There are large, pink (pure copper) spongy areas that appear to be "attacking" the beta matrix of the two phase, alpha plus beta microstructure.
There are three photomicrographs: 50X (top) ...
Note the iron-zinc compound "stars."
The zinc-rich beta phase corroded first because it had 40% zinc, whereas the alpha only contained 35% zinc.
Refer to the copper - zinc phase diagram in Lesson 1.
The last specimen in this lesson is another example of stress corrosion cracking.