Simultaneously improving the strength and ductility of an Ag-free 2195 Al-Li alloy by T8 treatment with cryogenic pre-rolling

Abstract

Zn has promise to substitute Ag in Al-Li alloys, but an equal atomic amount substitution of Ag with Zn generally reduces both strength and ductility. In this work, we demonstrated that T8 treatment with a cryogenic pre-rolling (CPR) can simultaneously improve the strength and ductility of Zn micro-alloyed, Ag-free 2195 model Al-Li alloys. The optimal combination of an ultimate tensile strength of 664.1 MPa and an elongation of 8.1% was achieved for the Al-4Cu-1Li-0.4Mg-0.25Zn-0.1Zr (wt%) alloy under T8 with a 10% CPR. The improved strength and ductility can be attributed to a higher fraction of low angle grain boundaries (LAGBs), a higher precipitation density of T1, and a more uniform distribution of dislocations and T1. Similar as Ag, Zn is more energy-favored to segregate to the T1/Al interface than to the θ'/Al interface, which helps promote the precipitation of T1 in preference to θ'. Besides, Zn or Ag segregation at the T1/Al interface has no negative impact on the adhesion strength.