Microstructure evolution and loss in mechanical properties due to ageing, in cast aluminium alloys used by different manufacturers for cylinder-heads with various initial heat treatments and amount of copper was studied. Two of them have been chosen as references, namely AS7U3G T5 (ASTM319) and AS7G03 T7 (ASTM356). They were submitted to different heat treatments, from the as-received state to saturated ageing state and studied in fatigue, with hardness evolution and by TEM image analysis. After numerical identification, a link was made with microstructural evolutions.