Rick Girard wrote:

I spent three years documenting and inspecting the heat treat operations
at a Boeing facility. While the process depends on the alloy, it is
generally the same for all aircraft alloys. First the material is placed
in an anaerobic oven where the temperature is around 850 to 900 degrees
F for up to eight hours. It is shock cooled in a water tank. At that
point the material is in "O" condition. If it is placed in a freezer, it
will remain soft. If it stays at room temperature it will naturally
harden up to a "T4" condition in 24 to 96 hours. at that point it has
about 75% of the properties of fully processed material. To reach a "T3"
or "T6" condition (we're talking 2024, 6061, and 7075 alloys) the part
is placed in the oven at a lower temperature for two to three hours.
This is referred to as artificial aging.

Rick Girard

I suspected this. No telling how old the bends are when you get them
from Burns.

Paul Lamar
 
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