Copper content also plays a role. Consider the
comparison of alloys 7075 and 7050, where 7050
has a higher copper content. ForWtemper, 7050
is more susceptible to IG forms of corrosion
(SCC, IGC, exfoliation), than 7075. It is believed
that the higher-copper alloy retains more copper
in grain boundary precipitates during the quench.
In T6 and T7X tempers, 7050 is less susceptible
than 7075. A clear mechanism for this effect is
still an area of active research. One hypothesis,
based on a hydrogen embrittlement model, is that
the additional copper content leads to more copper
incorporation into precipitates, which in turn
provides enhanced trapping of hydrogen, thereby
slowing the rate of hydrogen embrittlement