On Jan 9, 4:49*pm, Jerry Wass wrote:

HEY!Thanks for the answer---Hadn't heard of that alloy--mosta *my
castings . . . .

----------------------------------------------------------------------

Sorry Jerry, but 'Electrum' (as I believe it's spelt), whilst the
cat's pajamas's in the 1930's because Germany produced about 90% of
the world's magnesium, thanks to one of their companies holding the
patent to the most efficient sea-water extraction process, by the
1950's everyone was discovering that the alloy, which was about 95%
magnesium, the other 5% made up of aluminum, zinc, copper and what-
have-you (remember, these are the folks who came up with 2024-T6), it
was discovered that the alloy -- which was vvery popular for the gear-
cases on helicopters -- was susceptible to AGE HARDENING. (Volkswagen
discovered the same thing... and changed their alloy in 1972.)

The problem was not discovered for about 25 years, when they noticed
that the Universal Replacement Crankcase often developed fatal cracks
from simply sitting on the shelf in the dealer's parts department.
These parts had never been assembled; had never been subjected to any
form of stress. Yet they still cracked. The quick fix was to
increase the percentage of Aluminum in the casting meta from about 2%
to about 4%. But engineers opined that the additional aluminum may
NOT be a permanent cure... but we would have to wait another 25 years
to find out.

Boeing found out the hard way. Their Vertol Division experienced
similar cracking problems in their helicopter crankcases.

The best solution was to go to aluminum vs magnesium.

-Bob