Superplastic Flow and Deformation Mechanism of the Rolled Al-Mg-Li-Sc-Zr Alloy with Banded Microstructure

Abstract

A hot rolled Al-5Mg-2Li-0.2Sc-0.12Zr alloy sheet with an initial banded microstructure was subjected to high-temperature tensile tests in the temperature range of 450–550 °C, at strain rates ranging from 3 × 10−4 to 1 × 10−2 s−1. The microstructural evolution of the present non-ideal superplastic microstructure (banded morphology) was characterized by electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). The results show that the hot rolled non-ideal superplastic microstructure exhibited excellent superplasticity. The optimal superplastic forming temperature appeared at 500 °C and the largest elongation of 1180% was achieved at 500 °C and 1 × 10−3 s−1. As far as we know, this is the largest elongation for Al-Mg-Li-Sc-Zr alloys. The superplastic deformation of the present hot rolled banded microstructure can be divided into two stages: (i) dynamic globularization due to the dislocation movement and continuous dynamic recrystallization (CDRX), which is responsible for the plastic deformation in the low strain range; (ii) superplastic flow of the spheroidized equiaxed grains with a high ratio of high-angle grain boundaries (HAGBs) and random grain orientation in the high strain range, during which grain boundary sliding (GBS) plays the dominant role in influencing the superplastic deformation.