Why magnesium alloy????

Started Apr 19, 2013 | Discussions thread
Joseph S Wisniewski
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Nothing to do with burning...
In reply to IainD, Apr 20, 2013

IainD wrote:

Magnesium will burn with great heat in powder form or as pieces of metal.

It will not ignite easy as "pieces of metal" with appreciable thickness. The surface area to volume ratio goes down with increased thickness, which is why magnesium intended for burning is powdered, drawn into thin wire, or extruded as ribbon.

Magnesium ignites around 880 degrees F. By the time you get the camera up to that temperature, all the plastic parts are already burning and throwing off copious amounts of toxic gasses.

The alloy reduces this tendency and increases the temperature required for ignition. It is light and convenient.

Well, sure, if you reverse the accepted meanings of "reduces" and "increases". Alloying with 4% aluminum (the typical alloy used for camera bodies) lowers the ignition temperature, more than it lowers the energy output of the combustion, making it both easier to ignite and to sustain combustion.

If you want to get an idea how much fun aluminum compounds are to burn, look up "thermite".

Magnesium-aluminum alloys have lower ductility (creep) than pure magnesium. Paradoxically, aluminum-magnesium alloys also have lower ductility than pure aluminum. Has to do with messing up the pure metal's crystalline structure. More here:

http://www.dpreview.com/forums/post/51324928

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Rahon Klavanian 1912-2008.
Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed.
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