Repairing a cracked frame?

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  • Repairing a cracked frame?
  • Premier Icon rhid
    Subscriber

    How viable is it to repair a cracked weld on an aluminium frame?

    Can a specialist welder do the work to make it as good as new or is it time for a new frame?

    rainbow
    Member

    If it’s aluminium frame, dump it and time to get a new frame, with steel frame it can be repaired.

    z1ppy
    Member

    Can be done: done well and work or done not so well and still work.. though may depend on where your crack is.

    I have a friend whose swinging are developed a crack, it was given to a some-one who ‘can’ weld aluminium and had it back with a very nasty looking weld but it’s held for the last 2 years..

    Though some-one on here had a bike (Intense Tracer/Uzzi[?]), IIRC the seatpost has the damage, repaired to look like new, can’t remember who posted it though. Very professional job.

    perfectly possible to repair an aluminium frame. However due to the materials properties of some aluminium alloys it may weaken the frame and thus it may crack again.

    Personally I would take it to one of the expert aluminium fabricators around the country and get them to weld it

    Premier Icon rhid
    Subscriber

    I would definately send it to a someone with the tools and all the skills necessary. Does anyone know how much the work could cost? Also Has anyone ever had to buy a new front end for a 224? If so how much?

    woodsman
    Member

    It is easy enough to weld aluminium, but it would need to be heat treated – de-stressed to have anything like the original strength. Jusy welding a crack isn’t ideal either, ideally and common practice on steel is to replace the tube, again not so straight forward on aluminium. Sorry about the negative comments, find a good engineering shop, they should know about the heat treatment/de-stressing.

    Best of luck

    Premier Icon Lummox
    Subscriber

    i have an orange 66 swingarm awaiting the results of this thread, watching with interest.

    I was told the metal used would need heat treatment after welding to retain it’s strength, orange refused to repair saying they wouldn’t gaurante the result, they did say however there are plenty of ‘specialists’ out there

    z1ppy
    Member

    The repair was thinking of… Intense Socom

    schrickvr6
    Member

    I’ve had an Orange 5 welded that had a hairline crack in the swingarm. Orange wanted £300 to weld, heat treat and pownercoat it. I had a local alu welder who is very good do it for £15, He removed a little bit of material and zapped it a good un. I let it just sit for a few months in an attempt to let it age harden and since then it’s been fine touch wood, used a couple of times a week including regular DH and a trip to the Alps.

    Rhid haven’t you only just bought this frame?

    garethh
    Member

    Rhid – i’ve got a very good condition 224 dd front end if thats what you’re after. Drop me an email

    Macavity
    Member

    When welding a crack in aluminium, steel, titanium the main problem is getting any contamination out of the crack. Cleanliness is the main problem in TIG welding.
    For aluminium any contamination in the weld means even lower fracture toughness.
    http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Mechanical/FractureToughness.htm

    If it is possible to clean the crack so that there is absolutely no dirt, oil etc then it is fairly simple to make a good repair.

    Aluminium can be TIG welded or even Oxyacetylene welded.
    http://www.youtube.com/user/tinmantech?blend=3&ob=5#p/u/0/aF1Srs_e1Aw

    The heat treatment of aluminium is of less concern than cleanliness.

    andyl
    Member

    get it fixed but start saving for a new frame and keep an eye on it. The longer it lasts the more money you have for a nice new one 🙂

    toys19
    Member

    The heat treatment of aluminium is of less concern than cleanliness.

    Ahhh that explains why Orange frames are expensive tat, they waste loads of money on heat treating their frames..

    Premier Icon rhid
    Subscriber

    It was an option to buy a cheap frame with a hairline crack in a weld but after the advice here I went for a less cheap but hopefully uncracked one!

    I think for piece of mind that it probably was a better option!

    The heat treatment depends on the type of alloy used. Some need it, some don’t

    Generally 6000 series will need a post weld heat treatment, ideally a full solution anneal followed by aging to the T6 condition. 7000 series can sometimes get away without. If you can find a decent welder who knows their metallurgy and you can find out which grade your frame is it’s doable.

