Evaluation of Fracture Mechanisms in Al-Si Metal Matrix Nanocomposites Produced by Three Methods of Gravity Sand Casting, Squeeze Casting and Compo Casting in Semi-Solid State

Magnetic stirring is considered to be the most useful stirring method in semi-solid casting processes which doesn't have the restrictions of the mechanical stirring. In this research, fracture mechanisms of aluminum-Al2O3 nanocomposites produced by three methods of gravity sand casting, squeeze casting and compo casting in semi-solid state using electromagnetic stirring were studied and discussed. For this purpose, microstructure and fracture surfaces obtained from broken tensile test samples were analyzed using optical and scanning electron microscopies. On the fracture surfaces of all the samples, dimples were observed, which are the sign of ductile fracture. It was revealed that the dimples on the samples produced by the compo casting method are smaller, more spherical and uniformly distributed in the metal matrix in comparison with the ones from sand and squeeze casting. It also investigated that on the fracture surfaces of compo casting samples less cleavage planes, dendritic fracture and particles agglomeration were observed in comparison with the ones from the sand and squeeze casting processes.