functionally graded microstructure

To evaluate the effect of inoculant addition on functionally graded microstructure of centrifugally cast Al-Mg2Si composites، two cylinders of Al-13. 8 wt. % Mg2Si with and without the addition of 1 wt. % Al-5Ti-B inoculant were cast in a vertical centrifugal casting machine. The chemical composition، microstructures and microstructural phases of the different radial sections of the cast cylinders were studied using induction coupled plasma (ICP) method، optical/scanning electron microscopes، and X-ray diffractometry، respectively. The results showed that in the inoculant content cylinder، owing to the prevailing thermal regime as well as the specific mode of eutectic solidification in this composite، the titanium and boron compounds were segregated towards the middle layer of the cylinder and caused the formation of primary Mg2Si particles and non-eutectic Al () in this layer. In addition، due to the effect of centrifugal force during solidification، a higher volume fraction of the light primary Mg2Si particles، according to Stocks law، was segregated towards the inner layer of the cast cylinders.

The modification of microstructural grading of the cast hollow cylinders of eutectic composite Al-13.8 wt.% Mg2Si was studied via 0.5 wt.% Al-75Fe addition to the melt during centrifugal casting. The chemical composition, microstructure and hardness of different radial sections of the cast cylinders were studied using energy dispersive spectroscopy (EDX), optical microscope, scanning electron microscope, X-ray diffractometry and hardness testing, respectively. The results show that due to specific thermal regime, prevailed in centrifugal casting, the rod-shape fine eutectic microstructure in external periphery of the cast hollow cylinder changes to a coarse lamellar-shape eutectic microstructure in its internal periphery of cylinder. Also owing to segregation of FeAl3/Al8Fe2Si brittle particles with needle morphology towards the inner periphery of cylinder, thus their effective role in heterogeneous formation of Mg2Si and developing the α-Al in matrix phase, the inner periphery of the iron-contained cylinder showed the lower hardness in compared with the outer periphery of cylinder.