A data acquisition system and the SAD2 software, that provide characteristic cooling curves, in combination with microstructure analysis were used to study precipitates formation in the AA 380.0 aluminium alloys modified by adding extra magnesium. The samples were solidified with distinct cooling rates caused by carrying out the solidification in shell and permanent molds. The mathematics processing of the cooling curves in agreement with the microstructure analysis have confirmed the remarkable presence of both the Al-Si dendrite network and the Mg 2 Si interdendritic phase in the alloys with the addition of extra magnesium.