Introduction and Objectives: Functionally graded materials are an advanced class of composites which their microstructure change continuously in a specific direction. The main purpose of this paper is to study the microstructure of the Al-13.8 wt.% Mg₂Si eutectic alloy produced by centrifugal and gravity casting methods and comparison the effect of addition of Al-5Zr inoculant on the changes in their casting microstructure.
Materials and methods: In this research, with gravity and centrifugal casting of Al-13.8wt.% Mg₂Si alloy and adding an appropriate amount of Al-5Zr inoculant, microstructural changes in the radial direction of the casting cylinder were compared with gravity casting samples. The chemical composition and microstructural characteristics of the samples were studied using energy-dispersive X-ray spectroscopy and optical microscopy, respectively.
Results: The microstructure of the centrifugally cast Al-5Zr inoculant-free cylinder exhibited columnar Al/Mg₂Si eutectic cells along the radial direction, accompanied with an accumulation of primary Mg₂Si particles in the inner layer of the cylinder. Upon the addition of Al-5Zr inoculant, the morphology of Mg₂Si secondary phases changed from cubic to Chinese script shape. However, the microstructure of the conventional gravity casting sample containing and without zirconium showed Al/Mg₂Si eutectic cells without a specific targeted distribution, an accumulation of primary and light Mg₂Si particles in the upper layer of the casting cylinder, which is due to the separation of these particles against the upward direction of gravity.
Conclusion: The microstructure of the cast cylinder processed by centrifugal casting containing Al-5Zr inoculant showed a targeted distribution of Al/Mg₂Si eutectic cells and aggregation and reduction in the size of Mg₂Si particles in the inner radial layer of the cast cylinder.