Commuting - Metal Strength : Magnesium, Steel, Aluminum

Which of these are the strongest: magnesium, steel, aluminum

is magnesium stronger than aluminum?

steel.

Think of it this way. The skeleton of Skyscrapers are built from steel. Beer cans are built from aluminum.

Not familiar with Magnesium.

I think in terms of strength per weight, magnesium is the strongest. Magnesium is also horribly expensive and difficult to machine.

Magnesium and titanium are used in satellites where weight is very important and cost is no object.

I think in terms of strength per weight, magnesium is the strongest. Magnesium is also horribly expensive and difficult to machine.

Magnesium and titanium are used in satellites where weight is very important and cost is no object.

so like in terms of strength would it be something like this:

Aluminum - 56 units of strength
Steel - 72 units of strength
Magnesium - 73 units of strength
Titanium - 89 units of strength

per 100g of each metal/alloy

i see that some forks have aluminum for the uppers and lowers made of magnesium, even on downhill and mountain forks

Magnesium is the most fun to burn.

More to it then that. If titanium were as cheap as steels it would replace steel in skyscrapers. Aluminum can fatigue-fail at stresses below the tensisle strength, and designing around that problem adds weight. The one real attempt at a magnesium bike ran into what sounds like design problems. An old saying applies here: You can get it cheap, strong, light; any two, not all three.

Berylium has some good points but the toxicity of the pure Be dust is nasty.

More to it then that. If titanium were as cheap as steels it would replace steel in skyscrapers. Aluminum can fatigue-fail at stresses below the tensisle strength, and designing around that problem adds weight. The one real attempt at a magnesium bike ran into what sounds like design problems. An old saying applies here: You can get it cheap, strong, light; any two, not all three.

Berylium has some good points but the toxicity of the pure Be dust is nasty.

mr. cummings you seem the expert on such matters,

can you comment on my previous post above...

"""
so like in terms of strength would it be something like this:

Aluminum - 56 units of strength
Steel - 72 units of strength
Magnesium - 73 units of strength
Titanium - 89 units of strength

per 100g of each metal/alloy
"""

say for example would it be suitable to use magnesium to uphold high stress applications such as a bike frame dropout and adding a high torque 60mph motor on it, you would use such as magnesium, but wouldn't trust it to aluminum

Where would something like Reynolds 953 fit into the scheme of things?

1) Chromoly Steel (http://www.matweb.com/search/SpecificMaterial.asp?bassnum=MS182A): S_yield = 310 MPa

2) Aluminum (6061-T6) (http://www.matweb.com/search/SpecificMaterial.asp?bassnum=MA6061T6): S_yield = 276 MPa

3) Magnesium (http://www.matweb.com/search/SpecificMaterial.asp?bassnum=AMEMg02): S_yield = 115-140 MPa

Note that all these change depending on how the metal is processed. Especially aluminum. Most of the high yield strength of aluminum comes from the heat treatment and cold working processes. It can, under some circumstances, be weaker than magnesium.

EDIT: I should add that most of the materials used in bicycle frames are custom metallugies and their properties are trade secrets.

The problem is more complex than looking at a few numbers. There are a lot of material properties to consider (yield and ultimate tensile strengths, stiffness, toughness, fatigue resistance, corrosion resistance, to name a few), and you can't simply name a material and declare it "the best" without knowing a lot of details of the problem. For example, do geometry considerations limit the parts to particular sizes or geometries that would drive the choice of one material over another? If a part must be as strong as possible in the minimum amount of space, steel might be chosen; if a part has to be a particular size to connect the bits that it's supposed to, that might drive the choice of another material.

Keep in mind that there are a tremendous number of alloys of steel, magnesium, titanium, and aluminum, each with distinct properties. Comparing 1018 steel to 7075 aluminum is pointless, as is comparing 4340 steel with 1050 aluminum. CP titanium is very different from 2.5Al3.5V, and different again from 6Al4V.

In short, you need to run a stress analysis of your proposed system, then select an alloy capable of handling the stresses with a reasonable safety factor. It would be wise to run your stress analysis for a worst-case scenario, pick your safety factor per industry standards, and consider the expected life of the system and the expected number of stress cycles to determine if the selected material and geometry are likely to fail in fatigue.