    I’ll be back at work with access to specs tomorrow but iirc 6061 has around 25% of its fully aged yield strength when it’s fully annealed – that’s the strength you’d have around your weld if the heat input is excessive and there’s no HT afterwards

    Macavity
    Member

    If aluminium breaks due to lack of ultimate tensile strength, then there will be yeild before failure. If there is just a crack with no deformation of the metal around the crack then it is less likely to be a lack of ultimate tensile strength.

    Even on a new frame the weld is in the as cast condition (a weld is a casting) and the adjacent parent material in the heat affected zone (exposed to the harsh very high welding temperature) where the solution treated and aged wrought material (tube etc) has effectively decomposed. Then there is the parent material that has been unaffected by the welding.
    So what type of heat treatment would sort this out?

    toys19
    Member

    Ahhh I think you are forgetting about the actual reason why his frame broke in the first place and what you may want to prevent.

    It is related to fracture toughness, yield and uts. But it isn’t actually covered by anything you have said so far….

    Macavity – solution annealing the frame after welding puts the whole frame into the T0 condition, regardless odf condition before HT, that’s the point of a solution anneal. After that you age the frame and it’s all in the same aged condition.

    As for importance of uts vs yield vs fracture toughness, without knowing if this is a fatigue fracture or a brittle fracture after a big drop etc it’s not worth getting into, incorrect post-weld HT will adversely affect all 3 for most compositions. As would excessive oxidation during welding – metallurgy and cleanliness are both important for a decent repair so find a decent welder and find out more about the frame materials first

    toys19
    Member

    I’ve worked on about 60 ‘in service’ failures with cracks that have been detected by NDT in welded aluminium. Only a small percentage have actually gone undetected and finally failed by fast fracture at the end but every single crack has been down to fatigue.

    Now it is possible that the crack may have been there since welding due to liquation or hot cracking, other than that it’s a fatigue crack. The only brittle failures I’ve seen are just that – total failures.. If its a crack it’s either fatigue, or it was there from the welding process, and the paint has flexed an exposed it.

    If you don’t pwht then you’ll have a structure that will be crap at resisting fatigue crack initiation and growth.

    But this is all theoretical. As it might be that the crack was initiated by a liquation crack and even in the best material it may well grow from such a big initiator. So you could put all that aside and get it welded and ride it. Just watch carefully around the weld looking for cracks. It might fail soon, it might last forever..

    But if you dont pwht them locally at the weld the material will have low yield, so you might find the frame buckles or bends under load, and for that reason more than any other I would say bin it.

    If you don’t pwht then you’ll have a structure that will be crap at resisting fatigue crack initiation and growth.

    Eggsackerly. I’ll take your word on Al alloys since ferrous is more my thing, but personally I’d be happier riding something like 7005 than 6061 if I knew there was no pwht

    toys19
    Member

    it might be 7005, in which case this is all moot.

    Macavity
    Member

    It is the extreme heat of the welding process that causes the annealing.
    The weld will be the softest part of the frame after it is welded. There are a number of different types of welding wire to chose from 4043, 5356 etc. Not all of them are heat-treatable, some will not precipitation harden.

    The process of heat treating a bike frame (6061) would involve heating the whole frame (super saturated solid solution) then quenching in water. This would induce some distortion and would do little to stress relieve it.
    Further heat would then be require to precipitate harden it, to get peak strength.

    “It is not easy to make materials that are both strong and tough. All the [aluminium] alloys have a higher strength and lower toughness than pure aluminium”
    Materials engineering, science, processing and design. Michael Ashby, Hugh Shercliff, David Cebon.

    The precipitation hardening heating process (6061) is by coincidence at a similar temperature and time as that for powder coating.

    A good weld needs as high a standard of weld preparation /cleanliness as possible to avoid contamination.

    toys19
    Member

    MacAvity are you just cutting and pasting?

    I think we know all this hence the don’t bother fixing Zeitgeist..

    Macavity
    Member

    No.
    Sometimes I weld things.

    toys19
    Member

    Ahh jolly good. Unless you are anodizing after then 4043 is the best as it only causes a 10-15% drop in props after PWHT. There is a new one coming which is ‘apparently’ better than both. I’m waiting to see mech testing results though..

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