Effect of Casting Condition on Density and Hardness Gradients of Al-Al<sub>2</sub>Cu Alloy FGM Fabricated by Centrifugal <i>In Situ</i> Method

Abstract

Functionally graded material (FGM) is a combined material that has a component gradient from one material at one surface to another material at the opposite surface. As one of the fabrication processes of FGM, centrifugal in-situ method has been proposed. Centrifugal in-situ method is a casting that centrifugal force is applied during solidification to both the primary crystal and the matrix. In a previous study, the density and hardness gradients of Al-3mass%Cu FGM ring fabricated by centrifugal in-situ method have been investigated. According to the study, Cu concentration within the FGM ring monolithically increases towards the ring's inner position, and its density also increases toward inner region. This is because the density of the primary -Al crystal is larger than that of the molten Al-Cu alloy in the early stage of solidification. Based on this solidification process, it is considered that the casting condition and the initial Cu concentration of Al-Cu master alloy affect on the density and hardness gradients in the Al-Cu FGM ring. In this study, effects of the casting condition on the density and hardness gradients of Al-Al2Cu FGM rings fabricated by the centrifugal in-situ method were investigated. It was found that density gradient of the Al-Al2Cu FGM rings increases with increasing Cu concentration of Al-Cu master alloys. Also, processing temperature for Al-Cu master alloy can control density gradient of Al-Al2Cu FGM rings. These phenomena were explained by variation of the densities of primary -Al and the molten Al matrix during the solidification.