Equiaxed dendrite growth in non-refined Al-base alloys in real-time

Abstract

Dendritic structures are very common in metallic metals produced by solidification. The developing grain morphologies and the growth dynamics characterize the final microstructure of an alloy. We study the evolution and growth morphologies of dendrites using in-situ X-ray radiography and post-mortem electron backscatter diffraction (EBSD). The growth velocities of the dendrite tips and the change of solute composition in the extra-dendritic liquid in thin (< 0.5 mm) alloy samples are monitored in real-time. The experimentally determined tip velocities are compared to growth models that predict dendritic tip growth. The orientations of the solidified dendrites are analyzed post-mortem using EBSD. We observe different dendrite orientations in Al-Ge and Al-Cu alloys. Dendrites in Al-Cu alloys grow along the crystallographic <100> direction, whereas dendrites in Al-Ge alloys show variable growth directions. We find an influence of germanium content on the selected dendrite orientiations.