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  • dusse123
    started a topic 6082 aluminium heat treating, help?

    6082 aluminium heat treating, help?

    Hey everybody,

    I've done a fair bit of mild steel welding but now I am making an aluminium project for the first time. I'm making a ski bike, it will be a bit like a north legion smx if anyone is interested.

    I will be buying 6082 box section aluminium and it comes in a T6 condition. I know from my research that this type of aluminium will lose a lot of its strength when welded so I should get it heat treated to get it back to T6 condition.

    But here is my problem, as I said earlier the metal will already be in T6 and when I weld it only a small part of the aluminium will lose its T6 temper, is it possible to heat treat to aluminium normally without changing the metal that is already in T6 condition?

    Sorry if my wording is a bit hard to understand, I tried my best but if you dont understand the question please say.

    Thanks for the help

    Angus

  • Jigantor
    replied
    None of us can tell you what to do we can only advise. After all this is your design.
    Bill was not suggesting you use T4 he was just filling in some gaps.
    As he stated the T6 process will distort or buckle the frame and that is why mountain bike frame builders don't post heat treat.

    Seeing how there is no shock absorbers in your design here is a test you can do that may help with thickness choice.
    Get a 2mm thick flat bar and a 3mm thick flat bar.
    Put one in a vice, drill a 10mm hole in it, slide a 10mm steel round bar or bolt through the hole, now place a steel channel over the flat bar so the legs of the channel are resting on the round bar only. Take a 10 kilo weight and drop it onto the channel from a set height say 1 meter. Remove the bolt and see if the hole is now oval shaped. Measure and record elongation. Repeat the process for the other flat bar. Increase weight and height dropped until you get a result. This will be what happens in the rear swing arm area of your frame but with more force and with more times done.

    Ji

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  • dusse123
    replied
    I've found a place where I might be able to buy the aluminium in T4 so hopefully that'll work out. I need to order the metal ASAP so will order more than necessary, as I said I'm going to overbuild, strength is more important than weight. Do you think 2mm without a heatreat will be ok or should I do the heatreat or/and use 3mm?

    Leave a comment:


  • dusse123
    replied
    Unfortunately I can only get T6...

    Leave a comment:


  • BillC
    replied
    On the subject of heat treating the frame, filler metal is an important consideration. 4043 or 5356 filler metals are not likely to have the same response to heat treatment as the base metal, so the weld metal will be the weak link. 4643 filler metal is designed for welding 6XXX series aluminum with post weld heat treatment.

    The T6 aged condition strength is due to precipitation of alloying elements (magnesium and silicon) in the aluminum. If you weld in the T6 condition, the heat affected zone will lose strength due to overaging. The heat treater will solution anneal the frame to re-dissolve all of the precipitates, then artificially age the material to T6 temper again. Solution annealing requires a quench and can result in distortion of your weldment. If you weld in the naturally aged T4 temper you can age the frame to T6 without having to solution anneal first.

    Regards,

    Leave a comment:


  • Jigantor
    replied
    Bungee cords.
    Well if you offset the connection bracket to counter balance the ski's weight you will not have to completely rely on the cord. You can test the position with maths or trial and error.

    Ji

    Leave a comment:


  • dusse123
    replied
    bungee chords! And I'm beginning to think that I might put the vertical box section on the rear leaning in.

    Leave a comment:


  • Jigantor
    replied
    Well have you worked out how you are going to get the pivots to work?
    They have to be able to rotate perfectly with each other at the same time then when you stop leaning return to their upright position. Also I think you are going to hit your legs on the ski posts, after all the foot pegs are attached to them. They are vertical where your legs angle up to your hips.

    The skis have to be able to rotate front to back so they can ride over bumps or they will spear into a mound of snow and you will go over the bars. When in the air gravity will make the front of the ski point towards the ground. If you land like this over the bars. Take look at some other designs you will see a lanyard attached to the front of each ski.

