Journal of Advanced Materials in Engineering (Esteghlal)

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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.

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In this study, centrifugal casting process was used for producing Al/Mg bimetal. Molten Mg was poured at 700 ^oC, with 1.5 and 3 melt-to-solid volume ratio (Vm/Vs) into the 450 ^oC preheated solid Al rotating at 800, 1200, 1600 and 2000 rpm. Castings were kept inside the centrifuged casting machine and cooled down to 150 ^oC. Investigating the effect of melt-to-solid volume ratio showed that increasing volume ratio from 1.5 to 3 results in diminishing metallurgical bonding in Al/Mg interface, because the force of contraction overcomes the resultant force acted on the interface. The results of study by scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) showed that bimetal compounds of Al₃Mg₂, Al₁₂Mg₁₇ and δ+Al₁₂Mg₁₇ eutectic structure (δ is the solid solution of Mg in Al) are formed in the interface. Atomic force microscopy (AFM) image of Al surface showed that the surface was rough in atomic dimentions, which can result in the formation of gas pores in the interface.