Microstructural Grading of Al- wt.%MgSi Hypoeutectic Alloy by Centrifugal Casting

Centrifugal casting as a high capable technique has been frequently used for production of high performance castings. In two decades its capabilities has been progressed towards the production of cast components with functionally graded microstructures. A controlled attribution of the centrifugal force in this technique can cause a desirable grading of the microstructures hence properties in different sections of the castings. In this research, functionally graded Al-wt.%MgSi hypoeutectic alloy with graded distribution of α-Al phase was cast as a cylindrical specimen using the centrifugal casting. During the solidification, the initially formed α-Al grains due to the higher density in compared with the remained melt, were segregated in the centrifugal force direction. The microstructural observations reveal two distinguished layers in radial direction of the cast cylinder: the outer layer with a higher volume fraction of α-Al grains and the inner one with the eutectic structure. To modify the cast structure hence mechanical properties, the cast sample was subjected under solution and ageing heat treatments. The microstructural observations of the heat treated sample shows no noticeable change in the cast graded microstructure; however the eutectic structure was distorted from laminar to a fine dot-like structure. This minor microstructural evolution is accompanied with an increase in hardness of different sections of the sample.