Brasses are immune to dealloying when the
zinc compositon is less than approximately 15 at.%.
For alloys with greater than 15% Zn, uniform
dealloying has been observed in both marine
and acidic freshwater environments, while plug
(or local) dealloying is typically observed under
deposits in seawater environments (Ref 7, 14,
15). Plug dealloying (Fig. 2) occurs spontaneously
in 70:30 brass tubes after immersion in seawater
at elevated temperatures for a few days and
is associated with the formation of a white zincsalt
deposit. Dealloying has also been observed
in ammonia-containing solutions (Ref 16–18),
sodium nitrite solutions (Ref 19), and dilute
acidic solutions (Ref 14, 15). The dealloying of
b-brass (and also two-phase brass alloys) is particularly
severe, owing to the high zinc composition
of the b phase. In two-phase alloys, the b
phase is attacked first, leaving behind a porous
copper structure that can act as a cathode, driving
the dealloying of the a phase. Dezincification is
directly related to the stress-corrosion cracking
of copper-zinc alloys