I might be able to help with your question on "aging" if you could define
more clearly what you mean by "aging". Metals, unlike organic (read, e.g.,
human cells), do not age. Their microstructures might change over time given
the appropriate time/temperature conditions. Metals, such as lead, tin, zinc
and gold in a pure state (that is, purity of about 99.9%) will show grain
boundary changes over relatively short times. They will also show
recrsytallization over time given the requisite amount of strain produced by
external stresses (mechanical. temperature and sometimes chemical), provided
there are no impurities of the type that inhibit grain boundary migration. On
the other hand, metals such as silver, copper, iron will show no changes
other than those brought about by corrosion (or stress/corrosion) since they
are seldom in a pure enough state to either recrystallize during their
millennia internment or, for that matter, show much (if any) grain boundary
migration. This is certainly so for steel and for alloys of silver and copper.
I suggest that you access a book on Materials Science and look under the
heading Recrystallization and/or Grain Boundary Migration.
"Aging" in materials refers specifically to a particular phenomenon where
conditions of solid solubility at an elevated temperature permit a heat
treatment to increase the strength of the alloy.
I hope this helps.
R. Maddin
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