Mechanical Properties and Microstructure Evolution of Al-Li Alloy Under the PHF Process

TL;DR

This paper introduces a new PHF process to improve the mechanical properties of Al-Li alloys while reducing treatment time.

Contribution

A novel PHF process is proposed to regulate multiphase precipitation and shorten thermomechanical treatment cycles in Al-Li alloys.

Findings

The PHF process achieves optimal tensile and yield strength of 565.3 MPa and 531.2 MPa in 2A97 Al-Li alloy.

Pre-strain promotes T1 phase nucleation and dynamic recrystallization during warm forming.

Extended warm-maintaining time leads to T1 phase coarsening and reduced strength.

Abstract

Currently, Al-Li alloys have been widely concerned in the aerospace and other fields due to their excellent comprehensive mechanical properties. However, the limitation of the long thermomechanical treatment still needs further improvement. Therefore, for an Al-Li alloy with multiple strengthening phases, this work proposes a pre-strain and pre-aged hardening warm forming (PHF) process. In the process, the multiphase precipitation and phase transformation are regulated by macro-control of the pre-strain, pre-aging, and warm forming stages. It is discovered that the 2A97 Al-Li alloy, with “7% pre-strain + 80 °C/16 h pre-aging + 250 °C/10 min warm forming”, exhibits the relatively optimal tensile/yield strength of 565.3 MPa/531.2 MPa. The addition of pre-strain facilitates the nucleation and precipitation of T1 phases through the consumption of δ′ phases and θ′ phases and promotes dynamic recrystallization during the warm forming process. The fine and uniform T1 phases are observed at the warm-maintaining time of 10 min. However, further extension of warm-maintaining time results in the coarsening of T1 phases and the reduction in strength. The proposed PHF process significantly shortens the thermomechanical treatment cycle of Al-Li alloys, which provides theoretical guidance for exploring the new short-process forming method.

Figures