Due to their superior strength to weight ratio heat treatable Al-Cu alloys (2XXX-Series) are widely used particularly in aerospace industry. Although the hardening precipitates in these alloys are well-known, the very early stages of decomposition are still topic of ongoing research. Scanning transmission electron microscopy is used to investigate the influence of different parameters, such as thermal history, on early-stage precipitation in Al. Based on state-of-the-art transmission electron microscopy, single Cu atoms can be imaged and natural ageing in form of Guinier*Preston zone formation accelerated by excess vacancies can be investigated, which was possible before only by diffraction experiments. In addition, resistivity and hardness measurements are performed to evaluate the temper state of the specimens. The results are compared to numerical simulations. A better understanding of the mechanisms leading to precipitate formation in these alloys for light-weight construction could be tuned more precisely regarding their intended use.