tryabean Posted June 25, 2008 Report Share Posted June 25, 2008 heya i have noticed quite allot of people asking about heat treating frames after being welded, but i want to explain why you dont need to heat treat alluminum. heat treating is a process that makes carbon rise to the surface of a metal to harden it and strengthen it. the reason why there is no reason to do this to alluminum is that it dosnt have carbon in unless its a wacky kinda alloy but still you would only heat treat high carbon steel or gun metal wich is basically high carbon steel haha just thaught i would share that and i hope i have helped people michael x Quote Link to comment Share on other sites More sharing options...
Mark W Posted June 25, 2008 Report Share Posted June 25, 2008 I thought the deal was was that after welding, the metal near the joint would heat up, causing it to be a different hardness or strength to the rest of the material, and so by heat treating you balanced it out? Quote Link to comment Share on other sites More sharing options...
tryabean Posted June 25, 2008 Author Report Share Posted June 25, 2008 I thought the deal was was that after welding, the metal near the joint would heat up, causing it to be a different hardness or strength to the rest of the material, and so by heat treating you balanced it out? noo because when you weld alluminum you match the grade of ally to the same rod or atleast should do so its all the same strength even if it aint the same grade it will still be strong and 100% reliable aslong as the weldor did a good job Quote Link to comment Share on other sites More sharing options...
ogre Posted June 25, 2008 Report Share Posted June 25, 2008 I thought the deal was was that after welding, the metal near the joint would heat up, causing it to be a different hardness or strength to the rest of the material, and so by heat treating you balanced it out? wurd, i asked my chemisty teacher last year she said it affected the stiffness of the metal, kinda like the different amounts of carbon in steel affect it's characteristics. i'm sure a clever tfer will explain for realsies this evening. Quote Link to comment Share on other sites More sharing options...
Mark W Posted June 25, 2008 Report Share Posted June 25, 2008 noo because when you weld alluminum you match the grade of ally to the same rod or atleast should do so its all the same strength even if it aint the same grade it will still be strong and 100% reliable aslong as the weldor did a good job I didn't mean the grade would be different or anything, I meant that the metal immediately surrounding the weld (Which you can see way better on welded steel frames) would get super, super hot, and that would change how brittle/hard/something it was compared to the areas further down the tube which didn't get particularly hot? Quote Link to comment Share on other sites More sharing options...
tryabean Posted June 25, 2008 Author Report Share Posted June 25, 2008 I didn't mean the grade would be different or anything, I meant that the metal immediately surrounding the weld (Which you can see way better on welded steel frames) would get super, super hot, and that would change how brittle/hard/something it was compared to the areas further down the tube which didn't get particularly hot? if you let it cool and dont use a major f in high amperage there will be no need to heat treat on other hand you could quench it if need so for extra strength i wana say at this point i didnt say heat treating dont work im jus saying the reason why there is no need i just thaught id clear before some one says heat treating does work haha Quote Link to comment Share on other sites More sharing options...
Luke Rainbird Posted June 25, 2008 Report Share Posted June 25, 2008 If you ask any decent frame builder (*** etc spring to mind, I've seen various discussions of it on OTN) they'll generally tell you it's a given to produce a top strength build I can't remember the reasoning for it myself, but I'm sure a bit of searching on frame forum or similar would haul it up Quote Link to comment Share on other sites More sharing options...
psycholist Posted June 25, 2008 Report Share Posted June 25, 2008 (edited) Rate of cooling affects the grain size in a material. If you cool something suddenly it forms small grains, making the material brittle. If you cool it slowly it has time to form larger grains, making it more ductile. It's more favourable for bike frames to aim for the more ductile side of this range. Particular medals are chosen with compositions to improve hardenability or ductility depending on the final application and the heat treatment available. Welding tends to heat and cool the material very quickly (Especially in Al which is about 10 times as thermally conductive as steel IIRC). Heat treatments such as T6 are more involved again. They require the material to have a composition that allows certain compounds to form in the material at temperatures below phase transition temperatures (Where the material either turns from a solid to a liquid or from a solid with one crystalline structure to another structure). This is also known as aging as in many materials, especially aluminium, this process continues to happen very slowly at room temperature... To sum up regarding bike frame materials - some steels and aluminiums can be welded without requiring heat treatment (Either they're designed to handle welding without losing too much strength or they're built much heavier than they'd need to be to give the same strength/life if they were heat treated). Pretty much all aluminiums suffer a massive drop in either strength of fatigue resistance if they're not heat treated. This is why if you break an aluminium frame and get it welded up, the chances are it'll fail just beside the new weld (In the heat affected zone where the material is most brittle) if it's not heat treated. Edited June 25, 2008 by psycholist Quote Link to comment Share on other sites More sharing options...
