Regular and high resolution transmission electron microscopy observations on the precipitates in a naturally aged Al–Mg–Si alloy AA6022

The precipitates in the Al–Mg–Si alloy AA6022 naturally aged for 2–3 years were investigated by regular and high resolution transmission electron microscopy (TEM and HRTEM) and by selective area electron diffraction (SAED). The shape of the particles was generally either nearly circular or circular with one or more bulges. They had an approximate log-normal size distribution with a peak diameter dp = 2.75 nm. Their crystal structure matched that of the c-centered monoclinic β// phase (GP-II Zone) reported in the literature for aging of this alloy type at elevated temperatures.