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Thread: Full Magnesium Chassis(??)

  1. #1
    Hello all,
    We are a new team, starting to design our first car. A big Manufacture has offered us his assistance. They are willing to provide us magnesium extrusion profiles and their welding capabilities, for an all magnesium AZ80 space-frame Chassis.

    From topic http://fsae.com/eve/forums/a/t...48/m/95210885821/p/1 , we understand that using magnesium for a space frame is not recommended.
    Our main concern is welding fatigue strength. Any information about magnesium weldings can be in great use to us.
    Other advices are also more than welcome.

    Thanks,
    Daniel R
    Ben-Gurion Racing

  2. #2
    "The Welder's Handbook" by Richard Finch gives stress-relief charts by alloy (callouts for heat treatment). It also talks about the phenomenon of "stress-corrosion cracking".

    How did the 2005 venture turn out? Is there currently noticeable fatigue on that car?
    "Good judgement comes from experience. Experience comes from bad judgement."

  3. #3
    I'd rather fabricate frames from dynamite than magnesium.

    Try one tiny shaving of mag and a cigarette lighter. Just do it outside on concrete. Then think about how many cuts you will have to make to fab a frame. Then think about having to repair the frame at the competition.

    That issue is entirely aside from the extreme difficulty of welding mag successfully, and the loss of heat treat in the heat affected zone.

  4. #4
    Stick with 4130 and be happier for it....

  5. #5
    Not to sound like an ass, but those of you scared of magnesium have obviously never worked with it. It seems you make your advice based on hearsay and myth rather than experience. Magnesium is perfectly safe to machine and weld with the proper precautions, just like any other material. I will give anyone a box of matches and a machined magnesium piece and challange them to light it on fire, it's just not possible. Sure, lighting a thin shaving of mag on fire is easy, but imagine the heat necessary to light a chassis on fire! Good luck. Look at the thermal conductivity of mag, any heat input is quickly dissapated by the rest of the material. Small chips light on fire easily due to the low mass to dissepate the heat.

    For machining mag, take heavy cuts wherever possible and use sharp, new tooling. You will never have a problem. Keep a class D fire extinguisher near by for extra precaution. Don't use coolant, use air. All will be fine.

    I'm not advicating the use of mag as a chassis material as I certainly wouldn't use it for many reasons (many mentioned in this and other threads), but certainly not for fear of the fabrication process. If you have a vendor willing to give you magnesium, take advantage of it, just look for other areas of its advantage than the chassis.
    Billy Wight
    University of California, San Diego - Formula SAE 2004-2006

  6. #6
    I have to agree with Neil Roberts on this one. Making a chassis from magnesium would truly be a dangerous proposition. Just think of grinding parts of the chassis (if you can build an entire chassis without grinding and/or filing then good for you) and the small shaving of magnesium that are being dispersed into the air. Now, all it takes is one of those particles to combust and you have the potential for a massive exothermic reaction of these clouds of particles. We are taking about a flame temperature approaching 3100 degress centigrade [Dreizin, Edward L.; Berman, Charles H. and Vicenzi, Edward P. (2000). "Condensed-phase modifications in magnesium particle combustion in air". Scripta Materialia 122: 30]

    I am not saying that the entire chassis is going to combust on you. But a similar phenomenon can occur at any time you are doing any operation on magnesium in a oxygen enriched environment (air). All it takes is one moment of error (too much heat in a large enough particle of magnesium) and then you will have a problem on your hands.

    This is akin to smoking in a grain silo or grain mill. Do so and I guarantee it will be the last thing you do (at the very least you will not have any eyebrows left).

  7. #7
    Soooo, did you even read Billy's post? I had no trouble machining cast mag either.

    Is no one remembering that tubular and formed magnesium airframes were being fabricated 60+ years ago quite successfully for airplanes?

    Also, the original poster said that the company was offering them structural magnesium extrusions, it would be very easy to make a bulkhead structure and riveted stressed skins with bolt-on hardpoints, and would be a lot more along the lines of a production sort of construction, rather than a fabricated tubing structure.

    Think WWU Viking 30/35 perhaps?

    http: / / dot.etec.wwu.edu/fsae/viking30.htm

    Ditto - free material plus offers of manufacturing help to do things a little differently than everyone else at least merits some thought. Decide if it will benefit you at the competition, and go from there. You're too early in the design process to be ruling out material and process selection if you're asking this question.

    Best,
    Drew
    _______________________________________

    Northwestern Formula Racing Alum
    Head Engineer, Frame/Suspension 2006-2009

    My '73 Saab 99 Road Race Build

  8. #8
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    I think the problem would be when you lose a wheel and start dragging the chassis on the ground. There would be a situation where flakes of magnesium could ignite.
    Scott Brenaman
    Portland State - 2009-11
    Desire is the key to motivation, but it's determination and commitment to an unrelenting pursuit of your goal - a commitment to excellence - that will enable you to attain the success you seek. - Mario Andret

  9. #9
    Originally posted by sbrenaman:
    I think the problem would be when you lose a wheel and start dragging the chassis on the ground. There would be a situation where flakes of magnesium could ignite.

    Several people have said this, but it sounds like nobody actually knows. Instead of playing guessing games, I would just go ahead and test it out.
    -Evan Hoglund

    Manufacturing Guru 08-10
    SDSM&T FSAE

  10. #10
    If wheels are falling off your car, you've got a bigger problem than frame design.

    Both SJSU cars this year (FSAE and Hybrid) experienced major suspension failures during their dynamic events and both retained the wheels.

    To EHog, how do you test that? With a driver seated?
    "Good judgement comes from experience. Experience comes from bad judgement."

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