Microstructure Evolution of Novel Al-Cu-Li-Ce Alloys during Homogenization

The present work is aimed to clarify the formation of the τ1(Al8Cu4Ce) phase and its formation mechanism in the high Cu content alloys with Ce addition, i.e high Cu/Li Al-Cu-Li-Ce alloys. The microstructure evolution of the alloy during the two-step homogenization annealing process was investigated. Results show that the coarse Ag+Mg enriched TB (Al7Cu4Li) phase and the primary AlCuCe phase occur under solidification. Two types of the minor τ1 phases are formed after homogenization. It is concluded that the τ1 phase nucleation mechanism could involve either nucleation on an existing TB phase by Ce diffusion from the Al matrix or the transformation of the primary AlCuCe phase into the τ1 phase by Ce diffusion through the coarse primary AlCuCe phase shrink. It is deduced that the grain refinement is attributed to the primary AlCuCe, which can promote α (Al) nucleation and further prohibit the grain growth for the experimental alloy.