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Re: [T3] AS21 vs. AS41 magnesium alloys


A bit more on the alloys I've found...

First off, in general, the AS-series Mg alloys are used for applications
requiring high temperatures and good creep strength.  This makes perfect
sense why they were used by VW...

And, check out http://www.type2.com/library/misc/mageng.htm  - there's some
more interesting info on the two alloys there...

But, the end result is this:  the answer to our question is that it IS
cheaper to produce a magnesium case than an aluminum one, despite the
intuitive opposite thinking because the material cost to you and me at the
store is higher.  Then again, material cost is almost always the minor
component to the cost of a casting/forging/etc.  Case in point: one method I
was looking at (and abandoned...) for casting the cylinders for my cylinder
set had a material cost of about $5 and a casting cost of over $100.  And,
that didn't including the machining cost, either... (in the case of the
engine cases again, Mg is easier, cleaner, and less tool-destructive to
machine than Al...)

Take care,

> Hey group-
> I asked around at work today, and found an excellent website:
> It's a free web database of tons of materials info...
> Magnesium AS21X1
> http://www.matweb.com/SpecificMaterial.asp?bassnum=MMAS21&group=General
> Magnesium AS41XA-F
> http://www.matweb.com/SpecificMaterial.asp?bassnum=MMAS41&group=General
> Magnesium AS41XB-F
> http://www.matweb.com/SpecificMaterial.asp?bassnum=MMAS42&group=General
> 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
> a larger elongation, i.e. how much you can bend it before it breaks (I
> think this is as important - 4% and 9% elongation means the case geometry
> 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
> 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
> 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
> 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,
> Shad
> -------------------------------------------------------------------
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