Member

    I am currently making up a Ti exhaust for one of our racecars, from 2 system's. I have got some rods from a mate, but when I look at the weld, there is a yellow dust, and if cleaned off, the weld looks dull. If I weld without the filler rod, the wels looks lovely, and no yellow dust. Any idea's why

    John
  2. Autolupus Member

    There are various titanium alloys, could be you're using mismatched rods?
  3. hotrodder Member

    Posts: 3,285
    SE England
    If all is good/clean with autogenous welds then typically it's a heat input and/or gas shielding issue i.e. running a bit hotter and/or slower when adding wire.

    The end of the wire needs to be kept within the gas shield or it'll be contaminated by the atmosphere and then those oxides/nitrides etc will be added to the weld next dip of the wire. If the end of the filler wire is discoloured when you finish a weld then (assuming you kept it in place during post flow) that's a good indication

    If the hot weld isn't protected from the atmosphere for long enough it'll become discoloured as it oxidises etc. Weld length often needs to be limited for this reason when welding Ti outside of an inert chamber without a trailing cup, more likely to be an issue (or a bigger issue) with wire than for autogenous welds. Pulsed TIG can help in this regard, on thin sections pulse tends to exaggerate the 'sticky' nature of the wire i.e. pulse lowers the heat input which makes the wire more likely to stick to the part/weldpool. For this reason i normally use a lay wire technique

    The yellow dust/soot is a new one to me. Too hot/bad shielding usually shows itself as discolouration, initially purplish blues getting lighter then with a greenish tinge. Cook the crap out of it and greenish hues get duller grey and finally white. Ti nitrides are a bronzish colour, combined with heavy oxidation i guess it could be more yellowish. Closest i've seen is whites with a tinge of yellow (but not dusty) on the back of a scrap when testing torch shield quality. Pics?
  4. johnny99 Member

    I done what you said Hotrodder, I got a gas lens, and made sure the rod was covered, about 10 seconds of pre and post on the gas. I done some more welding, and it's the same. I am pretty sure it must be the filler rod. how do I know what Ti alloy I'm welding when I bought the exhaust systems second hand, any way of telling

    John
  5. hotrodder Member

    Posts: 3,285
    SE England
    Not unless you get it analysed but there's not too many suspects used for exhausts and (as with other metals) not matching the filler wire typically effects weld properties more than weldability. For example could weld grade 5 (6Al4V) with erTi-2 wire or visa versa without problems although the weld properties would be quite different to the base material

    Commercially pure Ti is commonly used, often CP2. Several 'exhaust grades' have been developed to cope with the heat better... Akrapovic use grade 37 (Ti-1.5Al), Timet came up with something they call Timetal XT (used on the Corvette IIRC) and i've read about a few others too. With the exception of Timet they're all Ti-Al-Si flavours

    Found a scrap that's been badly oxidised, looks more yellowish in the pic than in the flesh but FWIW...

    P7220506.jpg

    Not dusty, texture is more like flux residue. Look familar? Do you know what grade the wire is? Is it definately some flavour of Ti (spark test would at least confirm that)? Only other thing i can think of (and it's a shot in the dark) is that when using wire the higher heat input is pulling crap through from the back i.e. purge problem or contaminants from the used exhaust
  6. Delgado Member

    Posts: 369
    Slough UK
    If you're worried about matching the filler, could you not cut some strips off a bit of scrap (if you have any), and use them as filler?
  7. johnny99 Member

    should have thought of that. I tried it this morning, and the weld is so much better. Having difficulty concentrating keeping the rod cover with gas, but practice will cure that. There is no yellow/green dust, but the weld is not 100% pretty, but I'm putting that down to the Ti not being completely clean, exhaust is very old. Thanks folks

    John
  8. hotrodder Member

    Posts: 3,285
    SE England
    Getting things like this clean is typically a major chunk of the job as Ti will react (and form brittle compounds) with most things at welding temps
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