Quantifying the Effects of Grain Refiner Addition on the Solidification of Fe-Rich Intermetallics in Al–Si–Cu Alloys Using In Situ Synchrotron X-Ray Tomography

The presence of Fe-rich intermetallics, particularly β-Al5FeSi, in aluminium alloy cast components can often limit fatigue life. There is an on-going effort to control the formation of these detrimental phases through the additions of trace elements and grain refiners. However, the role of grain refinement on the formation of intermetallics is still unclear and conflicting results exist. To gain better understanding, in situ synchrotron X-ray tomographic microscopy experiments were performed on a commercial Al–Si–Cu alloy with grain refiner addition. Three-dimensional microstructure evolution and intermetallic precipitation were quantified. The influence of the β-intermetallics on the evolution of permeability during equiaxed dendritic solidification was also investigated numerically. The results illustrate that grain refinement affects α-Al grain structure as well as nucleation temperature of primary and intermetallic phases, but there is no evidence that it alters the precipitation sequence of intermetallics or their morphology. The simulation results reveal that intermetallics block interdendritic liquid flow and hence reduce permeability.