Microstructure Characterization and Thermal Analysis of Aluminum Alloy B206 During Solidification

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 SEM–energy dispersive spectroscopy 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 (20 °C). 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 with cooling rate for use in numerical simulations of casting processes.