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[T3] AS21 vs. AS41 magnesium alloys

Hey group-

I asked around at work today, and found an excellent website: www.matweb.com
It's a free web database of tons of materials info...

Magnesium AS21X1

Magnesium AS41XA-F

Magnesium AS41XB-F
http://www.matweb.com/SpecificMaterial.asp?bassnum=MMAS42&group=General  (is
this a.k.a. AS42???)

According to these data, AS41 is considerably stronger, i.e. it takes more
before you can break it or permanently change it's shape.  However, AS21 has
a larger elongation, i.e. how much you can bend it before it breaks (I don't
think this is as important - 4% and 9% elongation means the case geometry is
trash before it actually snaps).  The elasticity moduli are the same, i.e.
they both have the same "springyness" or stiffness.  Then again, these
figures are taken at room temperature... I wonder how dissimilar at all they
would be at 200-250F.

They're all listed as die casting materials, which makes sense.  All are
VERY easy to machine and VERY easy to cast, which definately points to
superiority (and economy!) over aluminum in this regard.  All are probably
poured at similar temperatures (and the coefficients of thermal expansion
are similar), so the casting process itself is probably near identical for
the Mg alloys.  There is one other interesting note: AS21 is listed there as
being used for high temperature applications whereas AS41 is not.  I don't
know if this noteworthy or if it is just because two different sources were
used with different kinds of comments.  But, if it is noteworthy, then
here's something interesting: VW changed to AS21 on the FI T1 at the same
time that they increased the thermostat opening temperature... perhaps the
change to AS21 was because they decided to raise the operating temperature
of the engine...

Take care,

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