Microstructure evolution and deformation mechanisms of a banded-grained 2A97 Al–Cu–Li alloy during superplastic deformation

Abstract

The microstructure evolution and superplastic deformation mechanisms of a 2A97 Al–Cu–Li alloy (Al-3.4Cu-1.5Li-0.5Zn-0.4Mg-0.3Mn-0.15Zr) with initial banded grains were studied by using electron backscatter diffraction and focused ion beam techniques. The uniaxial superplastic tensile tests were carried out at a temperature of 430 °C and an initial strain rate of 2 × 10−3 s−1. The surface studies under a large true strain range (0–1.61) were achieved to investigate the superplastic deformation mechanisms. The results showed that the banded grains transformed into equiaxed grains due to dynamic recrystallization during deformation, accompanied by texture spreading, misorientation distribution randomization, and dislocation density reduction. The superplastic deformation process can be divided into two stages according to the microstructure characteristics and deformation mechanisms. In the primary deformation stage, the alloy was mainly composed of banded-grained structures, the intragranular dislocation slip (IDS) dominated the deformation and accounted for 54.1% contribution to the total deformation. When the true strain raised to 1.1, the deformation entered the second stage where the equiaxed grains became dominant, the grain boundary sliding became the main deformation mechanism and accounted for 54.4% contribution to the total deformation. A modified Ashby−Verrall model accompanied by IDS is suggested, which plays a crucial role in the superplastic deformation of the studied alloy.