Abstract: The results of fractographic investigation with SEM and EPMA on the weld metal solidification crack of A1-4.5Cu-Si-Mg alloy and its liquation crack during multi-pass welding are presented. The temperatures at which the solidification cracks formed were recorded by oscillograph. The fractographic features of solidification cracks formed at these temperatures were analysed. The fractographic features of liquation cracks found in the weld metal and in the base metal adjacent to the weld metal were also examined and analysed. Thus, both types of cracks can be identified.