Microstructure characterization and thermal analysis of aluminum alloy B206 during solidification

Abstract

The solidification kinetics of a high strength B206 aluminum casting alloy as a function of cooling rates between 1 and 15 K/min has been characterized through a combination of differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and optical microscopy. Three different peaks were detected in the DSC analysis, which corresponded to the nucleation of an α-Al solid solution, an Al-Cu-Fe intermetallic and the eutectic phases. The presence of these phases was confirmed using a coupled scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) analysis. The α-Al nucleation temperature was found to be independent of cooling rate while the eutectic and the intermetallic formation temperatures were depressed by up to 20 K. The evolution of the fraction solid, particularly during the solidification of α-Al was also affected by the cooling rate in such a way that slower cooling was accompanied by a higher fraction solid at a given temperature. Concurrently, microscopy was used in order to quantify the variation in secondary dendrite arm spacing (SDAS) with cooling rate for use in numerical simulations of casting processes.