Do magnesium bits need special care?

alomac
alomac Posts: 189
edited October 2010 in MTB workshop & tech
Do magnesium bits like fork lowers or pedals (have MG-1s) need any special attention to protect them from corrosion if the paint gets damaged? I know corrosion was meant to be a problem with Mg frames...

Comments

  • The Rookie
    The Rookie Posts: 27,812
    Corrosion of Magnesium alloy parts is very dependant on the alloying involved, however as a rule they are no worse than alumium alloys except for having an extreme dislike of salt in any form (so don't use a washing up liquid as many contain salt), which is why RAF Harriers have mag alloy wheels and Navy Harriers aluminium alloy ones!

    Simon
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • getonyourbike
    getonyourbike Posts: 2,648
    What he said ^^^. But if you remember years back when you did chemistry, magnesium (pure) can react quite natily with water and even worse with acid.
  • Smithy123
    Smithy123 Posts: 1
    I got some mag parts coated by a cambridge company. http://www.keronite.com/ Found them because Mavic and Rock Shox have used them on a new product range. Worth checking it out.
  • The Rookie
    The Rookie Posts: 27,812
    Pure Magnesium would be useless for a lot of reasons (not least of which is how soft it it), however magnesium alloys are fine, I had some second hand Magnesium lowers on Suntour forks and they were about 10 years old when I sold them still in excelent condition.

    And its Sodium that reacts badly with water, or Manganese, not Magnesium!

    Simon
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • UncleMonty
    UncleMonty Posts: 385
    I have a deep nick on the lowers of my Tora 318's where the bare metal is exposed, I've ridden through two winters and it's still as shinny as ever, no sign of any corrosion.
  • Cferg
    Cferg Posts: 347
    The Beginner wrote:
    And its Sodium that reacts badly with water, or Manganese, not Magnesium!
    It's magnesium, it goes bang :wink: Obviously since its an alloy it'll be fine but as has been said I wouldn't like to get much salt involved, it'll probably take a disliking to it, nothing to obvious like a big bang, but it'll weaken it.
  • bennett_346
    bennett_346 Posts: 5,029
    Cferg wrote:
    The Beginner wrote:
    And its Sodium that reacts badly with water, or Manganese, not Magnesium!
    It's magnesium, it goes bang :wink: Obviously since its an alloy it'll be fine but as has been said I wouldn't like to get much salt involved, it'll probably take a disliking to it, nothing to obvious like a big bang, but it'll weaken it.
    No, it isnt. Only clean pure magnesium will react with cold water, and the reaction is very slight. The group 1 alkali metals are what you're thinking of. :wink:

    The magnesium is in compound anyway.
  • Cferg
    Cferg Posts: 347
    Yeah, clean magnesium is what I'm talking about, not in an alloy. And it does go bang, although maybe I'm thinking of it burning and then put in water, ie. its oxide? :oops:
  • cooldad
    cooldad Posts: 32,599
    Magnesium burns if you light it.

    Lithium, sodium and potassium burn/explode when you put them in water.
    I don't do smileys.

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  • Anonymous
    Anonymous Posts: 79,667
    But regardless, saltwater is BAD for magnesium
  • cooldad
    cooldad Posts: 32,599
    yeehaamcgee wrote:
    But regardless, saltwater is BAD for magnesium

    Which is why they don't make dolphins out of it.
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  • The Rookie
    The Rookie Posts: 27,812
    See Darwin was right, all the Magnesium dolphins have died off!

    Simon
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • chiefgrooveguru
    chiefgrooveguru Posts: 80
    Cferg wrote:
    Yeah, clean magnesium is what I'm talking about, not in an alloy. And it does go bang, although maybe I'm thinking of it burning and then put in water, ie. its oxide? :oops:

    You can't use pure magnesium for bike parts, it's too soft! Always an alloy - same as aluminium, same as iron (steel).
  • Anonymous
    Anonymous Posts: 79,667
    edited October 2010
    Ignore what the pure metal is. What you've got is an alloy and the properties are quite different. Magnesium alloys used on bike parts are strong, lightweight and fairly corrosion resistant.

    And yes, pure magnesium reacts slowly in water. It's oxygen it reacts with well, but mainly when on fire, producing a very bright flame. Water isn't good at putting out magnesium fires either. I forget the chemistry of it but I guess the fire releases oxygen in the water and it reacts with that.

    Sodium is the one that's fun to drop a block of into a tub of water and see it explode :D

    Ah the days at school before health & safety got involved. I these days kids can only watch a video of it.
  • Cferg
    Cferg Posts: 347
    chiefgrooveguru wrote:
    Cferg wrote:
    Yeah, clean magnesium is what I'm talking about, not in an alloy. And it does go bang, although maybe I'm thinking of it burning and then put in water, ie. its oxide? :oops:

    You can't use pure magnesium for bike parts, it's too soft! Always an alloy - same as aluminium, same as iron (steel).

    Obviously not, that wasnt the point I was getting at.
  • bluechair84
    bluechair84 Posts: 4,352
    I find they break easily:
    PicturesOnline#5503464153543312386

    I had some mag v12s once and crack all the corners of them.
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