tryabean Posted June 25, 2008 Author Report Share Posted June 25, 2008 the reason why i bring this topic up is that i started my apprentice work at a fabrication place local to me and iv been with a bloke who welds ally. and i brought it up and thats what he told me hes made a few mountain bikes himself like but i dont wana cause argument haha! Rate of cooling affects the grain size in a material. If you cool something suddenly it forms small grains, making the material brittle. If you cool it slowly it has time to form larger grains, making it more ductile. It's more favourable for bike frames to aim for the more ductile side of this range. Particular medals are chosen with compositions to improve hardenability or ductility depending on the final application and the heat treatment available. Welding tends to heat and cool the material very quickly (Especially in Al which is about 10 times as thermally conductive as steel IIRC). Heat treatments such as T6 are more involved again. They require the material to have a composition that allows certain compounds to form in the material at temperatures below phase transition temperatures (Where the material either turns from a solid to a liquid or from a solid with one crystalline structure to another structure). This is also known as aging as in many materials, especially aluminium, this process continues to happen very slowly at room temperature... To sum up regarding bike frame materials - some steels and aluminiums can be welded without requiring heat treatment (Either they're designed to handle welding without losing too much strength or they're built much heavier than they'd need to be to give the same strength/life if they were heat treated). Pretty much all aluminiums suffer a massive drop in either strength of fatigue resistance if they're not heat treated. This is why if you break an aluminium frame and get it welded up, the chances are it'll fail just beside the new weld (In the heat affected zone where the material is most brittle) if it's not heat treated. thats a really good explanation Quote Link to comment Share on other sites More sharing options...
Mark W Posted June 25, 2008 Report Share Posted June 25, 2008 Pretty much all aluminiums suffer a massive drop in either strength of fatigue resistance if they're not heat treated. This is why if you break an aluminium frame and get it welded up, the chances are it'll fail just beside the new weld (In the heat affected zone where the material is most brittle) if it's not heat treated. Cool, I thought that was the case. Cheers for the post Quote Link to comment Share on other sites More sharing options...
Tango Posted June 25, 2008 Report Share Posted June 25, 2008 the reason why i bring this topic up is that i started my apprentice work at a fabrication place local to me and iv been with a bloke who welds ally. and i brought it up and thats what he told me hes made a few mountain bikes himself like but i dont wana cause argument haha! Maby mountain bikes he's built dont go under the same stresses that trials frames go under. Meaning he doesn't need them heat treated. Quote Link to comment Share on other sites More sharing options...
Bionic Balls Posted June 25, 2008 Report Share Posted June 25, 2008 sorry but...hahaha..! listen to psycholist...he knows his stuff! Quote Link to comment Share on other sites More sharing options...
Shaun H Posted June 26, 2008 Report Share Posted June 26, 2008 LOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOL Hold on, I need to call Dr. Smith my materials and processes lecturer and tell him he's gone mental and has been teaching mechanical engineering students shite. I can't believe someone who works in the actual business of ally welding told you that. Is he a qualified welder? Or just good at it? Quote Link to comment Share on other sites More sharing options...
dave33 Posted June 26, 2008 Report Share Posted June 26, 2008 they actually nomalise not heat tread bike frames, which returns the grain structure back to normal rather that changing the mechanical properties of the material like they do when you aneal or harden and temper, but these later are generaly for carbon steels Quote Link to comment Share on other sites More sharing options...
psycholist Posted June 26, 2008 Report Share Posted June 26, 2008 Normalising is a heat treatment pretty much the same as annealing (For most metals - the cooling rate is faster for normalising than annealing, but it's often enough to give th required properties. Normalising is more popular in industry because the furnace can be refilled with new parts rather than allowed to cool with the parts in it as for a full anneal, improving production rate and lowering unit cost... Read on: http://en.wikipedia.org/wiki/Heat_treatment Quote Link to comment Share on other sites More sharing options...
dave33 Posted June 26, 2008 Report Share Posted June 26, 2008 (edited) Normalising is a heat treatment pretty much the same as annealing (For most metals - the cooling rate is faster for normalising than annealing, but it's often enough to give th required properties. Normalising is more popular in industry because the furnace can be refilled with new parts rather than allowed to cool with the parts in it as for a full anneal, improving production rate and lowering unit cost... Read on: http://en.wikipedia.org/wiki/Heat_treatment anealing is only after a part has been already hardend, to make it less brittle basically, what you would have to do to machine a hardend part normalising is basically to return to the original grainstructure ie-after welding or machining when large amounts of material has been removed Edited June 26, 2008 by dave33 Quote Link to comment Share on other sites More sharing options...
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