Magnesium as a frame material
 

It should work.

Proponents state it’s a bike material with no downside. They argue magnesium provides a smoother ride than any other frame material, yet is stiff, lighter by volume than aluminum and titanium, and incredibly durable. Sounds like a lot of good properties.

But magnesium options remain limited. If extruding and welding the tubes were easier, would magnesium compete with carbon?

Leonard Zinn thinks so....

http://zinncycles.com/Zinn/?p=1312

You would need to be really careful where other metals contact the magnesium frame to avoid bimetallic corrosion.

Paketa makes an uberlight tandem out of magnesium.

http://www.paketabikes.com/

And not to mention fire. That thing would go up fast!

I believe the original Pinarello Dogma was magnesium. Now it's the Dogma FPX.

Until it rains and your bike bursts in to flames. :)

Maybe you're thinking of sodium or potassium?

Most high-end metals have very similar specific stiffnesses and specific weights. Steel, Ti, AL, Mag all fall into this category. Being much less dense in an absolute sense means that you are able to theoretically build a mag bike with very big, thin walled tubes to reduce weight. At some point you start to loose practical fabrication ability. At that point, Carbon again becomes a very good alternative. The older Dogma was a good example. Interesting bike, but the carbon version is lighter. I really can't comment on the ride characteristics.

do you know anything about chemistry or are you just blabbering? you do realize it's not magnesium metal but an alloy, right?

No sir, I do not. I do know my magnesium fire starting stick makes a nice camp fire though. But thanks for the enlightenment. Try not to be a dick though OK.

There was a small mag frame maker here and they loaned our club a bike for a few weeks. I didn't ride it, it was too small, but everyone who rode it said it was good. Nobody cared for the looks, however. Some months later we heard they went belly-up.

The fact is marketing and sales will determine what is out there and even if something is better, (not saying mag is better), it won't be in your lbs if people aren't buying it.

The only things I would be worried about would be anodic corrosion as mentioned earlier. Also if I remember correctly magnesiums crystal structure is hexagonal, which limits its ductility at lower temperatures (generally). That could have some impact on its failure mode, especially with larger diameter, thinner walled tubing.

But what do I know?

Not uncommon to the mtn bike world. I've seen Mg used a fair bit in forks, I think primarily in the lowers.

Also, I remember some small frame builders touting Scandium, as well. I may be wrong, but I recall reading that their were issues with the welding letting off highly toxic gasses.

Uh, even magnesium alloy makes a really pretty flame. Saw a set go up on a race car. Very impressive.

Scandium just means adding a small amount of Sc to Al alloys (usually 7xxx series). Increases strength with dispersoids, along with the normal precipitatin hardening of 7xxx series alloys. I really haven't heard of any additional weldability issues with Sc additions beyond the normal hurdles associated with welding aged alloys.

i apologize for being brunt, but adding incorrect information when you are ignorant about the topic is not conducive for discussion

the tendency of any metal (or anything, for that matter) to burn is a measure for its ease to combine with oxygen; alas, burning is nothing but an extremely fast and exothermic mode of corrosion. pure Mg is quite combustible (large quantities are often stored in inert argon atmosphere dry boxes), pure Ti will corrode and form titanium oxide (albeit much slower than pure iron). this is why chromium and molybdenum are alloyed with iron to make cro-moly steel, and why aluminum and vanadium is alloyed with titanium to make titanium frames. Mg is usually alloyed with aluminum and zinc. so when you read that your titanium frame is 3Al2.5V, it means that the actual composition is 3% Al, 2.5% V, some trace amount of other elements, and mostly titanium.

i suspect that the crystal structure of the particular Mg alloy would be different from that of pure Mg

"As the remains of the 300 SLR slowed its somersault, the fuel tank, situated behind Levegh's seat, ruptured. The ensuing fuel fire raised the temperature of the remaining Elektron bodywork past its flashpoint, which due to its high magnesium content was already very low. Since magnesium is easily combustible in air, the alloy burst into white hot flames, sending searing embers onto the track and into the crowd. Rescue workers attempting to put out the burning wreckage were initially unsuccessful, as they unknowingly used water on the magnesium fire, which only intensified the inferno. As a result, the car burned for several hours. In total it is estimated that 83 spectators were killed, either by flying parts and debris, or from the fire, with a further 120 injured."

http://en.wikipedia.org/wiki/1955_Le_Mans_disaster
http://www.youtube.com/watch?v=aVdyD73Kv9k

Probably not considering the frames are probably made from AZ61 which will only have ~7% alloying additions. It's also not a homogenous alloy either.

I have my ASM handbook in front of me so I'm not pulling this information out of my ass.

and your point is? it's quite different when you are putting it to a flame source than just having it sit in the atmosphere. did you know that at a high enough temperature, you can't fight fire with water as you now have sufficient energy to actually turn water into hydrogen? i believe this actually occurred in the pacific northwest some years back

I've turned magnesium. It absolutely will go up in flames. But then, so will titanium and steel. I've seen the results of a lathe that had a chip pan full of fine titanium chips that caught fire. Talk about a flash fire.

More than most, considering everything you've written is spot on.

I think you seriously need to lighten up. Anyone can tell that I was kidding around. Why would I think his bike would burst into flames?

:thumb:

Of course mag will burn, but not under normal bicycle usage. In fact, often racecar suspension pieces (uprights) are made of mag and the brake calipers are bolted to them. Naturally, brakes get pretty damned hot. There are never mag fires due to brake heat. If it can life through that, then it can live through anything we're likely to put it through. The discussion is about whether it's mechanical properties lend it to being a good bike frame material. Frankly, it seems like a little more trouble than it's worth. Between Carbon, Steel, AL and Ti, I think we're pretty well covered.