Abstract
The –AlCu phase in an Al–4Zn–2Cu–1Mg–0.7Si (wt.%) alloy was investigated by means of scanning transmission electron microscopy. With our specific alloy composition, the phase is often formed with stacking faults on and planes. The stacking faults on planes are often regularly spaced and create a previously unreported superstructure. Structural damage by electron irradiation is observed, even at a low acceleration voltage of 80 kV. The damage is more pronounced in the precipitates with stacking faults, which agrees with theoretical calculations of knock-on scattering cross-sections. These two very different forms of disruptions of the structure are linked to its spacious interstitial sites and the ease at which Cu atoms diffuse into and between them.