Full Magnesium Chassis(??)

[Daniel BGR]

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 (http://fsae.com/eve/forums/a/tpc/f/125607348/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

[thewoundedsoldier]

"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?

[Neil_Roberts]

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.

[Ben K]

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

[billywight]

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.

[Xeilos]

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).

[Drew Price]

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

[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.

[EHog]

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.

[thewoundedsoldier]

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?

[EHog]

Please note: Frames can scrape the ground without wheels falling off...


To thewoundedsoldier:
Its a bit redneck but...

The test could be as simple as weighing down a piece of mag extrusion and dragging it behind a pick-up truck...



Isn't 4130 great? You don't even have to think twice http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

[thewoundedsoldier]

Then your stuck in a truck dragging a burning fireball of magnesium.

Hehe I like it.

[Pico]

My opinion is that as a first time car you should stick to the basic materials (steel, aluminium). You could ask them if they want to weld your mild steel frame, thats a big aid? On the other hand you could make uprights using extruded profiles. I'd personally make that a two year project though to make sure it's well done.

[SamB]

Don't also forget, one of the main design points for a steel space frame chassis is that you (the weekend racer) can weld anything back on that falls off. I know many people who can weld steel, but nobody who can weld Mg. Surely, a Mg chassis therefore removes this design point?

You don't have to be a genius to realise it's not going to just burst into flames so I wouldn't worry about that. What exactly are your pro's and what are your con's?

[Peter7307]

Originally posted by Daniel BGR:
Hello all,
We are a new team, starting to design our first car. A big Manufacture has offered us his assistance.

From topic http://fsae.com/eve/forums/a/t...48/m/95210885821/p/1 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/95210885821/p/1) ,
Daniel R
Ben-Gurion Racing

Then take advantage of it.

If you are fortunate enough to have specialist advice then talk to that specialist first since it is after all what they do.

They will be able to answer any questions you have about fabrication , machining castings, fatigue life , suitable alloys and so on.

Peter.

[cjanota]

I wouldn't worry about making small parts from it, but I would stay away from it for a chassis/body. http://en.wikipedia.org/wiki/1955_Le_Mans_disaster

[tamir5005]

Hi everybody

My name is Tamir and I'm from Daniel's FSAE team.
First - thank you all for helping and creating this discussion.
Second - about us using Mag for the frame - Our car from 2006 with the Mag chassis was not complete so it has almost no milage, hence no noticeable fatigue (unless you take into account the surface oxidation). Our team agrees with the ones saying that Mag is not that scary, we mechined a few parts from it and made minor repairs at our lab and it behaves much like Aluminium. We are not scared that the frame will scrape the road because we will use Aluminium plates at the bottom of the frame, and for our new design we will try to integrate Mag as much as possible (for parts other than the frame - uprights, pedals, pushrods and so on) because it is light and we have a big Mag factory helping us.

The main question is if you ignore the fact that Mag powder burns and other saftey issues - is it a good material for a space frame?
Our pro's are: Mag is light and with proper design will result in a light frame, a have big sponsor that will extrude the tubes and weld the frame (even create a new die if we insist!).
Our con's are: We are a new team and using Mag means "to boldly go where no man has gone befor" - not a good idea, for structural equivalence the diamater of the tubes will be bigger which result in bigger frame and packaging issues (not to mention that achieving good deep weld in a thick tube is not easy), the rool hoops (will connect by bolts - more parts and weight), welding parts to the chassis means sending it to the factory (about 200 km from our university), and the minor issue with the welds and their resistance to fatigue.

Right now it seems that the logical decision is to use 4130 this year, but it is not decided yet.

[Mikey Antonakakis]

Originally posted by thewoundedsoldier:
Then your stuck in a truck dragging a burning fireball of magnesium.

Hehe I like it.
How awesome would that be?!?

[Big Bird]

If your rationale is to play with magnesium, then go for it.

If your rationale is to do well in the competition, then try the following:
Step 1. Build a steel frame car (any motor), complete it, then compete in event
Step 2. Repeat step 1 until you are consistently scoring over 750 points at comp (I'd suggest at least 2-3 events. Any vehicle concept can compete at this level)
Step 3. Upon completion of step 2, objectively assess your performance relative to others. IF your pointscore assessment indicates vehicle mass is what is holding you back from winning, and IF AND ONLY IF you have exhausted cheaper and easier ways of making your car lighter, then start considering fancier materials.

I think you are making life unnecessarily hard for yourselves. I also think you can end up looking rather silly when your unobtainium wonder car gets beaten by a plain old, cheap as chips, mild steel spaceframe FSAE standard.

Kind regards,

[Richard Pare]

Compare the stiffness to weight ratio of mag vs steel, then factor in the cost difference, repairbility difference, fatigue difference and packaging differences to get equal frame stiffness. Your answer will be pretty obvious.

[Mike Cook]

All logistics aside of using magnesium, I did some calculations.

4130 : stiffness to wt = 104, strength to wt = 221
6061 : stiffness to wt = 102, strength to wt = 410
extruded mag: stiffness to wt = 101, strength to wt = 158


So it seems like from a stiffness to weight ratio, all of the materials are similar. However, the strength to weight ratio is pretty bad for magnesium, so to pass the SEF, you would probably have to have pretty thick extrusions, which is going to make the car heavier.

The other thing I noticed was that if you look at elongation % at yield:

4130: 25%
6061: 12%
Mag: 5%

I didn't do any true energy calculations (area under the stress strain curve) but I'm going to assume that Mag is pretty bad, so in an impact, you will have pretty high g loading, and the frame is going to break pretty quickly before absorbing much energy.

In terms of cost, I'm not sure how much magnesium is, but for the other two materials,
for a 1"x.065" tube, the costs are

steel: 12$/lb
6061: 32$/lb


It doesn't sound like magnesium is a good material choice for frames. Also, its compression strength is a lot lower than tension, only 6.3ksi yield.

Mike