Paranoid thought of the day:Magnesium components - stability?

[tylercheung]

So, in an act of foolish procrastination, I was poking around the description of different components and noticed a lot of "top end" stuff is made out of magnesium.


My layperson's high school chemistry seems to remember pure magnesium being somewhat soft and prone to catch on fire.

The Shimano manuals all seem to say "don't put this Mg component next to" certain materials or they will corrode...

Are Mg components a good idea? or is this really meant for "pros" who replace equipment every year, and corrosion/stuff catching on fire be damned...?

(I am sure the good metallurgists and engineers have figured this out w/ alloy this, alloy that but still..)

[Hindmost]

My Pinarello Dogma has yet to spontaneously combust. My old well-used Bontrager bar ends look a little crusty, however.

[dddd]

A lot of what is called magnesium is actually aluminum alloyed with magnesium.

So maybe not much worse than 7000-series aluminum?

I recall a certain pucker factor when heating magnesium drum-brake hubs with a propane torch adjusted to a "soft flame", as instructed when replacing (motorcycle) hub bearings.

[oldpotatoe]

Originally Posted by dddd

A lot of what is called magnesium is actually aluminum alloyed with magnesium.

So maybe not much worse than 7000-series aluminum?

I recall a certain pucker factor when heating magnesium drum-brake hubs with a propane torch adjusted to a "soft flame", as instructed when replacing (motorcycle) hub bearings.

Yup, like calling something 'scandium'..is really aluminum with about 5% scandium 'dirt' thrown in..

[goonster]

Don't know the exact compositions involved, but while many magnesium alloys have a very high activation energy, they will burn.

Consider that many old aircooled VW engine blocks were made out of Mg alloy. This is a material suitable for the construction of internal combustion engines, but was also frequently the highlight spectacle of VW club bonfires.

[martl]

Originally Posted by tylercheung

So, in an act of foolish procrastination, I was poking around the description of different components and noticed a lot of "top end" stuff is made out of magnesium.

I know about precisely *one* bicycle part produced in larger numbers ever to be made out of Magnesium, which were the Avid Mag V-Brakes in the early 2000s. They were discontinued after an accident at their factory which, i believe, cost one life (see below).

Almost any technical Aluminum alloy contains Magnesium as an alloying element, 7020, for example, would be AlZn4,5Mg1 and contain around 1% of Mg. This doesn't make the material "Mg", in the same way a tube of Reynolds 531 (25CrMo4) is Steel and not "Chrome".

Elementary Magnesium can react with O2 (=burn/think Bengal fire) if the surface/mass ratio is big enough, this means: Mg dust, Mg filings etc. are highly flammable and *will* burn (which is what happened at the Avid factory), a solid piece of Mg isn't. I

It would take a heat source very hot indeed to burn my Avid Mags (yep, still riding them), and no, brake heating isn't hot enough. (solid Magnesium *will* burn if heated enough, as demonstrated by above cylinderhead/bonfire anecdotes, or ugly youtube videos of 1970ies racing car accidents, almost all racing car rims that era wer Magnesium and they were the nightmare of every fireman)

Btw, Avid replaced the Mag Model with a Titanium one at no weight disadvantage. Apart from the exotic touch, there is no need to use Mg for bike components at all, and no one does it consequently, not even Shimano

[93KgBike]

Originally Posted by tylercheung

So, in an act of foolish procrastination, I was poking around the description of different components and noticed a lot of "top end" stuff is made out of magnesium.


My layperson's high school chemistry seems to remember pure magnesium being somewhat soft and prone to catch on fire.

The Shimano manuals all seem to say "don't put this Mg component next to" certain materials or they will corrode...

Are Mg components a good idea? or is this really meant for "pros" who replace equipment every year, and corrosion/stuff catching on fire be damned...?

(I am sure the good metallurgists and engineers have figured this out w/ alloy this, alloy that but still..)

If you are riding in a lightening storm, and being struck by lightening, then yes your magnesium parts could burn - and the nickel metal-hydride or lithium ion batteries in your tech could explode - but so too could your carbon parts, your aluminum parts, even your steel and titanium parts.

But, "welder dies in bike-fire" is a story I've yet to hear.

ITM's "the stem" has never been recalled for failure, and still sets the bar (npi) for weight, even if it is almost equally ugly.

You should be fine, imho. Ride on.

[Mark McM]

Originally Posted by oldpotatoe

Yup, like calling something 'scandium'..is really aluminum with about 5% scandium 'dirt' thrown in..

Wait - you mean my chrome-moly frame tubing isn't made from just chromium and molybdenum? The next thing you're going to tell my is that my Vittoria Graphene tires are made from 100% graphene!

