Why magnesium alloy????

Started Apr 19, 2013 | Discussions thread
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Joseph S Wisniewski Forum Pro • Posts: 34,124
What alloys really do
5

bflood wrote:

Pure magnesium, powder or solid, burns at a very high temperature and such a fire is extremely difficult to put out.  An alloy changes all that - much less combustible and harder to ignite.

Where did you hear that?

Because it's not true. The most common magnesium alloys contain less than 10% of other metals, with 4% aluminum being the most common. That has essentially zero effect on either ignition temperature or energy release.

What it affects is ductility. Magnesium has a nice, uniform grain structure. So, hit it with sufficient stress, and grain boundaries sheer, grains slide over each other, and you get permanent (plastic) deformation. Aluminum grains form with a different shape, so a few percent of aluminum will cause scattered "misshapen" grains that "jam" the whole sliding process.

A small amount of magnesium will do exactly the same thing to aluminum. Aluminum with 4% magnesium acts an awful lot like magnesium with 4% aluminum.

It only takes a few peecent of one to alter the other. Mix closer to 50% of each, and you get a mess, a eutectic alloy with an annoying low melting point, hard to machine, low strength, just a pile of scrap.

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Rahon Klavanian 1912-2008.
Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed.
Ciao! Joseph
www.swissarmyfork.com

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