Effects of Cerium Addition on Solidification Behaviour and Intermetallic Structure of Novel Al-Cu-Li Alloys

The microstructure evolutions of novel Al-Cu-Li alloys with rare earth cerium (Ce) additions (0, 0.1, 0.3, and 0.5, wt%) were investigated. The as-cast samples were characterized by optical microscopy, scanning electron microscopy, X-ray diffraction meter and electron probe microanalysis with wavelength dispersive spectroscopic. The microstructural observation shows that the grains are significantly refined with increasing the addition of Ce. Mg+Ag-rich Al7Cu4Li intermetallic phase can be observed in all experimental alloys except for the one with addition of 0.5wt%Ce, which an extra gray CuSi(AgMg) phase emerges. Furthermore, the coarse rodlike Al2CuLi phase is completely absent upon Ce level up to 0.3wt%. The analysis shows that the Ce addition introduces changes in the precipitation sequence and consequently in the solidification behavior of the alloy. It is deduced that the grain refinement is mainly the result of the primary Al8Cu4Ce promoting α (Al) nucleation and further prohibiting the grain growth for the experimental alloys with cerium addition.