[Ozz]

Here you go:

"Metallurgy for cyclists"

https://www.ibiscycles.com/support/t..._for_cyclists/


Skip ahead to chapter 6 ("Try Something Exotic") for magnesium.

[Mark McM]

Originally Posted by martl

I know about precisely *one* bicycle part produced in larger numbers ever to be made out of Magnesium, which were the Avid Mag V-Brakes in the early 2000s. They were discontinued after an accident at their factory which, i believe, cost one life (see below).

I think you'll find that there are and have been many bike parts made from magnesium. For example there are magnesium frames (Kirk Precision used cast magnesium and Pinarello and Merida used welded magnesium tubing), magnesium rims (American Classic made from rims from extruded magnesium), and brakes (such as the Avids mentioned). But probably the biggest use of magnesium has been in suspension forks. Rock Shox gained their initial fame with the Mag21 magnesium fork, and many other fork makers have and continue to use cast magnesium in forks. Cast magnesium is actually well suited for suspension fork sliders, where you want high stiffness at low weight in a part that has a complex shape.

As you've said, the hazards with magnesium are mostly during production. A finished magnesium part presents no particular danger to the user. It is not suited for every bike component, but where it is, is a very viable material.

[NHAero]

Weren't some mountain bike fork lowers made of magnesium?
Oops, Mark beat me to it

[bfd]

Originally Posted by Mark McM

I think you'll find that there are and have been many bike parts made from magnesium. For example there are magnesium frames (Kirk Precision used cast magnesium and Pinarello and Merida used welded magnesium tubing), magnesium rims (American Classic made from rims from extruded magnesium), and brakes (such as the Avids mentioned). But probably the biggest use of magnesium has been in suspension forks. Rock Shox gained their initial fame with the Mag21 magnesium fork, and many other fork makers have and continue to use cast magnesium in forks. Cast magnesium is actually well suited for suspension fork sliders, where you want high stiffness at low weight in a part that has a complex shape.

As you've said, the hazards with magnesium are mostly during production. A finished magnesium part presents no particular danger to the user. It is not suited for every bike component, but where it is, is a very viable material.

Lol, I was wondering when someone was going to mention Kirk Precision magnesium frames! Those were maybe the ugliest frames ever made and just about every single one broke!



Good Luck!

[martl]

Originally Posted by Mark McM

I think you'll find that there are and have been many bike parts made from magnesium. For example there are magnesium frames (Kirk Precision used cast magnesium and Pinarello and Merida used welded magnesium tubing), magnesium rims (American Classic made from rims from extruded magnesium), and brakes (such as the Avids mentioned). But probably the biggest use of magnesium has been in suspension forks. Rock Shox gained their initial fame with the Mag21 magnesium fork, and many other fork makers have and continue to use cast magnesium in forks. Cast magnesium is actually well suited for suspension fork sliders, where you want high stiffness at low weight in a part that has a complex shape.

As you've said, the hazards with magnesium are mostly during production. A finished magnesium part presents no particular danger to the user. It is not suited for every bike component, but where it is, is a very viable material.

yup. For me it had sounded as if the OP thought almost every modern bike part was made of Mg, and that is clearly not the case, most stuff is made from Aluminum and/or plastic.
Was aware of he Kirk frames and hence i used the phrase "in significant numbers" - i've been trying to locate one (preferably the racing bike one) for years
Wasn't aware about the use in forks, i've never been that much into MTB parts and i always thought the "Mag" in the name was just marketing - thanks for the info! still have and use a Rock Shox SID SL, the 1100g one, is that one of those?

[Mark McM]

Originally Posted by martl

Was aware of he Kirk frames and hence i used the phrase "in significant numbers" - i've been trying to locate one (preferably the racing bike one) for years

Yes, frames are a poor use of cast magnesium. But welded magnesium tubing has been successfully used for decades. One big user of magnesium tubes is Merida, although they don't have much penetration in the USA.

Originally Posted by martl

Wasn't aware about the use in forks, i've never been that much into MTB parts and i always thought the "Mag" in the name was just marketing - thanks for the info! still have and use a Rock Shox SID SL, the 1100g one, is that one of those?

Just about any mid to high end suspension forks with cast sliders use a magnesium casting - Rockshox Sid, Reba, Pike, Judy; Fox Float; Marzocchi Bomber; etc.

A quick search found a few other uses of magnesium in modern bike components - for example, the shift levers on SRAM Force Double Tap levers are magnesium.

[martl]

Originally Posted by Mark McM

Yes, frames are a poor use of cast magnesium. But welded magnesium tubing has been successfully used for decades. One big user of magnesium tubes is Merida, although they don't have much penetration in the USA.

i'll think aobut one of those when it beats my Scott Sc (910g confirmed in "M") in weight and riding characteristics)...