Effects of pre-strain deep cryogenic aging on the mechanical and corrosion properties of 2A97 aluminum–lithium alloy

Abstract

In order to improve the mechanical properties and corrosion resistance of 2A97 aluminum-lithium alloy, this research develops a novel strain heat-treatment technology. Surprisingly, 2A97 alloy treated by 4% pre-strain and 48 h deep cryogenic aging exhibits excellent mechanical properties, whose yield strength, tensile strength, and elongation are 573.7 MPa, 593.6 MPa, and 14.25%, respectively. Furthermore, the corrosion resistance of samples treated by the above pre-strain deep cryogenic aging process is two times as much as traditional T6 aged. This study deeply investigates the influence of various precipitates in 2A97 alloy on its performance through microstructure analysis. The results show that the introduction of pre-strain inhibits the precipitates of the T1 and δ′ phases at the grain boundaries, and prevents the formation and widening of precipitate-free zones. At the same time, it reduces the potential difference between grain boundaries and matrix, and enhances the corrosion resistance of 2A97 alloy. Deep cryogenic can inhibit recovery and maintain deformation dislocation, so that a large number of defects produced by pre-strain promote the nucleation and diffusion of precipitates in the matrix, resulting in tiny and uniformly distributed precipitates. Therefore, the novel pre-strain deep cryogenic aging not only endues 2A97 alloy excellent performance, but also offers a new strategy for controlling precipitation.