    Ji

    Leave a comment:


  • dusse123
    replied
    Awesome! So what did you mean about this "The next issue is that pivot swing arm. How ever you are going to do it work them out before ordering. These will be very difficult to get to work perfect the first time. The front of the skis when in the air will tilt down, you have to come up with an idea to make them always stay level or tilt up. Or when you land the bike will nose dive.!

    Leave a comment:


  • Jigantor
    replied
    I have been snow boarding since 2002.
    I also mountain bike as training for motocross.

    Ji

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  • dusse123
    replied
    over 20kg!? When I'm over estimating I cant get above 15kg! And anyway, the way I'm doing it is that you go on chairlifts the same way as on the north legion smx and tow lifts should be easy.

    What did you mean by this?: "The next issue is that pivot swing arm. How ever you are going to do it work them out before ordering. These will be very difficult to get to work perfect the first time. The front of the skis when in the air will tilt down, you have to come up with an idea to make them always stay level or tilt up. Or when you land the bike will nose dive."

    Just out of interest do you ski or mountain bike or are you just an experienced welder?

    Leave a comment:


  • Jigantor
    replied
    50x50x3mm SHS aluminium square tube has a mass of 1.52kg/m length.
    I estimate that there is about 5.45meters of this tube having a net mass of 8.3kgs.
    The unit still needs handle bars, head stem single or duel front steering arms, rear swing arm pivot hardware, foot pegs, seat and three skis to account for weight wise.

    The unit will be at least 20 kgs.
    Are you sure you can carry/handle/hold that all day?
    And hold on to it on a lift.

    Work out what all the parts weigh and check my assumptions, then go carry something around that weighs a similar weight. An aluminium 88cf scuba tank weighs around 20kgs and it is not easy to carry more than 20 meters on flat ground.

    Ji

    Leave a comment:


  • Jigantor
    replied
    Before you order anything.
    Have you worked out dimensions of each member?
    If so estimate how much this thing is going to weigh including the skis for 2mm and then 3mm.
    Next check the slopes where you intend using it to see if they will let you on their lift with it.
    Remember on a lift you will have to hold it for the length of the trip to the top.
    If they will not let you on than you will have to push/carry this thing to the top.
    Weight will be a major factor.
    Not all lift operators will let you on with a hand held bike.

    The next issue is that pivot swing arm. How ever you are going to do it work them out before ordering. These will be very difficult to get to work perfect the first time. The front of the skis when in the air will tilt down, you have to come up with an idea to make them always stay level or tilt up. Or when you land the bike will nose dive.

    Big air is not a length. You will have to work out what you think your body can absorb to a flat landing and then use it for the design. Without shocks it won't be much as your ankles/knees will collapse and your men bits will smash on the cross bar.

    Ji

    Leave a comment:


  • dusse123
    replied
    Originally posted by Jigantor View Post
    Yes I mean your weight including clothes, safety gear, back pack, water........
    Also will you be jumping this thing? if so what height and to a flat landing or to a down ramp?
    Ji
    And I forgot to answer this, I shouldn't weigh more than 70kg with all of my stuff but I'm only 15 so will still grow quite a lot, and yes I am definitely planning on going big on the jumps and I will probably ending up jumping or dropping to flat. I know that everything will eventually break but I want to eliminate the risk of it breaking on me in real world conditions, eg I want it to be built like a tank but weight is still a concern, just secondary to strength. Ideally I would like to order metal tonight, (uk time) school deadlines. Do you think 2-3mm would be ok or should I go thicker?

    Leave a comment:


  • dusse123
    replied
    Originally posted by Jigantor View Post
    Yeah, in my portfolio I did research on several ski bikes and that was one of them, I cant believe that the best solution was starring me in the face the entire time! I'll be wearing snowboard boots when I ride it and that sketch you did, would it still be able to edge the skis because I cant see how, it would need another horizontal beam at the top, it could be a lot smaller than the lower one though.

    Leave a comment:

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