Influence of AlCuSc Ternary Phase on the Microstructure and Properties of 1469 Alloy

Microstructure evolution and mechanical properties of a 1469 alloy and a Sc-free1469 type alloy were examined. SEM observation indicates that AlCuSc ternary phases (W) are formed after homogenization annealing, and cannot be dissolved during the following heat treatments. These coarse particles consume abundant Cu atoms from the Al matrix that are available for solutioning, which results in the decrease of precipitation of the T1 phase during aging treatment. The W phase has negative effects on the examined alloy’s mechanical properties. The tensile strength of Sc-added alloy is 40MPa lower than that of the Sc-free alloy. The formation of the W phase has a close relationship with Cu/Sc ratio, which shows the importance of controlling the concentration of Cu and addition of Sc. Formation of W phase suppress the effect of precipitation hardening of the T1 phase in high strength Al-Cu-Li alloys