FWIW, magnesium is not particularly difficult to machine, but it's important to keep it cool during machining processes. I once sent a set of drawings to the shop to have some brackets fabricated from magnesium. When I went by later to check on the progress, I found all the machinists standing around outside the back door of the shop watching my nearly-completed brackets burn - the machinist ran it with too high a feed rate, the part overheated and burst into flames, and he unclamped it and dropped it into a bucket of sand so it didn't make a mess out of his milling machine table. Needless to say, I didn't get may parts on time. :)

More info on magnesium here:

http://www.paketa.com/index.htm

I read something somewhere about a new process being developed to refine titanium. Apparently they'll be able to reduce titanium dioxide (which is apparently extremely common in soil). The story was that they may be able to drop the price of titanium below the current price of steel. If that happens, lots of stuff may change. Sorry, I don't have a link.

Ding!

Potentially cheaper titanium refinement (http://www.techreview.com/read_article.aspx?id=16963&ch=nanotech)

Though it probably won't happen this year.

Actually I think magnesium must be pretty easy to machine; many transmission casings are made from magnesium, and they're heavily machined. Also "mag wheels" - machined wheels were originally made from magnesium to reduce weight.

Magnesium and titanium aren't all that expensive. Raw titanium isn't anyway. Stuff made from titanium is because it's a PITA to work with.

The problem with building from magnesium (especially in buildings) is that once magnesium catches fire, you basically sit back and watch it burn. In fact burning magnesium reacts violently with water (which can be fun if that's your intention).

Titanium *is* difficult to machine. It tends to just chip rather than turn easily. However, it's useful when alloying with aluminum.

More to it then that. If titanium were as cheap as steels it would replace steel in skyscrapers. Aluminum can fatigue-fail at stresses below the tensisle strength, and designing around that problem adds weight. The one real attempt at a magnesium bike ran into what sounds like design problems. An old saying applies here: You can get it cheap, strong, light; any two, not all three.

Berylium has some good points but the toxicity of the pure Be dust is nasty.

American submarines are made of steel, many russian subs are made of Ti. Don't look for an Al submarine anytime soon (or CF for that matter)!

American submarines are made of steel, many russian subs are made of Ti. Don't look for an Al submarine anytime soon (or CF for that matter)!

So Skyscrapers are steel, submarines are steel or Ti, airplanes are Al or CF. I guess in a submarine/airplane collision, I'd rather be in the sub (esp. if the airplane was slowed by going through water in the first place). Airplane/Skyscraper, generally the skyscraper comes out ahead. Not sure of any submarine/skyscraper collisions but I'm sure there's at least a CGI version in some movie somewhere. Need to do more research.

Actually the new Reynolds 953 tubing made of a stainless steel alloy is now the strongest of anything out there with an MPA of between 1750 and 2050! http://www.reynoldscycles.co.uk/steel953.html

Actually the MPA figures quoted by Brian Ratliff may not be correct according to the Reynolds site. If you drag your cursor over the other materials they make you will find their MPA figures to be higher then that listed by Brian. Regardless the new 953 is the strongest.

The 953 is indeed the SUPERSTEEL!

Ding!

Potentially cheaper titanium refinement (http://www.techreview.com/read_article.aspx?id=16963&ch=nanotech)

Though it probably won't happen this year.


That's it! Thanks.

Titanium is challenging to machine because it's rather tough and it work hardens rapidly. I've drilled titanium with high speed steel drill bits; it does great until the bit gets just a little dull, then the titanium hardens and immediately dulls the bit the rest of the way. Once that's happened, you have to drill through the hardened area with a carbide drill bit, which are expensive and tend to shatter if you so much as look at them cross-eyed.

If the process linked to above can get the cost of titanium down to the point that it's affordable, you'll see a lot more research going into how to machine it economically and it'll get easier to work with.

Magnesium machines rather well, unless you catch it on fire; then you can either watch it burn or put it out with a class D fire extinguisher.

Magnesium make a splended flare, mixing it with other compounds will make for various colored flares. Just think how a hot brake on a long twisty downhill would turn out when the frame caught fire. :)
You know what burns my butt? A flame about three feet high.
Steven

Magnesium make a splended flare, mixing it with other compounds will make for various colored flares. Just think how a hot brake on a long twisty downhill would turn out when the frame caught fire. :)

Magnesium isn't that easy to light. I've done it a lot. If you have magnesium wool or very thin ribbon and a blowtorch, or some hot coals and a dewar of liquid oxygen, you're good, but I don't think a brake shoe getting town to the metal is going to do it.

They've made car and aircraft wheels, transmissions and lawn mower decks from magnesium for years, and they don't just spontaneously combust. Heck, you can even weld magnesium if you use the right filler and don't have any small shavings and such in the area.

Magnesium fires are fun and all, but they are really pretty hard to get going if the metal is more massive than flakes and splinters.