In the present work on Al-W master alloy for modification of silumina casting alloy was studied. This alloy was characterized by XRD analysis and SEM/EDX methods. The XRD investigations of Al-W sample enabled the identification of Al, Al4W, Al5W phases. The contents of Al4W and Al5W phases are similar and equal 7.6 wt.% and 7.8 wt.%, respectively. SEM and EDS show the microstructure diversification and the shape of Al4W (cubic) and Al5W (oblong) particles in Al-matrix.