The microstructure obtained in conventional and lost foam compound casting of Al/Mg alloy was examined and compared. X-ray diffraction, optical and SEM examinations showed that casting magnesium melt around the aluminium insert, in both methods, is caused formation of an interface consisting three different layers. Layer I, beside aluminium consists of Al3Mg2 intermetallic compound, layer II consists of Al12Mg17 phase and layer III, in the vicinity of magnesium, is formed of Al12Mg17+(Mg) eutectic. The result of Vickers microhardness tests, at the interface zones, showed that the hardness of the middle layer is increased substantially (200–250 HV) in comparison to the hardness of the base metals, namely aluminium and magnesium. Using the LFC method reduced the thickness of interface as a result of both, lowering the temperature and the speed of melt. The mean thicknesses of the interface in the conventional and LFC processes were 600 and 200 μm respectively.
